Ask The Pilot

[AviatorInsight]

Does air temperature vary with altitude according to any formula/Rule of Thumb?. Like air pressure and altitude?

2º per 1000ft.

 

[jb747]

The rate of change of the temperature is called the 'lapse rate'. As AV has said, the standard model assumes 2ºC/1,000 feet. Once it reaches -56ºC, the temperature is then assumed to be constant, until about 80,000' at which point it rises again.

But...2ºC per thousand is actually the average lapse rate. Dry air cools slightly faster, and moist air slightly slower (which is why those big CBs can grow higher as you watch them).

Probably all you ever wanted to know here:
https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/06_phak_ch4.pdf

 

[Quickstatus]

Will a lower latitude affect temperatures at the altitudes you operate in?.

 

[docjames]

Watching the temperature rise in ADL and knowing it's going to be hot in MEL tomorrow, is there a "maximum" allowed temperature for operations? No doubt some variation by aircraft, and there's the (previously mentioned) reduction in MTOW etc, but is there an "absolute" limitation?

 

[jb747]

Will a lower latitude affect temperatures at the altitudes you operate in?.

The standard atmosphere model is an average of the Earth's atmosphere. According to the model, the sea level temperature is 15ºC, and the pressure is 1013 mb. We all know that in reality those figures are anything but fixed.

The tropopause, is the level at which the lapse rate changes to zero, and that varies dramatically, with seasons and latitude. Highest I've seen recently was about 55,000', and the lowest 33,000'. That flight from HK that I mentioned earlier encountered temperatures in the -70ºC region. The latitude would have been in the region of 50-55ºNorth.

 

[jb747]

Watching the temperature rise in ADL and knowing it's going to be hot in MEL tomorrow, is there a "maximum" allowed temperature for operations? No doubt some variation by aircraft, and there's the (previously mentioned) reduction in MTOW etc, but is there an "absolute" limitation?

Yes, but this will vary amongst aircraft types. Looking at the limitations for the A380, the temperature is an eye watering 54ºC.

The performance will be massively limited. In more normal conditions, you'd be able to take off out of Adelaide at MTOW of 572 tonnes. But, at 54ºC, the weight would reduce by over 100 tonnes. I'm sure the ground crew, amongst many others, would give up long before that temperature.

It's entirely possible that any flights that operate out of Adelaide at heavy weights, will be adversely affected even if the temperature is in the early 40s. The 787 out of Perth becomes weigh limited at quite low temperatures, and is probably one reason why that flight departs at night. Out of Melbourne, the 93 to LA becomes temperature limited in the mid to late 30s.

 

[flyer89]

Talk of performance figures reminds me that this week the BEA released its final report on an AF 777F that took off with an assumed weight 100 tones lighter than it actually was.

What I found interesting was that whilst the FO had entered the wrong weight into the performance calculations the captain had entered the correct weight. However, when entering it into the FMC the captain made a typo and thus the weight he entered was the same as the FO’s, both erroneous.

Incident: Air France B772 at Paris on May 22nd 2015, 100 tons missing in inserted takeoff weight

 

[jb747]

Talk of performance figures reminds me that this week the BEA released its final report on an AF 777F that took off with an assumed weight 100 tones lighter than it actually was.

What I found interesting was that whilst the FO had entered the wrong weight into the performance calculations the captain had entered the correct weight. However, when entering it into the FMC the captain made a typo and thus the weight he entered was the same as the FO’s, both erroneous.

Well, I guess the Captain's error was that last hole in the cheese that lined up. I always find it strange that when you have heavy crews like this, that the blokes who aren't in the seat don't do any calculations. They're probably in the best position to pick up these errors. Our SOs don't have access to the laptops that we use, but can work out the performance data on their iPads. The logic isn't exactly the same, but the answers should be within a knot or two. Makes for a good extra check.

The way that the performance tools optimise the data has had the effect of invalidating rules of thumb, so people have become used to correct answers that don't feel right. A technological solution (as so many on AvHerald gibber about) will have the effect of increasing that disconnect. Same as BTV (brake to vacate), it disconnects people from braking, which is a pretty basic function, and it's one which by the time you realise the BTV has gotten it wrong, may well be too late.

 

[AviatorInsight]

Watching the temperature rise in ADL and knowing it's going to be hot in MEL tomorrow, is there a "maximum" allowed temperature for operations? No doubt some variation by aircraft, and there's the (previously mentioned) reduction in MTOW etc, but is there an "absolute" limitation?

