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Welcome

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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If you see any errors or omissions, please contact me to correct the information. 

Journal Archive (Newest First)
Tuesday
Sep202016

White Caps for Locking Toggle Switches on Overhead

It has taken a very long time to collect the assortment of OEM needed parts to complete the forward and aft overhead panels.  Finally the build is now in progress and it’s hoped completion will be towards the end of 2016.

LEFT:  Lower electrical panel showing reproduction latex-style cap (ELEC 2) and OEM Honeywell Switch Accessory 15PA90-6W (ELEC 1). Click to enlarge.   For those with keen eyes - yes that is a voice recorder in the lower panel - more to follow in later posts.  Of interest are the two different white caps (read main text). 

Earlier on, I had purchased several dozen Honeywell toggle switches, however, for whatever reason the white caps on the toggles were either missing or damaged.  I was intending to use reproduction white push-on caps (aka white condoms), but the caps failed to  fit snugly to the OEM switches, and their appearance was slightly different to the OEM version - the ends of the caps looked rather bulbous.

My next choice was to use latex caps that are used in automotive industry.  Once again, the appearance was slightly different and the automotive caps sported a small nipple at the end of each cap where they had been connected to the plastic retaining spur; I found the appearance of the nipple disconcerting.

Short of viable options, I purchased the OEM white caps from Honeywell which is the company that supplies Boeing.  If you carefully look at the above picture of the lower electrical panel (click image to enlarge picture), you will observe the nearest toggle switch has been fitted with an automotive style cap; the nipple and joining line is clearly visible.  The second toggle switch is fitted with the Honeywell white cap.

OEM White Cap Anatomy

The reproduction slip-on caps currently available on the market bear little resemblance to those made by Honeywell.

LEFT:   Honeywell Switch Accessory 15PA90-6W showing internal screw thread.  The thread screws onto the stem of the toggle switch (click to enlarge).

Most of the reproduction white caps are either a push-on condom style, or are a white-capped head attached to a slender hollow shaft.  The shaft then slides over the existing switch stem.

The Honeywell caps are not slip-on latex but a solidly-produced head with an internal aluminium thread.  The head is designed to be screwed directly to the shaft of the toggle switches.  Firmly attached to this head is the white latex cap. 

Mounting

To mount the white cap on a toggle, witch you must first gently heat the switch stem which will loosen the head of the toggle.  It then is an easy matter to screw off the head and replace it with the OEM head.

Measurements

Not everyone wants to utilise OEM parts.  As such I have provided the measurements of the switch head (courtesy of Honeywell) for those who wish to try their hand at making their own white caps.

As the overhead build continues, I will be posting more articles that showcase the overhead and the various panels and functionality.

Glossary

Honeywell – Avionics conglomerate that is heavily involved in the defence and aviation industries.
OEM – Original Equipment Manufacture (aka real aircraft part).

Friday
Aug262016

Assembly of Forward Overhead Panel

Construction of the simulator began in 2011.  It is now 2016 and I am perplexed to why the build has taken so long to complete.   Of course, opting to try and use OEM (Original Equipment Manufacture) parts whenever possible has added significant time to the project -  especially the procurement of parts.

LEFT:  Forward overhead using OEM parts (click to enlarge).

Most of the parts that make up the forward overhead have now been obtained and assembly of the components is well advanced.   Very soon the wiring from the panels to the Phidgets cards will begin.  This will be followed by several hours of testing to check correct functionality and to ensure perfect harmony between components and systems. 

A basic frame has been constructed to enable the overhead to be easily positioned to enable the wiring to be done with a little more ease.  After the forward overhead is completed, work on the aft overhead will commence.  Rome, it seems, was not built in a day.

Certainly, completion of the forward overhead will be the major project over the next few months.

Thursday
Aug042016

FS-FlightControl Instructor Operating Station (IOS) - Review

Virtual flyers can be grouped into three broad groups.  Those that are satisfied using a desktop simulator, those that gravitate toward a professional simulator, and those that strive to replicate, as close as possible, a Level D simulation.  No matter which group you belong, there is a requirement for a feature-rich, reliable, and stable Instructor Operator Station (IOS).

LEFT:  Opening screen for FS-FlightControl IOS on the server computer.  IOS can be easily configured to automatically open after Windows start-up.  (click to enlarge).

This post will introduce the Instructor Station FS-FlightControl, developed by AB-Tools GmbH, a company located in Germany.  The review is not meant to be comprehensive as such a document would be as long as the product’s operating manual.  Rather, we will examine some of the product’s features prior to making an assessment of the software’s reliability and ease of use.

