alaskan9974 From United States of America, joined Oct 2011, 2 posts, RR: 0 Posted (1 year 3 months 3 weeks 1 day 16 hours ago) and read 4058 times:
Not sure how common this is? It happened at our local airport though. Apparently pressure was too high to set altimeters and the airline had to contact Boeing to get an exemption so they could fly all of their aircraft out of PAOT. A high pressure system has settled up here though, temperatures have been in the -50's. I copied a link to the article below. http://www.thearcticsounder.com/arti...igh_pressure_grounds_planes_at_otz
RoseFlyer From United States of America, joined Feb 2004, 8737 posts, RR: 52 Reply 1, posted (1 year 3 months 3 weeks 1 day 16 hours ago) and read 3832 times:
This does happen on occasion. It isn't that the airplane is not safe to fly, but rather the airplane is outside the envelope of the performance charts. It is more common in extreme heat. I've never heard of it due to pressure. I have heard of it happening due to low temperature. There are many limitations on an airplane and the performance charts have limits for reasons. Exemptions can be made and it looks like this was the case.
I can't imagine high atmospheric pressure pushing the airplane against one of its operating limitations like high temperature and low density can. However it can cause problems with various indicating systems as the whole pitot static system is quite sensitive.
If you have never designed an airplane part before, let the real designers do the work!
yeelep From United States of America, joined Apr 2011, 526 posts, RR: 0 Reply 2, posted (1 year 3 months 3 weeks 1 day 15 hours ago) and read 3730 times:
In this case, the altimeters could not be physically set. The adjustment tops out at 31.99in-hg.
Northwest727 From United States of America, joined Jul 2005, 491 posts, RR: 1 Reply 3, posted (1 year 3 months 3 weeks 1 day 15 hours ago) and read 3728 times:
Quoting RoseFlyer (Reply 1): I've never heard of it due to pressure.
Yes, pressure can exceed the charts, with a legal maximum of 31.00 inHg according 14 CFR 91.144. Reference AIM 7-2-2(a)(2)(a) and 7-2-4 as far as the procedures required when the barometric pressure exceeds 31.00 inHg.
yeelep From United States of America, joined Apr 2011, 526 posts, RR: 0 Reply 4, posted (1 year 3 months 3 weeks 1 day 14 hours ago) and read 3656 times:
Quoting yeelep (Reply 2): The adjustment tops out at 31.99in-hg.
alaskan9974 From United States of America, joined Oct 2011, 2 posts, RR: 0 Reply 5, posted (1 year 3 months 3 weeks 1 day 12 hours ago) and read 3588 times:
Quoting RoseFlyer (Reply 1): This does happen on occasion. It isn't that the airplane is not safe to fly, but rather the airplane is outside the envelope of the performance charts. It is more common in extreme heat. I've never heard of it due to pressure.
I understand it is still safe to fly I just found this interesting since it is the first I have heard of it happening. It is still in the -50's here. It is really cool to see the planes taking off with thick contrails from the exhaust, both piston and turbine powered aircraft have them.
Scooter01 From Norway, joined Nov 2006, 1153 posts, RR: 8 Reply 6, posted (1 year 3 months 2 weeks 4 days 12 hours ago) and read 2808 times:
I hear on the news today that a planned exersise in northern Sweden, at F 21, flying the JAS-39 Gripen, has been cancelled for safety-reasons as a high-pressure system (some reports say the highest in 40 years) makes the altimeter and airspeed readings unreliable.
Added info: I also understand that the cancellation is only for the JAS-39. The Finnish (F/A-18?) and Norwegian (F-16?) aircraft should be able to participate as planned.
[Edited 2012-01-31 15:50:50]
[Edited 2012-01-31 15:54:30]
"We all have a girl and her name is nostalgia" - Hemingway
HAWK21M From India, joined Jan 2001, 31201 posts, RR: 58 Reply 9, posted (1 year 3 months 1 week 5 days 1 hour ago) and read 1988 times:
Quoting BAe146QT (Reply 8): Just a guess... Maybe when the aircraft was designed and certificated, no-one foresaw that later models might be able to fly in those conditions
Upgrading a model Altimeter should not be a tough ask though......
pilotpip From United States of America, joined Sep 2003, 3081 posts, RR: 12 Reply 10, posted (1 year 3 months 1 week 3 days 15 hours ago) and read 1791 times:
Quoting HAWK21M (Reply 9):
Upgrading a model Altimeter should not be a tough ask though......
Is it worth the cost of certification for an event that rarely happens? Temperature limitations are a great example and can be exceeded on both ends of the spectrum. I once sat in YEG for almost 8 hours waiting for it to get above -40 because it's a limitation on the 170/190.
romeomike From Canada, joined Nov 2005, 36 posts, RR: 0 Reply 11, posted (1 year 3 months 1 week 3 days 12 hours ago) and read 1731 times:
I've seen it at the low end as well. A Jazz Dash-8 told me they couldn't leave until the pressure got to 28.17. It was 28.12 at the time (still the lowest I've seen.)
Perhaps someone can shed some light on that lower limit -- 28.17 seems like a fairly random number to me, but I assume there's a reason.
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