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Altimeter Accuracy  
User currently offlineDanialanwar From Switzerland, joined Mar 2001, 421 posts, RR: 0
Posted (12 years 3 months 1 week 3 days 11 hours ago) and read 4341 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?)

Thans!
Daniel


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11 replies: All unread, jump to last
 
User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 1, posted (12 years 3 months 1 week 3 days 6 hours ago) and read 4307 times:

One of the preflight checks is to check alitmeter accuracy with the current field alitmeter setting.

Must be within plus or minus 100ft of actual field elevation.

JET


User currently offlinePW4084 From United States of America, joined Mar 2001, 291 posts, RR: 0
Reply 2, posted (12 years 3 months 1 week 3 days 1 hour ago) and read 4296 times:

JET, Isn't the FAA standard within 75 feet of field elevation? In that case dual altimeters could potentially be 150 feet apart and not require adjustment.

PW4084


User currently offlineBroke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 3, posted (12 years 3 months 1 week 3 days 1 hour ago) and read 4296 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.

User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 4, posted (12 years 3 months 1 week 2 days 23 hours ago) and read 4281 times:

Sorry 75 ft.....

No more early morning posting for me.

JET


User currently offlineRendezvous From New Zealand, joined May 2001, 516 posts, RR: 0
Reply 5, posted (12 years 3 months 1 week 1 day 7 hours ago) and read 4217 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.


User currently offlineDanialanwar From Switzerland, joined Mar 2001, 421 posts, RR: 0
Reply 6, posted (12 years 3 months 6 days 19 hours ago) and read 4186 times:

Thanks guys. I think I can work with these numbers. Great people on this forum!


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User currently offlinePositive rate From Australia, joined Sep 2001, 2143 posts, RR: 1
Reply 7, posted (12 years 3 months 5 days 1 hour ago) and read 4150 times:

What is the altimeter accuracy of high flying aircraft such as Concorde? What about other experimental a/c like the X-15 flying at 300,000'+?

User currently offlineWardialer From United States of America, joined Sep 2001, 1183 posts, RR: 0
Reply 8, posted (12 years 3 months 4 days 23 hours ago) and read 4146 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.

User currently offlineJohnM From United States of America, joined Feb 2001, 348 posts, RR: 0
Reply 9, posted (12 years 3 months 4 days 14 hours ago) and read 4119 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.


User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 10, posted (12 years 3 months 3 days 15 hours ago) and read 4090 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...
(s) Skipper


User currently offlineApathoid From , joined Dec 1969, posts, RR:
Reply 11, posted (12 years 3 months 3 days 15 hours ago) and read 4088 times:

AC 43-13/1B Appendix E lists altimeter accuracy and acceptable leakage rates for American certified aircraft. Look it up.

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