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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).

 

All funds are used to offset the cost of server and website hosting (Thank You...)

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Journal Archive (Newest First)

Entries in B737-800 Boeing Flight Simulator (17)

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.  The A/T provides 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 autothrottle 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 autopilot or autothrottle.

A search on aviation forums will uncover a plethora of comments concerning the use of the autothrottle which, combined with autopilot use and non-normal procedures, can be easily be misconstrued.  An interesting discussion can be read on PPRuNe.

This post will examine, in addition to normal A/T operation, some of the non-normal conditions, their 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.

Autothrottle (A/T) Use

The autothrottle 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. 

The autothrottle is usually engaged during the takeoff roll by pressing the TO/GA buttons located under the thrust lever handles.  This is done when %N1 stabilises for both engines at around 40%N1.  This will engage the autothrottle in the TO/GA command mode.  The reason the autothrottle is used during takeoff is to simplify 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.

The use of the autothrottle 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’.

When to Engage / Disengage the Autothrottle

A question commonly asked is: ‘When is the autothrottle disengaged and in what circumstances’  Seemingly, like many aspects of flying the Boeing aircraft, there are several answers depending on who you speak to or what reference you read.

In the FCTM, Boeing recommends the autothrottle be used only when the autopilot is engaged (autopilot and autothrottle coupled).

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

My preference during an approach is to disconnect the autothottle and autopilot no later than between 1500 and 1000 feet.  However, disconnecting the autothrottle and autopilot earlier in the approach provides additional time to transition from automated flight to manual flight, and establish a 'feel' for the aircraft well before landing.  It's not uncommon that a flight crew will manually fly an aircraft from 10,000 feet to landing using the Flight Director (FD), ILS, VNAV and LNAV cues on the Primary Flight Display (PFD) for guidance and the information displayed on the Navigation Display (ND) for situational awareness.  Many pilots enjoy hand-flying the aircraft during the approach phase.

Important Point:

  • Whenever hand flying the aircraft with the autothottle not engaged, it's very important to monitor the airspeed.  This is especially so during the final approach, when 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 autothrottle 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 autopilot.  But, when the autopilot is disengaged and the autothrottle retained, its reliability can be questionable.

Some crews believe that if a landing is carried out with the autopilot off and the autothrottle engaged, and a fall in airspeed occurs, such as during the flare, then the autothrottle will 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 autothrottle and autopilot together are:

(i)      Speed is stabilized;
(ii)     Speed floor protection is maintained;
(iii)    Task loading is reduced; and,
(iv)    Flight crews can concentrate on visual manoeuvring and not have to be overly concerned with wind additives

The disadvantages of using the autothrottle without the autopilot engaged are:

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

Boeing 737 Design

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

LEFT:  B737 NG thrust levers.

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

Pitch Coupling

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

If the pitch inputs are excessive, the autothrottle 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 autothrottle engaged and the autopilot not engaged, and a brief wind change causes a reduction in airspeed. The autothrottle will slightly advance the throttles to maintain commanded speed. This in turn will cause the aircraft to pitch slightly upwards, triggering the autothrottle 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 to decease pitch. As airspeed increases, the autothrottle 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 autothrottle thrust control.

Autothrottle Non-Normal Operations (Arm Mode)

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 autothrottle in ARM mode, the  A/T toggle solenoid on the MCP is set to ARM, but the SPEED button 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 is not selected (the annunciator is extinguished).  This enables thrust to be controlled manually.

Scenario - speed button not selected during approach

Some flight crews prefer during an approach, to arm the autothrottle, but not have the speed option engaged (speed annunciator extinguished). 

By doing this during a non-precision approach, it enables a Go-Around to be executed more expediently and with less workload  (the pilot flying only has to push the TO/GA buttons on the thrust lever and the autothrottle will engage).

If the approach proceeds smoothly and a Go-Around is not required, the crew will prior to landing, disengage the A/T solenoid switch on the MCP by either 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).

Autothrottle Speed Protection and Vref in Windy, Gusty and Turbulent Conditions

To provide sufficient wind and gust protection, when using the autothrottle during an approach in windy conditions, the command speed should be set to Vref +5 knots, or set to the correct wind additive based on wind speed, direction and gusts.   The use of an additive creates a safety envelope that takes into account potential changes in wind speed and minimises the chance of the autothrottle commanding a speed that falls below Vref.  Remember, that as wind speed varies the autothrottle will command a thrust based on the speed.

During turbulence, the autothrottle will maintain a thrust that is higher than necessary (an average) to maintain command speed (Vref).

Important Points

  • When the autothrottle is not engaged, or the speed option deselected, minimum speed protection is lost.
  • Always add a wind additive to Vref based on wind strength and gusts.  Doing so provides speed protection when the autothrottle is engaged.

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 autothrottle. 

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 usually white and not grey in colour.  Depressing this button will disengage the autothrottle and disconnect the A/T solenoid switch on the MCP.

