wheel-well fire??

[RAT 5]

Boeing have stressed that the B737 wheel-well fire indication is from an overheat sensor. If the source of the heat is from the undercarriage then when this is lowered the source of the heat has been removed from the sensor and the indication may extinguish. It does NOT mean the fire has gone out.
If such a warning is received on departure, and after the gear has been lowered the indication extinguishes, what will you do?
I've asked various crews and the discussion is very circular. "I'd go to a hold and follow the company procedure for assessing the situation and consider the options and then action the chosen one." I explained this could take >10 mins longer remaining in the air. "I'd rip it round and land ASAP." But what if it was an NPA and for a VNAV/LNAV approach the plates need finding and the FMC programmed? If it is an ILS at a familiar airfield, then it is much easier and only a Vref and the chart is required. The rest can be flown without FMC.
What would you do if it was VMC? Just a Vref and rip it round? What about NITS & PA to pax? Some yes, some not bothered.
Guys had experienced this in the sim as a Landing Gear QRH systems item. Fire warning out, exercise finished, sim re-set and move on. But what would you do in real life?
I've only had it happen once and that was at medium level on climb out en-route. Must be a false warning, but when there's doubt there is no doubt. Then the indication went out with gear lowered. CAVOK and return to familiar engineering base. No drama: it was known wiring problem, but not to me. One friend had one on stand after landing = evac. Who's to say he was right or wrong.
So, back to question in a scenario where it might well be an honest warning. I expect 20 pilots 20 opinions, so let's hear them.

[Jwscud]

I would be deeply uncomfortable doing anything other than a fairly rapid return after any sort of fire indication, especially in an area where all my hydraulics, flap motors &c are located.

The weather and the approach would be the main variables. Hopefully it's either a home base or we've conducted an approach there 45 minutes or so ago so we are reasonably familiar with what to expect so not much to set up.

The main worry for me could potentially be stopping distance and what's hanging off the end of my gear struts. Of course I still only occupy the right seat but that is the position I would advocate!

[perantau]

Per jwscud. Flight 2120 ex-JED comes to mind.

[megan]

A follow up to the post by perantau

Swissair Flight 306 (Caravelle) airborne for 8 minutes Swissair Flight 306 - Ask.com Encyclopedia (http://www.ask.com/wiki/Swissair_Flight_306?qsrc=3044)

Nigeria Airways Flight 2120 (DC-8) airborne for 10 minutes Nigeria Airways Flight 2120 - Ask.com Encyclopedia (http://www.ask.com/wiki/Nigeria_Airways_Flight_2120?o=2802&qsrc=999)

Mexicana Flight 940 (727) airborne for 15 minutes Mexicana Flight 940 - Ask.com Encyclopedia (http://www.ask.com/wiki/Mexicana_Flight_940?qsrc=3044)

If it's for real you don't have much time seems to be the lesson to take away.

[vapilot2004]

Scenario: post-departure, wheel well fire warning. Gear down, light extinguishes. Land at nearest suitable is the guidance. Why would one do anything different?

I understand that an inop wheel well fire detection is not a MMEL item in the UK. Can anyone comment on this? Is the EASA/JAA the same?

[RAT 5]

Scenario: post-departure, wheel well fire warning. Gear down, light extinguishes. Land at nearest suitable is the guidance. Why would one do anything different?

There are difference of opinions about "land at nearest suitable" and "land ASAP."
I agree guys, but the point is being missed. There are airlines who have extensive TEM procedures and other problem solving sequences. There is much cockpit conferencing to satisfy the never ending CRM; there have procedures in place to ensure there's no rushing into the first choice, but examine ALL the options. NITS & PA etc. It takes forever. This discussion is about the dangerous, IMHO, cosy feeling that as the fire indication has extinguished then all is OK and you can go to a HOLD and follow all those various procedures which are fine for some scenarios, but not all. In the sim this is what is taught. Obviously, if any fire warning remains lit then land ASAP is the name of the game. This is a grey area, but I feel it is not stressed enough in the sim: hence my curiosity about other's opinions. As there is a wide spectrum of 'what you would do on the spot', but it is not necessarily what sim training advocates, then here needs to be some clarification from the training department as to what is acceptable so there is not a flight deck dispute as the raw F/O demands full procedure while grey-haired fox whats to land ASAP. In Swissair MD-11 I think it was the other way round, interestingly.
In 30 years of training I was never subjected to an inextinguishable engine fire in the air. It was only used to cause a pax evac. Cabin fire? yes, but so far from a landing option that there was time. I have given the engine scenario as an instructor, and the reactions were very mixed and disappointing. They varied from a speedy and well managed return with minimum fuss, to rabbits in headlights what to do confusion. The rules said one thing, but survival said another. Agh!

