737NG overheat
 

Dear all

I have experienced an overheat the other day Overheat on the fire panel with master caution with the fault inop switch trying to trigger on the left engine during climb,but all the left engine parameters were intact in fact left than the right engine,it kept triggering ON and OFF several times from level 290 till we reached 360,still crosscheckingengine parameters which were all correct,we decided to continue climb to FL380 to see if it's temperature related,stable at FL 380 it stopped.I assumed it's due to heat.Perhaps anyone with a deep knowledge of the matter can help answer my question

Engine overheat may or may not be accompanied by abnormal Engine parameters. Indeed all may show normal.
The only time I would suspect false warnings would be if it was on both Engines as in your case. Otherwise FOLLOW the QRH.

Hi, can you please clarify a couple of things so that I understand what you were seeing?
I don't understand what you mean by this. The only thing. I can think of is that you were also getting a FAULT light on the fire panel, is that right?
Also, was the overheat only on the left engine or was it on both as suggested above? Like. Nitpicker says, parameters may be normal.

I never really understood Boeings "Engine Overheat". I have idled or shut down RR engines on 757 4 times due to Engine Overheat. But it really has little to do with the engine itself, but is a bleed leak in the Strut (pylon if you will). As it is upstream of the Bleed Valve, switching the bleeds OFF does nothing. Having really hot air for long around fuel and hydraulic lines is not a good idea so the Boeing procedure is to idle the engine, and if the warning goes away after some cooling time (Boeing does not specifiy, used the 2 min they suggest for engine shut-down ) keep the engine running at idle, or if warning still on, shut it down.

It has been a long time but on the 737 Classics IIRC it was the same thing.

It will not show up on your engine instruments in any way.

Spurious warnings are a different thing though, probably a wiring or a plug issue. Turned out, my events were all actual leak.

Possibly you had one loop fail and the other sensed a FIRE.

Either way, why not follow the QRH? That's what the light is for.

(I believe there are four areas in each engine that are monitored - strut, fan upper, fan lower, and engine core areas.)

@nitpicker330,the fault inop switch was pushing like a click each time there was a master caution overheat.There was not Fault like tough.So if i understood the best course of action in this case is to follow QRH,reduce the thrust to idle.The overheat was on the left engine.

On the NG,the sensors for overheat and Fire are located about the Fan and the engine Core...so quite a good idea to idle the engine..

EGT on your dials shows just that..Exhaust Gas temperature after the LPT.

Follow the qrh next time. Is better to shutdown an engine because a false alarm and not to have a severe damage thinking that is a false alarm.

737NG overheat
 

You mentioned that you checked engine parameters. Although thats always good to do, You do realize that OVERHEAT comes from the fire loops, with a lower trigger threshold than a fire? It's not EGT, its not oil temp, its in the area outside of your core, underneath "the hood".

Indeed, tnx Skyjob!

Can you please explain that again.
Do you mean that the switch itself was moving of it's own accord? Moving by itself without you touching it?

JeorenC: copied pasted a bit of the wrong message? :O

Spoooooooky:p

Why on earth were you fiddling with the fault test switch when the warning illuminated? And why did you ignore an engine overheat? An overheat warning is for overheat of the engine shroud, not the engine core, so the engine indications are not likely to be relevant - overheats are almost invariably hot gas leaks into the shroud or nacelle, which as mentioned already, can cause all sorts of problems with fuel, electrical and hydraulic systems, not least fires.

I would suggest that ignoring the warning and maintaining climb thrust until the cruise shows a serious lack of understanding of your aircraft and procedures. Best get back into the books. The fact that the warning stopped as you throttled back for the cruise shows that this was the case and that you should have followed the QRH (and stopped the climb).

QRH, is not the Quick Recommendation Handbook...

Why bother looking if you are not going to follow the procedure.

BTW, the only thing I can think of that would click in that area is the solenoid for the fire handle.

As stated before, the overheat and fire warning are the same loops, just different trigger points.

My 737 NG AMM says otherwise..sensor is by the engine core.,on the high pressure turbine case.
Rest i agree.

Overheat of the engine core???

Fire/overheat have nothing to do with the temperature of the engine core. What a load of nonsense. Please remember this: The engine is always on fire, unless you got a flameout!

Fire/overheat in inside the engine cowling, and has nothing to do with what takes place inside the engine itself.

Shuffler,


Agree with your post but there is another "hidden" problem with a hot gas leak in the strut area and that is the STRUCTURAL INTEGRITY of the strut itself if exposed to extremely hot gases for a period of time.

The strut area is covered by the "wing body overheat light" Totally different system.

The engine overheat covers upper and lower fan case, and the left and right core case.

The clicking noise the OP refers to was the fire handle unlocking.

It appears it does...from the B738 MRG


Each engine has eight overheat/fire detectors, four in loop A and four in loop B. The detector consists of a 3-level pressure switch. Each detector is connected to an individual stainless steel, gas charged sense tube.


The detectors monitor four sections of the engine ; the upper and lower fan case and the left and right core section.

In each section, two detectors (one of each loop) are mounted around the engine and make an assembly.

Gas in the sense tube is charged with a minimum pressure to keep the FAULT pressure switch closed. A leak in the sense tube causes the gas pressure to decrease and opens the FAULT pressure switch. Except for the OVHT/FIRE test, there is no flight deck indication of single loop failure. However the overheat/fire detection system will take the fault into account.

If both loops in one engine sense a fault in one of its detectors, the FAULT light on the flight deck illuminates and the system is inoperative.

A temperature rise inside and around the engine will cause the gas in the tube to expand. The increasing gas pressure will close the OVERHEAT pressure switch and further on the FIRE pressure switch.


Upper Fan Case
174 °C / 345 °F Overheat limit
304 °C / 580 °F Fire limit
Lower Fan Case
174 °C / 345 °F
304 °C / 580 °F
Left Core Section
343 °C / 650 °F
454 °C / 850 °F
Right Core Section
343 °C / 650 °F
454 °C / 850 °F

It uses the word core but the tubing is still outside of the core, essentially measuring the temp in the shroud adjacent to the core.
I agree that it was not wise to forego the memory items and continue the climb in the OP's situation.