| gengis |
1st Dec 2005 07:03 |
Jon, there are 2 types of glideslope antennae on the -400. 1st one, the "Glideslope Capture Antenna" is located in the radome. This is used during the intercept of the glideslope & during the capture. After the gear is extended, the system switches to the "Glideslope Track Antenna" located on the forward part of the nose gear door, which gives a slightly better correlation of the position of the nose gear to the localiser than the capture antenna (due to the size of the airplane). This is the one used for the remainder of the approach. The reason that the "capture" antenna is used for the initial part of the approach is that prior to nose gear extension the track antenna is of no use.
It is an interesting point, because in a max crosswind approach, if you use the crab technique, the amount of drift that you lay off to track the centreline will actually give a slightly upwind of localiser indication, since the nose gear will be significantly displaced due to the crab angle. I have noticed this. However, if you use the sideslip technique, or watch the performance of the autopilots in an automatic-coupled approach where the system adopts a partial sideslip during the later part of the approach, the localiser indicates on centreline due to the reduced crab angle in a sideslip approach, leaving the nose gear much closer to the centreline.
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