As has been discussed on the 'Airbus handling improvement' thread it is about using the simulator to its full potential for positive and constructive training, not ticking boxes.

[de facto]

Its just about setting priorities as the situation evolves.

[Jwscud]

RAT 5, I don't know who you work for, but that sounds a lot like some issues at my airline. We have a structured decision model, the the NITS PA framework. The training department have started realising that they were training robots to follow their sequence almost no matter what the failure.

They are now trying to emphasise that the key issue is making the decision, and that one does not have to go through a full set of drills all the time. However, this is shall we say taking time to trickle down to all the trainers.

The fundamental problem with a very rigid approach to SOPs as practiced by the major LoCos is that everything in the manuals is treated as a diktat, and has led to checking that is biased towards making sure everyone is "following the script."

[enicalyth]

What if the warning light went out because the wire burnt through?

Yes I know "Matilda told such awful lies it made one gasp and stretch one's eyes..."

So... let's say a known occurrence occurs and CRM is followed and the consensus is that it is that microswitch again and an edict says we'll do it "shortly". So... wheels down, wheels up, light goes out. Dam' microswitch. Except it wasn't. All perish.

[de facto]

You land it a nearest suitable airport,,its in the NNC...
If the fire indication remains on,do the same....a NITS is essential without the need to blabla for an hour and fly into a holding that is miles away...
A slighly extended downwind to do all is plenty enough in that scenario..

[Skyjob]

To throw a spanner in the light goes out scenario:
If the overheat detection was due to a fire on the wheel assembly, when it is lowered the heat source is removed from the detection loop, thus extinguishes, but will the fire be out on the extended undercarriage?


Answer to OP: return to land ASAP as fire/overheat situation may not be resolved, leave cabin crew in seats, position to 10nm final should give ample time for all checks to be completed and company models to be satisfied

[vapilot2004]

There are difference of opinions about "land at nearest suitable" and "land ASAP."

Feet dangling, fire indicator still on, ASAP, light out, nearest suitable?

On the 737 and, I believe the 57 and 67, wheel well fire detectors are single loop. The engines and APU utilize more reliable dual loops. I've been told Airbus tends not to have wheel well loops at all, relying on brake temp sensors instead.

It is ironic to think that following TEM procedures would increase the hazard, RAT 5! I can think of alternate CRM scenario with your silver haired gent saying: "Ignore it sprog, I've seen it xx times in my career and they all turned out to be duds."

If the overheat detection was due to a fire on the wheel assembly, when it is lowered the heat source is removed from the detection loop, thus extinguishes, but will the fire be out on the extended undercarriage?


200+ knot airflow should take care of a rubber-fueled fire, but if the fire is fueled by Skydrol, or worse, magnesium, all bets are off.

[vapilot2004]

Some aircraft are equipped with brake temperature sensors - one for each set of brakes (wheel), while others have overheat sensing loops in the wheel well. Some aircraft, like Boeing wide-bodies, have both. On narrow-bodied Boeing aircraft, brake temp sensors are typically customer options, however I understand the A320 series comes with them out of the box.

[Skyjob]

is the fire/overheat sensors BOTH in the wheel and wheelwell ?

Only in the wheelwell.
Hence my question, if the light goes out can you be ASSURED any possible fire on the assembly is out?
Granted it is hanging in the rushing air and likely to be blown out as a result...

IMHO, wheel well fire warning light out thus can refer only to the fact that the HEAT SOURCE HAS BEEN REMOVED from the proximity of the single loop. It does not mean the (possible fire) heat source is EXTINGUISHED.

[vapilot2004]

It may be of use to the discussion to know the (exponentially) primary generators of heat in the wheel wells, by sheer mass and heat sink/radiation qualities, are the main wheel brake assemblies. Only a fuel leak would have more potential energy in this area of the aircraft.

would having Halon bottles in the wheelwell help extinguish the fire/overheat condition?