What is IOS - Do I need It

IOS is an acronym for Instructor Operating Station.  At its simplest, it's the menu system in Flight Simulator that enables you to choose from several parameters to create a pre-programmed flight scenario. 

A dedicated instructor station is far more than a few options to alter the time, place, and scenario in the simulator.  A good instructor station should enable you to set basic flight scenarios, in addition to being able to monitor set tasks and parameters.  The software should provide clear and readable displays, be set out logically, be easy to operate, and also be able to initiate system failures.  Furthermore, the software must be stable, reliable and consistent in its output.

There are several Instructor Operating Stations available on the market and most high-level avionics suites come with a ready-made IOS as part of their software.  Therefore, the question must be asked - why is there a need to purchase a stand-alone IOS.  

Put bluntly, many generic instructor stations have been added at the back-end of an avionics suite.  These instructor stations can lack functionality, features, and ease of use.  Furthermore, their layout is often not optimal or configurable.

IOS Features - FS-FlightControl

The features and functionality that are supported by IOS are extensive, however, bear in mind that the instructor station has been designed to operate across different simulator platforms and avionics suites; not every feature may operate with the intended avionics suite.  For example, flight plans can be generated and sent to FSX in the standard .pln format, but they cannot be send directly to ProSim-AR in the correct format (as at the time of writing).

LEFT:  Screen shot showing the POSITION page display of IOS.  Note the easy to navigate menu at the bottom area of the screen (twelve modules).  This menu system is available on all IOS pages and enables quick and easy navigation between modules (click to enlarge).

I have purposely not duplicated what has already been written on the FS-FlightControl website.  The website provides a well detailed description of the features and functionality of the software and includes numerous screen shots.

Broadly speaking, IOS has been developed around 12 main modules.  Like-minded themes have been grouped into whatever module is specific to the subject.  If the information exceeds what can be displayed on one page, then one or more sub-pages (sub-tabs) are provided.  There is a gamut of features

Main Modules

Position:   Aircraft re-position, runway preference, aircraft scenario, approach presets, airport selection and re-position options.

Map:   Street map, satellite map and height map.   Navaids, AI aircraft, weather, aircraft location, compass and route/flight plan overlay.

Flight Planing:   Route and flight plan generation with load tool.  Importing and exporting of data with flight plan generated onto roving MAP.

Conditions:   Environmental conditions relating to weather (artificial and real-time), visibility (CAT presets), winds, clouds, precipitation, altitude levels, barometric pressure, presets, time and season, accelerated time, and user-generated conditions.  This section is very detailed and is examined in several sub-tabs.  Many of the presets are as easy as clicking a button on the screen.  For example, ILS visibility conditions can be generated by clicking one of the CAT buttons (CAT I, II, III, IIIa/b/c).

Push back:   Graphical interface enabling push back of aircraft at any angle and distance.

Fuel/Load:   Fuel volume, passenger, crew and cargo weights, aircraft weights (ZFW), center of gravity (%CG) and load tool.

View/Slew:   Alters external camera views of aircraft and enables the slewing of aircraft.

Failures:   Aircraft system failure conditions that can be triggered immediately, at pre-defined times, or at random.

Statistics:   Approach statistics - Graphical representation of aircraft in relation to vertical and lateral position, aircraft position, ground altitude, vertical speed, pitch, and bank angle.  Results can be exported to Google Earth for further analysis.

Network:   Module to control all computers and software within your simulation network (server and any number of client computers).

Aircraft:   Selectable list of aircraft options re: altitude, speed, direction, radios, TCAS alert status, engine parameter outputs, throttle outputs, autopilot, light and switches, etc. 

Settings:   Customization of all aircraft, map, and program parameters: colours, fonts, map layouts, etc.  Additionally, other variables can be customised such as CAT visibilities and decision heights.

Favoured Features

I’ll be honest, the more I use IOS the more I enjoy my simulation experience.  At the very least, IOS provides a reliable way to store various approach scenarios to numerous airports at different times, seasons and weather conditions.   Granted, that this can be done from the flight simulator menu, however, it cannot be done as cleanly nor as quickly as it can from the IOS module.

Although I do not use all the features available in the program, there are several that I continually use.  It is these I will discuss in further detail.

