Quote:
Originally Posted by Scott Hersha
Does anybody even use these things anymore? I doubt it. I haven't flown an airplane with a marker beacon antenna in at least ten years. We have an NDB, but its not needed here either. The final approach segment is defined by Glide Scope Intercept as far as I know. If someone ran over that thing with a lawn mower, it may be weeks before anyone even noticed. It should be in a museum.
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Even if you are just shooting the ILS from radar vectors, it's a good idea to cross check your position at glide slope intercept using the OM, or suitable substitute (NDB, DME, GPS) and monitor your VVI (VSI) for two reasons:
1) Antenna side lobes create false glide paths considerably higher than the true glide slope. (AIM 1-1-9.d.4)
2) During certain failures of the ILS system, localizer and/or glide slope indications will center regardless of your position, with no warning flags. (A Quantas flight ran into this several years ago, I think GPWS saved their bacon).
As a side note, the approach we are looking at has a bunch of interesting features: the ILS signal is unreliable inside 1.8 DME, the at or above 2100' restriction over open ocean, 2000' MSA over open ocean, 2400RVR required with a 300' decision height.
Paige