Halon will not put out a magnesium fire and due to wheel wells being poorly closed compartments, the concentration levels needed for fire suppression would be difficult to sustain - the bottles would need to be very large. Halon also reacts poorly with hot metal, including that hot set of steel brake rotors and disks that most likely was the heat source for initiating the fire/overheat condition in the first place.

So, going back to the principal source of the heat, air, and lots of it is the best way to cool the brake assemblies. Gear down = happy feet.

[RAT 5]

So, going back to the principal source of the heat, air, and lots of it is the best way to cool the brake assemblies. Gear down = happy feet.

The wheel well contains hydraulic pipes and wiring. There have been problems with wiring insulation breaking down and sparking. There have been minute hydraulic leaks with a very fine spray. Put the 2 together and you might get a fire that will extinguish with airflow and then perhaps re-ignite. There's lots of oil & grease residue too. So the hot brake, or hydraulic fluid dripping on hot brake, may not be the only cause of a fire. What is the flash temp of hydraulic fluid? Could a brake get so hot on departure as to ignite it, or grease?

[vapilot2004]

I believe type IV hydraulic fluid's flash point is around 3-400 degrees F, RAT 5. I also think grease is in such limited quantities (bearings/joints) to preclude it being the cause of a serious fire - tires are more likely suspects in comparison.

There have been minute hydraulic leaks with a very fine spray. Put the 2 together and you might get a fire that will extinguish with airflow and then perhaps re-ignite.

Quite true. Gives even better reason for leaving the gear down, yes?

There have been problems with wiring insulation breaking down and sparking. There have been minute hydraulic leaks with a very fine spray.

MD-80 AUX HYD pump wiring comes to mind!

[Skyjob]

but how would you verify fire out with gear down? how would you verify the condition of tires to make a landing?

Without outside help, you cannot from within the flightdeck

[B737900er]

Unless your on the CL and use the viewing mirror.:ok:

I think KISS comes to mind. Unless you can confirm the fire is out just land it ASAP.

[JammedStab]

With no final opinion, and listening to arguments on both sides, I am going to play the devil's advocate......

If we have an engine fire after a heavy takeoff from a short, slippery runway and the fire warning remains after blowing the bottles, the procedure is to land ASAP.

What do you do if the engine fire light goes out after blowing the bottles. Frequently, take the time to dump fuel then land. But you might say...hey, I can inspect the engine to ensure that the fire has extinguished. Not necessarily on a freighter or with tail mounted engines. Do you still dump fuel and then land? Seems to happen that way.

Why then, is it any different for a wheelwell fire compared to an engine fire. In fact, if the wheelwell fire light has been out for 20 minutes, doesn't Boeing say that the gear can be retracted for performance reasons. Why.....because it was hot brakes, not a wheelwell fire and the brakes have now cooled.

But some say...dual fire sensors are in engine/APU versus a single sensor in the wheelwell, therefore the extinguishing of the fire warning for the engine/APU is more reliable than for the gear. But the dual sensors are intertwined with each other aren't they. If they are, a fire is going not going to burn one and leave the other one OK. So is it any more reliable or really just more redundancy for dispatch purposes.

Mexicana and Swissair were tire explosions, not wheelwell fires. Nationair was a landing gear fire in which the gear remained retracted. If you have an actual fire in your wheelwell, you will know soon. On the Nationair flight, within a very short time period, they had multiple secondary failures. Plus, they had other indications of a blown tire on almost the entire takeoff roll indicating that it was not just a brake overheat.

So if you had a wheelwell fire indication(which will likely be a certain time period after being airborne as the brakes take time before reaching max temp), drop the gear and typically turn around to go back to the departure airport and if there have been no further anomalies since the fire light extinguished 5 minutes ago, how likely is it that you still have or ever had a fire? Not very likely.

With those still fairly warm brakes now landing on a short runway when overweight, you might have trouble getting stopped if you automatically just return and land right away. Which would make you look rather silly to write off an aircraft due to a hot brake(which by the way will not help your stopping capability much).

