Posts: 635
Joined: Sat Nov 17, 2001 7:53 pm

Autopilot Drifting

Sun Nov 25, 2001 11:57 pm

hi evryone
i was just wondering are there any autopilot systems that allow u to select a heading and and the plane will fly that heading and automatically point the nose in the right direction to compensate for the winds? i know that u can just keep ur eye on the FMS and adjust the heading bug to make it so that the drift counter goes to 0 degrees. but i was wondering if there are any heading holders that do it for u?

cheers guiy

RE: Autopilot Drifting

Mon Nov 26, 2001 12:45 am

As far as FMS navigation is concerned....I don't belive heading is a factor. the FMS uses track. Simply because you could have a hdg of 250, but actually have a track of 260.
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Autopilot Drifting

Mon Nov 26, 2001 1:33 am

Autopilot "Heading" modes by definition do not apply wind correction. If they did, it would be called "Track" mode.

For the most part, AFCS (automatic flight control System) heading mode is only used to intercept tracks or courses and in the event that ATC issues vectors during the approach phase.

If some aircraft had a "wind corrected" heading mode as you suggest and others had a conventional heading mode, there is increased potential for collision.

For example, if you had 2 aircraft on parallel tracks, one with "wind corrected" heading mode and the other without, and both were issued a heading vector from ATC to maintain 120 degrees, then if the winds were right, one aircraft would eventually drift into the other aircrafts flightpath.

Some FMSs have an "FMS Heading" mode which simply supplies the AFCS with psuedo-heading reference using the selected RNAV mode (INS/LRN/FMS/GPS etc.). The FMS actually takes out any correction for track or winds in this mode. The convenience of this mode is that the pilot does not have to switch AFCS modes to execute vector commands.

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RE: Autopilot Drifting

Tue Nov 27, 2001 12:10 am

When you say "...automatically points the nose in the right direction to compensate for the winds?", this is in itself changing the heading.

Heading IS the direction the nose is pointing.

When the autopilot is flying TO/FROM a VOR on a specific radial, the autopilot adjusts its "heading" to compensate for crosswinds to remain on its selected course (radial).
You're only as good as your last departure.

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