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gekko
4th Apr 2008, 10:24
hello!

I have some doubts concerning a certain (simulator) scenario and hope there's someone who can help me out :ok:

You're experiencing a dual engine failure around FL170, you're flying rather slow due to other failures (230kts)...After a mayday call and some hesitation you take qrh (time delay approx 2min) for the dual engine failure checklist-fuel remaining...One of the first actions is engine mode selector IGN...

What would then be the chances that your engines will relight by windmilling restart? Assuming you keep green dot speed to reach your airfield...
I considered it as very small due to low speed, low altitude (and a small time delay) which, according to me, would make that you're out of the windmilling restart envelope...

I know as long as N2 still is 15% a windmilling restart should be possible.... (for a CFM56 engine)

What do you think?

Thanks in advance:ok:

JSF1
4th Apr 2008, 12:00
Errr...without going to the manuals, I believe the optimum relight speed is 280kts - not sure how you would get on at 230kts. The initial actions are taught as memory items where I work.

Once below FL200 APU bleed is available to assist engine start when at Green Dot.

I'm sure someone else will offer some better help!

Dream Land
4th Apr 2008, 15:08
Right engine, 30 seconds on, then off, Left engine, 30 seconds on, etc. NFP does the restart, FP points aircraft toward the nearest airport.

gekko
4th Apr 2008, 15:21
hey!

ok thanks, but my question is actually...

Is it very likely that with that speed and altitude (let's say 230kts FL150) you're engines will relight windmilling?

Because my idea is that (if APU is already running) just put bleed on and start the engines with starter assist...

thanks:ok:

wileydog3
4th Apr 2008, 16:57
So really this is a question about the CFM-56 and not about the A320 family?

seems the big thing is to make sure you are in the relight envelope to enhance the chance of getting it humming again. This is something the Pinnacle crew NEVER did and unfortunately they paid the ultimate price for the error.

lomapaseo
4th Apr 2008, 17:58
These simulator questions are subjective as hell. Mostly because the simulator programing is subjective to begin with.

Actual engine relight envelopes vary precisely by engine model and age while the simulator typically programs by-the-book. i.e. if you ain't in the envelope, it ain't gonna restart.

However, most engine failures don't result in the flame going out (EGT goes up) and as such it's up to the crew to shut down the engine, by turning off the fuel. There is some chance that with some engine failures the simple act of turning the fuel back on will recover the engine before it winds down below the inflight restart N2 and thus the engine will relight by itself and recover some power even at low aircraft speeds. Of course it's doubtful that the simulator has considered this, but then that's the subjective side of simulator programming/training.

gekko
5th Apr 2008, 08:24
ok! thanks for your opinions!:ok:

TheGorrilla
5th Apr 2008, 08:46
Assuming the engine is winmilling slower than required or recommended for a restart your N1 and airflow into the engine will be low therefore I'd say you'd risk a hung or hot start scenario. I'm not sure if the clever fuel control unit on the Airbus would alter the fuel flow to control this in the same way as it would on the ground. Ask someone smarter than me!

Old Fella
5th Apr 2008, 09:06
Your question points to the double double engine failure being due to "finger trouble". That said, the lower altitude should enhance your chances of a re-light provided the airspeed can be held close to optimum. Sounds like another simulator exercise thought up by someone with time on their hands to dream up the most unlikely scenarios. Unless of course you have flown through a volcanic cloud or some weather event which caused the engines to flameout.

aidey_f
5th Apr 2008, 09:31
Speaking in purely general terms about the sim, the FADEC will command the starter valve open if it decides it needs it. It's not something I've looked at in a while, but if memory serves it's normally based on corrected N2 and altitude (thus core airflow) - there may be an N1 / P3 term in there too, the head's a but fuzzy this morning - and will scheduel the fuel flow appropriately.

The engine model dynamics are checked by the QTG, and in more detail during the engine development, so in answer to lomopaseo's point about blipping the fuel lever and catching a quick relight, it is indeed possible.

N1 Vibes
6th Apr 2008, 06:19
As an engineer I often enjoy the discussions here. The basic point for me though - wouldn't you try anything you can to relight the engines, rather than debate if it would in a sim session or not?

For what it's worth, not trying to stir the pot here. As I am unfortunate/fortunate enough to have witnessed an unplanned 2 engine out event in real life during an A330 annual certification flight, where I was the riding engineer. The sound of the RAT deploying for real at FL200, 100NM from home was a very pogniant thing.

Wishing you safe flying in real life,

N1 Vibes

lomapaseo
6th Apr 2008, 14:01
wouldn't you try anything you can to relight the engines


be careful of that word anything

If you are outside the real inflight restart envelope, you will no doubt only meet the two of the three "S" in Spin-Spark-Spray As many pilots have found out, failure to get these in the right order can lead to permanent damage to the engine turbines. Blipping the fuel lever has to be thought of and executed quickly, else you will get a hung start. I'm not of fan of expecting pilots to act quickly in emergency situations. Instead I prefer trained predictable responses for both the crew and the airplane.

pakeha-boy
6th Apr 2008, 16:29
lomapaseo quote....."I'm not of fan of expecting pilots to act quickly in emergency situations. Instead I prefer trained predictable responses for both the crew and the airplane"

spoken like a true sim-instructer and refreshing to hear.....the only real way to look at this situation.Have practised this actual scenario in the sim,and as you say,by using the QRH,and working as a crew,the outcome was favourable...ugly,but favourable

....its not everday, one has a dual engine failure:{,...but when you do,you might as well give yourself the best chance by doing it right.....