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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.

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Entries in Non Precision Approaches (2)

Saturday
Jul092016

RNAV Approaches

My previous post provided of overview on RNAV and RNP navigation.  This article will explain what a RNAV approach is, provide incite to the operational requirements for a RNAV approach, and discuss specifically the RNAV (RNP) approach.  I will also briefly discuss Approach Procedures and Vertical Guidance (APV) and RNP/ANP values.

The operational criteria for RNAV approaches is complicated and not easy to explain.  There are a number of RNAV approaches (often different for differing areas of the globe) and each is defined by the accuracy of the equipment used in the execution of the approach.  As such, this article is not all encompassing and I encourage you to read other technical articles available on this website and elsewhere.

LEFT:  RNAV 07 L - one of several RNAV approach charts for Los Angeles International Airport (LAX).  The most important aspect of an RNAV approach is that it is a Non-Precision Approach (NPA).  Note the word GPS is written in the title of the approach plate.

RNAV Approaches - Background Information

The Global Positioning System (GPS) is the brand name owned by the US military.  Initially all RNAV approaches were GPS orientated, however, in recent years this has been updated to include Global Navigation Satellite System (GNSS) applications.  GNSS applications are not owned (or controlled) by the US military.  As such, RNAV approach charts often use the word GPS/GNSS interchangeably.

What is an RNAV Approach

The definition for an RNAV approach is 'an instrument approach procedure that relies on the aircraft's area navigation equipment for navigational purposes'.  In other words, a RNAV approach is any non ILS instrument-style approach that does not require the use of terrestrial navigation aids such as VOR, NDB, DME, etc. 

Rather than obtain navigational information directly from  land-based navigational applications, the aids for the approach is obtained from a published route contained within the aircraft's Flight Management System (FMS) and accessible to the crew by the Control Display Unit (CDU).   The  approach broardly uses signals that are beamed from navigational satellites orbiting the Earth to determine the position of the aircraft in relation to the information presented from the database.

All Boeing Flight Management Systems (FMS) are RNAV compliant and have the ability to execute a RNAV approach.

A RNAV approach is classified as a Non-Precision Approach (NPA).

Non-Precision Approaches (NPA)

Before writing further, a very brief overview of Non-Precision Approaches is warranted.

There are three ways to execute a Non-Precision Approach.

(i)   IAN (integrated Approach Navigation).   IAN is a airline customer option and makes a NPA similar to an ILS approach.  A separate article has been written that addresses IAN.

(ii)   Vertical Speed (V/S).  V/S is not normally used when flying a RNAV approach that uses positional information from the aircraft's database.  However, V/S can be used for other Non-Precision Approaches.

(iii)   VNAV (Vertical Navigation).  VNAV is the preferred method to execute a NPA provided the approach is part of the FMS database. 

(iv)   LNAV (Lateral Navigation).  LNAV is mandatory for all approaches that are GPS/GNSS/RNP based.

RNAV Approach Types

The following are RNAV approaches:

(i)    RNAV (GPS) approach;

(ii)   RVAV (RNP) approach;

(iii)  RVAV (RNP) AR approach; and,

(iv)  RNAV (GNSS) approach.

The RNAV (GNSS) approach covers an additional three possible types of approach with each identified by a different minima.  The approaches are:

(i)    RNAV (GNSS) LNAV;

(ii)   APV Baro VNAV approach;

(iii)  APV SBAS approach.

It's easy to become confused by the various types of RNAV approaches, however, the actual flying of a RNAV approach does not differ greatly between each approach type.  The main difference lies in the level of accuracy applied to the approach and the methods used to enable this accuracy that determines what minima can be flown.

Approach Procedures with Vertical Guidance (APV)

APV refers to any approaches which are designed to provide vertical guidance to a Decision Height (DH).  An APV approach is charactertised by a constant descent flight path, a stable airspeed, and a stable rate of descent.  They rely upon Performance Based Navigation.  For an overview of PBN please refer to my earlier post.

The difference between the two APV approaches is that the APV Baro VNAV approach uses barometric altitude information and data from the FMS database to compute vertical guidance.  in contrast the APV SBAS approach uses satellite based augmentation systems, such as WAAS in the US and Canada and EGNOS in Europe, to determine lateral and vertical guidance. 

I will now discuss RNAV approaches in general and specifically, the RNAV (RNP) approach.

