Airbus Pro Required (Temp Limitations)

[electricdeathjet]

Hi this is a repost from the Tech Log forum...
Looking for anyone who could shine some light on this.....
Thanks



A320 Min Temp??
In the limitations section of the FCOM, the minimum air temperature indicated in the environmental envelope is SAT -70 C.
What exactly is the limitation for?? Is it structural? Fuel cold soak? Airconditioning? Hydraulics?
Recently we have encountered temperatures below this, -73C at flight level 380, there were no ECAM warnings and the wings didnt fall off... Now what are we to do?? Descend? Speed up?
Loads of other airbuses at the same and at higher levels with their wings still attached.
Is it safe to assume that Airbus could not find air cold enough to test in for certification? Or are we all about to have a nasty shock one day soon?:\

[Sgnr de L'Atlantique]

Hi there,


the reason why airbus puts a clear minimum temperature in its environmental enveloppe is because of airframe flexibility as well a fuel freezing points.

Airframe flexibility means that the structure ( especially wings) becomes too rigid due to the extreme cold to absorb any possible turbulence encountered.
The reason why min temp on ground is usually about 20 degrees higher that min temp on altitude is simply because of the effect of TAT when flying. Usuallay TAT is 20 deg higher than SAT when flying at M.79.
So in case you encounter temperatures this low you will not fall out of the sky nor will you freeze to death, but you do have to descent to warmer atmospheres ( watch out for temp inversions though!;)) just to put yourself in the safe zone in case of encountered turbulence.

A secondary reason are the fuel freezing points off course. Long periods of cold soak, especially in an A320, might cause fuel temp to drop below its min temperature. This could have an impact on several other systems as well on the viscosity of the fuel itself.

Hope this helps...

[electricdeathjet]

Thanks, it shines some light on the matter :ok:

[CarbonBrake]

Sgnr

Interesting statement you are posting regarding the structural flexibility of airframe structures at low temperatures.

Looking at the environmental envelope of state of the art regional jets (e.g. the Embraer 145), narrow-bodies (A320-series) and wide-bodies (B747-400) shows a different picture. Since all of those airplanes are using the same selection of aluminum alloys for their primary structural components (spars, ribs, frames, stringers and skins), their low temperature margin is quite different: E145, -65°C up to FL370; A320, -70°C up to FL398 and last but not least, B747-400, -80°C up to FL451.
For example, spars and ribs of the 320-series are manufactured out of aluminum/zinc alloys (type 7010 and 7050), top skin panels of the main wing out of 7050 and the bottom skin panels out of aluminum/copper alloy 2024. They show excellent fatique strength over a broad temperature range even at low temperatures mentioned above.
Aluminum alloys are materials of choice even for cryogenic structural applications.
The structural components made out of the aluminum alloys chosen in all three aircraft are NOT the limiting factor for the environmental envelope.

Environmental envelopes are defined and tested during the FAR/JAR25 certification process according FAR/JAR 25.1527

[Milt]

Temperature Effects on Aircraft Structures.

Technology has advanced us to the stage where we now have an upper and lower temperature limiting envelope.

The upper limit for titanium currently limits Mach nos to a bit over 3.0. Tiles on the space shuttle get us to my guess of about Mach 10.0+ for a short period.

At the low temp end we have to contend with the two known coldest areas in our planet's atmosphere where temps get as low as -95 C. One of these areas is NE of Darwin, Australia. The other is off the West coast of South America. Oddly upper air tempertures are coldest over the tropics and warmest over the poles.

Most metals become more brittle as their temperature lowers resulting in a lowering of their tensile strengths. This is particularly relevant if there happens to be a crack or an anomoly in the material. Recognition of this for the steel structure of the F-111 contributed to the development of the the "Cold Proof Test" which subjected every aircraft to repetetive full equivalent flight load testing (+7.3 to -3.5 g) at a temperature of -40 C. A successful test gave/gives confidence for 5,000 hours of normal flying to a Mil 8866 g exceedence spectrum. The 5,000 hours was given a 50% safety factor and became 2,500 hours.

Don't yet know how composites behave approaching their temperature limits. Can anyone comment?

[electricdeathjet]

How does carbon fiber (ie 787) structures cope with the cold, is there a marked difference to conventional materials?

[Chris Scott]

Quote from electricdeathjet:
How does carbon fiber (ie 787) structures cope with the cold, is there a marked difference to conventional materials?

Quote from CarbonBrake:
For example, spars and ribs of the [A]320-series are manufactured out of aluminum/zinc alloys (type 7010 and 7050), top skin panels of the main wing out of 7050 and the bottom skin panels out of aluminum/copper alloy 2024. They show excellent fatique strength over a broad temperature range even at low temperatures mentioned above.


But what about the composite tailplanes and fins of A320s and other current types, not to mention nose-cones and belly fairings?

[engineer07]

all this talk about the limits being related to a/c structure is simply rubbish ! Wings do not become too rigid !!!

the limits applied are quite simply related to the min temperature at which the equip installed on the a/c are qualified. this does not mean they will stop working at lower temperatures, but they have not been tested and qualified at these lower tempertures.

[theavionicsbloke]

Engineer 07 is correct.

When avionics equipment is designed it will normally be tested and certified to a TSO or TSO's. The TSO normally call up RTCA Minimum Performance Standards. The equipment is then built and demonstrated to meet the requirements of the specifications

The equipment is then considered for approval by the National Airworthiness Authorities based upon meeting these specifications.

RTCA/DO-160 "Environmental Conditions and Test Procedures for Airborne Equipment" specification that is called up by just about nearlly every TSO and it is here that you will find the temperature range of -55 C to +70 C.

The Aircraft Manufacture will apply a general Flight Manual temperature limitation upon the aircraft taken from RCA 160 of which is the limiting temperature factor that the equipment has been tested & certified to.

Regards having a suprise.... I think you may find a recent AAIB report regarding a certain Boeing 777 is currently of Interest where the temperature of the Fuel is being investigated.

Hope that has cleared that one up for you

[FlightDetent]

Hi this is a repost from the Tech Log forum...

A320 Min Temp??
In the limitations section of the FCOM, the minimum air temperature indicated in the environmental envelope is SAT -70 C.
.....
Recently we have encountered temperatures below this, -73C at flight level 380, there were no ECAM warnings and the wings didnt fall off...

Noticed a unusual sound at -68 SAT one day. No alerts from the aircraft but system pages review showed Skin air extract valve at intermediate position indicated in amber. Study of FCOM 1 pointed at skin heat exchanger. Pulled temp. envelope only to realise that we were just outside. Within 5 minutes after returning back the indication disappeared and so did the sound.