[Mach E Avelli]

It is surprising to me that most QRHs do not require a fire warning system test after completion of any fire drill.
Many years ago I experienced a momentary fire warning just after takeoff on a performance test flight in a brand new F27 that had only a few hours of ferry time. We were conducting 'hot and high' tests in temperatures approaching ISA plus 35.
The warning illuminated, but within a few seconds cancelled. Wrongly we assumed a false transient, caused we thought by the extremely hot ambient conditions. This was not uncommon in earlier versions of this aircraft type with the usual cure being to increase climb speed. Fortunately a deadheading pilot sitting in the passenger cabin saw the flames and yelled out to us.
After completing the drill and making an immediate landing we found that a combustion chamber had a faulty weld. This had opened up enough to allow hot flame to reach the fire wire and set off the warning. Then it opened more and became a blow torch which destroyed the complete loop system. The design was such that at that point the entire warning system was disabled. In the short time it had been burning through the combustion chamber, considerable damage had also been done to the engine control linkage for HP fuel.
So since then I have taught crews to conduct a fire test after any drill involving fire. If the system does not test, assume the worst and land RFN (right.......now)

[megan]

Mexicana and Swissair were tire explosions, not wheelwell firesYes, but the tire explosions initiated fires in both cases.

Mexicana: The left main gear brake was overheated during the take-off run. When the aircraft had reached FL310 the heat caused a tyre on the left hand main gear to explode. Fuel and hydraulic lines were ruptured and electrical cables severed resulting in a cabin decompression. An emergency was declared, but spilt fuel ignited and caused a massive fire on board. Control was lost and the aircraft crashed into a mountain.

Swissair: The aircraft's brakes overheated due to the application of full engine power during taxiing. This caused the aluminum wheels to burst, one of them on the runway prior to departure. Upon retraction of the landing gear, the hydraulic lines in the gear bay were damaged. This was caused either by the wheels that had exploded, or the bursting of the other wheel rims during the climb. Subsequently, spilled hydraulic fluid ignited when it came in contact with the overheated landing gear rims. The fire damaged the gear bay, followed by the wing. Finally losing its hydraulic pressure, the aircraft became impossible to control. The cabin and the cockpit were filled with smoke, adding to the predicament of the crew. Control of the aircraft was lost totally, and the ensuing final dive and impact destroyed the aircraft.

[JammedStab]

Yes, but the tire explosions initiated fires in both cases.



If there is an explosion on board, it is almost certain that the pilots will know from sound, feel, and indications of other system failures. In this case, there will likely be an immediate landing. Explosion scenario likely answers that question if you are lucky enough to remain in control.

For the scenario discussed earlier, we are talking about a wheel well fire indication only with no other indications of a problem after the gear was extended and with the fire indication extinguished. Should one head back and land immediately is the question.

[vapilot2004]

considering potency of the risks involved in a wheelwell fire...i would recommend having fire/overheat sensors in the wheels and pressure transducers in the tires to enable reject a take off...and Halon bottles in the wheelwell i believe would be a safer bet rather than just rely on ram air to extinguish a fire/overheat condition.am

J69, your belt and suspenders approach is not without merit, yet realize tire failures are regular occurrences that typically have no more consequence than a maintenance write up, replacement of the offending bits, and inspection. In fact, Airbus recommends continuing the takeoff under V1 for a single tire failure. Boeing also states their aircraft can takeoff and land safely with one flat tire per bogie. Statistics are sparse in this area - airlines are not required to issue an incident report on a tire failure without collateral damage.

In cases of a locked brake, there will eventually be an EICAS/ECAM warning generated (temperature limit reached), along with an immediate tendency to pull in the direction of the lock, but an RTO based on temps alone would be unlikely since the heat rise lags the physical event. Once airborne, lowering the gear is simple and effective in getting things cooled off. History has shown at or near V1 RTOs due to brakes or tires can lead to overruns.

am i missing something ?
Yes, an earlier reply regarding Halon and wheel well fires.

Halon will not put out a magnesium fire and due to wheel wells being poorly closed compartments, the concentration levels needed for fire suppression would be difficult to sustain - the bottles would need to be very large. Halon also reacts poorly with hot metal, including that hot set of steel brake rotors and disks that most likely was the heat source for initiating the fire/overheat condition in the first place.

[latetonite]

The 737 is a very safe plane. It has three fire extinguishing bottles in the wheel well.:8
On a more serious note, I would get the thing on the ground as soon as possible.
Regardless of the state of the tires, I land anyway. You will figure that out after landing.
All this based on a real experience where on an A300 I burned away a tire during take off, resulting in a immediate , overweight landing and a complete bogey replacement later.
The discussion about it was held in a hotel with a coffee, not in a crippled burning plane in the sky at night.

[JammedStab]

vapilot2004: "consider potency of the risks involved in a wheelwell fire..." witness Mexicana,Swissair,Nationair.

