Poor GPS coverage.
Hi EESDL.
Interested to know whether the above comment about poor GPS coverage is from personal experience, or just repeating what you have heard/read elsewhere.
The reason for asking - I spent 12 southern summers flying over about 1/3 of the Antarctic, including flying to the South Pole, and do not ever recall having any issues with full GPS coverage.
I have read that the theoretical coverage of the GPS satellites is better at the equator and poorer at the poles, but never found it to be a problem in practice.
(Apparently, GLONASS is the opposite, better at Poles and worse at equator, but our nav kit only received GPS)
(Slight thread drift, but a similar comment on RadAlt performance - I have frequently seen references to RadAlts not being reliable over snow surfaces, but never experienced any issues at all with the RadAlts in the Twin Otters I was flying. In all the snow landings I did, everything from rock hard icy surfaces to deep soft powder snow, the RadAlt always read zero as we touched down. In fact, we used a last resort emergency blind landing technique that relied totally on RadAlt, and the skis would touch as the RadAlt reached zero.
I accept that other aircraft/radalt systems may behave differently, but do have a suspicion that reports of erroneous indications may be more due to loss of pilot's depth perception in conditions of poor surface and horizon definition)