The Boeing autothrottle system is fitted with a clutch assembly that enables the flight crew to either advance or retard the thrust levers whilst the autothrottle is engaged.  By moving the thrust levers, the clutch assembly is engaged and the autothrottle goes offline whilst the levers are moved.

The clutch is there to enable the autothrottle to be manually overridden, such as in an emergency or for immediate thrust control.

ProSim737 does not (as at 2018) support manual autothrottle override.

Simulation Nuances

The above information primarily discusses the systems that operate in the real aircraft.  Whether these systems are functional in a simulation, depends on the avionics suite used (Sim Avionics, Project Magenta, etc).

For example, the autothrottle may not maintain the speed selected in the MCP during particular circumstances (ie: turns in high winds). If this occurred in the real world, a crew would manually override the autothrottle.  However, if the avionics suite does not have this functionality, then the next best option is to either:

(i)      Disengage the autothrottle and manually alter thrust; or,

(ii)     Deselect the speed annunciator on the MCP.

Deselecting the speed annunciator will cause the throttle automation to be disengaged; however, the autothrottle will remain in the armed mode.  The second option is a good way to overcome this shortfall of not having manual override.  By deselecting the speed option, the thrust levers can be jiggled forward or aft to adjust the airspeed.  When the speed has been rectified by manual input, the autothrottle can be engaged again by depressing the speed  button.

It's important if the autothrottle is not engaged, or is in the ARM 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 autothrottle and autopilot 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 autothrottle 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 policies often dictate how a flight crew will fly an aircraft, and while some policies are expedient, more often than not they are based on economics (cost savings) for the company in question.

Policies vary concerning autothrottle use.  For example, Ryanair has a policy to disconnect the autothrottle and autopilot simultaneously, as does Kenya Airways.  Air New Zealand and QANTAS have a similar policy, however, define an altitude that disconnection must occur at or before.   If an airline doesn't have a policy, then it's at the discretion of the flight crew who should follow Boeing's recommendation in the FCTM.

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 autothrottle is engaged or disconnected at landing.  To simplify,

  • If the autothrottle 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 autothrottle is not engaged as during the approach the speed can decay close to stall speed.
  • If the autothrottle 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 autothrottle 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 autothrottle without the use of the autopilot; 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 autothrottle and autopilot 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,  the recommendation made by Boeing preclude autothrottle use without the autopilot being engaged.

Disclaimer

The content in this post has been proof read for accuracy; however, explaining procedures that are convolved and often subjective, can be challenging.  Occasionally errors occur. 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.

LAST UPDATE 06 March 2019

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)

Thursday
Dec122013

Adding A New Forward Section To The Existing Platform

After spending time working with some minor, but frustratingly time consuming 'teething problems' with the throttle quadrant, I decided it was time to do something different.  Therefore, I have added a meter or so to the front of the platform.  The reason for the addition was to make an area on the platform for the computers and power supplies to reside, rather than just sit on the floor of the room.

Addition From Wood - Not Aluminium

To use aluminium for the forward addition is a  waste of material and resources.  After all, the forward section of the platform is located behind the Main Instrument Panel (MIP) and is not readily visible.  I have used wood obtained from the local recycling center - I enjoy recycling products as much as possible... 

The platform I am using is modular, and it's comparitively easy to add sections to increase its overall size.

In the photograph above, a Nicolson router is being used  to make the circular holes that will be used to route the cables from the throttle unit to the IMM and computer.   While most of the cabling will be under the platform, several custom VGA cables coming from the throttle unit will lie above the platform and be secured in a tube surround.

Nicolson Tools (USA)

Nicolson tools are made in the USA and the company produces very heavy and beefy products; the very sharp router made short work of the wood!

The forward platform addition will fit snugly against the existing aluminium platform and blend almost seamlessly.

Other articles dealing with the floor structure can be read below.

Construction Commenced - New Platform to Install OEM Control Columns

Modular Floor Base Platform Installed

Friday
Nov222013

B737 Throttle Quadrant - Trim Wheels and Trim Indicator Tabs 

This post, the third last concerning the throttle quadrant conversion, will discuss the spinning of the trim wheels and movement of the trim tab indicators; both integral components of the throttle quadrant.  For a list of posts dealing with the conversion of the 737 TQ see the bottom of this page for links - B737 Throttle Quadrant.

1:  TRIM WHEELS

The trim wheels were implemented by Boeing in the mid 1950’s with the introduction of the Boeing 707 aircraft and been a part of the flight deck ever since.  The main reason Boeing has continued the use of this system in contrast with other manufacturer, who have removed the spinning trim wheels is redundancy.  Boeing believes that the flight crew should have the ability to manually alter trim should a number of cascading failures occur.

Whatever the reason for Boeing continuing with this older style technology, many flight crews have learnt to “hate “ the spinning trim wheels.  They are noisy and distracting, not to mention dangerous if a flight crew accidently leaves the handle in the extended position; there is a reason that they are called “knee knockers”.  

