B737 fire warning
 

Have you ever noticed (hopefully in the sim only) if you get ALSO an OVERHEAT light when there's an engine FIRE warning?:*

Not so fast. On the B737s (-300 thru -900), the amount of loop sensing a fire has nothing to do with whether an overheat or fire warning is generated.
The fire loops have different alarm settings. As the resistance decreases in the kidde system used on the B737-3/4/500s, the first alarm setting will generate an overheat warning. As the resistance lowers further, the second alarm setting will generate a fire warning. The Systron Donner system used on the Next gens, though using the gas pressure method, still has the different alarm settings.

One loop sensing a fire or an ovht won't give any kind ogf warning until both sense it (during normal ops).

I will be honest, I can't say with the-200s

737 classic:
what I mean is:
as the temperature increases, you get an OVHT caution.
The temperature increases more: you get a FIRE warning.
But my question is, when you get the fire wrng, the OVHT
remains illuminated or goes away ?
Will we have TWO lights (one red and one amber) or just one (red)?

Sorry, got off topic.
Yes, the Overheat light will remain illuminated if the temperature increases to the Fire Warning level. It will remain illuminated until the temperature lowers below the engine overheat alarm setting.

In our 737 simulator anyway, if the instructor triggers a fire warning, the overheat light comes on first, followed approximately five seconds later by the fire warning light and bell. After 80 knots we are taught to ignore the master caution and overheat light.

Which brings up an interesting point of view. If an overheat light comes on above 80 knots but well below V1 - the Boeing philosophy is that a caution light above 80 knots is not grounds for an abort. In this case, however, the captain is gambling that the overheat will not turn into a full blown engine fire warning. Going by what Boeing recommend he would continue the take-off.

If on the other hand he gambled wrong and the overheat light was a precursor to a fire warning, then that extra five seconds between overheat light and fire warning would place the aircraft closer to V1 (at the all engines acceleration speed).

The captain is now between a rock and the hard place where an abort at high speed due fire warning is a serious event on a runway length limiting take off - and taking an engine fire of unknown intensity into the air could be equally dangerous.

Back to simulator training (or is it testing?). An engine overheat caution light coming on say at 100 knots would, I venture to say, cause many pilots in real life to abort immediately before the situation turned into a nightmare. One does not consider whether it is a false warning or not. But this would surely be criticised as not de rigeur SOP. Far better for one's career to take the overheat into the air and risk the fire warning, and get the box ticked off, rather than risk being accused of thinking outside the square.

I wonder which any of us would do, if this actually happened on line - an engine overheat between 80 knots and say 15 knots below V1, that is. And your wife and children were down the back....

It is interesting that on the 757, i believe there is some kind of inhibition to fire warnings on take off, never flown one but i think it is from nose leg extension till 400 feet ot x seconds after t/ off

FF - Yes.

On 757 Master warning lights and fire bell inhibited from nose oleo extension to 400 ft radio, or 20 seconds. EICAS is not inhibited.

Advisory messages are inhibited from 80 knots onwards.

The Overheat light will be illuminated assosciated with a full Fire warning. Look at the QRH drill, it states some way down to rotate the fire warning switch if the SWITCH or the ENG OVERHEAT light remains illuminated.

As for the Captain being between a rock and a hard place re MENEN, not so. If the Captain decides to STOP before V1 then all performance criteria will be met if the actions are completed as per training. Boeing do not RECOMMEND stopping for a Master Caution alone, even if it is an Eng Overheat. Unless a catastrophic event occurs, ie more than just a Matster Caution, it is far better to continue the takeoff (even an Eng Overheat becoming a Fire at V1) and resolve the situation in the air, AS YOU HAVE BEEN TRAINED TO DO. The reason? TIME. Simply TIME. Now you can think, assess and deal with the problem. As soon as you try to hurry things all hell breaks lose, training falls apart and people are hurt.

LEM, are you in the middle of a type conversion ?:ok:

Pancho, on the old manuals 737 classic (the only ones I have for the moment), the QRH drills just refer to the Fire Warning Light ,
not to the OVHT light.
Anyway, I believe now both lights will be illuminated.

I agree with Menen when he raises the point that continuing the takeoff with an OVHT implies the risk of having a fire JUST BEFORE V1.
You assume that the fire wrng will come only in the air, and you'll have time to manage it.
But actually, the fire wrng could come just before V1, and you'll have to abort at high speed, and we all know the dangers af aborting close to V1.
That's one of those matters where it's impossible to find absolute truth....
Probably the best solution is to select the lowest V1 possible on short/slippery runways... V1 wet minus 10, as David Davies suggests in Handling the big jets.
....
The master wrng light and the fire bell are inhibited after V1 till 400 ft or 25 seconds, which frst, on the 747/400.


LEM

Hi LEM, no, I am not assuming the fire warning comes on only when airborne. The scenario stated is that the Overheat light comes on above 80kts and then later (near V1) the fire warning occurs. If the crew have completed their performance data correctly for the conditions and the stopping procedure is commenced before V1 then the aircraft should stop within the distances available, limiting runway or not. V1 is a GO speed not a STOP speed. Boeing say that stopping for a Master Caution alone is not recommended, that does not mean you cannot stop if you think it necessary. It is incorrect to ignore the Master Caution as Menen has been taught, a call must be made.The problem arises when you approach V1, things are now happening fast and it is conceivable that V1 may be exceeded by the time the stopping procedure commences, ie: too late. Bear in mind that an Overheat does not automatically become a Fire. I have had such an event when operating up to max in hot/high steamy conditions and the QRH has a drill to cover it.

As regards the QRH you are using I am not sure what date it was issued but I have one from 1990 for the -200 that has the same Eng Fire drill as my current one, an NG, including the reference to the Overheat light.:)

Just a bit off topic, but a question regarding RTO due to a master caution light:
Buddies, would you reject a takeoff - let's say at 15-10kt below V1, on a balanced field - if there's a MC light because of hydraulic warning and the frightened PNF callout: "Master Caution - Loss of System A & B".?:E

Bokomoko, absolutetly NO!

Pancho, in a perfect world aborting 0ne knot before V1 guarantees you will stop a few inches from the runway end.
In our much unperfect world, as Boeing says in the training manual, " NOTE: Past experience has shown that rejecting a takeoff at OR CLOSE to V1 speeds has, in too many cases, ended in the aircraft stopping beyond the end of the runway."
:{

LEM. You say that "As soon as you try to hurry things all hell breaks loose, training falls apart and people get hurt".

Ye Gods, man! What a frightening scenario. Which airline are we talking about here?

Please say again, Menen, I'm reading you one.