Depending on the type of 737 it is (engine thrust) out of ADL for example we can take it up to 54º with an assumed temperature up to 60º if performance allows. At that temperature the MTOW becomes 65.6t, a good 13.5t below structural MTOW. If it's at 54º with no assumed temperature method then that limit become 68.8t, 10.2t below structural MTOW.

 

[lastrow]

Yes, but this will vary amongst aircraft types. Looking at the limitations for the A380, the temperature is an eye watering 54ºC.

Is this high temperature influenced by the material used in the construction of the aircraft? Can the A380, being of non metallic structure, have a greater insulation factor that an all aluminium air frame?

 

[straitman]

Is this high temperature influenced by the material used in the construction of the aircraft? Can the A380, being of non metallic structure, have a greater insulation factor that an all aluminium air frame?

It’s ambient temperature that is considered. The largest impact is on the engines.

 

[maccaisking]

A photo from last night on the way back from CNS shows the Australian coastline with airports. View attachment 151132

Based on the number if airports in that image I assume these include both major airports as well as regional ones with grass runways? In an emergency is there a way to filter the display down to ones you could land at?

 

[Flying Fox]

Yes, but this will vary amongst aircraft types. Looking at the limitations for the A380, the temperature is an eye watering 54ºC.

The performance will be massively limited. In more normal conditions, you'd be able to take off out of Adelaide at MTOW of 572 tonnes. But, at 54ºC, the weight would reduce by over 100 tonnes. I'm sure the ground crew, amongst many others, would give up long before that temperature.

It's entirely possible that any flights that operate out of Adelaide at heavy weights, will be adversely affected even if the temperature is in the early 40s. The 787 out of Perth becomes weigh limited at quite low temperatures, and is probably one reason why that flight departs at night. Out of Melbourne, the 93 to LA becomes temperature limited in the mid to late 30s.

ADL peaked at 46.2ºC whilst out at Edinburgh my friend posted a pic of 47.1ºC.

I'm assuming DXB exceeds these temps and possibly 50ºC+. Would EK do anything to keep its fleet flying?

Apparently North West Kuwait has recorded 54ºC; does this mean that A380's simply don't fly?

 

[AviatorInsight]

Based on the number if airports in that image I assume these include both major airports as well as regional ones with grass runways? In an emergency is there a way to filter the display down to ones you could land at?

All runways greater than 1000m (capable of landing a 737) and that are 30m wide or greater and that have asphalt or better. In the manual it states what is to be used as an emergency port, however if you had an uncontrolled fire I'd have no hesitation in putting it into one of those ports. The runway may not even be hard enough to take 737 but it's better than nothing.

 

[jb747]

This is a similar display from the 380, over Europe. In this case, runways of 6,000'.

In an emergency, you may only care about getting down. Whether it ever gets up again is someone else's problem.

 

[mjt57]

Certainly enough of them.

What dictates which one you select? It's closest, how busy it may be?

 

[jb747]

Certainly enough of them.

It's a pretty large scale, showing a number of countries. The next scale up, has so much data that the system chokes on it, and displays a message to say that it can't show it all.

What dictates which one you select? It's closest, how busy it may be?

Basically the degree of desperation. If you've reached the point that any bit of bitumen will do, then you will only care about being able to get onto it. There won't really be any other considerations.

Most of the airports displayed won't appear in our Jeppesen charts, and we may have very limited, or even zero, data on them. In amongst a confused display like that, there's likely to be a number of major airports. The aircraft was actually just about over the top of Vienna when the shot was taken. We keep track of immediate options along the way, mostly by marking them as fixes on the FMC, and getting the system to draw circles around them. That's what the dotted blue lines are.

 

[SenZubEanS]

QF36 in the air on it's way to MEL. Congratulations on a long and successful aviation career JB and thank you for your countless hours of contributions to this forum, A truly amazing sharing of knowledge.

 

[lastrow]

JB, I too want to congratulate you on a magnificent flying career and particularly I want to thank you for your contributions to this forum. Your answers have often gone beyond explaining flying procedures offering an insight into the physics involved as well.
Not only is the depth of you knowledge awesome, but your ability to express it in understandable terms has made this thread immensely interesting for all of us.

 

[jb747]

Hopefully this thread won't die out. Firstly, I'll continue answering questions, though my internet connection may not always be as reliable as it is when at home...also because I'm not the only person who answers. AV is going great guns, and we've had a number of other posters from quite disparate aircraft types...so hopefully that will continue.

But...I don't intend doing any more flying myself. For a lot of reasons, but mainly because I doubt that anyone is willing to lend me a 767 level aircraft, and to also pay the bill.

So...this is probably the last landing...