High Temp operations - Considerations

[Dirty Steve]

When operating in hot places with temps of say over ISA + 15 what are the considerations to the operation of a jet aircraft. Im not talking hot and high, just hot. eg possble EGT over temps etc.

Thanks....

[VinRouge]

I operate in some pretty hot conditions (ISA +40 celcius enough for you?)

Even with FADEC, MGT/EGT overtemp can be an issue, especially if you are operating close to the aircraft max operating envelope.

Overcome typically by setting bleeds off and if things get really tough (queue sucking of teeth) setting less than T/O power on the roll.

Bearing in mind we were operating at far less than Perf A at the time, in a warzone, in an aircraft that could get airbourne in 1/2 the runway available. (TODR < 0.5 TORA) Not reccommended I agree, but lives depended on it. And I didnt quite fancy sticking around where we were.

Brake temps and in particular cooling times can become an issue at these temps, not to mention avionics overheating (BIG problem, probably our biggest).

Just remember to leave the oil cooler flaps in Auto if you have them, unlike one of our pilots, in an aircraft that got airbourne and nearly necessitated 4X engine changes! (HIGH oil temps) :E Just got away with that one by 2 degrees!

DONT operate outside your aircraft limits, even if you really need to go flying (unless you have TP at the end of your name).

[barit1]

It goes without saying, perhaps, but I'll say it anyway:

Operate at as low a TOGW as possible. Little or no tankering, COMAT, other non-rev load. Even if you can only gain 3 or 4 degrees worth of Tflex, you'll do yourself and the machine a big favor.

[411A]

Operate at as low a TOGW as possible. Little or no tankering, COMAT, other non-rev load. Even if you can only gain 3 or 4 degrees worth of Tflex, you'll do yourself and the machine a big favor.


Yes, but...oftentimes simply not possible.
Many of our departures with the L1011 are right at max weight, and often as not, high ambient temperatures, as well.
The airplane does just fine, EGT's always within limits, but...long takeoff rolls are thereby assured.
Initial climb performance?
Not a problem, we have plenty.
However...we sometimes have a very long taxi, so I taxi slowly and carefully, and if I think it necessary, the landing gear remains extended after takeoff...not for brake cooling, but wheel/tire assembly cooling.

[muduckace]

I have operated out of a few airports in DC-10's where it was common to get EGT lights at takeoff thrust. About 7k feet and close to the equator were the worst. It was usually in the breifing just to maintain awareness that a exceddence needed to be monitored to reduce thrust if possible after a safe altitude had been achieved.

Sorry for the high and hot ref. At sea level weight, temperature and RWY length is much easier to calculate. I have often experienced scenarios when a AM departure was delayed and freight had to be removed as the temp increased, thermal expansion in the fuel tanks started to vent fuel overboard. Seems to be taken more seriously.

[Old Fella]

Interesting comment. "It was usually in the briefing just to maintain an awareness that an exceedance needed to be monitored to reduce thrust, if possible, after a safe altitude had been achieved". If the operations were being conducted to require thrust settings which, it seems, regularly resulted in exceeding EGT limits, with the attendant degradation of turbines, I am pleased I was not operating those aircraft. The only two turbine failures I encountered with the RB211-524 series happened following previously unreported engine over-temperature events which showed up when the DFDR data was downloaded.

[hawk37]

Vin Rouge,

"Even with FADEC, MGT/EGT overtemp can be an issue, especially if you are operating close to the aircraft max operating envelope"

Today's FADECs do not have overtemp protections? Seems this would be something designed into them. Doesn't the T5 sensor, ITT sensor, EGT sensor, or whatever is in use provide an input to the computer, which then reduces fuel flow to keep temps at or below the maximum?

[Phil Squares]

Yes, the FADEC/EEC will prevent overtemp, overspeed and overboost. If you need a Full Thrust takeoff, it's there with a FADEC/EEC engine. Not like the days of the old fuel control units.

[Intruder]

FADECs/EECs are not fail-safe, though. They may try to regulate too close to the limit, and dynamic conditions may result in transient exceedences.