Many virtual pilots are accustomed to using manual trim when flying a Cessna or a small twin such as the King Air.  In such aircraft altering trim by hand is straightforward and a necessary part of trimming the aircraft.  However, a jet such as the B737 it is a tad different; to alter the trim by hand would require the flight crew to manually rotate the trim wheels several dozen times to notice any appreciable result in trim.  As such, the electric trim switches on the yokes are mainly used to alter trim.

LEFT: Captain-side trim wheel and trim tab indicator.  I was fortunate that the throttle unit I aquired retained its light plates in excellent condition.  It's not uncommon to find that the light plates are faded, scratched and cracked from removal of the unit from the aircraft.

Motors, Interface Cards and Speed of Trim Wheel

The power to spin the trim wheels comes from two 12 Volt DC pump motors installed within the throttle unit.  A Phidget High Current AC Controller card is used to interface the trim wheels to the flight avionics software (proSim737). The cards are located in the Interface Master Module (IMM) and connected to the throttle unit by customised VGA cables.

The trim wheels can spin at two speeds.  The autopilot producing a different speed to that of manual trim (no automation selected).  A Phidget card is used to control the variability, with each of the two channels programmed to a different speed.  To alter the actual revolutions of the trim wheel, each channel is accessible directly from within the ProSim737 software configuration.   

To allow the trim system to be used by CMD A and/or CMD B, a second card is installed to ensure duplicity.  

Correct Timing

The trim wheels have white longitudinal line painted on each trim wheel.  This line serves two purposes: as a visual reference when the trims wheels are spinning, and to determine the number of revolutions per second during calibration.  To ascertain the correct number of wheel revolutions per second, a digital tachometer is used in the same way a mechanic would tune an older style motor vehicle.

Out of interest, in manual trim, 250 revolutions of the trim wheels are necessary to move the trim tab indicators from full up to full down.

Two Speed or Four ?

The B737 has four different trim revolution speeds, each speed dependent upon the level of automation used and the radio altitude the aircraft is above the ground.

Although it is possible to program this logic into the Alpha Quadrant cards and bypass ProSim737 software entirely (closed system), it was decided not to as the difference in two of the four speeds is marginal and probably unnoticeable.  Further, the level of complexity increases somewhat programming four speeds. 

Autopilot mode rotates the trim wheels at a faster rate than when in manual trim.

Trim Wheel Braking

The real B737 incorporates a braking mechanism on the trim wheels that inhibits wheel movement when there is no input received to the system from either the auto pilot or electric trim switches. The brake operates by electromagnetic radiation and is always on, being released when an input is received.  

LEFT:  Trim wheel removed showing heavy duty spline shaft.

An unsuccessful attempt was made to replicate this using two military specification high torque brake motors.   The motors incorporate a brake mechanism, but the torque was so high and the breaking potential so great, that when the brake was reengaging/disengaging there was a loud thud that could not be ignored.  Further, the motor became very hot when the brake system was engaged and vibrated excessively due to its high power rating.

At the time, a lower torque motor could not be procured and a decision was made to use the 12 volt pump motors.  Therefore; the trim wheels take an extra second or so to spin down – not a major imposition and barely noticeable when flying the aircraft..

Deactivating Trim Wheel Spinning

Most of my virtual flying is at night and noisy and vibrating trim wheels can easily aggravate others in the house attempting to sleep.  To allow easy disconnection of the trim wheels, I have configured the right side trim stabilizer toggle to cut the power to the trim wheels.  Although not authentic, sometimes minor alterations need to be made to a system to make it more user friendly.

2:  TRIM TAB INDICATOR MOVEMENT

The trim tab indicators are used as a visual reference to indicate to the flight crew the trim of the aircraft.  The trim and subsequent movement of the indicator tabs are activated either by depressing the electric trim switch on the yoke or by turning the trim wheels by hand.

Phidget Card

A Phidget Motor Controller Advanced Servo card and servo is used to control the movement of the two trim tab indicators, while the logic to activate the servo is directly from the flight avionics software.  The speed that the trim tabs move is set through ProSim737 (trim speed).

Hardware Modifications

To allow the servo to connect directly to the trim tab indicators, a small tab of aluminium was welded to the main trim tab shaft.  A thin screw wire was then connected from the servo to the tab to allow nay movement of the trim tab to be registered by the servo. 

LEFT:  Aluminium tab connected to servo.  Servo is mounted behind aluminium plate.  You can just make out the screw wire between the servo and the tab (click image to enlarge).

Determining Accuracy

There is little point in implementing movement of the trim tab indicators if a high level of accuracy is not possible; therefore, it’s important that that the position of the tabs matches that of the flight avionics software and virtual aircraft.  To ensure positional accuracy and maintain repeatability the servo was calibrated throughout its range of movement and checked against the “virtual trim tab strip” that can be placed on the EICAS screen within the ProSim737 software.  

The short video below shows the smoothness in movement of the trim tab indicators.  You will note the TQ vibrates somewhat.  This is because I have yet to secure it to the platform.