Flying The RNAV (GNSS) Approach

The RNAV (GNSS) approach is designed to be flown with the autopilot engaged.  The recommended roll mode is LNAV or HDG SEL.  The preferred method for pitch is VNAV.  If LNAV and VNAV are engaged, the aircraft will fly the lateral and vertical path as determined by the FMS database; the route is displayed in the LEGS page of the CDU.

The aircraft uses the FMS database to determine its lateral and vertical path.  As such, it is very important that the RAW data published in the navigational database is not altered by the flight crew.  Furthermore, the data presented in the CDU should be cross-checked to ensure it is identical to that presented on the RNAV approach chart.

As discussed previously, a RNAV (GNSS) approach is classified as a Non-Precision Approach.  Therefore, minima is at the Minimum Descent Altitude (MDA).   It is good airmanship to add +50 feet to the MDA to reduce the chance of descending through the MDA.  If a RNAV (RNP) or APV approach is being flown, the minima changes from a MDA to a Decision Height (DH). Whatever the requirement, the minima will be annotated on the approach chart.

RNAV (RNP) Approaches

RNP stands for Required Navigation Performance which means that specific navigational requirements must be met prior to and during the execution of the approach.

There are two types of RNAV (RNP) approaches:

(i)   RNAV (RNP) approach; and,

(ii)  RNAV (RNP) AR approach.

Both approaches are similar to a RNAV (GNSS) approach, however, a RNAV (RNP) approach, with the use of various sensors and equipment, achieves far greater accuracy through the use of Performance Based Navigation (PBN), and can therefore be flown to a DA rather than a MDA.

LEFT:  LIDO chart (Lufthansa Systems) depicting the RNAV (RNP) 01 approach into BNE-YBBN (Brisbane Australia).  Note that this chart has a Decision Altitude (DA) rather than a Minimum Descent Altitude (MDA).  Chart courtesy of NaviGraph (click to enlarge).

RNP/ANP - How It Works

A RNAV (RNP) approach uses RNP/ANP which is the comparison between the Required Navigation Position (RNP) and the Actual Navigation Position (ANP).   If the data becomes erroneous such as from the loss of a GPS signal, the ANP value will exceed the RNP value.    The use of RNP/ANP enables greater accuracy in determining the position of the aircraft.

RNP/ANP Alerts

If an anomaly occurs between RNP and ANP one of two RNP alerts will be generated:

(i)    VERIFY POSITION - displayed in the scratchpad of the CDU; or,

(ii)   UNABLE REQD NAV PERF-RNP - displayed on the Navigation Display (ND) on the EFIS Map. 

It should be noted that different versions of CDU software will generate different alerts.  This is because newer software takes into account advances in PBN.  To determine which software version is in use, press IDENT from the CDU main page (lsk1L) and check OP PROGRAM.  ProSim-Ar uses U10-8a.

The variables for RNP/ANP can be viewed in the CDU in the POS REF page (page 3), the LEGS page when a route is active, and also on the Navigation Display (ND).

A second type of RNP approach is the RNAV (RNP) AR approach.  This approach enables you to have curved flight paths into airports surrounded by terrain and other obstacles. Hence why special aircraft and aircrew authorization (AR) is required for these approaches.  Other than AR and additional flight crew training, the approach is identical to the RNAV (RNP) approach.

Advantages of RNAV and RNAV (RNP) Approaches

The benefit of using a RNAV approach over a traditional step-down approach is that the aircraft can maintain a constant angle (Continuous Descent Final Approach (CDFA)) until reaching minima.  This has positive benefits to fuel savings, engine life, passenger comfort, situational awareness, and also lowers flight crew stress (no step-downs to be followed).   Additionally, it also minimises Flight Into Terrain (CFIT) events.

A further advantage is that the minimas for a RNAV approach are more flexible than those published for a standard Non-Precision Approach not using RNAV.  RNAV approach charts have differing descent minima depending upon the type of RNAV approach.

For example, if flying a RNAV (RNP) approach the MDA is replaced by a DH.  This enables a lower altitude to be flown prior to a mandatory go-around if the runway threshold is not in sight.  The reason that a RNAV (RNP) approach has a DH rather than a MDA (and its resulting lower altitude constraint) is the far greater accuracy achieved through the use of Performance Based Navigation (PBN).

Approach To Land Using RNAV

The following addresses the basics of what is required to execute a RNAV approach.

