737NG overheat

[N1 Limit]

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

[nitpicker330]

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.

[framer]

Hi, can you please clarify a couple of things so that I understand what you were seeing?
with the fault inop switch trying to trigger
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.

[oceancrosser]

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.

[ImbracableCrunk]

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.)

[N1 Limit]

@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.

[de facto]

But it really has little to do with the engine itself, but is a bleed leak in the Strut (pylon if you will)

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.

[7Q Off]

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.

[JeroenC]

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!

[framer]

the fault inop switch was pushing like a click each time there was a master caution overheat.
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?

[Skyjob]

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

[de facto]

Moving by itself without you touching it?

Spoooooooky:p

[Aluminium shuffler]

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).

[flyingchanges]

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.

[de facto]

An overheat warning is for overheat of the engine shroud, not the engine core

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

[cosmo kramer]

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.

[Capt Quentin McHale]

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.

[flyingchanges]

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.

[snakeslugger]

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.

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

[framer]

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.

[Centaurus]

In one B737 Classic simulator I flew, actuation of the fire warning switch on the simulator instructor panel would cause an immediate overheat warning light (with appropriate Master Caution/Overheat lights on). Approximately five seconds later the fire warning switch actuated. This was useful to the pilot as even a few seconds early warning of an engine fire was helpful.

Yet another 737 Classic simulator was wired up so that the same actuation of an engine fire warning on the instructor panel instantly produced a fire switch illumination.

The difference in philosophy between the two simulators is quite significant. In the case of the first simulator in order for the simulator instructor to "arrange" a fire warning close to V1, it meant the overheat light would come on several seconds earlier than the selected fire warning thus alerting the crew. The Boeing advice is to reject below 80 knots and continue if an overheat warning occurs after 80 knots.

On the other hand, a rejected take off up to VI is advised for a fire warning. So, in the first simulator, the crew are faced with a period of uncertainty - especially if they (rightly or wrongly) assume in that particular simulator that the overheat warning will be followed by a fire warning. By rejecting the take off below V1 if the overheat light illuminates, there is less chance of running off the end of the runway if the take off performance is runway limiting.

I would be interested to know the applicable philosophy in other B737 Classics. In other words in the real thing (engine fire) would you always get an overheat warning first? If that is a correct statement, then is the second simulator mentioned above, where a fire warning actuation is not preceded by an overheat indication, indicative of faulty fidelity?

[de facto]

Cosmo Kramer, you wrote 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. and Fire/overheat have nothing to do with the temperature of the engine core. What a load of nonsense.

I wrote: sensor is by the engine core.,on the high pressure turbine case

You know what the word "by" means?
Maybe you should process info before shouting about nonsense,hopefully not an accurate insight into your managing of a flightdeck...:=

[Aluminium shuffler]

For clarification, the fire detection loops do activate both the overheat and fire warnings, just with differing temperature thresholds. None of the detectors are inside the engines - they are around them. They detect heat build up inside the nacelle, not inside the exhaust or turbine, and so have no relationship with engine DU indications. An overheat warning can be triggered by a bleed air leak, as suggested, but also a core leak (combustion gasses leaking between combustion, turbine and exhaust stages) or a small fire. It is a very serious condition.

I take the comment about further effects including structural integrity of the pylon, too. While one might anticipate a bleed duct warning instead, that may or may not happen - a turbine leak could end up going all sorts of places, especially once things start burning or melting away. Even if the pylon was unaffected, the structural integrity of the nacelle could be affected.

[cosmo kramer]

An overheat warning is for overheat of the engine shroud, not the engine core

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

You wrote your AMM says otherwise, than what you quoted. The poster wrote overheat is not for the engine core - "otherwise" must then be that overheat is for the core - which is a load of nonsense.

Just because the loops are located near, but outside, the core, doesn't mean that anything going on in the core is being monitored.

In the engine core there is both heat and fire, and you don't really want to put either out, unless parked at the gate. :ok:

[cosmo kramer]

My objection here, is that people seem to mix 3 things together: Engine fire, severe damage and engine separation - just because it is the same same steps that are necessary (hence same checklist) to bring the situation under control.

