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Mission Statement 

The purpose of FLAPS-2-APPROACH is two-fold:  To document the construction of a Boeing 737 flight simulator, and to act as a platform to share aviation-related articles pertaining to the Boeing 737; thereby, providing a source of inspiration and reference to like-minded individuals.

I am not a professional journalist.  Writing for a cross section of readers from differing cultures and languages with varying degrees of technical ability, can at times be challenging. I hope there are not too many spelling and grammatical mistakes.

 

Note:   I have NO affiliation with ANY manufacturer or reseller.  All reviews and content are 'frank and fearless' - I tell it as I see it.  Do not complain if you do not like what you read.

I use the words 'modules & panels' and 'CDU & FMC' interchangeably.  The definition of the acronym 'OEM' is Original Equipment Manufacturer (aka real aicraft part).

 

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Entries in Boeing B737 Flight Simulator (21)

Sunday
Jan042015

Integrated Approach Navigation (IAN) - Review and Procedures

Increased navigational accuracy obtained from software and hardware improvements have led to several enhanced approach types being developed for the Boeing 737.  These augmented approach types provide a constant rate of descent, following an approximate 3 degree glide path, and eliminate the traditional step-down style of approach.  The benefits being a  stabilized and safer approach, greater passenger comfort, less engine wear, tear and fuel usage, and a lower workload for the flight crew.

LEFT:  Nippon Airways (ANA), one of Japan’s premier airlines uses Integrated Approach Navigation (IAN) on many of its routes.  Utilizing IAN can produce considerable savings to an airline by minimizing engine wear, fuel costs, and standardizing flight training.  Click image to enlarge.

In this post, I will discuss the concept of Integrated Approach Navigation (IAN) and explain the procedures recommended by Boeing to successfully implement IAN. 

I have attempted to cover all the detail concerning IAN in one article, however, when a lot of detail is discussed it can, on occasion, lead to confusion.  Therefore, I recommend you read the Boeing Flight Crew Training Manual for more in-depth information.

The Navigation Performance Scales (NPS) which augment IAN will not be discussed.  NPS will form part of a future topic.

Overview

Integrated Approach Navigation (IAN) provides a display similar to the Instrument Landing System (ILS) and allows the flight crew to fly any published approach that exhibits a glide path within the navigational database of the Flight Management System (FMS).  Flight path guidance is derived from the Central Control Unit (CDU), navigational radios (NAV1/2 & ADF 1/2), or combination of both.  For IAN to engage correctly, an appropriate approach (an approach with glide path) must be selected from the CDU database.

IAN is an airline option, and not every airline carrier will have IAN as part of their avionics suite.  However, the technology is becoming more popular as the safety and economic benefits of IAN are understood by airline carriers.

Geometric Path

The geometric path used by IAN approximates a 3 degree glide path; nevertheless, this glide path may not comply with the CDU designated altitude constraints prior to the Final Approach Fix (FAF).  This said, the generated glide path will always be at or above the altitude constraints between the FAF and the Missed Approach Point (MAP) published in the CDU approach procedure.

Critically, IAN is a Category I Non Precision Approach (NPA) and is not to be confused with an ILS precision approach.  Therefore, NPA procedures must be adhered to when initiating an approach using IAN.  

Although the automation provided by IAN will guide an aircraft (in most cases) to the threshold of the runway, IAN has not been designed to do this.  Rather, IAN has been designed to guide the aircraft to the Missed Approach Point (MAP) published on the approach chart.  The flight crew will then disengage IAN by disengaging the autopilot and autothrottle and fly the remainder of the approach manually as per NPA protocols.

In some instances, the final approach course (FAC) is offset from the runway centreline and manoeuvring the aircraft for direct alignment will be necessary, whilst following the glide path (G/P) angle.

Although the final approach is very similar to an ILS approach, IAN does not support autoland; therefore, if the aircraft is not in a stable configuration and the crew not visual with the runway at or beyond the MDA, a missed approach procedure will need to be executed

Ground Proximity Warning System (GWPS) Aural Warnings and Displays

GWPS warnings will annunciate if at any time the aircraft deviates below the glide path, and failure of a crew to disengage IAN at the appropriate altitude will trigger an GPWS aural warning alert ‘autopilot autopilot’ at 100 feet radio altitude.  This is in addition to the words ‘autopilot’ being flashed on the Primary Flight Display (PFD).

Benefits of Using IAN

There are multiple benefits to an airline using IAN, the foremost being flight safety. Unstable approaches contribute to many aircraft accidents, and flight crews strive to always establish a stabilised approach profile for all instrument and visual approaches.  

The Global Position System has enabled stabilized approaches at many airports and advanced features such as IAN take advantage of this technology to provide consistent, intuitive displays that support stabilized approaches. 

18 Approaches Types to 1

Through the use of IAN, the number of approach types has been reduced from 18 to 1, greatly simplifying the approach procedure and minimizing the amount of time an airline needs to train pilots in numerous approach types.  Time is money and utilizing advanced technology such as IAN can increase airline productivity.

Additional Data - Increased Awareness

The distance to runway threshold, approach guidance information, and vertical and lateral deviation markers are displayed when IAN is in range of a designated runway.  Whether IAN is used or not, this information provides additional guidance when executing an approach. 

For example, when executing a VOR approach, this information has been displayed on the Navigation Display (ND) as the distance to the actual NAVAID (VOR) - which may or may not be aligned with the threshold of the runway.  IAN will by default, display the lateral and vertical deviation, and distance to the runway threshold, allowing for greater precision during a non-automated approach.

These are but a few of the advantages to using the Integrated Approach Navigation system.

Using IAN - General

The following information provides guidance in the general use of IAN.

IAN can be used for the following approach types: RNAV, VOR approach, GPS, NDB approach, LOC, LOC-BC or similar style approaches. If using IAN to execute a Back Course Localizer approach (B/C LOC), the inbound front course must be set in the MCP course window (either Captain/First Officer side, or both depending on CDU set-up).

LEFT: IAN approach to VOR/DME RWY 24.  FAC is engaged while G/P is armed. The lateral and vertical deviation pointers are displayed and will, change colour to solid magenta when the G/P engages.  A benefit if using IAN is that it provides an accurate distance from the threshold to the aircraft - in this case 9.7 miles. (ProSim737 avionics suite).

Although the use of IAN is recommended only for straight-in approaches, field use suggests that flight crews routinely engage IAN when no more than 45 degrees from the runway approach course.  During the approach the crew must monitor raw data and cross check against other navigational cues.  

IAN does not need to be specifically ‘turned on’ for it to function; the functionality, if installed in the aircraft is always functional.  When the aircraft is within range of the designated approach, the runway data will annunciate on the PFD. At any time after this point has been reached, IAN can be armed/engaged by pressing the APP button on the MCP.

LEFT: An example (not related to PFD image) showing a typical CDU generated approach which is IAN compliant.  The altitude (3000 feet) positioned above the entry GP3.00 is the altitude set to the MCP altitude window.  An approach may have several glide path entries; always select the first entry.  CDU is manufactured by Flight Deck Solutions (FDS).  Click image to enlarge.

Navigation Radios

An IAN approach can be executed without the guidance from navigation radios; however, this is not recommended as correct tuning of the radios can provide increased visual awareness and redundancy should a failure occur with the CDU, or the dataset becomes corrupted. 

LEFT: Montage of four PFDs showing various annunciations and displays for the IAN system.  Sequence is top left to right and bottom left to right. Click image to enlarge (ProSim737 avionics suite).

Boeing strongly advise to tune the radios to the correct frequency for the approach, to eliminate the possibility of the radio picking another approach from a nearby airport and providing erroneous data to the crew.  If using IAN for an ILS approach (glide slope inoperative) the radio must not be tuned to the ILS frequency.

Minimum Descent Altitude (MDA)

As discussed earlier, an IAN approach is a NPA and when authorized by the Regulatory Authority, non-ILS approaches can be flown to a published VNAV Decision Altitude/Height (DA/H) or to a published MDA (the MDA is used as a decision altitude).  If not authorized to use the MDA as a decision altitude, crews must use the MDA specified for the approach flown.

To comply with the MDA protocols during a constant angle approach where a level off is not planned at the MDA, it is necessary to add +50 feet to the published MDA.  If a go-around is required, this allows an adequate buffer to prevent incursion below the MDA.

