Aircraft maintenance

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Revision as of 15:49, 10 December 2011 by T3r (talk | contribs) (→‎Tanks)
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Some bugfixes and improvements require aircraft to be adapted/fixed to remain airworthy, to be working correctly, or to be taking full advantage of latest FlightGear version. The following Airworthiness Directives and Aviation Maintenance Alerts issued by the FlightGear Aviation Administration (FAA) should be considered for aircraft maintenance (A/B/C/D checks).


Deprecated engine properties "egt_degc" and "egt_degf"

Properties will be removed with a future JSBSim/FlightGear version. Replace "_" with "-", i.e. use:



With >= FG2.4.0 the "level-gal_us" and "level-lbs" properties of tanks


are connected and computed automatically. Aircraft should only set one of these properties manually (i.e. on start-up), and NOT try to configure both.

The properties for mass, volume and density are interconnected and so are those representing the same property with just individual units. Usually, fuel density is set statically, so volume is derived from mass and vice versa. The last set property wins. The used formula is mass = volume * density Internally, content, density, capacity and the usable fuel is stored in metric units and the (US-)English units are derived by constant built in conversion factors:

  • LBS_PER_KG = 2.20462262;
  • KG_PER_LBS = 1.0/LBS_PER_KG;
  • USGAL_PER_M3 = 1000.0/3.785411784;
  • M3_PER_USGAL = 1.0/USGAL_PER_M3;
  • IMPGAL_PER_M3 = 1000.0/4.54609;

The value of the property "usable-xxx" is constantly compared against "content-xxx" and drives the value of the boolean property "empty". If content is less than usable, empty is true.

All the individual tanks are summed up to the properties /consumables/fuel/total-fuel-xxx

Not sure, there is something about it that results in an issue for some aircraft who try to mess with several properties. Torsten knows more...


Realistic NAV radio

With >= FG2.6.0 the NAV and DME radios are more realistic. Signals are "flickering" when at the edge of a station's range. The properties


may flicker on-off-on-... frequently. Some autopilots (mainly airliners) try to capture a localizer as soon as a NAV station is "in-range", which results in an issue when signal isn't stable yet. As a work-around, only use the properties above to enable/disable the NAV/DME cockpit display (to get the realistic display flickering effect), but use the property


to detect a valid signal for the autopilot's capture logic, e.g. add a condition that requires a high signal strength, say above 0.9, to avoid capturing too early while the signal is still unstable.

DME vs NAV radio

Aircraft with DME displays must include a DME instrument. With <=FG2.4.0 is was enough to add a "nav" instrument in order to also get some DME properties - this is deprecated. Add the DME instrument:


The use of the NAV radio's DME properties is also deprecated. Instead of




The deprecated DME properties are still supported with FG2.6.0, but will be removed with a later version.

Incorrect DME range displayed

Many aircraft (mainly airliners) do not display the correct DME distance. To obtain the correct DME distance, use DME instrument properties - not the nav instrument's properties. For DMEs, do not use:


which does not reflect the correct DME distance. Instead use


DME/NAV display beyond station range

Many aircraft (mainly airliners) display DME and/or NAV information, even though the DME/VOR/ILS is out of range - or even when the selected station doesn't even provide DME/NAV information - which is not realistic. NAV/DME displays should have a condition respecting


for DME displays and a condition on


for NAV/ILS displays, and otherwise blank/disable the distance/direction/display.

Attitude indicator

The FG attitude indicator supports caging, usually triggered by a push/pull switch next to the attitude indicator. The correct property name of FG's attitude indicator instrument is named


Apparently a copy & paste issue has resulted in a large number of FlightGear aircraft incorrectly using the property


which has no effect. "caged" should be replaced by "caged-flag".


Stereo sound files unsupported

Stereo sound files can not (/no longer) be used for sound effects and must be converted to mono. Proper sound effects always required single channel wave sources. A 3D sound engine uses information on position, direction, speed of every source to render realistic 3D sound. This does not work with stereo files, since both channels would be rendered at the same position (no stereo effect anyway). Stereo files were usable with <=FG2.4.0, but resulted in many effects being broken (Doppler etc). To avoid such issues, >= FG2.6.0 produces a warning and rejects loading stereo files.

Avoiding sound file duplication

We have a large number of sound file duplicates in the FG repositories, which blow up the repository and download size. Generic sound files should be placed in the central /fgdata/Sound folder - and not be copied by individual aircraft. Check if a sound sample is available in the central "Sounds" folder, before copying it into an aircraft. New generic sounds may also be submitted to the central folder (use "git merge request" or mailing list) - which is better than producing loads of duplicates.


The default FlightGear flight recorder matches propeller/piston aircraft only. For >= FG2.6.0 the correct flight recorder configuration file matching the aircraft type should be selected. It is also possible to add custom properties.

Rating System

A new rating system was introduced. Aircraft ratings should be encoded in the aircraft -set.xml file from where they are be picked up by launchers like FGRun, web pages etc. See Formalizing Aircraft Status.