Absolute minimum temperature?

[FlightDetent]

Competitor's airframe. Ugly point at FL330 with -65 degrees,
- Avionics ventilation gets confused and misbehaves, although nobody understands what the skin heat exchanger normal operation is anyway.
- Fuel temperature in the outer, wing-tip tanks is not manageable over extended periods of time (low limit for JET A1 is -45 or so)

[George Glass]

Originally Posted by Check Airman

Isn’t it clear? It’s the 8th of the 9th of the 2nd

It would be clear except for the fact that in the good old US of A you swap the day and the month around compared to the rest of the English speaking world.

[747-8driver]

[mcdhu]

I was told, some years ago, that the min temp was for 'metallurgical' reasons (Airbus)
mcdhu

[blind pew]

John T

BA 38..jury out..mate operated the first service and wrote to his manager about the intense cold over Siberia..told not to worry.
Apparently the fuel wasn't allowed to settle after refuelling before the water check in Peking.
Crew ignored the planned descent into warmer warmer in the later stages of the flight.
iirc no fuel heat.
On the iron duck we had different min fuel temps depending the type uploaded.
Could have been either ice or wax but what is definate it didn't put BA in good light.

[pedroalpha]

Back in the mid 70s, we were conducting an external load lift of a 105mm howitzer in the Norwegian mountains. The indicated OAT was -44 degrees C. The recirculating snow was an issue but dissipated quickly although much blew into the cabin through the open doors. My lasting memory is of the crewman using a brush to clear the snow out of the door. The joy of operations in such cold temperatures is that the snow does not stick. Engine and airframe entirely happy but not sure about the PUMA HC1 ODM.

[lomapaseo]

Originally Posted by mcdhu

I was told, some years ago, that the min temp was for 'metallurgical' reasons (Airbus)
mcdhu

I don't recall any military jets falling out of the air at high altitudes. Do you suppose that air friction might be significant in limiting the metallurgical effects

[Dave Therhino]

BA38 was conclusively determined to be water ice in the fuel, not the fuel reaching its wax point. The event led to fuel/oil heat exchanger changes required by AD 2010-07-01.

https://lessonslearned.faa.gov/ll_ma...abID=1&LLID=79

[FlightDetent]

Originally Posted by lomapaseo

I don't recall any military jets falling out of the air at high altitudes. Do you suppose that air friction might be significant in limiting the metallurgical effects

I share your confusion over the newly suggested fact. The possibilities are
- above tropopause the temperature gets warmer
- we're discussing ISA -20 conditions so far, which at high flight levels are quite rare (frequency of exposure) yet encountered repeatedly by civilian craft on polar routes
- military would not stay in such cold air mass for the duration of many hours unless purposely built
- it could be a case of certification / guaranteed performance / uncharted territory
- higher TAS and Mach do make a difference, for the cold fuel case that's what the QRH drill is

Still sounds a far fetch.

[compressor stall]

Originally Posted by lomapaseo

I don't recall any military jets falling out of the air at high altitudes. Do you suppose that air friction might be significant in limiting the metallurgical effects

likely made from different thicknesses. Might be an issue of brittleness at the thickness of a Airbus skin.

Although I suspect - as Flight Detent posted above - the reason is that at in the A320F at the limit of -70*C ventilation valves can start to play up. Seen it.

[Capt Quentin McHale]

Dave Therhino,

With regards to BA38, I'm not totally convinced of the results of the investigation, extensive as it was. My point being, after having read the final report, with all that was done throughout the investigation I believe one important thing was omitted. That being undercowl "heat soak".

With the aircraft flying for 12 plus hours all engine components are subject to heat soak and with the cowls closed the surrounding undercowl environment will be rather warm and well and truely above room temperature. Therefore the FOHE casing and components should be warmed not only by the hot oil passing through the internals of the FOHE but also from the surrounding heat soak. With the combination of heat soak, hot oil and cold fuel over time, the FOHE should reach a " happy medium" temperature wise and this temp IMHO would be above freezing. This was not done in the investigation process.

From experience from being around an engine when an aircraft has arrived on chocks and the cowls immediately opened, things are well and truely warm to touch and some components too hot to touch. Open to correction, but food for thought.....

Rgds McHale.

[FlightDetent]

Originally Posted by compressor stall

likely made from different thicknesses. Might be an issue of brittleness at the thickness of a Airbus skin.

Although I suspect - as Flight Detent posted above - the reason is that at in the A320F at the limit of -70*C ventilation valves can start to play up. Seen it.

My hunch is the other way around, the valves are tuned down to the limit and a little less, once exceed they get confused. A symptom as opposed to reason. BTW, have you not actually also first heard it?

[tdracer]

Originally Posted by Capt Quentin McHale

Dave Therhino,

With regards to BA38, I'm not totally convinced of the results of the investigation, extensive as it was. My point being, after having read the final report, with all that was done throughout the investigation I believe one important thing was omitted. That being undercowl "heat soak".

Capt, I was involved in the early portion of the BA38 investigation. Fuel waxing/freezing was one of the very first things we looked at. Short answer is that the fuel never actually got that cold - very cold, yes, but cold enough to cause the observed problems, no. And remember, there was quite a bit of fuel recovered after the accident, so we had solid data on the fuel characteristics.
I was no longer involved by the time they were testing the FOHE icing (I was working 747/767 at the time, brought into the early investigation as a subject matter expert), but I know several people who were and they were quite convinced they'd found the smoking gun. Further, we were able to go back through historical data and find evidence that this wasn't the first time the FOHE had iced up (e.g.otherwise unexplained increases in oil temp during steady state operation) - just the first time it had caused a major problem.

[wiggy]

Originally Posted by blind pew

Crew ignored the planned descent into warmer warmer in the later stages of the flight.

I may well be wrong, I'm working from memory, happy to be corrected etc etc but I thought BA introduced the low temp step down into the flight planning procedure for T7s after the BA38 accident. Whenever it was introduced, and again as I recall it, a descent i.a.w. with the flight plan wasn't mandatory. You descended if the observed fuel temp demanded it, OTOH if the temp didn't demand it you were free to ignore the descent.

The step down built into the fuel plan was to simply make sure you had loaded enough fuel in the tanks to make destination if the step down to a significantly lower level was was needed..

tdracer - thanks for your insight, much appreciated.

[Capt Quentin McHale]

tdracer,

Thanks for the feedback, very interesting indeed.

Rgds McHale.

[TopBunk]

As an aside, I recall flying over Siberia in winter probably about 15 years ago.

We were in a B744 @ FL370 or so. The SAT outside was pretty much standard ISA at about -56degC, the temperature on the ground at Irkutsk (or wherever) was -57deg C!

[wiggy]

Originally Posted by TopBunk

As an aside, I recall flying over Siberia in winter probably about 15 years ago.

We were in a B744 @ FL370 or so. The SAT outside was pretty much standard ISA at about -56degC, the temperature on the ground at Irkutsk (or wherever) was -57deg C!

Yup, Certainly looking at trop level on the Siberian charts some winters days it was clear you'd have to descend a heck of a long way before you saw the OAT increase. I've certainly seen the SAT rise by a degree or two as a result of a step climb when "up north" .