Using IAN - Understanding IAN Displays

IAN generates several visual displays which inform the flight crew of the status of the system.  These displays, which are triggered at various operational phases, are visible on the attitude display of the PFD and on the Flight Mode Annunciator (FMA).

Approach Guidance: The PFD will display the method of initial approach guidance in white whenever IAN is active.  The display will differ and is dependent on the approach type selected.  For example, LNAV/VNAV, FMC, LOC or ILS, depending on the source of the navigation guidance used for the approach (navigation, radio or CDU approach data).  An IAN approach will display FMC.

Approach guidance is activated when a crew selects TO/GA during the take-off roll, or when the aircraft is within range for the system to be armed/engaged.

Runway Data:  Whenever IAN is within range of a selected approach, the PFD will display the runway data (type and name of approach, runway designator and distance to threshold).  The display of the runway data is the crew’s first ‘notification’ that the IAN functionality is able to be used.

Final Approach Course (FAC):  FAC is displayed on the center FMA when the APP button on the MCP is pressed, and IAN is in range of the approach selected.

Glide Path (G/P):  G/P is displayed in the right FMA to indicate that the aircraft has a associated glide path to follow.

Two FMA colours are used.  White indicates that FAC or G/P is armed.  Once the aircraft is closer to the Final Approach Point, the FAC annunciation will change colour from white to green.  Green indicates that the final approach course is active.  Likewise, when G/P changes colour to green, it indicates that the aircraft has a dedicated glide path to follow.

It stands to reason, that FAC is usually annunciated prior to G/P, but depending upon the position of the aircraft when APP in pressed on the MCP, both annunciations may annunciate singly or together, in white or in green.

Lateral and Vertical Guidance Deviation Markers:  These are the magenta coloured diamonds, familiar to ILS approaches.  The diamonds provide the lateral position of the aircraft relative to the designated runway course and the vertical position relative to the glide path.  The diamonds are initially displayed in outlined magenta followed by solid magenta when the aircraft captures the glide path.

SINGLE CH:  SINGLE CH will be displayed in green, when the aircraft captures the glide path. At this time, the deviation markers will change from outline to solid magenta.  FAC and G/P on the FMA will also change from white to green.  At this point the aircraft will be guided automatically along the glide path.

Using IAN - Proceedure

  • IAN is engaged only after clearance for final approach has been received from Air Traffic Control (ATC).  By this time, the aircraft is probably on a straight in approach.  IAN is not designed to navigate to the airport.
  • IAN cannot be used for STARS and is not designed to be engaged when the aircraft is miles from the designated runway.  Flight crews transition to an IAN approach from any of several roll modes (VNAV/LNAV, Level Change, V/S or manual-controlled flight).
  • To arm/engage IAN, the flight crew press the APP button on the Mode Control Panel (MCP) similar to performing an ILS approach.

The APP mode is only to be selected when:

  • The guidance to be used for the final approach is tuned and identified on the navigation radio;
  • An appropriate approach has been selected from the CDU database which has a glide path attached to it;
  • The appropriate runway heading is set on the MCP course window;
  • The aircraft is on an inbound intercept heading;
  • ATC clearance for the approach has been received; and,
  • Both lateral and vertical deviation pointers are visible on the attitude display in the PFD.

IMPORTANT NOTE:  It is possible to select APP prior to the display of the deviation pointers, however IAN will be in armed mode.  IAN will only engage following aircraft capture of either the lateral or vertical flight path (FAC & G/P).  IAN can be armed whenever the aircraft is in range of the airport - in other words whenever the runway data is displayed on the PFD.

Many flight crews engage IAN only after the deviation pointers are visible (this follows the similar ILS approach method).

Using IAN - Set-Up

  • Select the appropriate approach to use from the CDU database.  Ensure that the selected approach has a glide path.  Do not alter any of the approach constraints.  Set the glide path altitude to the MCP altitude window.
  • Fly the aircraft in whatever roll mode to the Initial Approach Fix (IAF).  Remember straight-in approaches are recommended – a 45 degree offset to the approach course is also suitable (varies).  Do not engage IAN until the aircraft is in the correct position relative to the approach course.  IAN will usually become active – the approach guidance will be displayed on the PFD – at around 20 miles from the runway threshold.
  • Configure the navigation radios to the correct frequency for the designated approach.  Do not use an ILS frequency.
  • Set the barometric minimums to the altitude published on the approach chart.  Add 50 feet to avoid breaking NPA protocols.
  • Set the correct runway approach course to the MCP course window.
  • When the runway data is displayed on the PFD, IAN is in range.  At this point, the APP button on the MCP is pressed to arm IAN (this action can be delayed if not on straight-in approach heading).  The FMA will annunciate FAC and G/P in white to indicate the IAN system is armed.
  • When the aircraft is alligned with the lateral and vertical profile, the colour of the FAC and G/P annunciations will change from white (armed) to green (engaged).  The lateral and vertical deviation markers will also annunciate with a magenta outline.
  • As the aircraft closes on the runway threshold, and when the glide path has been reached, the deviation markers will become solid magenta and SINGLE CH will annunciate on the PFD.  The FAC and G/P annuniations on the FMA display will now be green.  The aircraft will begin to descend along the glide path.
  • Once the aircraft has descended, at least 300 feet below the altitude previously set in the MCP altitude window; the missed approach altitude (MAA) can be set on the MCP.  This figure is published on the approach chart.  Failure to wait until the aircraft descends 300 feet will cause the ALT HOLD annunciation to display and the aircraft levelling off.

Using IAN - Pilot Procedures

The procedures used for an IAN approach are derived from current ILS procedures and are consistent for all approach types.  This is the procedure after IAN has engaged.

  • When 2 miles from the Final Approach Fix (FAF) - GEAR DOWN, FLAPS 15, SPEED CHECK.
  • At glide path capture – FLAPS 25/30 (landing flaps), SPEED CHECK.
  • At 300 Feet below glide path capture, reset the MCP altitude window to the missed approach altitude.
  • At minima – Disengage autopilot and autothrottle, manually align aircraft and follow vertical deviation markers and Flight Director (FD) cues to runway threshold.  Maintain the glide path to the flare and do not descend below the visual glide path.  Although glide path guidance can be used as a reference once the aircraft descends below the MDA, the primary means of approach guidance is visual.  If not visual at MDA, execute a go-around.  Remember using IAN is a Non Precision Approach (NPA).

IMPORTANT NOTE:  The transition from roll mode to IAN approach can be quite sudden and a flight crew must be vigilant and anticipate actions and events before they occur.  If the aircraft is travelling too fast, slowing down after IAN has engaged can be difficult. 

Likewise, if the aircraft is too high and IAN engages, the vertical descent can be steep as the aircraft attemptes to follow the IAN generated glide path.

Therefore, maintaining the correct approach speed and altitude is paramount to a successful IAN approach.  If using VNAV, it often is good idea to engage SPD INTV to manually control MCP speed.

Flight crews often transition to IAN from whatever automation mode they are using at the Initial Approach Fix (IAF), or they manually follow the deviation pointers generated by IAN until confident that the aircraft will not behave erratically when IAN is engaged by pressing the APP button on the MCP.

FIGURE 1:  Visual representation of an IAN approach and transition from roll mode.  Copyright Boeing FCTM, 2014.

On another note, when an IAN approach mode is selected, the APP mode in the EFIS can be selected to display the approach (as in an ILS approach in the Navigation Display).

Using IAN - Situations To Be Mindful Of

Automation can have its pitfalls, and IAN is no different.  However, once potential shortcomings are known, it is straightforward to bypass them.  The most common mistake, especially with virtual pilots, is not following the correct procedure.

Possible 'surprises' associated with IAN are:

1:  Failing to configure the aircraft prior to IAN engaging in FAC and G/P mode.

Unlike an ILS approach, where configuration for landing is initiated when the glide slope comes alive (solid magenta deviation markers), during an IAN approach, configuration for landing is initiated approximately 2 miles from the Final Approach Fix (FAF).  

The reason for this, as discussed in the overview section, is that IAN creates a glide path from the designated runway threshold to the position of the aircraft.

If the crew wait until the IAN glide path becomes alive (solid magenta deviation pointers), there may be insufficient time for the crew to complete recommended actions and checklists before intercepting the glide path. 

2:  Forgetting to set the Missed Approach Altitude (MAA) in the MCP.

Failing to wait until the aircraft has descended 300 feet below the glide path capture altitude to reset the MCP altitude to the MAA.  Failure will cause the aircraft to revert to ALT HOLD.

3:  Approaching the runway not on the correct intercept course

IAN operates flawlessly with straight-in approaches and to a certain extent with approaches roughly 45 degrees from the main approach course.  IAN will not engage if you approach the assigned runway at 90 degrees.  Nor will IAN engage if you are attempting to fly a STAR.

4:  Transition from roll mode to the IAN approach can be abrupt with loss of some visual data

The PFD will display differing annunciations depending on the type of approach configured from the CDU database, and the roll mode being flown prior to IAN engaging. When IAN is in range, some of this displayed data will be replaced with data from the IAN system.

For example, if the primary navigation is using VOR/LOC, and when IAN comes into range, the approach guidance, runway data and deviation markers will be displayed in the PFD.  However, simultaneously, the Navigation Display (ND) will display EFIS MODE/NAV FREQ DISAGREE.  If executing a VOR approach, and not wanting to use IAN, loosing the VOR directional marker in the ND, if unexpected, can be disconcerting. 

Note that this will occur whenever IAN is in range of the designated runway (IAN does not necessarily have to be armed or engaged)  But, be assured that the VOR/LOC is still being followed, despite the VOR directional marker not being able to be viewed in the ND.  The FMA will indicate what the aircraft is doing - in this case the FMA will display VOR/LOC (always y look at the FMA to determine what level of automation the aircraft is using). 

5:  Forgetting to set the altitude in the MCP (from the CDU glide path)

A common mistake is to not set the altitude in the MCP altitude window to the altitude that is associated with the glide path for the desired approach.

ProSim737 and IAN

Integrated Approach Navigation has only recently been introduced to the ProSim 737 avionics suite (late December 2014).  As such, there are ‘teething issues’ associated with its use.  With time, it is envisaged that the developers of ProSim737 will rectify shortfalls to ensure accurate and trouble free operation.

Five known shortfalls at the time of writing are:

(i)     ProSim737 does not display the IAN runway data immediately following the engagement of TO/GA during the take-off roll.  This is incorrect.  In the real aircraft, this information is displayed immediately following the engagement of TO/GA during the take-off roll while the aircraft is on the ground.

(ii)     The colour of the approach guidance display (LNAV/VNAV) after TO/GA is engaged is currently white.  This is incorrect.  The colour should be green (further research required, F2A).

(iii)     The runway data and approach guidance displays are not identical to the real aircraft – they are the incorrect font size.  This is a minor issue.

(iv)     Interestingly, ProSim737 allows an IAN approach to dunction with any CDU generated approach procedure (with or without glide path).  This is incorrect.  An IAN approach can only be generated with an approach that displays a glide path.  Although the reason for this is uncertain, I am lead to understand that it is associated with the navigational database, which is beyond the scope of ProSim737 (course is an outside source).

(v)     Once IAN is armed/engaged and an approach selected from the FMC database via the CDU, the ability to fly a standard VOR approach ceases.  The message EFIS MODE NAV FREQ DISAGREE will be displayed on the Navigation Display when VOR is selected on the EFIS.  The only way to fly a VOR approach is to not select a VOR approach from the FMC database.  This is not correct.  IAN should not take control of a VOR approach.

ProSim737 users should also note, that for IAN to function within the avionics suite, it must be activated in the cockpit set-up page of the instructor station (IOS).

Final Call

Aircraft fitted with IAN, are capable of using the APP button located on the MCP, to execute an instrument ILS-style approach based on flight path guidance from the CDU.  This makes Non Precision Approaches easier to execute with increased safety.  It also enables a constant descent angle, less engine spooling, wear and tear, and improved passenger comfort.  Furthermore, IAN utilises a standardised procedure and as such, when installed, is usually used in place of LNAV and VNAV due to its straightforward method of use.

Nevertheless, a flight crew must be vigilant when using any automation, especially during the critical approach phase where there is little margin for error.  First and foremost is the innate ability to fly the airliner manually, and although automation such as IAN can enhance safety, it does so at the detriment of manual flying skills.

References

Several sources were used to obtain the information documented in this post, including: personal communication with a B737-800 pilot, the Boeing Flight Crew Training Manual, 2014 and the Boeing 737 Technical Guide by Chris Brady.

If any discrepancies are noted in this article, please contact me so they can be rectified.

Acronyms and Glossary

APP – Approach button located on MCP
CDU – Control display Unit (aka Flight Management Computer – FMC - I use CDU and FMC interchangeably)
FAC – Final Approach Course
FAF – Final Approach Fix
FMA – Flight Mode Annunciators
FMS – Flight Management System
G/P – Glide Path (non precision approach)
G/S – Glide Slope (precision approach)
IAF – Initial Approach Fix
IAN – Integrated Approach Navigation
ILS – Instrument Landing System
MAP – Missed Approach Point
MCP – Mode Control Panel
MDA - Minimum Descent Altitude
PFD – Primary Flight Display
STAR - Standard Terminal Arrival Route

  • Reviewed and updated 25 August 2017.
Saturday
Nov012014

B737-600 NG Fire Suppression Panel (Fire Handles) - Evolutionary Conversion Design

Originally used in a United B737-600 NG and purchased from a wrecking yard, the Fire Supression Panel has been converted to use with ProSim737 with full functionality.

LEFT:  B737-600 NG Fire Suppression Panel installed to center pedestal.  The lights test illuminates the annunciators (click to enlarge).

This is the third fire panel I have owned.  The first was from a Boeing 737-300  which was converted in a rudimentary way to operate with very limited functionality in Flight Simulator. The second unit was from a B737-600 NG; but, the conversion was an ‘intermediate’ design with the relays and interface card located outside the unit within the now defunct Interface Master Module (IMM).  Both these panels were sold and replaced with the current 600 NG series panel.

I am not going to document the functions and conditions of use for the fire panel as this has been documented very well in other literature.  For an excellent review, read the Fire Protection Systems Summary published by Smart Cockpit.

LEFT:  B737-600 NG series Fire Suppression Panel light plate, fire handles, annunciators and installed interface card and relays (click to enlarge).

Nomenclature

Before going further, it should be noted that the Fire Suppression Panel is known by a number of names:  fire protection panel, fire control panel and fire handles are some of the more common names used to describe the unit.

'Plug and Fly' Conversion

What makes this panel different from the previously converted B737-600 NG panel is the method of conversion.  

LEFT:  Panel with outer casing removed showing installation of Phidget and and relays.  Ferrules are used for easier connection of wires to the Phidget card.  Green tape has been applied to the red lenses to protect them whilst work is in progress  (click to enlarge).

Rather than rewire the internals of the unit and connect to interface cards mounted outside of the unit, it was decided to remove the electronic boards from the panel and install the appropriate interface card and relays inside the unit.  To provide 5 and 28 volt power to illuminate the annunciators and backlighting, the unit uses dedicated OEM (Original Equipment Manufacture) Canon plugs to connect to the power supplies.  Connection of the unit to the computer is by a single USB cable.  The end product is, excusing the pun - ‘plug and fly’.

Miniaturization has advantages and the release of a smaller Phidget 0/16/16 interface card allowed this card to be installed inside the unit alongside three standard relay cards.  The relays are needed to activate the on/off function that enables the fire handles to be pulled and turned.

LEFT:  Rear of panel showing integration of OEM Canon plugs to supply power to the unit (5 and 28 volts).  The USB cable (not shown) connects above the middle Canon plug (click to enlarge).

The benefit of having the interface card and relays installed within the panel rather than outside cannot be underestimated.  As any serious cockpit builder will attend, a full simulator carries with it the liability of many wires running behind panels and walls to power the simulator and provide functionality. Minimizing the number of wires can only make the simulator building process easier and more neater, and converting the fire handles in this manner has followed through with this philosophy.

Complete Functionality including Push To Test

The functionality of the unit is only as good as the flight avionics suite it is configured to operate with, and complete functionality has been enabled using ProSim737. 

One of the positives when using an OEM Fire Suppression Panel is the ability to use the push to test function for each annunciator.  Depressing any of the annunciators will test the functionality and cause the 28 volt bulb to illuminate.  This is in addition to using the lights test toggle located on the Main Instrument Panel (MIP) which illuminates all annunciators simultaneously.

At the end of this post is a short video demonstrating several functions of the unit.

The conversion of this panel was not done by myself.  Rather, it was converted by a gentleman who is debating converting OEM  units and selling these units commercially; as such, I will not document how the conversion was accomplished as this would provide an unfair disadvantage to the person concerned.

Differences - OEM verses Reproduction

There are several reproduction fire suppression panels currently available, and those manufactured by Flight Deck Solutions and CP Flight (Fly Engravity) are very good; however, pale in comparison to a genuine panel.  Certainly, purchasing a panel that works out of the box has its benefits; however the purchase cost of a reproduction panel is only marginally less that using a converted OEM panel.

By far the most important difference between an OEM panel and a reproduction unit is build quality.  An OEM panel is exceptionally robust, the annunciators illuminate to the correct light intensity with the correct colour balance, and the tension when pulling and turning the handles is correct with longevity assured.  I have read of a number of users of reproduction units that have broken the handles from overzealous use; this is almost impossible to do when using a real panel.  Furthermore, there are differences between reproduction annunciators and OEM annunciators, the most obvious difference being the individual push to test functionality of the OEM units.

Classic verses Next Generation Panels

Fire Suppression Panels are not difficult to find; a search of e-bay usually reveals a few units for sale.  However, many of the units for sale are the older panels used in the classic B737 airframes. 

LEFT:  B737-200 Fire Suppression Panel.  The differences between the older 200 and 300 series and the NG style is self evident; however the basic functionality is similar.

Although the functionality between the older and newer units is almost identical, the similarity ends there.  The Next Generation panels have a different light plate and include additional annunciators configured in a different layout to the older classic units.

Video

The video demonstrates the following:

  • Backlighting off to on (barely seen due to daylight video-shooting conditions)
  • Push To Test from the MIP (lights test)
  • Push To Test for individual annunciators
  • Fault and overhead fire test
  • Switch tests; and,
  • A basic scenario with an engine 1 fire.

NOTE:  The video demonstrates one of two possible methods of deactivating the fire bell.  The usual method is for the flight crew to disable the bell warning by depressing the Fire Warning Cutout annunciator located beside the  six packs on the Main Instrument Panel (MIP).  An alterative method is to depress the bell cutout bar located on the Fire Suppression Panel. 

Tuesday
Sep022014

B737 Autothrottle (A/T) - Normal and Non-Normal Operations

The AutoThrottle (A/T) is part of the Automatic Flight System (AFS) comprising the Autopilot Flight Director System (AFDS) and the Autothrottle (A/T).  The A/T can provide automatic thrust control through all phases of flight. 

LEFT:  Mode Control Panel (MCP) showing A/T on/off solenoid switch and speed window.  The MCP shown is the Pro model manufactured by CP Flight in Italy (click image to enlarge).

The A/T functionality is designed to operate in unison with the Autopilot (A/P), Nevertheless, a flight crew will not always adhere to this use, some crews preferring to fly manually or partially select either the A/P or A/T.

A search on aviation forums will uncover a plethora of comments concerning the use of the A/T which, combined with A/P use and non-normal procedures (conditions), can be easily be misconstrued.  An interesting discussion can be read here.

This post will examine, in addition to normal A/T operation, some of the non-normal conditions  and there advantages and possible drawbacks.  Single engine operation will not be addressed as this is a separate subject.

For those interested in revising the AFDS system in detail, I recommend perusing the Boeing B737 Automatic Systems Review.

When to Engage / Disengage the Autothrottle (A/T)

The A/T is engaged whenever the A/T toggle is armed and the speed annunciator is illuminated on the Mode Control Panel (MCP).  Either of these two functions can be selected together or singularly.  Likewise, during the takeoff roll the A/T can be engaged (usually after reaching 80 knots ground speed) by pressing the TO/GA buttons located under the thrust lever handles.  This will engage the A/T in the TO/GA command mode.  The main reason that TO/GA command mode is engaged to control the A/T during takeoff and climb is that it simplifies thrust procedures during a busy segment of the flight.

Once engaged, the TO/GA command mode will control all thrust outputs to the engines until the mode is exited, either at the designated altitude set on the MCP, or by activating another automaton mode such as Level Change (LVL CHG).  When TO/GA is engaged, the Flight Mode Annunciator (FMA) will announce TO/GA providing a visual cue.

ABOVE:  FMA Captain-side PFD showing TO/GA annunciated during takeoff roll.

A question commonly asked is: ‘When is the A/T disengaged and in what circumstances?’  Seemingly, like many aspects of flying the Boeing aircraft, there are several answers depending on who you speak to.

Ultimately, A/T use is at the discretion of the pilot flying, however, airline company policy often dictates when the crew can engage and disengage the A/T.  The Flight Crew Training Manual (FCTM) states:

‘A/T use is recommended during takeoff and climb in either automatic or manual flight, and during all other phases of flight’. 

In the FCTM, Boeing recommends the A/T is only used when the A/P is engaged (the A/T and A/P are coupled).

In general, a flight crew should disengage the A/T system at the same time as the A/P.  This enables complete manual input to the flight controls and follows the method recommended by Boeing.

My preference during a non-precision approach is to disconnect the A/T and A/P no later than between 1500 and 1000 feet, or for precision approaches at whatever height is stipulated on the approach chart.  It is not uncommon that a flight crew will manually fly an aircraft from 10,000 feet to landing using the ILS, VNAV and LNAV cues for guidance and situational awareness.  Many pilots enjoy hand-flying the aircraft during the approach phase.

When hand flying the aircraft with the A/T not engaged, it is very important to monitor the airspeed.  This is especially so when during the final approach as thrust can easily decay to a speed very close to stall speed. 

The Autothrottle is Designed to be used in Unison with the Autopilot

The A/T is a sophisticated automated system that will continually update thrust based on minor pitch and attitude changes, and operates exceptionally well when coupled with the A/P.  But, when the A/P is disengaged and the A/T retained, its reliability can be questionable.

Some crews believe that if a landing is carried out with the A/P off and the A/T engaged, and a fall in airspeed occurs, such as during the flare, then the A/T will engage to apply thrust causing the potential for a tail strike.  Likewise, if during the approach there are excessive wind gusts, pitch coupling (discussed below) may occur.

The advantages of using the A/T and A/P together are:

•    Speed is stabilized
•    Speed floor protection is maintained
•    Task loading is reduced
•   Flight crews can concentrate on visual manoeuvring and not have to be overly concerned with wind additives

The disadvantages of using the A/T without the A/P engaged are:

•    Additional crew workload and possible loss of situational awareness
•    Potential excessive and unexpected throttle movement caused by pith and attitude changes
•    Potential excessive airspeed when landing in windy conditions with gusts
•    The potential for pitch coupling to occur (discussed below)
•    A loss of thrust awareness (out of the loop)

Boeing 737 Design

The design of the Boeing 737 is prone to pitch coupling because of its under wing mounted engines.  This causes the thrust vector to pitch up with increasing thrust, and pitch down with a reduction in thrust.

LEFT:  B737 NG style thrust levers.

The A/T is designed to operate in conjunction with the A/P, to produce a consistent aircraft pitch under normal flight conditions.  If the A/P is disengaged but the A/T remains engaged, pitch coupling may develop.

Pitch Coupling

Pitch coupling is when the A/T system actively attempts to maintain thrust based on the pitch/attitude of the aircraft. It occurs when the A/P is not engaged and manual inputs (pitch and roll) are used to control the aircraft. 

If the pitch inputs are excessive, the A/T will advance or retard thrust in an attempt to maintain the selected MCP speed.   This coupling of pitch to thrust can be potentially hazardous when manually flying an approach, and more so in windy conditions.

Scenario - pitch coupling

For example, imagine you are in level flight with A/T on, A/P off, and a brief wind change causes a reduction in airspeed. The A/T will slightly advance the throttles to maintain commanded speed. This in turn will cause the aircraft to pitch slightly upwards, triggering the A/T to respond to the subsequent speed loss by increasing thrust, resulting in further upward pitch. The pilot will then correct this by pushing forward on the control column decreasing pitch. As airspeed increases, the A/T will decrease thrust causing the aircraft to decrease more in pitch.

The outcome is that a coupling between pitch and thrust will occur causing a roll-a-coaster type ride as the aircraft increases and then decreases pitch, based on pilot input and A/T thrust control.

Non-Normal Operations of the Autothrottle (speed button not engaged)

The primary function that the A/T ARM mode is to provide minimum speed protection.  A crew can ARM the throttle but not have it linked to a speed.  To configure the A/T in ARM mode, the solenoid A/T toggle is set to ARM, but the SPEED button located on the MCP is not selected (the annunciator is not illuminated).

LEFT:  A/T ARM solenoid, N1 and speed button.  The N1 and speed button illuminate when either is in active mode.  In the image, the A/T is armed; however, the speed option not selected allowing thrust to be controlled manually.

Scenario - speed button not engaged during TO/GA

To facilitate a TO/GA, some flight crews arm the A/T but do not engage the speed option (speed button on MCP).  This allows a TO/GA to be accomplished more expediently and with less workload during a non-precision approach (the pilot flying only has to push the TO/GA button and the A/T will automatically become operational). 

If a Go-Around is not necessitated during the approach, the A/T solenoid switch is disengaged prior to landing, either by manually 'throwing' the toggle or pressing the A/T buttons located on the thrust levers.  Although favoured by some flight crews, this practice is not authorized by all airlines, with some company policies expressly forbidding the ARM A/T technique.

The recommendation by Boeing in the B737 Flight Crew Training Manual (FCTM) states:

 ‘The A/T ARM mode is not normally recommended because its function can be confusing. The primary feature the A/T ARM mode provides is minimum speed protection in the event the airplane slows to minimum manoeuvring speed. Other features normally associated with the A/T, such as gust protection, are not provided’.  (When the A/T is armed and the speed button option not selected).

A/T Speed Protection and Vref in Windy, Gusty and Turbulent Conditions

When using the A/T during an approach in windy conditions, to provide sufficient wind and gust protection, the command speed should be set to Vref +5 knots.  Variances above or below command speed will cause the A/T to either increase speed (if command speed falls) or conversely decrease speed.  The Vref +5 knots will provide a safety buffer to protect against these variances.   During turbulence, the A/T will maintain a thrust that is higher than necessary (an average) to maintain command speed (Vref).

If the A/T is disengaged or the speed option not engaged, minimum speed protection will be lost.

Refer to ‘Crosswind Landings Part 2’ for additional information on Vref.

Manual Override - Engaging the Clutch Assembly

Occasionally, for any number of reasons, the flight crew may need to override the A/T automation. 

LEFT:  A/T disengage button on throttle thrust lever.  This is an OEM throttle from a B737-300 series.  The button is identical to that used in the NG with the exception that the handles are white and not grey.  Depressing this button will disengage the A/T and disconnect the A/T solenoid switch on the MCP.

The Boeing A/T is fitted with a clutch assembly that allows the flight crew to either advance or retard the thrust levers whilst the A/T is engaged.  Moving the thrust levers during automation will engage the clutch allowing the thrust to be controlled manually.

Whilst this style of flying is usually not recommended, the clutch is there to allow the A/T to be manually overridden, such as in an emergency or for immediate thrust control.

Most flight crews, will not use this override facility, preferring to dial into the speed window of the MCP an altered speed.

Currently ProSim737 does not support manual A/T override.

Simulation Nuances

This discussion relates to the flight dynamics of a real aircraft. Whether these traits present in a simulation depends on how well the flight controls are calibrated, the finesse of the avionics package used, and the accuracy of the aircraft flight model.

For example, depending on which avionics suite is used, the A/T may not maintain the speed selected in the MCP.  This is especially prevalent during extended turns such as during a procedure turn in windy conditions.  To counter against incorrect airspeed you must either, change the speed in the MCP speed window, disengage the A/T and manually alter thrust,  or press the speed annunciator on the MCP.  Pressing the speed annunciator will cause the throttle automation to be turned off; however, the A/T remains in the arm mode.

The last option is a good way to overcome this shortfall of not having manual override.  By disconnecting the speed option, the thrust levers can be jiggled forward or aft to adjust the airspeed.  When the turn has been completed with manual input to maintain the correct airspeed, the automation (A/T) can be engaged again by depressing the speed annunciation button.

It is important if the A/T is not engaged, or is in the ARM only mode, that the crew maintains vigilance on the airspeed of the aircraft.  There have been several incidents in the real world whereby crews have failed to observe airspeed changes.

Manual Flying (no automation engaged)

The benefit of flying with the A/T and A/P not engaged is the ease that the aircraft manoeuvres.  The crew sets the appropriate %N1 that produces the correct amount of thrust to maintain whatever airspeed is desired; gone are the thrust surges as the A/T attempts to maintain airspeed.

Granted, it does take considerable time and patience to become competent at flying manually in a variety of conditions, but the overall enjoyment increases three-fold.

Company Policies

Airline company policies often dictate how a flight crew will fly an aircraft, and while some policies are expedient, more often they relate to cost savings for the company in question.

Policies vary concerning A/T use.  For example, Ryanair has a policy to disconnect the A/T and A/P simultaneously, as does Kenya Airways.  Air New Zealand and QANTAS have policies that encourage a crew to disengage the A/T and A/P by a certain altitude for non-precision approaches. 

Confusion and Second Guessing - Vref with A/T Engaged or Disengaged

There is considerable confusion and second guessing when it comes to determining the Vref to select dependent on whether the A/T is engaged or disconnected at landing.  To simplify,

  • If the A/T is going to be disconnected before touchdown, the command speed should be adjusted to take into account winds and gusts (as discussed above and in ‘Crosswind Landings Part 2’).  It is vital that a flight crew monitor airspeed when the A/T is not engaged as during the approach the speed can decay close to stall speed.
  • If the A/T is to remain engaged during the landing (as in an autoland precision approach), the command speed should be set to Vref +5.  This provides speed protection by keeping the engine thrust at a level that is commensurate with the Vref command speed.

Final Call

There is little argument that the use of the A/T is a major benefit to reduce task loading; however, as with other automated systems, the benefit can come at a cost, which has lead several airlines to introduce company policies prohibiting the use of A/T without the use of the A/P; pitch coupling, excessive vertical speed, and incorrect thrust can lead to hard landings and possible nose wheel collapse, unwanted ground effect, or a crash into terrain.

Ultimately, the decision to use or not use the A/T and A/P as a coupled system is at the discretion of the pilot in command, and depends upon the experience of the crew flying the aircraft, the environmental conditions, and airline company policy.  However, as mentioned earlier, the recommendation made by Boeing preclude A/T use without the A/P being engaged.

Disclaimer

The content in this post has been proof read for accuracy; however, explaining procedures that are convolved and subjective can be challenging.  Errors on occasion present themselves. If you observe an error, please contact me so it can be rectified.

Acronyms and Glossary

A/P – Autopilot (CMD A CMD B)
A/T – Autothrottle

AFDS – Autopilot Flight Director System

Command Speed - In relation to the Autothrottle, Command Speed is Vref +5 knots.
FCTM – Flight Crew Training Manual (Boeing Corporation)
FMA – Flight Mode Annunciator
Manual Flight – Full manual flying. A/T and A/P not engaged
MCP – Mode Control Panel
Minimal Speed Protection – Function of the A/T when engaged.  The A/T has a reversion mode which will activate according to the condition causing the reversion (placard limit). (For example, flaps, gear, etc.)
Pitch Coupling – The coupling of A/T thrust to the pitch of the aircraft.  A/T thrust increases/decreases as aircraft pitch and attitude changes.  Pitch coupling occurs when the A/P is not engaged, but the A/T is enabled
Selected/Designated Speed – The speed that is set in the speed window of the MCP
Take Off/Go Around (TO/GA) – Takeoff Go-around command mode.  This mode is engaged during takeoff roll by depressing one of two buttons beneath the throttle levers
Vref – Landing reference speed

Monday
Aug042014

Boeing 737-800 Takeoff Procedure (simplified)

One aspect many ‘virtual pilots’ find difficult to grasp is the correct method of flying the aircraft, especially the takeoff and transition to climb and cruise. 

LEFT:  Captain-side B737 trim tabs with backlighting turned on (OEM throttle quadrant).

The sheer volume of information available on the Internet often results in ‘information overload’ and it is understandable that many become bewildered to the correct way of completing a task.  The boundaries between fact and fiction quickly become blurred.  Add to this that many articles on the Internet have not been peer reviewed and you have a recipe set for disaster!

New Flyers

This post is to cater towards the new flyer rather than the advanced flyer.  I will not discuss before and after takeoff checklists, how to determine aircraft weights, use of the Control Display Unit (CDU) or how to configure the overhead, but rather instruct on the basic procedures used to takeoff, climb and transition to cruise.

I have attempted to try and simplify the procedure. 

Variability Allowed

The first aspect to take on board is that there is no absolute correct method for takeoff and climb.  Certainly, there are specific tasks that need to be completed; however, there is an envelope of variability allowed.  This variability may relate to how a particular flight crew flies the aircraft, environmental considerations (ice, rain, wind, noise abatement, obstacles, etc.), flight training, or a specific airline policy. 

The second point to consider is what FMC software the avionics suite replicates.  There are different protocols between FMC U10.6 and FMC U10.8 and these equate to different procedures that should be followed.  This is especially so when engaging VNAV and LNAV prior to takeoff. 

I have purposely not addressed in detail these differences, as they can be confusing (another article will discuss VNAV and LNAV departures).  As at writing, ProSim-AR uses U10.8A.

Whenever variability is injected into a subject you will find those who work in absolutes having difficulty.  If you’re the kind of person who likes to know exactly what to do at a particular time, then I’d suggest you find a technique that fits with your liking and personality. 

Table 1 is a ‘ready reckoner’ that explains much of what occurs during the takeoff roll, climb out and transition to altitude.  Like anything there are some specific terms that you need to remember and more importantly understand.

Peer Review

The information in the below chart has been peer reviewed by B737 Captain.  He agreed with the content; however, reiterated the variability allowed by flight crews when flying the B737. 

TABLE 1: Condensed points that need to be addressed during a takeoff and climb.  The procedures are outlined in more detail below the table. The table does not reflect any particular airline operation and is for reference only. 

Procedure

The following procedures assume other essential elements of pre-flight set-up have been completed.

1.    Using the Mode Control Panel (MCP), dial into the altitude window an appropriate target altitude, for example 13,000 feet.

2.    Command speed is set in the MCP speed window.  The speed is set to V2.  The V2 speed is determined by the CDU and is based on aircraft weight and several other parameters.

  • V2 is the minimum takeoff safety speed and provides at least 30° bank capability with takeoff flaps set.
  • A white-coloured airspeed bug is automatically propagated on the speed tape of the PFD at V2 +15/20. V2+15 knots provides 40° bank capability with takeoff flaps set.   The bug is a visual aid to indicate the correct climb-out speed (more about this bug is discussed later on).
  • A flight crew may fly either +15/20 knots (maximum +25 knots) above V2 command speed to lower/increase pitch during takeoff depending on the weight of the aircraft and other environmental variables.  Company policy frequently dictates whether +15/20 knots is added to V2. (this assumes both engines operational).

3.    Turn on (engage) the Flight Director (FD) switches (pilot flying side first).

4.    Set flaps 5 and trim the aircraft using the electric trim on the yoke to the correct trim figure for takeoff. This figure is shown on the CDU (for example, 5.5 degrees) and is calculated dependent upon aircraft weight with passengers and fuel.  It is usual for the trim figure to place the trim tabs somewhere within the green band.

5.    Arm the A/T toggle (the airline Flight Crew Operations Manual (FCOM) may indicate different timings for this procedure).

6.    Release the parking brake and advance the throttle levers manually to around 40%N1 (some Flight Crew Training Manuals differ to the %N1 recommended.  ie: 60% N1). 

  • You do not have to stop the aircraft before initiating 40%N1. A rolling takeoff procedure is recommended for setting takeoff thrust as it expedites the takeoff (uses less runway length) and reduces the risk of foreign object damage or engine surge/stall due to a tailwind or crosswind.
  • After thrust has reached 40%N1, wait for it to stabilise (roughly 2-3 seconds).  Look at the thrust arcs on the EICAS screen to ensure both N1 arcs are stable.  Takeoff distance may be adversely affected if the engines are allowed to stabilize for more than approximately 2 seconds before advancing the thrust levers to takeoff thrust.

7.    Once the throttles are stabilized, advance the thrust levers to takeoff thrust or depress one or both        TO/GA buttons.  If TO/GA is used the thrust levers will  automatically advance by the A/T to the correct %N1 output calculated by the Flight Management System. 

  • Do not push the thrust levers forward of the target %N1 - let the A/T do it (otherwise you will not know if there is a problem with the A/T).  See point 10 concerning hand placement.
  • Ensure target %N1 is initiated by 60 knots ground speed.

8.    Maintain slight forward pressure on the control column to aid in tyre adhesion. Focus on the runway approximately three-quarters in front of the aircraft.  This will assist you to maintain visual awareness and keep the aircraft centered on the centerline.

9.    During initial takeoff roll, the pilot flying should place their hand on the throttle levers in readiness for a rejected takeoff (RTO). The pilot not flying should place his hand behind the throttle levers.  Hand placement facilitates the least physical movement should an RTO be required. 

10.    The pilot not flying will call out ‘80 Knots’.  Pilot flying should slowly release the pressure on the control column so that it is in the neutral position.  This will soon be followed by V1 indicated on the speed tape of the Primary Flight Display (PFD).  Takeoff is mandatory at V1 and Rejected Takeoff (RTO) is now not possible.  The flight crew, to reaffirm this decision, should remove their hands from the throttles; thereby, reinforcing the ‘must fly’ commitment (the speed is beyond the limits for a safe RTO).

11.    At Vr (rotation), pilot not flying calls ‘Rotate’.  Pilot flying slowly and purposely initiates a smooth continuous rotation at a rate of no more than 2 to 3 degrees per second to an initial target pitch attitude of 8-10 degrees (15 degrees maximum).

  • Takeoffs at low thrust setting (low excess energy) will result in a lower initial pitch attitude target to achieve the desired climb speed.
  • Normal lift-off attitude for the B737-800 is between 8 and 10 degrees providing 20 inches of tail clearance at flaps 1 and 5.  Tail contact will occur at 11 degrees of pitch if still on or near the ground.
  • Liftoff attitude is achieved in approximately 3 to 4 seconds depending on airplane weight and thrust setting.

12.    After lift-off, continue to raise the nose smoothly at a rate of no more than 2 to 3 degrees per second toward 15 degrees of pitch attitude.  The Flight Director (FD) cues will probably indicate around 15 degrees. 

  • Be aware that the cues provided by the flight director may on occasion be spurious; therefore, learn to see through the cues to the actual aircraft horizon line.
  • The flight director pitch command is not used for rotation.

13.    You will also need to trim the aircraft to maintain minimum back pressure (neutral stick) on the control column.  The B737 is usually trimmed to enable flight with no pressure on the control column.  It is normal following rotation to trim down a tad to achieve neutral loading on the control column.  Do not trim during rotation.

14.    When positive rate has been achieved, and double checked against the speed and vertical speed tape in the PFD, the pilot flying will call ‘Gear Up’ and pilot not flying will raise the gear to minimize drag and allow air speed to increase.

15.    The Flight Director will command a pitch to maintain an airspeed of V2 +15/20.  Follow the Flight Director (FD) cues, or target a specific vertical speed.  The vertical speed will differ widely when following the FD cues as it depends on weight, fuel, derates, etc. If not using the FD cues, try to maintain a target vertical speed (V/S) of ~2500 feet per minute. 

  • V2+15/20 is the optimum climb speed with takeoff flaps.  It results in maximum altitude gain in the shortest distance from takeoff.
  • If the FD cues appear to be incorrect, or the pitch appears to be too great, ignore the FD and follow vertical speed guidance. 
  • Bear in mind that vertical speed has a direct relationship to aircraft weight - if aircraft weight is moderate use reduced takeoff thrust (derates) to achieve recommended vertical speed.

16.    Fly the Flight Director pitch bars maintaining command speed at V2 +15/20.  Maintain an air speed of Vr +15/20 until you reach a predefined altitude called the Acceleration Height (AH).  AH is often stipulated by by company policy and noise abatement.  It is usually between 1000-1500 feet ASL.

17.    At Acceleration Height, the nose of the aircraft is lowered (pitch decreased) to increase speed and lower vertical speed.  A rough estimate to target is half the takeoff vertical speed.  Press N1 on the MCP (if wanted) and follow FD cues to flaps UP speed. 

  • Note that N1 will automatically be selected at thrust reduction altitude (usually 1500 feet RA).
  • When N1 is selected, the autothrottle will control the speed of the aircraft to the N1 limit set by the Flight Management System (FMS).  Selecting N1 ensures the aircraft has maximum power (climb thrust) in case of a single engine failure. 
  • N1 mode does not control aircraft speed. The autothrottle will set maximum N1 power.   Speed is controlled by aircraft pitch attitude.
  • Selecting N1 on the MCP does not provide any form of speed protection.  

