Too Cold up here
Thread Starter
Joined: Aug 2001
Posts: 41
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From: HERE AND THERE
To Cold up here
Just a quick question.
In the cruise at FL340 the other day I heard an unusual amount of traffic asking for the SAT and different levels. We were asked and from memory it was something like -60 c or -65 c, ISA-12. Which prompted a lot of traffic to descend. Myself, the captain and a positioning capt were wondering what was the major problem with the cold temp that were forcing people to find "warmer" air. All we could think of was the fuel temp.
Were we sitting fat dumb and happy and missing some major issue?
Thanks a lot
S5FP
In the cruise at FL340 the other day I heard an unusual amount of traffic asking for the SAT and different levels. We were asked and from memory it was something like -60 c or -65 c, ISA-12. Which prompted a lot of traffic to descend. Myself, the captain and a positioning capt were wondering what was the major problem with the cold temp that were forcing people to find "warmer" air. All we could think of was the fuel temp.
Were we sitting fat dumb and happy and missing some major issue?
Thanks a lot
S5FP
Joined: Dec 2000
Posts: 523
Likes: 0
From: very close to STN!!
hydraulics?
on the 737-800 after an hour on so at -65C, (more than once)- i have gotten a low pressure indication on the electric driven pump-i think it was A system. stayed on until on short final where temp was much warmer.
i think i remember some of the older aircraft i flew actually had a cold temp limit for operation.
can't find the books to prove it.
i think i remember some of the older aircraft i flew actually had a cold temp limit for operation.
can't find the books to prove it.
Joined: Jul 2000
Posts: 17
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Too cold up here
On the B737 NGs there were a number of incidents whereby the hydraulic pumps used to fail one after another when the temperature at altitude was significantly below ISA. On one occasion,three of the four hydraulic pumps clocked out (both electric and one of the two engine driven) before a descent to warmer air fixed the problem. I understand that a modification of the hydraulic plumbing has largely fixed this problem, although the odd single pump failure isn't unheard of.
Also on the same subject (temperatures below ISA) it wasn't uncommon for the A340s to have to descend to lower (warmer) levels because the fuel temperatures were getting dangerously close to the freeze point. This was particularly common on the northern siberian routes (to Hong Kong / Tokyo) during the middle of winter. Airbus in their wisdom had decided that fuel heaters weren't necessary, but line experience proved them wrong. Transferring fuel around from tank to tank, flying faster, or as a last resort, descending, were all well tried "tricks" to fix the fuel freeze problem.
I suppose the day which prompted the original question had temperature conditions low enough to cause hydraulic problems for some aircraft types and fuel temperature problems for others?
Also on the same subject (temperatures below ISA) it wasn't uncommon for the A340s to have to descend to lower (warmer) levels because the fuel temperatures were getting dangerously close to the freeze point. This was particularly common on the northern siberian routes (to Hong Kong / Tokyo) during the middle of winter. Airbus in their wisdom had decided that fuel heaters weren't necessary, but line experience proved them wrong. Transferring fuel around from tank to tank, flying faster, or as a last resort, descending, were all well tried "tricks" to fix the fuel freeze problem.
I suppose the day which prompted the original question had temperature conditions low enough to cause hydraulic problems for some aircraft types and fuel temperature problems for others?
Joined: Jul 2004
Posts: 849
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From: UK
I'm surprised that on the newer generations of a/c with fairly sophisticated flight data computers, that there isn't some warning/caution generated if SAT falls below the 'safe' environmental limits for extended periods of time.
Joined: Mar 2005
Posts: 2
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From: London
For us it was a fuel temp problem that day. We crossed the North Atlantic at 65 North. The SAT that day got as low as -73C at FL370. As the fuel temp got to -36 we sped up by .02M but that did not stop the fuel temp decrease. Finally had to descend to warmer air.
Joined: Mar 2004
Posts: 435
Likes: 30
From: UK
As you will know American fuel JetA has a generic fuel freeze temperature of minus 40C as opposed to normal JetA1 elsewhere at minus 47C. We have been paying for an ACTUAL fuel freeze analysis of every uplift out of the US for some time and the results have shown that the worst uplift had an ACTUAL fuel freeze temperature of minus 45C so there would appear to be a good margin over the generic freeze limit. Best option would be to top up in Russia: their fuel is ok down to minus 50C!