POSITION:  Position refers to the position of the aircraft whether it be on the ground or in the air.  IOS enables the user to select from several ground positions such as the gate, runway, terminal, base approach, straight-in approach, etc. A click of the mouse will position your aircraft to any of several preset locations. 

I find this to be a very good time saver, especially if you do not want to simulate a long taxi or some other part of the flight but wish to concentrate only on one aspect – such as the approach phase.  In addition to various presets, this page also allows customized approaches to be generated and saved.

Another aspect of this page deserves mention; the ability to select a chosen aircraft livery, parameter list (fuel state, trim, radio frequencies, etc) and save this to custom-named 'slot'.  This is another time-saving feature and easy method to choose a pre-saved livery of an aircraft type.

STATISTICS:   For those who fly by the numbers and want to improve their approach techniques, the statistics section provides a graphical interface that records the vertical and lateral deviation of the approach.  It also records airspeed, vertical speed and several other characteristics.

CONDITIONS:   Conditions broadly refers to environmental and weather conditions at the airport selected, or at various pre-selected waypoints or weather stations.  Changing weather conditions, visibility, season and time is as easy as clicking a button.

This page is exceptionally feature-rich and the instructor station can generate live weather, weather from an imported METAR string or any number of pre-saved weather themes.  For those interested in setting up specific weather events, for flight training, it is very easy to do so.  

MAP:  The map is a hidden gem that enables you to overlay a wealth of information onto a street or satellite map of the area of operation. 

LEFT:  Screenshot showing MAP display page.  Many advanced features that can be displayed as a map overlay.  The tabs along the sides of the page can be clicked to turn features on or off (click to enlarge).

 For example, the user aircraft and AI aircraft are graphically represented along with all navigation aids which includes VORS, NDBs, high and low jetways, ILS feathers and waypoints.  Wind direction and current barometric pressure can also be displayed along with the current SID, STAR or route.  Whilst on the ground all aprons, runways and taxiways are shown.  Navigating to an assigned runway could not be easier as the user aircraft icon shows the position of the aircraft at all times. 

As with all windows, the MAP can be displayed as a separate screen on another monitor.  Therefore, it is possible to have IOS open on two monitors with one monitor showing the MAP view while the other monitor displays a different view.

An added advantage is the ability to position your aircraft anywhere on the map and create a position fix along with altitude, direction, pitch, bank, airspeed and radio frequencies.  This information can be saved for future activation from the POSITION page.  This enables you to quickly and easily set-up an approach and save this approach for future use.

For those that fly on-line, VATSIM, IVAO and PilotEdge are supported.

NETWORK:  IOS enables the user to program the software to control what programs open or close on any computer that is connected to the network.

For example, I use a batch file  to open and close flight simulator, ProSim-AR and other FS related programs (weather, flight analysis, etc).  IOS when turned on from the client will automatically execute the opening of the batch file on the server computer.  Likewise, when triggered, IOS will engage the batch file I use to close flight simulator and other ancillary programs.  Additionally, a time delay can be configured to cause a delay between the closure of programs and the turning off of the server computer.  

Installation of IOS - Server and Client

The software package is downloaded from the developer’s website and consists of a self-extracting .exe file. 

As IOS has networking capability, it's not necessary to install IOS to the computer that has flight simulator installed; it will operate on a client computer.  Additionally, a wizard is used to direct you through the installation process and configuration.  Networking to a client is done via SimConnect.  FSUPIC and WideFS are not required.

LEFT:  Screenshot showing the PUSH BACK display page (click to enlarge). 

Although networking is achieved through the use of SimConnect which can, at times, be problematic, I did not experience any issues with SimConnect in relation to the installation and networking of the instructor station. 

Configuration

Configuring the program to suit your requirements is done from the SETTINGS page.  Variables can be altered for each aircraft, and aircraft profiles can easily be created that save particular parameters or conditions.  Likewise, the software can be altered to enable a particular font style and colour to be displayed along with a zoom value and size.  The process is straightforward.

Pretty much everything in IOS is able to be configured to your liking.

One aspect of IOS I found to be very handy, was that when you close the instructor station it will keep the last known settings.  This means the parameters for the next flight session (if not altered) will be identical to the last.

Ease of Use

The IOS program is set-out intuitively and the various pages (modules) follow a logical sequence with like-minded themes bundled together on the same page.  The twelve page main menu located at the bottom of each page is promulgated across all pages and enables quick access to various features. 