18.    The following should also be done at, or passing through Acceleration Height. 

  • Flaps should be retracted on schedule.  If noise abatement is necessary, flaps retraction may occur at Thrust Reduction Height.  Retract flaps as per the flaps schedule (retract current flap setting as the aircraft's speed passes through the next flap increment setting.  Observe the speed tape of the PFD).
  • When flaps retraction commences the airspeed bug will disappear from the speed tape on the PFD.
  • Do not retract flaps unless the aircraft is accelerating and the airpeed is at, or greater than V2+15/20 - this ensures the speed is within the manoeuvre margin to allow for over-bank protection.  Do not retract flaps below 1000 feet RA.
  • The speed window in the MCP is set to the speed that corresponds to flaps UP speed.  This speed can be read from the speed tape on the PFD.

19.    At flaps UP, either manually fly to altitude or engage automation (Level Change, VNAV, LNAV, V/S, CWS, CMD A/B engaged).  Remember, that unless you select a different mode, the TO/GA command mode will be engaged from takeoff until you each the assigned altitude on the MCP. 

  • Selecting N1 on the MCP does not disengage TO/GA mode.  NOTE:  If you want to disengage/cancel TOGA mode prior to reaching 400 feet ASL, then both Flight Director switches need to be turned off.
  • Some flight crews when reaching acceleration height (AH) call 'Level Change, Set Top Bug' or 'Bug-Up'.  The pilot will then dial into the airspeed window on the MCP the flaps UP speed (as indicated on the PFD).  This does 3 things.  It cancels TOGA speed mode, it causes the Flight Director (FD) cues to lower on the PFD, and it causes the aircraft to increase airspeed so that flaps can be retracted as per the flaps retraction schedule (FRS).
  • Other flight crews may engage Control Wheel Steering (CWS) following flaps UP and fly in this mode to 10,000 feet before engaging the autopilot (CMD A/B).  Whatever the method, it is at the discretion of the pilot in command and the method is often stipulated by company policy.

20.    The aircraft is usually flown at a speed no faster than 250 KIAS to 10,000 feet.  At 10,000 feet, climb speed is automatically populated if automation (VNAV) was engaged at a lower altitude.  The same will occur for cruise speed. 

  • If the aircraft is being flown by hand (manually), then the appropriate climb and cruise speeds will need to be dialed into the MCP.  At 10,000 feet, dial 270 KIAS into the MCP speed window and then at 12,000 feet dial in 290 KIAS.  Follow the Flight Director cues or maintain roughly 2000-2500 fpm vertical speed.  At cruise altitude, transition to level flight and select on the MCP speed window 290-310 KIAS or whatever the optimum speed is (see CDU).

Guidelines Only (FCOMs Differ)

The above guidelines are general.  Specific airline policy for a particular airline may indicate otherwise.  Likewise, there is considerable variation in how to actually fly the B737, and when and what type of automation to engage. 

LEFT:  Qantas Airways departs Queenstown, New Zealand.

There are also, located within the CDU, several parameters which if altered before takeoff can have a marked effect on aircraft performance.

Confusion

It's very easy to become confused during the takeoff phase - especially in relation to automation, V speeds and how and when to change from TOGA to MCP speed.  The takeoff phase occurs quickly and there is a lot to do and quite a bit to remember - there is little time to consult a manual or cheat sheet. 

One way to gain a little extra time during the takeoff transition, is to select an appropriate derate.  Apart from being standard practice in the real-world for many takeoffs, a derate will also help control over-pitching and high vertical speeds which are common when the aircraft is light due to minimal fuel loads and cargo.

% N1

During the initial takeoff, thrust (%N1) is automatically selected when you engage the TOGA buttons.  N1 (%N1) is a measurement in percent of the maximum rpm, where maximum rpm is certified at the rated power output for the engine (most simple explanation).  Therefore, 100%N1 is maximum thrust while 0%N1 is no thrust.

At 80 knots the automated system will engage thrust to N1 at a percentage commensurate with the settings set in the CDU (aircraft weights, climb etc.).  N1 (TOGA command mode during takeoff) always controls the speed of the aircraft with pitch.   To determine what is controlling the thrust of the aircraft, always refer to the Flight Mode Annunciations (FMA) in the PFD.

To enable a quick overview of annunciations during the takeoff refer to Table 2.

After acceleration height has been reached, the nose lowered to increase speed, and flaps retracted; it is at the discretion of the pilot flying (or company policy) to what mode of automation is selected.  It is common place to either use Level Change (LVL CHG) or Vertical Navigation (VNAV) and Lateral navigation (LNAV). 

Theoretically, a crew can fly the F/D cues at V2+15/20 to the altitude set in the MCP; however, there will be no speed protection available.  If the pitch recommendation (Flight Director cues) are not followed, then airspeed may be either above or below the optimal setting.

Unless an alternative mode is selected, the aircraft will remain in TOGA command mode and be controlled by N1 until the altitude set in the MCP is reached.  Other modes which will exit the TOGA mode are LVL CHG, VNAV and Vertical Speed (V/S), or you can engage Altitude Hold (ALT HOLD).  Engaging the A/P will also disengage TOGA command mode.

It is important to understand what controls which command mode.  For example, LVL CHG is controlled by N1 and pitch and in this mode the A/T will use full thrust while the speed will be controlled by pitch.

TABLE 2:  PFD and FMA annunciations observed during takeoff and climb.

Speed Protection

Speed protection is relevant only when a level of automation is selected.  Protection, depends upon the FMC software in use, the automation mode selected, and whether the flaps are extended or fully retracted.

When you select LVL CHG the speed window will open allowing you enter a desired speed.  LVL CHG is speed protected meaning that the aircraft's speed will not precede past the speed set in the MCP.  The LVL CHG mode, which is controlled by N1, will adjust the pitch of the aircraft to match the speed set in the MCP.  

VNAV also has speed protection but not with flaps extended.  The speed in VNAV is defined by the value (speed) set in the CDU (this differs depending upon which FMC software is in use). 

In contrast, Vertical Speed (V/S) provides no speed protection as it holds a set vertical speed.  In V/S, if you are not vigilant, you can easily encounter an over speed or under speed situation. 

Selecting N1 only on the MCP without any other mode engaged does not provide speed protection and only ensures maximum thrust (as set in the FMS).

It is imperative that you carefully observe (scrutinise) the Flight Mode Annunciator (FMA) to ensure the aircraft is flying the correct mode.

Think Ahead

The takeoff can be very fast, especially if you have an aircraft which is light in weight (cargo, passengers and fuel). 

LEFT: B737 CDU showing Takeoff page.  A takeoff can occur without the completion of data; however, some automation features such as VNAV and LNAV will not be available, and V1, V2 and Vr will not be propagated on the speed tape (click to enlarge).

Soon after rotation (Vr), the aircraft will be at acceleration height and beyond…  It’s important to remain on top of what is happening and try to think one step ahead of the automated system that is flying the aircraft. 

Flight crews typically fly manually at least until all the flaps are retracted and the aircraft is in clean configuration.  A command mode is then selected to continue the climb.

If the aircraft is light, flight crews often limit the takeoff thrust by one of several means.  Typically, it is by using a thrust derate and selecting either CLB 1 or CLB 2, or entering an assumed temperature thrust reduction - both done in the CDU.  Selecting either option will cause a longer takeoff roll, delay the rotation point (Vr) and cause a less aggressive high pitch climb than observed if these variables were not altered.

Final Call

Reiterating, the above guidelines are generalist only.  Flight crews use varying methods to fly the airliner and often the method used, will be chosen based on company policy, crew experience, aircraft weight and other environmental factors, such as runway length, weather and winds.

Additional takeoff information - mainly in relation to acceleration height, thrust reduction height, and derated thrust can be read on these pages.

The two tables in this post can be downloaded in PDF format: 

Takeoff Proceedure Table

PFD and FMA Annunciations

Disclaimer

The content in this post has been proof read for accuracy; however, explaining procedures that are  convolved and subjective can be challenging.  Errors on occasion present themselves.  if you observe an error (not a particular airline policy), please contact me so it can rectified.

