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frequentflyer
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Outside Air Temp Limits

Thu Jan 12, 2006 4:21 am

Hi Folks

Is there such a thing as minimum/maximum outside Air Temps under/over which -jet- aircraft operations are not possible/authorized?

Cheers,

Pat
 
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Starlionblue
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RE: Outside Air Temp Limits

Thu Jan 12, 2006 4:25 am

I would guess there is no absolute min since jets routinely fly in temperatures below -50C. But that's just a guess.

I imagine that operating procedures change quite a bit though.

[Edited 2006-01-11 20:25:39]
 
Pihero
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RE: Outside Air Temp Limits

Thu Jan 12, 2006 5:00 am

It depends on each aircraft certification.
As an example, the 320family is restricted to temps between ISA +40 c and -40 c at sea level. that range would go to 40.000 ft to between -70 and -20 c.
 
shindig31
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RE: Outside Air Temp Limits

Thu Jan 12, 2006 10:29 pm

At Outside Air Temperatures of -65c or colder ,jet fuel freezing becomes a concern.Jet fuel freezes at different temperatures depending on its composition.Also aircraft types have different characteristics which make them less or more susceptible to fuel freeze such as airspeed (more less frictional heating),and fuel tank thickness.Generally speaking it would only effect flights operating at extreme latitudes such as polar operations.And are normally planned for.American produced jet fuel for civilian operators has a fuel freeze value somewhere between -40c and -50c again depending on its chemical composition.We can monitor both outside air temperature and fuel temperature on most modern aircraft types allowing for safe flight through or around cold air pockets.
 
Goldenshield
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RE: Outside Air Temp Limits

Thu Jan 12, 2006 11:22 pm

ISA will also come into play as to where final cruise altitude will be at any given gross weight.
 
LHBrasil
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Joined: Sat Sep 17, 2005 11:28 pm

RE: Outside Air Temp Limits

Wed Feb 15, 2006 4:15 am

Quoting Shindig31 (Reply 3):
At Outside Air Temperatures of -65c or colder ,jet fuel freezing becomes a concern

Others things that shall be taking into account are, for example, Pull-Down, Pull-Up, electrical equipments operation, e-bays cooling, etc.  cold   hot 
 
SFOMB67
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RE: Outside Air Temp Limits

Wed Feb 15, 2006 4:33 am

I think I remember a situation in Phoenix 6 or 8 years ago when the temp exceeded the maximum on the charts used to compute T/O. Think it was ok after they recieved revisions to the charts.
 
buckfifty
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RE: Outside Air Temp Limits

Wed Feb 15, 2006 4:57 am

For some reason, Americans tend to use fuel with lower freezing points (normal Jet A fuel) rather than the Jet A1 which is used at most other industrialized nations. The Jet A turns waxy (not freeze, as fuel does not freeze immediately, but rather turns into a gelatin like substance) at around -40C, and Jet A1 at around -47. This does affect our polar ops, because we do often fly at temps near or under -70C, especially over Siberia during the wintertime. Even at the tropics, where the tropopause is really high, temps such as -65 are often seen. So we fly around temperatures like this all the time.

However, fuel only cools at a rate of around 3C per hour, so it isn't a major concern, and it can be monitored. If it does go below our warning threshold (usually around -40C in the outer tanks, and -35C in the inners), we can descend (if there is no inversion), or speed up to increase the TAT. However, as the fuel is cold soaked after a long flight, going into a hot and humid airport, ice could form on the wings due to this fact, even if it is 30 degrees outside.

On the ground, operating temps are more of a concern only when it's too hot, as it limits the takeoff performance of the aircraft. Other than that, haven't had an example where we had to delay any T/O due to temperature factors.
 
A342
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RE: Outside Air Temp Limits

Wed Feb 15, 2006 5:12 am

Quoting Pihero (Reply 2):
As an example, the 320family is restricted to temps between ISA +40 c and -40 c at sea level. that range would go to 40.000 ft to between -70 and -20 c.

Hmmm, do you remember a previous tread where I asked about the coldest OAT ever recorded ? You replied that you´ve encountered -84°C in an A321. As you said, it was a "bubble" of cold air. Does this mean that this temperature wasn´t forecasted and you ran into it without previous warnings ?
 
OPNLguy
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RE: Outside Air Temp Limits

Wed Feb 15, 2006 10:10 am

Quoting Sfomb67 (Reply 6):
I think I remember a situation in Phoenix 6 or 8 years ago when the temp exceeded the maximum on the charts used to compute T/O. Think it was ok after they recieved revisions to the charts.

Each aircraft type has a MOT (maximum operating temperature), and for our JT8D-9 powered 737-200s, MOT was 120F. The summer day you're thinking about was on July 28th, 1995, and PHX hit 121F for 2-3 hours IIRC. Flights on the ground didn't depart, and flights didn't land, since there was no performance data for temps above 120F. Other aircraft like the 737-300s had 126F MOTs, and were not precluded from operating... Once the temp came back down to 120F, the -200s started operating again as well, but the max weights were dog poop...

http://www.usatoday.com/weather/wmth7.htm
 
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NWOrientDC10
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RE: Outside Air Temp Limits

Thu Feb 23, 2006 10:09 am

Quoting Starlionblue (Reply 1):
I would guess there is no absolute min since jets routinely fly in temperatures below -50C. But that's just a guess.



Quoting Pihero (Reply 2):
40.000 ft to between -70 and -20 c.



Quoting Shindig31 (Reply 3):
Jet fuel freezes at different temperatures depending on its composition

These are good points; on the other hand, the freezing point/temperature of liquids (such as fuel) decreases with increasing altitude. In other words, the lower the ambient pressure, the lower the freezing point (Ideal gas law: PV=NrT).

What I'm getting at is that high altitudes, OAT's (outside air temperatures), machinery (lack of better terminology, sorry) doesn't "break down" "as quickly".

On the other hand, when at places extreme cold, maybe a/c fuel and hydraulic fluid will become more viscous "thicken" during decent.

Probably, designers already took this into account

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