737-E DME/DME autotune
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Join Date: Sep 2001
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737-E DME/DME autotune
OK, I'm no rocket scientist but I can't seem to work out the logic system of DME/DME autotune on the 737-E
What exactly is the DME selection criteria?
What exactly is the DME selection criteria?
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Not exactly sure what a "737-E" is, but...
normally, DME updating requires the best fix geometry of the (available) stations (within a specified distance from the aircraft). You're not going to get a very good fix if the station is too close or too far away... or if the angle formed between the first DME, the aircraft and the second DME is too acute or too obtuse. I believe the best angle is 90 degrees.
Depending on the type of DME Interrogator fitted to your aircraft, a single DME Interrogator can tune/scan/track many stations by itself....and I believe that if an interrogator fails (on a two DME Interrogator aircraft), you can still get a DME-DME update.
Were you looking for a more technical description than this?
Rgds.
Q
[ 18 September 2001: Message edited by: QAVION ]
normally, DME updating requires the best fix geometry of the (available) stations (within a specified distance from the aircraft). You're not going to get a very good fix if the station is too close or too far away... or if the angle formed between the first DME, the aircraft and the second DME is too acute or too obtuse. I believe the best angle is 90 degrees.
Depending on the type of DME Interrogator fitted to your aircraft, a single DME Interrogator can tune/scan/track many stations by itself....and I believe that if an interrogator fails (on a two DME Interrogator aircraft), you can still get a DME-DME update.
Were you looking for a more technical description than this?
Rgds.
Q
[ 18 September 2001: Message edited by: QAVION ]
The best navigation aids are broadly defined to be the 10 navigation aids closest to the aircraft's present position. In order to qualify as candidates for the best navigations aid list, these facilities must be within a range which is suitable for its class of operation and the present altitude of the aeroplane.
From the best navigation list the FMCS determines the best navigation aid pair as a function of the line-of-position (LOP) crossing angle. The crossing angle of LOPs must lie between 30° and 150°. The best navigation pair is defined as the combination which procuces a crossing angle closest to the ideal of 90°. Reselection of the best navaid pair will be performend every two minutes.
If one of the DME interrogators has been switched to MAN mode, the FMCS will attempt to use the manually tuned DME station and to find a complementary DME station that provides an acceptable LOP crossing angle. When this is not possible, the DME interrogator in the AUTO mode may be operated by the FMCS in a frequency-agile submode (if agility DME is installed) in order to preserve the primary dual-DME navigation solution. When this occurs, the single AUTO mode DME interrogator will be tuned alternately to each of two DME stations, selected by the FMCS as the best pair, at intervals of 5 seconds; otherwise, the FMCS may operate in a VOR/DME mode.
From the best navigation list the FMCS determines the best navigation aid pair as a function of the line-of-position (LOP) crossing angle. The crossing angle of LOPs must lie between 30° and 150°. The best navigation pair is defined as the combination which procuces a crossing angle closest to the ideal of 90°. Reselection of the best navaid pair will be performend every two minutes.
If one of the DME interrogators has been switched to MAN mode, the FMCS will attempt to use the manually tuned DME station and to find a complementary DME station that provides an acceptable LOP crossing angle. When this is not possible, the DME interrogator in the AUTO mode may be operated by the FMCS in a frequency-agile submode (if agility DME is installed) in order to preserve the primary dual-DME navigation solution. When this occurs, the single AUTO mode DME interrogator will be tuned alternately to each of two DME stations, selected by the FMCS as the best pair, at intervals of 5 seconds; otherwise, the FMCS may operate in a VOR/DME mode.
