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Absolute minimum temperature?

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Absolute minimum temperature?

Old 29th Dec 2020, 09:34
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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, 12:24
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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, 13:13
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For many things, they can only certify what they test to.
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Old 29th Dec 2020, 15:21
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I thought this thread was a discussion on thermodynamics. Iíll get my coat.
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Old 29th Dec 2020, 18:11
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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, 21:47
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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, 00:43
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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, 02:07
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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, 07:12
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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, 07:56
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-70C/FL360 over NE Russia is my record.
Iím going with temperature limitations on lubricants used.
Flight controls, gear, flaps, jackscrews etc.
Just a SWAG

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Old 30th Dec 2020, 10:58
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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, 14:42
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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 -75į C when above FL315.

On Airbuses the FCOM chart is pretty much the same.
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Old 30th Dec 2020, 16:36
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Originally Posted by FlightDetent View Post
Continental's 777-224, dated 08/09/02 (for whatever Christmas sake that means?).
Isnít it clear? Itís the 8th of the 9th of the 2nd

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Old 30th Dec 2020, 17:17
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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, 17:40
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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, 17:59
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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, 19:26
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For the 737 I could not find the environmental envelope chart in any of the FCOMs I caught online. Somebody above said it's inside the AFM.

The graph I posted is from Continental Airlines 772 FCOM, 2002 edition. Probably heavily tailored. https://curiozitydotnet.files.wordpr...ght-manual.pdf

The 747 FCOM found is ZK-SUI from ILFC and content-wise looks identical with the 737 in the Limitations Chapter. No Environmental Envelope Graph.
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Old 30th Dec 2020, 21:47
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TAT -65 is really cold, check the SAT
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Old 30th Dec 2020, 22:42
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Originally Posted by Alex Whittingham View Post
TAT -65 is really cold, check the SAT
Or very slow!
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Old 30th Dec 2020, 22:51
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Originally Posted by 70 Mustang View Post
Do you have a page number or a screenshot of your chart? I cannot find it.


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