LEFT:  Screenshot showing the FAILURES display page.  Note the open conditions call-out box.  There are several sub-pages (sub-tabs) that deal with failures.  Failures are an important asset to enthusiasts striving for realism (click to enlarge).

Unlike other instructor stations, all information relating to a specific theme is located on the one main page (for example, failures or position page); it is not necessary to navigate between several pages trying to find the information.  Furthermore, the screen display can resized to either fill your display or only part fill it.

Another advantage is the implementation of large-style buttons that enable quick and accurate identification of a module.  Everything is easy to find and access.

Program Administration

Program administration encapsulates the opening and closing of programs from one or multiple computers. 

Without an instructor station or the use of batch files, several programs must be opened on the client and server computer to begin a flight.  This takes time and the process can be unwieldy.

If the instructor station is configured correctly, it is a two-step process to begin a flight.  First the computers must be turned on.  Second, from the client the FS-ControlControl IOS icon is depressed.  Once IOS opens on the client computer it will communicate with the server computer (via SimConnect) and open any number of programs on the server (assuming they have been configured correctly in the IOS NETWORK page).  

Once Flight Simulator opens and you are on the flight line it’s only a matter of using the instructor station to alter any variables particular to the flight (airport, aircraft position, weather, fuel, weight, etc).  All changes are automatically promulgated across the network to Flight Simulator.

The important aspect to note, is that other than turning on the server and client computers, everything is done from the one screen on the client computer using the one mouse/keyboard.  Likewise, when closing the simulator session everything can be done, including turning off the server computer, from the instructor station.

Cross-Platform Operations

The IOS operates with Microsoft Flight Simulator X (FSX/FS10) including Steam Edition, and with Lockheed Martin Prepar3D® 1.x, 2.x and 3.x. in a Windows environment.  A separate APP is available for Android and Apple (iOS).  The software works traditionally using the keyboard and mouse in addition to being optimized for touch screens.  IOS can be run either on the computer that has Flight Simulator installed or from a networked client computer.

Stability and Speed

The last thing anyone wants is a crash to desktop caused by a bug-ridden piece of software that exhibits stability issues, poor performance, and does not operate consistently.  

The stability of the instructor station is excellent.  In my simulator set-up the IOS is installed on a client computer and networked to Flight Simulator located on a server computer.  The software loads quickly and interacts with the simulator seamlessly.  

The speed at which software interacts with Flight Simulator is important and it’s pleasing to note that IOS commands do not exhibit any significant time lag between the client and server computers.  There is no time lag when switching between any of the interface screens on the instructor station.  Surprisingly, this includes the MAP mode.  Often a high definition map with several overlays cannot generate its resultant map within an acceptable time. 

This said, internet connection speed may cause users to experience different speeds.

The time taken to open the instructor station from the icon on the client computer is approximately 10-15 seconds.

Updates to IOS

The software developer is very proactive and software updates with improvements, minor fixes and new features are regularly provided free of charge.  

LEFT:  Screenshot showing the CONDITIONS display page.  This page has several sub-pages that deal with conditions.  For example, real weather, presets, season, ILS visibility and accelerated time.  Note the display box in the lower left side that shows the frame rates (click to enlarge).

The developer realizes that each person’s requirements for an instructor station is different, and as such, entertains ideas and suggestions for additional features or improvements from end-users.

Support

FS-FlightControl does not have a dedicated forum, however the developer  replies promptly to all e-mails sent via the software help page.  

A benefit of sending e-mail directly from the software is that the log files from your system are automatically attached to any outgoing message.  This enables the developer to easily understand the issue, saves time in asking for further information, and leads to a faster resolution.

Dedicated Manual

A manual for any in-depth software is an absolute necessity.  It is pleasing to note that the developer has written a manual and does not rely on a forum to provide answers to common questions.

The manual, which reflects the latest software build, is accessed from the FS-FlightControl IOS website.  If necessary a .pdf is available on request.  

Additionally, the manual can also be accessed directly from the software.  Each page has several small question marks (?) that when clicked navigate the user to the appropriate help section in the manual.  If you find the questions marks unsightly, then they can be turned off from the SETTINGS page.

Software Trial

This review has only examined several of the features that the instructor station is capable of.  To enable a comprehensive examination of the software, IOS can be installed with full functionality (including any prospective updates) for a period of 14 days.  After this time has elapsed, the software will need to be purchased.

Final Call

Considering the scope of what an instructor station does and how it can be used to enhance the effectiveness of a simulator, there is little doubt that a good IOS is essential.    

