Danialanwar From Switzerland, joined Mar 2001, 421 posts, RR: 0 Posted (13 years 6 months 2 weeks 5 days 19 hours ago) and read 5839 times:
Does anybody have statistics on altimeter accuracy. That is, if the altimeter reads (say) FL360, how likely am I to really be at that altitude (or more precise, at that air-pressure-altitude) and how likely am I to be off? I guess hwat I'm looking for is a mean divergence (hope to be zero) and a standard deviation / variance, plus preferablytype of distribution (is divergence normally distributed?)
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Broke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 3, posted (13 years 6 months 2 weeks 5 days 9 hours ago) and read 5795 times:
The accuracy of the entire altimetry system (Altimeter, Air Data Computer, Static Ports and Lines) must be no more than +- 135' for an airplane to qualify for operation in RVSM airspace. Prior to that, the system error had to be no more than +- 260'. This is for flights from FL 290 to FL 410.
Rendezvous From New Zealand, joined May 2001, 536 posts, RR: 0
Reply 5, posted (13 years 6 months 2 weeks 3 days 14 hours ago) and read 5716 times:
In the standard atmosphere, then air pressure drops 1hPa every 30' you go up, so altimetres are callibrated to show that change. The thing is though, on a hot day 1hPa could actually be a 35' increase in altitude because the air is less dense, or on a cold day 25' per hPa.
I imagine by FL360 there could be some substantial error, however, all altimetres will have the same error, so it doesn't mean planes are going to collide.
Wardialer From United States of America, joined Sep 2001, 1201 posts, RR: 0
Reply 8, posted (13 years 6 months 2 weeks 7 hours ago) and read 5645 times:
The rule is, your suppose to have 50 to 100 feet lead. For example when your at FL360 and your altimeter reads 35900 or 35950 thats OK. Altimeter readings are not always accurate because of such factors as wind, turbulence, and temp.
JohnM From United States of America, joined Feb 2001, 369 posts, RR: 0
Reply 9, posted (13 years 6 months 1 week 6 days 22 hours ago) and read 5618 times:
If memory serves, the limits for what I work are:
10,000 ft +or- 50 ft
29,000 ft +or- 75 ft
41,000 ft +or- 100ft
These are the RVSM limits that came out a few years ago. Almost every time, the actual altimeter indicator readings are about plus or minus 15 feet. The CADC is very accurate, as long as it is working. Most altitude errors that I find are static system leaks, not CADC problems.
B747skipper From , joined Dec 1969, posts, RR:
Reply 10, posted (13 years 6 months 1 week 5 days 22 hours ago) and read 5589 times:
According to our TCAS readings in European RVSM airspace, altimeters seem to be very accurate, "ours" or "theirs"... when crossing traffic above or below, we consistently read 900 to 1,100 feet vertical separation... and that is for levels such as 390...