Acronyms and Glossary

AFDS – Autopilot Flight Director System
AH - Acceleration Height.  The altitude above sea level that aircraft’s nose is lowered to gain speed for flap retraction.  AH is usually 1000 or 1500 feet and is defined by company policy.  In the US acceleration height is usually 800 feet RA.
CDU / FMC – Control Display Unit / Flight Management Computer (term used interchangeably on this website).  The visual part of the Flight Management System (FMS)
CLB 1/2 – Climb power
Command Mode – The mode of automation that controls thrust
EICAS – Engine Indicating and Crew  Alerting System
F/D – Flight Director (Flight Director cues/crosshairs)
FMA – Flight Mode Annunciation located upper portion of Primary Flight Display (PFD)
KIAS – Knots Indicated Air Speed
LNAV – Lateral Navigation
LVL CHG – Level Change Command Mode
MCP – Mode Control Panel
RTO – Rejected Take Off
T/O Power – Takeoff power
Throttle On & Off-Line – Indicates whether the throttle is being controlled by the A/T system.
TOGA – To Go Around Command Mode
TRA - Thrust Reduction Altitude.  The altitude that the engines reduce in power to increase engine longevity.  The height is usually 1500 feet; however, the altitude can be altered in CDU
V/S – Vertical Speed Command Mode
V1 – is the Go/No go speed.  You must fly after reaching V1 as a rejected take off (RTO) will not stop the aircraft before the runway ends
V2 – Takeoff safety speed.  The speed at which the aircraft can safely takeoff with one engine inoperative (Engine Out safe climb speed)
VNAV – Vertical Navigation
Vr – Rotation Speed.  This is the speed at which the pilot should begin pulling back on the control column to achieve a nose up pitch rate
Vr+15/20 – Rotation speed plus additional knots (defined by company policy)

Friday
Jul182014

Original Equipment Manufacture (OEM) Boeing 737NG Lights Test Toggle Switch - Wired and Installed to MIP

The lights test is an often misunderstood but simple procedure.  The light test is carried out by the crew before each flight to determine if all the annunciators are operating correctly (illuminating).  The crew will toggle the switch upward to lights test followed by a routine scan of each annunciator on the overhead, center pedestal and instrument panel.  An inoperative light may preclude take off.

LEFT: OEM Lights Test Switch (before cleaning...) One switch comprising several switches (click to enlarge).

The lights test switch is a three-way switch which can be placed (and locked) in one of three positions; it is not a momentary switch.  Toggling the switch upwards (lights test) illuminates all annunciators located in the MIP, forward and aft overhead and fire suppression panel (wheel well annunciator may not illuminate), while the central position (BRT) provides the brightest illumination for the annunciators (normal operation).  Toggling the switch downwards activates the DIM function dimming the brightness by roughly half that observed when the toggle is in BRT mode.

Depending upon which manufacturer’s Main Instrument Panel (MIP) you are using, the toggle switch may not function this way.  For example, Flight Deck Solutions (FDS) provide a three-way momentary toggle which is not the correct style of switch.  You should not have to hold the toggle to light test as you make your pre-flight scan.  The real toggle switch in the Boeing 737 aircraft is not a momentary switch.

Anatomy of the Toggle Switch

The OEM Light Test switch may appear to be a ‘glorified’ toggle switch with an aviation-sized price tag; however, there is a difference and a reason for this high price tag.  

The switch although relatively simple in output, encompasses 18 (6+6+6) high amperage individual switches assigned to three terminals located on the rear of the switch.  Each terminal can be used to connect to a particular aircraft system, and then to each other.  This allows the toggle switch to turn on or off multiple aircraft systems during the light test. 

The purpose of these multi-terminals is to allow the toggle switch to cater towards the high amperage flow of several dozen annunciators being turned on at any one time during the lights test, in addition to generators and other aircraft systems that are not simulated in Flight Simulator.  In this way, the switch can share the amperage load that the annunciators draw when activated during the light test.

The switch can control the annunciators (korrys) for the MIP, forward overhead, aft overhead, fire suppression panel and any number of modules located in the center pedestal.  

Terminals, Interfacing and Connection

To determine the correct terminals to be used for the light test is no different to a normal toggle-style switch. 

LEFT:  OEM Lights Test switch.  The appearance of the OEM switch is not dissimilar to a normal toggle switch; however, the functionality is different in that there are a number of terminals on the rear of the switch to allow multi-system connection (click to enlarge).

First, ascertain which of the six terminals correlate to the switch movement (toggle up, center and down).  The three unused terminals are used to connect with other systems in the real aircraft (not used in Flight Simulator).

To determine the correct terminals for wiring, a multimeter is set to conductivity (beep) mode.  Place one of the two multimeter prongs on a terminal and then place the other prong on the earth (common) terminal.  Gently move the toggle.   If you have the correct terminal for the position of the toggle, the multimeter will beep indicating an open circuit. The toggle switch does not require a power source, but power is required to illuminate the annunciators during the lights test.  

For an overview of how to use a multimeter see this post - Flight Deck Builders Toolbox - Multimeter.

Daisy Chaining and Systems

Any annunciator can be connected to the light test function, and considering the number of annunciators that the light test function interrogates, it is apparent that you will soon have several dozen wires that need to be accommodated. 

Rather than think of individual annunciators, it is easier to relate a group of like-minded components as a system.  As such, depending upon your simulator set-up, you may have the MIP annunciators as one system, the overhead annunciators as another and the fire suppression panel and modules mounted in the center pedestal as yet another.  If these components are daisy chained together (1+1+11+1+1=connection), only one power wire will be required to be connected at the end of the array.  This minimises the amount of wire required and makes connection easier with the toggle switch.

Two Methods to Connect to the Switch

There are two ways to wire the switch; either through the flight avionics software (software-based solution), or as a stand-alone mechanical system.  There is no particular benefit to either system.  The software solution triggers the Lights Test by opening the circuit on the I/O cards that are attached to the computer, while, the mechanical system replicates how it is done in the real Boring aircraft.

Switch in-line (software connection using ProSim737)

The on/off terminal of the toggle switch is connected to a Leo Bodnar card or other suitable card (I use a Flight Deck Solutions System card), and the card’s USB cable connected to the main computer.  Once the card is connected, the avionics suite software (ProSim737) will automatically register the card with to allow configuration.  Depending upon the type of card used, registration of the inputs and outputs for the card may first need to be registered in Windows (if using Windows 7 type into the search bar joystick and select calibration).

To configure the toggle switch in ProSim737, open the configuration/switches tab and scroll downward until you find the lights test function.  Open the tab beside the name; select the appropriate interface card (Leo Bodnar card) from the drop down menu and save the configuration.  

ProSim737 will automatically scan the interface cards that are installed, and if there is a card that has a power requirement, such as a Phidget 0/16/16 card (used to convert OEM annunciators, modules and panels), the software will make a connection enabling the lights test to function.

Considering the connection is accomplished within the ProSim737 software, it stands to reason the lights test will only operate when ProSim737 is open.

To illuminate the annunciators when the switch is thrown, a 28 volt power supply will need to be connected to the annunciators either separately or in a daisy chain array.

Stand-alone (mechanical connection)

The second method, which is the way it is done in the real aircraft, is to use an OEM 50 amp 6 pull/6 throw relay device. 

Depending upon the type of relay device used (there are several types), it may be possible to connect up to three systems to the one relay.

LEFT:  OEM aviation relay mounted in center pedestal (click to enlarge).

Lights Test Busbar

Although the Lights Test switch has the capacity to connect several systems to the switch itself, it would be unmanageable to attempt to connect each panel to the lights test switch.

To solve this issue a centrally-placed aviation-grade relay has been used in association with a busbar.

A benefit of using an OEM relay and busbar is that the relay acts as a central point for all wires to attach.  The wires from the various systems (panels, korrys, etc) attach to the busbar which in turn connects to the various posts on the relay.

The relay will then open or close the relay enabling power to reach the annunciators (via the busbar) when the switch is positioned to Lights Test.

The stand-alone system will enable the lights test to be carried out without ProSim737 being open.

Although the relay is not large (size of a small entree plate), it can be problematic finding a suitable area in which to mount the relay where it is out of the way.  A good location is to mount the relay inside the pedestal bay either directly to the platform floor or to a wooden flat board that is screwed to the lower section of the center pedestal.

Using the DIM Funtionality (toggle thrown downwards)

This post has only discussed the lights test.  The DIM switch is used to dim the OEM annunciators (korrys) for night work.  Another article explains the DIM functionality.

BELOW: Two very basic flow diagrams provide an overview of the two methods of connection (click diagrams to enlarge).