I've spent considerable time using the FS-FlightControl IOS and although this review touches on but a few of the features of IOS, I believe this software to be superior to other contemporary products.   It certainly has enhanced how I use the simulator leading to a more enjoyable experience.

The IOS software and further information can be downloaded at FS-FlightControl IOS.

  • Please note I have no affiliation with FS-FlightControl.  I have not been provided with ‘free’ software, nor did I receive a discount in return for a favourable review.  The comments and recommendations I have made are my own.
  • Flight Simulator, in this article, refers to the use FSX/FS10.  I use the B737 avionics suite developed by ProSim-AR.
Tuesday
Jul192016

VNAV 'Gotchas' - Avoiding Unwanted Level-Offs

One aspect of using VNAV during published instrument departures, arrivals, and approaches is that it can cause unnecessary level-offs. 

These level-offs can cause engines to spool needlessly, increase fuel cost and stagger a Continuous Descent Final Approach (CDFA) such as when executing  an RNAV approach. 

LEFT:  RAAF B737 Wedgetail transitioning a STAR into YSSY (Sydney Australia).  It is not only domestic airliners that must meet altitude constraints; military aircraft also  must meet the same requirements when landing at a non-military airport (click to enlarge).  Image is copyright xairforces.net.  For those interested in flying the Wedgetail, there is a model available for ProSim-AR users on their forum page.

To avoid this, and ensure that minimum altitude constraints are met, two techniques can be used.

METHOD 1Constraints Are Not Closely Spaced.

This technique is normally used when waypoints with altitude constraints are not closely spaced (in other words, there is a moderate distance between altitude constraints).

During climbs, the maximum or hard altitude constraints should be set in the Mode Control Panel (MCP).

Minimum crossing altitudes need not be set in the MCP as the FMC message function will alert the crew if these constraints cannot be satisfied.

During descent, the MCP altitude is set to the next constraint or clearance altitude, whichever will be reached first.

Immediately prior to reaching the constraint, when compliance with the constraint is assured, and when cleared to the next constraint, the MCP altitude is reset to the next constraint/altitude level.

METHOD 2:  Constraints Are Closely Spaced. 

Where constraints are closely spaced to the extent that crew workload is adversely affected, and unwanted level-offs maybe a concern, the following is approved:

For departures, set the highest of the closely-spaced constraints.

For arrivals, initially set the lowest of the closely-spaced altitude constraints or the Final Approach Fix (FAF) altitude, whichever is higher.

IMPORTANT: When using either technique, the FMS generated path should be checked against each altitude constraint displayed in the CDU to ensure that the path complies with all constraints.  Furthermore, the selection of a pitch mode other than VNAV PTH or VNAV SPD should be avoided, as this will result in the potential violation of altitude constraints.

To enlarge more on VNAV is beyond the scope of this post.  A future post will address this topic in more detail.

Crew Controls Automation - Not Vice Versa

However, the system is only as good as the knowledge of the person pushing the buttons.  It is very important that a flight crew control the automation rather than the automation control the flight crew. 

If VNAV begins to do something that is unplanned or unexpected, do not spend precious time ‘thinking about the reasons why’ – disconnect VNAV and use a more traditional method or hand floy the aircraft.  Then, determine why VNAV did what it did.  The most common comment heard in today's modern cockpits is ‘What is it doing now…

Final Call

VNAV is an easy concept to understand, but it can be confusing due to innumerable variables associated with vertical navigation.  VNAV is probably one of the more complicated systems that virtual and real pilots alike have to understand.  When using VNAV it is paramount to maintain vigilance on what it is doing at any one time, especially during descent and final approach.     Furthermore, it is good airmanship to always have a redundancy plan in place – a ‘what if’ should VNAV fail to do what was anticipated.

This is but one post that explains VNAV.  The below articles deal with VNAV:

Speed Intervention (SPD INTV) and VNAV Use
Cognitive Engineering Analysis of the Use of VNAV

Acronyms and Glossary

CDU - Control Display Unit (aka FMC)
FAF – Final Approach Fix
FMC - Flight Management Computer
FMS - Flight Management System.  Supply of data to the FMC and CDU
Gotcha - An annoying or unfavorable feature of a product or item that has not been fully disclosed or is not obvious.
LNAV – Lateral Navigation
MCP – Mode Control Panel
NPA - Non Precision Approach
VNAV – Vertical Navigation
VNAV PTH – Vertical Navigation Path
VNAV SPD – Vertical Navigation Speed

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