4.4 _The FMS

4.4.1 _Introduction

A Flight Management System is a modern automated flight planning and navigation instrument that is found on most modern airliners, military aircraft, corporate jets and a good number of helicopters and general aviation aircraft. The 'system' actually consists of several components, one of which is the screen/keypad terminal or display/input unit (terminology varies from source to source) that is usually situated, on airliners, on the forward-most section of the central pedestal. Airliners will also often have two or even three such units. In X-Plane, it is this display/input unit that is called the 'FMS'.

There are two variants of the FMS available in PlaneMaker, the 'FMS' and the 'FMS Small' - both have the same functionality and general layout, the only difference is the amount of space they occupy on screen. All our mainline fleet, as well as the EMB-120 is FMS equipped. At the moment, the instrument in the simulator is much less sophisticated than its real world counterpart, reproducing only a few functions of the real thing but using it can seem complicated to new X-Plane users nonetheless. The guide that follows is intended to show you how to manually enter a flight plan from one airport to another with several en route 'waypoints' (Waypoints are specific locations along your flight plan, the journey between two waypoints is known as a 'plan segment') at specified altitudes and how to get the plane to automatically fly that route. FreeWorld flight 1036 from Dublin, Ireland to London-Heathrow, UK is used to illustrate it.

4.4.2 _Entering a flight plan

To follow the example, open our A319/20 and locate it at Dublin, EIDW.
At the start of your flight, the FMS screen will display "Plan Segment 00" on the first line and "???" on the second, where each waypoint's type and code will be displayed (1). While at your airport of departure, before you move anywhere, click the INIT button (2) on the FMS's keypad to initiate a flight plan. You will see the top of the display change from "Plan Segment 00" to "Plan Segment 01" as the FMS has entered the airport you are currently at as the initial waypoint (00) and moved the flight plan on to the next entry for you to enter it.
Ok, so now the FMS knows where you are, you can tell it where you'll be going today. Generally speaking, there are four repeating steps to enter the second and subsequent waypoints in a flight plan:

To delete any waypoint, display it by using the NEXT or PREV button (6) and then click on the CLR button (7).

For the last waypoint, your destination, you will presumably enter an airport code such as "EGLL, London Heathrow" in our example. Note that if you enter the airport's height above sea level for this waypoint or even "00000ft", you are likely to fly into the ground before you get there! If you know that the penultimate waypoint is on the descent to or relatively near, i.e., within 80 miles, to your destination airport, then its best to enter either a pattern/approach altitude for the final waypoint (the airport). If the last leg is going to be fairly long, then enter an appropriate cruise altitude. Or, as in our example, the flight plan entered includes the STAR in detail and the last leg is essentially the final approach, you can enter an altitude which is the airport altitude plus your minimum safe altitude AGL for the approach.

Okay, now the FMS knows where we are, where we want to go and the route to follow. Its time to start up the engines...

4.4.3 _Following a FMS flight plan:

You can of course, fly your flight plan manually. Routes from one waypoint to the next are shown as bright red lines (8) on the EFIS Moving Map (the heading bug is a dark red line). Most aircraft that have an FMS will also have a moving map. Also, HSI instruments can have their sources switched to GPS/FMS mode to show the direction to the current waypoint. The EFIS should also have a DME-to-waypoint display (9) which will show the ID code for the currently active waypoint, the estimated time of arrival at current speed and the distance to it in nautical miles.

To fly a flight plan by autopilot, before you take off use the PREV/NEXT keys to get to the second waypoint ("Plan segment 02") and ensure it is the active waypoint by pressing the "->." button (10). Taxi to the runway (It is assumed that you'll use EIDW's Rwy28 in our example) and take off using manual controls. Once you've climbed out you can activate the autopilot's FMS-following mode by selecting GPS/CDU mode on the HSI selector, and pressing LNAV (11) (called 'LOC' on our Airbus fleet). The autopilot will start turning the aircraft towards the active waypoint. This action will also transfer the waypoint's 'Fly at' altitude to the target altitude display on the autopilot (12). Activate the autopilot's ALT/HLD mode and the autopilot will climb the aircraft to the target altitude at the climb rate set in the autopilot VVI setting (which you can change to a value suitable to your aircraft's performance). NB: if you want the autopilot to control throttle, you must set the desired speed and activate the autopilot's SPD, IAS or ATHR mode manually.

When the aircraft reaches the currently active waypoint, the FMS's active waypoint will automatically switch to the next Plan Segment and any altitude change will be passed to the autopilot. You do nothing unless you want to change the speed or rate-of-climb/descent settings on the autopilot.

