From: Alasdair C. <ala...@bt...> - 2001-09-24 14:01:24
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On Monday 24 September 2001 04:07, Alex Perry wrote: > > A back-course approach is a non-precision approach flown to circling > > minimums (i.e. no glide slope). For airports that have only a single GS > > transmitter the plates show the primary approach as the runway with the GS > > transmitter. Also a real back course has no marker beacons or other > > positional aids. > > Some BC approaches have straight in minimums. Some airports have markers > on the BC final, details are in the AIM (it uses the white marker light). > But yes, it is non-precision and not something you will encounter every > day in normal flight operations, so especially valuable on a simulation. > > > Keep in mind the localizer is not like a VOR heading defined by a signal > > phase shift, but a biphase signal left or right of the null, thus the > > reversal of instrument indications when flying a back course. Any solution > > should (to the extent feasible) reflect this and not require any unique > > logic, flags, or coding work arounds. > > Definitely; the code works that way right now and this shouldn't be changed. > FG does not permit using ILS for backcourses. The display is OFF when the aircraft is on the wrong side of the locator. It is after all an Instrument _Landing_ system. If the ILS were "visible" from the opposite direction to that intended: a) you would lose LOC info as you overflew the the antenna b) The GS transmitter would take you to the end of the runway instead of the threshold. You would need very good brakes. The code, as you say, works correctly, except in the case of airports which share the same ILS frequency for both runway ends. My FG works fine for all runways except that airport in France with 3 runways sharing a common frequency, so I will just boycott that one till they get their act in gear. Kind regards, -- Alasdair Campbell |