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Absolute minimum temperature?

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Absolute minimum temperature?

Old 29th Dec 2020, 10:34
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Absolute minimum temperature?

Is there a Boeing limit of absolute minimum OAT? (Not minimum fuel temp)
The lowest I personally observed was -74*C at FL450 over the Baltic, but was told by a BA F/E that he had seen -85*C over Siberia.
Is there a limit and why? Thanks.
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Old 29th Dec 2020, 13:24
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Most aircraft have an environmental envelope published in their AFM, for the B737NG the lower limit is -73.5C from FL360 and above.

Pretty sure somebody else can elaborate on why exactly it is needed.
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Old 29th Dec 2020, 14:13
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For many things, they can only certify what they test to.
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Old 29th Dec 2020, 16:21
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I thought this thread was a discussion on thermodynamics. Ill get my coat.
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Old 29th Dec 2020, 19:11
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Originally Posted by Check Airman View Post
I thought this thread was a discussion on thermodynamics. I’ll get my coat.
Good idea, it might get a bit cold out there🤣
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Old 29th Dec 2020, 22:47
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Originally Posted by Intruder View Post
For many things, they can only certify what they test to.
Not quite - you're allowed to extrapolate to some extent, but generally allowed when there is some previous data that validates the extrapolation methodology.

Another issue is many of the data tables only extend over a specific temperature and altitude range - e.g. engine ratings. I recall an issue perhaps six or seven winters ago when a big cold front hit part of Europe - it was bitter cold, but more importantly the pressure altitude dropped well below -1000 ft. The takeoff performance data for some types didn't go below -1,000 ft., resulting in several aircraft being grounded for several days.
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Old 30th Dec 2020, 01:43
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Most tends to be a fuel gel point, read about a DC10 over Russia years back that was reaching min tank temp. ATC wouldn't allow any deviation lower/faster etc....... the F/O suggested wing deice, the temp slowly rose due to hot bleed air in the leding edge. Several years back air canada was stuck in yzf for 2 weeks because the temps didn't rise above -48 during that time, what [email protected] makes a skidoo that doesn't run in the winter. Oh right some PQ numb nuts
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Old 30th Dec 2020, 03:07
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Been plenty of incidents over the years with fuel gelling. BA38 comes to mind. An aircraft which I was looking after, some years ago, nearly came to grief on the way to NZ - fortunately the PIC recognised the symptoms from a conference paper several years prior, descended, and the problem resolved.
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Old 30th Dec 2020, 08:12
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BA 38 was caused by water ice crystals in the fuel, not the fuel itself approaching its wax point.
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Old 30th Dec 2020, 08:56
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-70C/FL360 over NE Russia is my record.
Im going with temperature limitations on lubricants used.
Flight controls, gear, flaps, jackscrews etc.
Just a SWAG

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Old 30th Dec 2020, 11:45
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738-800 fuel filter bypass

Back around 2008, when flying in -64C +/- temps for any length of time, for example, from STN to Tampere, about the time of TOD, we could expect to get a master caution and fuel filter bypass which would clear by the time we had parked on the ramp. I think there used to be a bulletin but it was removed some time ago, due to some tech mods perhaps.
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Old 30th Dec 2020, 11:58
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Originally Posted by HILETI View Post
Is there a Boeing limit of absolute minimum OAT? (Not minimum fuel temp)
The lowest I personally observed was -74*C at FL450 over the Baltic, but was told by a BA F/E that he had seen -85*C over Siberia.
Is there a limit and why? Thanks.
Don't recall ever seeing an environmental limit for the 747-400 or the 777.
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Old 30th Dec 2020, 12:11
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boeing minimum temp...

I think i remember an implied minimum in either the QRH or performance manual, my experience limited to 737s, to no information below -65C.

Will look and get back later.
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Old 30th Dec 2020, 15:42
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Stolen shamelessly from the inter-web. Continental's 777-224, dated 08/09/02 (for whatever Christmas sake that means?).


The left edge-line is relevant, showing a binding limit at -75 C when above FL315.

On Airbuses the FCOM chart is pretty much the same.
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Old 30th Dec 2020, 17:36
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Originally Posted by FlightDetent View Post
Continental's 777-224, dated 08/09/02 (for whatever Christmas sake that means?).
Isnt it clear? Its the 8th of the 9th of the 2nd

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Old 30th Dec 2020, 17:55
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no joy....yet

after looking until eyes glazed over, using 50/50, ask the audience and phone a friend, I will stick with my memory of -65C. I am sure of winter before last, several other colleagues, in same airline and same a/c requesting descent due to low temperature enroute. i think I remember our ops manual or performance manual having a chart like the above 777 environmental envelope, but I cannot find it. Yet.

I did see, the lowest temperature on the TO performance charts as -40C for -800 and -60C for -700. And oddly, the quick turnaround brake charts show -54C.

the emergency O2 chart for flight deck shows a low of -10.

Last edited by 70 Mustang; 10th Jan 2021 at 15:02.
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Old 30th Dec 2020, 18:17
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Flight planning and performance manual...


theory is, since -65C is the lowest temp shown, we should limit our flight to -65C
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Old 30th Dec 2020, 18:40
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Originally Posted by 70 Mustang View Post
i think I remember our ops manual or performance manual having a chart like the above 777 environmental envelope, but I cannot find it. Yet.
AFM, under the performance section. ​​​​​​
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Old 30th Dec 2020, 18:59
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70 Mustang Your charts say TAT, mine OAT. Reader beware.

Check Airman It's the spirit of the date, not the format that matters. :-)
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Old 30th Dec 2020, 19:17
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Max min i could find...

TAT -65C is the coldest i could find in any chart.

Do you have a page number or a screenshot of your chart? I cannot find it.

I only have FCOM, FCTM and the above Flight Planning and Performance Manual.

I haven’t seen an AFM for the 737-800 since 2003 at Excell Air at LGW.

Last edited by 70 Mustang; 30th Dec 2020 at 19:42.
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