If for some reason, the FMS fails to switch to the next waypoint automatically, you can force it to step forward by using the NEXT button to display the desired waypoint and then the "->." button to activate it. You can also use this technique to skip waypoints if you so wish. Note that in v6.70 of X-Plane, the simulator does not anticipate changes in course as well as it did in earlier versions and, having reached one waypoint it may 'overcook' the turn and take some time to get on the right course to the next waypoint. Hopefully this will improve again in v7.xx. Tight turns (>45 degrees) will always cause the plane to stray some way from the point-to-point red line on the EFIS Moving Map (13).

As you approach your destination you will want to decouple the autopilot from the FMS by deactivating or changing the mode on the autopilot. Exactly when to do this depends on the precision of your entered flight plan and how you intend to land the plane. If you are intending an ILS approach or any other published approach which utilises navaids then you should have your flight plan bring you to a point, usually about 10-30 miles out where you can intercept the navaid signals. If you are going to use X-Plane's ATC to guide you in, you may want to disengage the FMS somewhat earlier. If you will be using a visual approach then you can enter a flight plan that will bring you to within sight of the airfield on the runway heading at an appropriate decent rate (14).

4.4.4 _ Saving and Reusing FMS Flight Plans

You will have noticed that it takes a while to enter a detailed flight plan. The good news is that you can save/load flightplans that you wish to use again and again to/from discreet files at any time using the LD and SV buttons on the bottom-left of the FMS keypad. File names should have a ".fms" extension and are stored in X-Plane's ../Output/FMS plans/ folder. We are working on providing prepaired dispatch packages containing flight plans, and other info for our routes, in the mean time the popular third-party appliction 'Goodway Flight Planner' can be used to decode our ICAO routes, and create .fms files. More information on the Goodway website.

4.4.5 _Example Flight Plan: FW1036 Dublin - London Heathrow

This flight plan is a short-haul flight served by FreeWorld from Dublin (EIDW) to London Heathrow (EGLL). This flight is scheduled on our A319/20, but if you are not rated for these aircraft yet you could fly it (but not log the flight) in our EMB-120. Today we will depart on Dublin's Runway 28 using the 'LIFFY2A' SID (Standard Instrument Departure) (click on first map) to join the company route between EIDW and EGLL, i.e., east via upper air route UL975 to the Wallasey VOR and then south-east via upper air route UL10, cruising at FL310 (31,000ft). We plan an aiirval intoto Heathrow's Runway 27L is via the 'BNN2A' STAR (Standard Terminal Arrival). Under normal operation, the STAR will take you as far as the Bovingdon (BNN) VOR at FL90 (9,000ft), after ATC will vector you to intercept the ILS for Rwy 27L. However, the FMS flight plan includes further segments that will allow the plane to be follow the correct radio-failure procedure to intercept the ILS or even to follow the glidepath to 1 mile short of the runway (click on second map).

You can download the ".fms" file for this flight plan here.

Seg Type Code Name Target Alt Notes
00 AIRP EIDW Dublin n/a Initial Waypoint
01 NDB OE Dublin NDB 3,000 SID "LIFFY2A", climb rate 2,500-3,000ft/min, IAS 245kt below 10,000ft, 270kt above 10,000ft
02 VOR DUB Dublin VOR-DME 5,000
03 NDB RSH Rush NDB 9,000
05 FIX GINIS GINIS 31,000 Upper air route UL975, climb rate 1,500-2,200ft/min, IAS 290kt/Mach 0.78
09 VOR WAL Wallasey VOR-DME 31,000
10 NDB WHI Whitgate NDB 31,000 Upper air route UL10, IAS Mach 0.78
11 VOR HON Honiley VOR-DME 31,000
12 NDB WCO Westcott NDB 14,000 STAR "BNN2A", decent rate 2,000-2,500ft/min, IAS Mach 0.70/ 270kt above 10,000ft, 250kt below 10,000ft
13 VOR BNN Bovingdon VOR-DME 9,000
At this point ATC would normally provide vectors to the ILS 27L
14 FIX BNN04 BNN04 6,000 Approach, decent rate 1,000-2,000ft/min to ILL85 then 3% glideslope, IAS 220kt to BNN19, 180kt to ILL82, 160kt to ILL04, then landing speed.
15 FIX BNN19 BNN19 4,000
16 FIX ILL82 ILL82 3,000
17 FIX ILL04 ILL04 1,400
18 FIX ILL01 ILL01 450
19 AIRP EGLL London Heathrow 83 Destination

Many thanks to Cormac Shaw of the X-plane Irish hub for allowing us to use and adapt his excellent FMS tutorial.
© 2004-2005 - Cormac Shaw / FreeWorld Airways