Already discussed. An explosion on board has a high likelihood of resulting in an immediate landing(if you are still controllable).

Nationair's first indication of a problem once airborne was a flight attendant report of a lot of smoke in the back. An immediate landing is required(I don't believe they had a wheelwell fire detection system).

In none of these cases used as wheelwell fire examples, was there was a delay in pilot intent to try to get safely back on the ground and in none of these cases was the scenario what has been discussed(wheelwell fire indication that has extinguished after the gear is lowered with no further anomalies noted).

It seems that there is a tendency to create a panic return when a procedure has been done and a warning has ended for the most likely cause.

For those that flew King Air's with engine fire indicators based on detection of light instead of heat, there could be occasional dual engine fire warnings when the sunlight was just at the proper angle entering the cowls. Turn a little bit and the warnings disappear. Or should the panic land immediately idea take over because maybe the sensors on each engine burnt out and therefore landing on that extremely short nearby runway somehow has become the only option.

After all...we are on fire.

[Capt Quentin McHale]

latetonite,


Indeed the 737 is a very safe aircraft, but of all the 737's that I have operated on, they have only ever had two firex bottles in the wheel well in the upper aft l/h corner. Your outfit may have a different bottle configuration. These bottles are the engine firex bottles and have absolutely nothing to do with the wheel wells apart from where they are located.

[JammedStab]

On a more serious note, I would get the thing on the ground as soon as possible.
Regardless of the state of the tires, I land anyway. You will figure that out after landing.
All this based on a real experience where on an A300 I burned away a tire during take off, resulting in a immediate , overweight landing and a complete bogey replacement later.
The discussion about it was held in a hotel with a coffee, not in a crippled burning plane in the sky at night.

But was there any evidence of having been a fire after you landed? Depending on the airport you were at, you could have easily been well above max landing weight with a serious lack of braking due to blown tires and hoping that reverse thrust would stop you prior to the end of a not so long runway, perhaps even wet runway.

I suspect in the case you experienced, you were fortunate to have a nice long runway.

[latetonite]

To Jammed Stab:

Was the plane burning? An Air France on approach reported me to be on fire, tower relied to me the same. To me in the cockpit, I could not see the extend of the fire, nor predict how much would be on fire in the next ten minutes.

Overweight? Yes. Max TO weight for a five hr sector. Fuel dumping on a fire? No.

And I do not need to be lucky to know that if CDG does not cut it, where else in your Jeppesen would you go?

[lomapaseo]

Megan

Mexicana: The left main gear brake was overheated during the take-off run. When the aircraft had reached FL310 the heat caused a tyre on the left hand main gear to explode. Fuel and hydraulic lines were ruptured and electrical cables severed resulting in a cabin decompression. An emergency was declared, but spilt fuel ignited and caused a massive fire on board. Control was lost and the aircraft crashed into a mountain.


Where did you get that from?

I recall quite a few more details leading to lessons learned.

[captjns]

BOEING 737 QRH is concise about the matter regardless if the fire had extinguished or not, and if the gear is left extended or retracted after the Wheel Well light has extinguished after the 20 minute period.

As I recall, it was the same for the 727, 757, and 767.

Plan to land at the nearest suitable airport.

[JammedStab]

Apparently the 777 wheelwell fire detection system is capable of actually detecting a fire as opposed to creating a warning due to hot brakes.

[rigpiggy]

oh for fudges sake haven't we learned from previous, have a fire indication treat it as real and get on the ground....... on average 8-12 minutes before your done. had a groundcrew signal an engine fire, captain shut them both down, and fired the bottles as per sop. we were called on the carpet as to why we fired both bottles for a stack fire. " because thats the way you wrote the SOPs".

[AeroTech]

Hi,

Rigpiggy,
oh for fudges sake haven't we learned from previous, have a fire indication treat it as real and get on the ground....... on average 8-12 minutes before your done. had a groundcrew signal an engine fire, captain shut them both down, and fired the bottles as per sop. we were called on the carpet as to why we fired both bottles for a stack fire. " because thats the way you wrote the SOPs

What I understand from your post is that the captain used both bottles after the ground crew informed you about the engine fire. If this is true, then you had engine tailpipe fire (internal fire) and not engine fire (external fire).

Did you have engine fire alarm in the cockpit?

Feedback appreciated.
Regards