Prior to beginning the approach, the crew must brief the approach and complete needed preparations. These include, but are not limited to, the following items, which may be included in an approach review card or other type of briefing aid:

(i)     Equipment that must be operational prior to starting the approach;

(ii)    Selection of the approach procedure, normally without modifications from the aircraft's navigation database;

(iii)    For airplanes without Navigation Performance Scales (NPS), one pilot should have the map display in the 10 NM or less range.  This is to monitor path tracking during the final approach Segment;

(iv)    For airplanes with NPS, the map display range may be set as the crew desires;

(v)     TERR display selected on at least the Captain or First Officer side of the ND;

(vi)     The RNP progress page displayed on the CDU (as needed). For airplanes equipped with NPS, selection of the CDU page is at the crew's discretion;

(vii)    The navigation radios must be set according to the type of approach; and,

(viii)   If a RNAV (RNP) approach is being executed, ensure that there is no UNABLE REQD NAV PERF - RNP alert displayed before starting the approach.

In addition to the above, airline Standard Operational Procedures (SOPs) may require additional caveats, such as range rings to be set up on the ND to provide enhanced situational awareness (CDU FIX page).

Select the approach procedure from the arrivals page of the CDU and cross-check this data with that published on the approach chart, especially the altitude constraints and the Glide Path (GP).

If the Initial Approach Fix (IAF) has an ‘at or above’ altitude restriction, it may be changed to an ‘at’ altitude restriction using the same altitude. Speed modifications are allowed as long as the maximum published speed is not exceeded. No other lateral or vertical modifications should be made at or after the IAF.

Beginning the Approach

Select LNAV no later than the IAF. If on radar vectors, select LNAV when established on an intercept heading to the final approach course. VNAV PTH must be engaged and annotated in the Flight Mode Annunciator (FMA) for all segments that contain a Glide Path (GP) angle, as shown on the LEGS page, and must be selected no later than the Final Approach Fix (FAF) or published glide path intercept point.

Speed Intervention (INTV), if desired, can be used prior to the GP.  Good airmanship directs that the next lower altitude constraint is dialled into the MCP altitude window as the aircraft passes through the previous constraint.  When 300 feet below the Missed Approach Altitude (MAA) re-set the altitude window in the MCP to the MAA.

Final Approach using RNAV

When initiating descent on the final approach path (the GP), select landing flaps, slow to final approach speed, and do the landing checklist. Speed limits published on the approach chart must be complied with to enable adequate bank angle margins. 

At minima, or as directed by the airline's SOP, the autopilot followed by the autothrottle is disconnected and a visual 'hands on' approach made to the runway threshold.

Once established on final approach, a RNAV approach is flown like any other approach.

Final Call

The Boeing aircraft is capable of several types of Non-Precision Approaches, however, outside the use of ILS and possibly IAN, the RNAV approach enables an accurate glide path to be followed to minima.  While it's true that the differing types of RNAV approaches can be confusing due to their close relationship, the approach is straightforward to fly.

This short article is but a primer to understanding an RNAV approach.  Further information can be found in the FCTM, FCOM and airlines SOP.

In my next article we will look some of the possible 'gotchas' that can occur when using VNAV.

References

Flight Crew Training Manual (FCTM), Flight Crew Operations Manual (FCOM) and airline SOP.

Acronyms and Glossary

Annunciator – Often called a korry, it is a light that illuminates when a specific condition is met
ANP - Actual Navigation Position
APV - Approach Procedure with Vertical Guidance
CFIT - Continuous Flight Into Terrain
DME – Distance Measuring Equipment
FAF - Final Approach Fix
FCOM - Flight Crew Operations Manual (Boeing)
FCTM - Flight Crew Training Manual (Boeing)
FMA - Flight Mode Annunciator
FMC – Flight Management Computer
FMS – Flight Management System
Gotcha - An unfavorable feature of a product or item that has not been fully disclosed or is not obvious.
GPS – Global Positioning System
GNSS - Global Navigation Satellite System
IAF - Initial Approach Fix
Korry - See annunciator
LNAV – Lateral Navigation
LPV - Localizer Performance with Vertical Guidance
MAA - Missed Approach Altitude
MCP – Mode Control Panel
ND – Navigation Display
NPA - Non Precision Approach
PBN - Performance Based Navigation
RNAV – Area Navigation
RNP - Required Navigation Performance
SOP - Airline Standard Operational Procedure.  A manual that provides additional information to the FCTM and FCOM
SBAS - Satellite based augmentation systems.  In the U.S. called WAAS and Europe called EGNOS.
VNAV – Vertical Navigation
VNAV PTH – Vertical Navigation Path
VNAV SPD – Vertical Navigation Speed
VOR – VHF Omni Directional Radio Range

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.