lmml 14/32
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B733 Engine Out - By Wind!

Sun Aug 29, 2004 5:10 pm

Recently I heard that one of our B733's aborted a take-off because one of the engines flamed out during the run. The story goes that inspection revealed nothing wrong and it was put down to a gust of wind!

This is all new to me. Is this possible?
 
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Starlionblue
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RE: B733 Engine Out - By Wind!

Sun Aug 29, 2004 8:18 pm

If you get sudden crosswind at low speeds to such a degree that airflow into the engine is severely disrupted this is possible. No air into the engine results in oxygen starved combustion.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Mr.BA
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RE: B733 Engine Out - By Wind!

Sun Aug 29, 2004 8:38 pm

Just wondering about that little bit of chemistry here, what do you actually mean by "oxygen starved combustion"? Lack of oxygen for combustion?

Thanks  Smile
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Starlionblue
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RE: B733 Engine Out - By Wind!

Sun Aug 29, 2004 9:02 pm

Sorry, yes. No air, no combustion. I assume that some air is present, but so little that the ratio of air to fuel becomes too low, and the flames go out.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
greasespot
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RE: B733 Engine Out - By Wind!

Sun Aug 29, 2004 10:09 pm

I am gonna have to go with a dissenting opinion here and say it is not possible. Yes wind can cause a compressor stall but it will not cause a flame out. One thing about a engine is it is really good about drawing air in.

Plus on your A/C it was on the T/O run so there engine was at high power therefore drawing in enough air. You would also need so much wind it would damage the A/C by moving it around.

If that was ever to happen you would also be changing the engine as the air volume decreased you would have EGT's shoot sky high and you would over temp the engine.


I will not say it is impossible because nothing is impossible but from a engine shop perspective I would say nope that was not the problem.

Greasespot
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Starlionblue
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RE: B733 Engine Out - By Wind!

Sun Aug 29, 2004 10:12 pm

Maybe the explanation given to LMML 14/32 was unclear. They may have meant stall or surge instead of flameout. Still, if the ignitors are off air starvation could stop combustion no? At least in theory.

EDIT: This thread goes into stalls in detail: http://www.airliners.net/discussions/tech_ops/read.main/95407/.

[Edited 2004-08-29 15:14:21]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
greasespot
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RE: B733 Engine Out - By Wind!

Sun Aug 29, 2004 10:40 pm

Yes in theory but you would need to change the engine as the EGT's would over temp. I thought of that after.

Maybe the captain shut it down due to stalls and now at the airline it has gotten around that the wind blew out the engine.

 Smile

Greasespot
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air2gxs
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RE: B733 Engine Out - By Wind!

Sun Aug 29, 2004 10:59 pm

You know, I was looking at this thread and wondered about it and decided that the engine probably did not flame-out from air-starvation. As greasespot put it: jet engines are really good about drawing in air.

I'm not sure what the fuel management system is like on a 737-300, but could fuel starvation have been the problem?

We had a DC8 (same base engine) flame out because the flight crew failed to properly configure the fuel system prior to take-off. Fairly easy to do on an 8, don't know about a -300.

We wound up changing that engine because of the thermal shock of going from TO to not running without cool down. He was well into the take-off roll when it flamed-out. Was also rather cold out as I remember.
 
SlamClick
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RE: B733 Engine Out - By Wind!

Sun Aug 29, 2004 11:49 pm

If this was possible it would be standard practice to select ignition to continuous during turbulence. Oh, that's right! We do!

Yes some kind of abormal airflow across the intakes might cause a momentary disruption of air supply through the compressors that would allow the flame to die - momentarily. That is actually called an "unstart" but it is pretty rare in routine ops. The igniters should have been on for takeoff and it should have relit almost without being noticed.

Rare? I'd say so. I've never had it happen. No one of my friends has had it happen that I know of. But the people who devise our procedures and write our manuals say it can.

After all that, I doubt that it was the real and complete explanation for this event.
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Starlionblue
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RE: B733 Engine Out - By Wind!

Mon Aug 30, 2004 12:03 am

If this was possible it would be standard practice to select ignition to continuous during turbulence. Oh, that's right! We do!

LOL Slamclick.

BTW in an arena not entirely unrelated to this one, military aviation, engines can and do "unstart" due to strange attitudes. You may have seen the Su-27/35/37 or the MiG-29 do the "Cobra", a very high angle of attack maneuver. Most military jets (and commercial jets assuming they could perform the maneuver, which they can't) would find their engines being starved at this point, and stopping, since the airflow over the intakes is essentially perpendicular to the direction of the intake (across instead of into) and at a later stage the plane is going slightly backwards.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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HAWK21M
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RE: B733 Engine Out - By Wind!

Mon Aug 30, 2004 12:10 am

Isn't it S.O.P. to select Ignition to Continous during T/o,Landings & Turbulence.
regds
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TripleDelta
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RE: B733 Engine Out - By Wind!

Mon Aug 30, 2004 12:26 am

Unstarts were quite a problem for the Olympus engines used on the Concorde, before the Rolls-Royce found a way to shutdown and restart the engines in flight. As I remember from watching Wings Over The World, this was due to the high-speed of the air entering the engine (above M0.3-0.5). An unstart usually, when it occurs, shuts down the engine due to the shock wave it produces and can even blow off a couple of engine parts.

However, I haven't heard of any unstarts on sub-sonic jets. This may be a bit naive, but can it be possible that instead of being starved of oxygen, the engine was "oversaturated" with it? Say, a sudden gust of wind hits the intake and from the shock and sudden speed change, an unstart, or a similar disruption of airflow, occurs. Or maybe even a shock to the fuel system as well. But then again, what would happen in turbulence in that case?
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air2gxs
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RE: B733 Engine Out - By Wind!

Mon Aug 30, 2004 3:34 am

A sudden gust of wind wouldn't not lean the mixture out enough to flame-out. The air going down the core is basically controlled by the variable stator vanes (VSV's), which are wide open at TO power, and the variable bleed valves (VBV's), which are closed at TO power. Tubo-fan engines take a lot more air into the inlet than they can use. Most of that air goes into the by-pass duct. The air that goes down the core is regulated by the VSV/VBV system. A huge slug of air may cause a slight disturbance at the intake but certainly would not cause a flame-out. Remember, there is all kinds of air going down the inlet in-flight (low altitudes). Much more than on the ground.
 
lmml 14/32
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RE: B733 Engine Out - By Wind!

Mon Aug 30, 2004 5:07 am

Wow !!

Thanks for the mature and sensible discussion. Someone mentioned Concorde and I have a question about this too: Why the delay in lighting the #4 burner during the takeoff roll? If I am not mistaken this is also due to an airflow issue. Can someone please elaborate?
 
QantasA332
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RE: B733 Engine Out - By Wind!

Mon Aug 30, 2004 6:07 am

I don't think that there's a delay in lighting Concorde's #4 engine afterburner on takeoff (it is weaker initially, though), but #4 is certainly a 'limited' engine in another way. Wingtip vortices around the right wing rotate in the opposite direction to the engine's/fan's rotation, which can cause all sorts of vibration and problems at low speeds (namely takeoff). As a result, #4 is limited to 88% N1 at speeds below 60 kts. Read more here, at the very bottom of the page.

Cheers,
QantasA332

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