"Hey man, you got to idle that engine if you got an overheat, otherwise it may lead to fire and then you'll get severe damage and your engine might fall off" - might seem like a logical train of thoughts. And probably could happen: Overheat of gearbox leads to fire, fire ruptures oil supply to the engine, bearings fail, causing severe internal engine damage, high vibrations cause engine mount to fail, engine separates. But for this to happen the flight crew would have to sit on their hands for several minutes (maybe 10s of minutes for all the things to develop), hence a very unlikely scenario.

Fact is you can have a overheat fire, without severe damage. Or you can have severe damage with out a fire. Or the engine might separate with out either.

An engine mount can fail without previous warning.
A fire in the cowling can take place due to a fluid leak.
An overheat condition can take place because of a bleed leak
A severe damage can be caused by a bird.
Etc.

The point is, to THINK about the situation, before reacting. In simulator we are taught drills - predetermined responses to predetermined situations. Which is not bad at all, because it's good to have a set of responses ingrained in your backbone.

But it is still useful, to think, and know what is going on. I.e. an engine (cowling) fire can burn for quite sometime before action is required. This is useful to know if you depart with critical terrain. The side with a cowl fire still has an perfectly good (internally) engine. It might make your life easier, to let it burn for 1-2 mins, and use the thrust to gain altitude, before attending to the cowl fire.

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..
Is a false statement, if I understand it the way it comes over. I.e. "reducing the thrust causes the core temperature to decrease and hence the overheat condition may disappear". Again, the temperature inside the core, is not being monitored by the overheat/fire detector loops. It might be a good idea to idle the engine for other reasons (like a bleed leak).

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.
Is a false statement. First, it won't go overheat -> severe damage. Considering the light came on off, it would probably either be an indication fault or the temperature had barely risen to trigger the overheat condition, hence still a way to go before the fire loops would trigger, as they have a higher threshold.

Just because the simulator is programmed to: overheat condition x 15 secs = engine fire. It doesn't mean it will happen like this in the aircraft.

An overheat flicking on/off like in the original posters scenario, might not require an immediate engine shutdown. The poster thought about the situation and monitored it, without acting - in the end the indication disappeared. All good and well. :)

In short, I think the original poster did a good job. Probably getting the aircraft to it's destination, without making a big drama. :D

N1 Limit, did you get information for your maintenance afterwards, as to what triggered the overheat condition?

[de facto]

AMM:
Purpose
The overheat and fire detector senses high temperatures in the engine compartment -
Location
Three sections of the detector are mounted around the fan case (the accessory compartment) and one section is mounted on the high pressure turbine case (core compartment).

Never did i say any temp sensors were INSIDE the core.

Considering not idling the engine as DIRECTED by the QRH is a poor advice and reminds me of this note in the QRH:
It should be noted that, in determining the safest course of action, troubleshooting, i.e., taking steps beyond published non-normal checklist steps, may cause further loss of system function or system failure. Troubleshooting should only be considered when completion of the published non-normal checklist results in an unacceptable situation.

QRH actions for overheat:
1 Autothrottle(ifengaged)...........Disengage
2 Thrustlever
(affected engine) . . . . . . Confirm . . . . . . . Close
3 If the ENG OVERHEAT light stays illuminated:
►►Go to the ENGINE FIRE or Engine Severe Damage or Separation checklist
Is a false statement, if I understand it the way it comes over. I.e. "reducing the thrust causes the core temperature to decrease and hence the overheat condition may disappear". Again, the temperature inside the core, is not being monitored by the overheat/fire detector loops. It might be a good idea to idle the engine for other reasons (like a bleed leak).
I told the OP that idling was a good idea,ie a better idea than running the engine at high thrust because he believed his normal engine parameters (EGT)was normal therefore an overheat was disregarded.

Just because the loops are located near, but outside, the core, doesn't mean that anything going on in the core is being monitored.

In the engine core there is both heat and fire, and you don't really want to put either out, unless parked at the gate.
True,but the sensors are strategically place around the core as it is considered a fire hazard area,to monitor heat/fire temp due to leaks.

[cosmo kramer]

Ok, then it sounds like we basically we agree :)

Except, the original poster didn't have a persistent overheat condition, but a flickering light. In any problem relating to the engine, I would say that looking at the engine parameters is common sense. I have no idea if a core leak would cause abnormal engine parameters? Most likely, it would certainly not produce a flickering overheat indication, but rather directly a fire warning.

Hence, with a flicking indication and everything else looking good, I think the original poster solved the problem in a reasonable manner. :ok: