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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.

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Journal Archive (Newest First)
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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 briefly discuss the concept of Integrated Approach Navigation (IAN) and explain the procedures recommended by Boeing to successfully implement IAN.  I have attempted to cover the main points, but 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 must be selected from the CDU database.

Although IAN is an airline option, and not every airline carrier will have IAN as part of their avionics suite, it is becoming more popular as the 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 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 and Manual Approaches

The distance to runway threshold, approach guidance information (FMC, RNAV, VOR , etc) and vertical and lateral deviation markers are displayed when IAN is in range of the designated runway - whether IAN is engaged or not engaged.  This provides additional guidance when executing a manual approach (no automation selected). 

For example, historically, 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 manual approach.

These are but a few of the advantages to using the new 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 beside CMD whenever IAN is active.  The display will differ, for example, LNAV/VNAV, FMC, LOC, depending on the source of the navigation guidance used for the approach (navigation, radio or CDU data).

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 arm/engage.

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 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 signally 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, but will become 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.  

Using IAN - Proceedure

  • IAN is engaged only after clearance for final approach has been received from Air Traffic Control (ATC). 
  • 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 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;
  • An appropriate approach has been selected from the CDU database which does have a glide path attached to it;
  • The appropriate runway heading is set on the MCP course window (Captian/First Officer side or both depending on CDU set-up);
  • The aircraft is on an inbound intercept heading;
  • ATC clearance for the approach has been received; and,
  • Both lateral and vertical deviation pointers (magenta diamonds) are visible on the attitude display, in their correct position.

Using IAN - Set-Up

  • Select the appropriate approach to use from the CDU database.  Ensure that the approach has a glide slope.  Set the glide slope altitude to the MCP altitude window. Do not alter any of the approach constraints.
  • 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 display – 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 (Captain/First Officer side or both depending on CDU set-up).
  • When the runway data is displayed on the PFD, IAN is in range.  At this stage the APP button on the MCP is pressed to engage 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
  • As the aircraft closes on the approach course, the FAC and G/P annunciations will alter colour from white to green indicating the IAN system is engaged.  At this stage the lateral and vertical deviation markers will 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 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 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.

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

IMPORTANT:  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 is engaged and the glide path captured can be difficult.  Therefore, maintaining the correct approach speed is paramount to a successful IAN approach.  If using VNAV/LNAV, it often is good idea to engage SPD INTV to manually control MCP speed.

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 to LVAV, Level Change or VNAV.  However, once the potential situations 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, which may differ to the CDU database for the chosen approach.

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 before intercepting the glide path.  Configuring the aircraft 2 miles from the FAF allows the crew to select landing flaps at the FAF and complete the landing checklist prior to, or at the same time that the glide path is engaged and becomes alive.

2:  Forgetting to set the missed approach altitude in the MCP.

Failing to wait until the aircraft has descended 300 feet after glide path capture, to reset the MCP altitude to the missed approach altitude, 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 convoluted approach course or 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 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. 

5:  Forgetting to set the altitude in the MCP as per the CDU glide path

A common mistake for newcomers 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.

Four shortfalls are:

  1. ProSim737 displays the IAN runway data when the aircraft reaches 400 feet radio altitude.  This is incorrect.  In the real B737-800, this information is displayed immediately following the engagement of TO/GA during the take-off roll. 
  2. 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)
  3. The runway data and approach guidance displays are not identical to the real aircraft – they are the incorrect font size.  This is but a minor issue, which can easily be rectified.
  4. Interestingly, ProSim737 allows IAN approaches with any CDU generated approach procedure.  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 (outside source). 

For those interested in replicating real world procedures, only approaches depicting a glide path should be selected from the CDU.

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.

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

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