Last week I had an engine overtemp (747, GE CF6-80) just after takeoff with an OAT of 35C. it was only 2 deg over limit for 2 seconds, but the EICAS dutifully recorded it and sent the message over ACARS. One of my colleagues had a similar (but slightly hotter/longer) one within a few days of that one.

[tightcircuit]

Hawk 37,

Just checked my manuals to confirm this. GE CF6 80C engines with FADEC have N1 limit protection but no EGT limit protection. I think the reason for this is that N1 is the measure of thrust on GE engines. If the calculated N1 for your take off resulted in an overtemp and the EEC then trimmed back the power your take off performance would become invalid. You would may have no idea it had happened or by how much.

TC

[barit1]

If the calculated N1 for your take off resulted in an overtemp and the EEC then trimmed back the power your take off performance would become invalid. You would may have no idea it had happened or by how much.

Same would be true for an EPR-controlled engine, wouldn't it?

[tightcircuit]

I was pondering that one barit1. N1 and EPR are very closely related. If the EEC were to trim back for an overtemp then yes you would be below your calculated EPR. As for an N1 overspeed that would mean that your EPR was higher than you needed anyway. Trimming back the N1 just brings you back to the power you wanted. I'm no engineer but that would seem to make sense to me.

The RR engines on our 75s which use EPR are not FADEC but they do have EECs and ELTs neither of which limit EGT either.

TC

[hawk37]

Tightcircuit, just making up a scenario here then to try and understand...

Say your aircraft was at it's temperature limit (Arizona, VERY hot summer day), max weight available, no reduced power take off. And then there was serious unknown engine wear that caused it to run too hot. Just guessing here, but a badly damaged flameholder or some other problem. Again, unknown.

So on take off, your Fadec would calculate and command an N1, and go happily on providing that N1, regardless of the EGT ITT T5 reading?

Just curious

[tightcircuit]

Hawk37,

Yes I believe it would. You would be warned of the overtemp by part of the EGT guage turning red. It would then be up to you to do something about it. You would then know exactly what you were doing with your own thrust at a time that may be thrust critcal.

Mr Boeing tells me that there is no overtemp protection on either our FADEC 76s or our non-FADEC 75s. I'm inclined to believe him.

Just imagine in your scenario what would happen if the EEC trimmed back your power for you to cure the overtemp and then you had an engine failure at around V1. You'd be ploughing the desert for quite some distance!

TC

[VinRouge]

the Fadec-equipped types I have flown (2 of) can most definately experience EGT overtemps on takeoff. The FADEC will not trim EGT whilst reducing EPR/Torque below the level calculated in TOLD.

Otherwise, your takeoff performance cannmot be guaranteed. Not exactly what you want when working at high isa conditions where takeoff performance is pretty tight.

Generally, up to V1, any red 'boxing' of the MGT/EGT would necessitate an abort on the types I have flown. Yellow boxing, depending on the exceedance and wear on the engine would determine a go/no go stiuation.

[hawk37]

FWIW, Honeywell has had "T5 limiting" on their early 731 engines (70's vintage), and I believe it's on the -20, 40 and 60 series but not sure (90's vintage). I'm told that if ITT gets to the magical number, the EEC, or DEEC in the case of the later, sends a signal that reduces fuel flow by 2%. Don't ask me for further, that's all I know. And I realize it's not a PW, GE, nor RR.

[muduckace]

"If the operations were being conducted to require thrust settings which, it seems, regularly resulted in exceeding EGT limits,"

Not so dramatic, engine exceedences are acceptable time/temp. Operations out of the airport I remember being the worst (medallin) were common. The briefing was to to prevent a high EGT exceedence as the EGT lights on the DC-10 indicate the initial limitation. To reduce thust if possible upon an indication would prevent an exceedence that would require maintenance action. I never had one out of there that required said action.

It was just responsible proactive agknowledgement to prevent engine damage as most normal operations are usually reactive (usually too late) requireing at the least a boroscope inspection of the engine.