(Jet) Engine restart after failure.

[Thinair]

I would like to know your opinions about which, after an engine has stopped in flight, are the (technical) conditions, in which an inflight restart could be attempted / desireable.

It is clear that after a fire or severe damage this should not be done; but what if the engine experienced 'less than severe damage'.
(in other words where would you draw the line between severe and other damage?, and what if you could not determine the exact raison of the failure...)

(Maybe some engine/aircraft manufacturers have produced guidelines for these situations ?)

[Mark 1]

It would be normal to go through a re-light drill following a simple flame-out.

A certain Captain Moody may well have an opinion on attempting a re-light after getting 4 engines out, while flying in volcanic plume.

[lomapaseo]

Most large jet engines will restart and run safely at idle, if you really need them.

Once you start spooling up above idle, pay attention to symptoms and act accordingly. Once you get above bleeds close the engine will be less reliable since it's wiorking harder at that point.

As usual it's a pilots decision.

[Intruder]

In general, if no fire or vibrations, and N1 an N2 are windmilling, try a relight. 0 N1 or N2 indicate possible severe damage.

[Max Angle]

Quite agree with that but don't rely on it keeping going, plan a single engine landing somewhere and get the aircraft on the ground, if it ran down or flamed out there is almost certainly something wrong with it.

[m&v]

As Intruder says:the industry yardstick would be the Main parameter for crosscheck as to a Severe Failure.Having said thatI believe the 'powering back'(throttle closed)aspect of Kegworth hid the Vibation evidence that might have 'told' them more??:confused:

the industry Yardstick of course would be "Vibration Levels"

[Thinair]

Thank you so far, guys,

I especially appreciated the answer of mr. "lomapaseo" because it gives some kind of operational testing of the engine after the restart.
Other than that, I believe that there are some cases which could be potentially hazardous if restart is attempted. I heard the story of a ruptured fuel line somewhere in the engine or FCU which leaked enough at high power settings to create a flame-out due to fuel starvation. At lower thrust settings, there may be enough fuel to keep the engine running without noticing this leak.
1-Do you think this is a possibility and if yes could you think of similar cases ?
2-Would the fact that you were or were not able to determine the cause of the failure be a factor when considering restart if all engine parameters are acceptable(N1,N2,Oil Qty) ?

[Ignition Override]

Thin air-roger the restart with normal parameters, and don't forget the failed-engine oil pressure. Each time we start the old Pratt & Whitney JT8D engines, after N2 rotation the next requirement is an increase in oil pressure or we stop the start very soon, and never use the 'low oil press' light as back-up, at least during a start. If we are a long way from a suitable airport, this will motivate us to consider a restart: it gives us, even at idle, a little better pressurization, plus electrical system and hydraulic back-up, but watch the crossfeed and fuel balance, and always use anti-ice systems when in cold clouds (i.e. +10 C down to -20 C etc) with continuous ignition. Will your APU even start if cold-soaked? Just don't switch anything off or on without total crew coordination and when necessary, per checklist and SOPs, especially in abnormal situations. A fairly minor problem can go bad very fast, if you rush onto things.

Two of our crews recently shutdown such engines (we only have two engines) while in cruise flight, and one of the FOs involved, and a mechanic (engineer) both told me that the oil temp. gauges had yellow arcs on the wrong temperatures!! They had both exceeded 15 minutes in the indicated yellow arc, but how could the temp. gauges have been painted wrong?? We have lots of intermixed engine types, -9/-15 etc.:confused:

[BlueEagle]

When I worked in the UK for a well known charter company flying twin jets we were told that unless you knew the reason the engine had failed then leave it alone, (shut down), divert and land on one.

If an engine stops there has to be a reason and by re starting it you may just exacerbate a condition and finish up wrecking the engine, such engine damage is not covered by the normal hull insurance and the cost of a new engine falls on the operator.

Obviously if it is a matter of life or death then, as in Capt Moody's situation, relighting would take priority.

Just another viewpoint for consideration.

[LOKE]

A couple of considerations:

What are the statistics of a relight after an engine failure – say at Takeoff.

In the event of an engine failure and a subsequent restart – when would you again be in the same condition of the original engine failure – a go-around?

LK

[javelin]

If the engine is FADEC equipped and you get a rundown with no fire, the system will try to salvage it as it spools down. If that fails, check the parameters very carefully 'cos it is trying to tell you that the engine is probably farked. Stall/surge would normally be detected by the system and indicated (Airbus). then there is a procedure to try and recover the engine.

Probably time to find somewhere to land - unless you are over the Ocean that is. If one runs down there - check you fuel crossfeed :E

[idg]

A very interesting thread! I would also like to hear of any stats on engines that successfully relit having just 'failed'. I suspect not many but am open to correction. I agree with the view that modern engines don't 'fail' for any reason.

On the last point that Javelin made regarding FADEC equipped engines I would agree that the engine will automatically try for a restart. Whether one would get an ECAM warning is a moot point. I know of an incident where a 320 V2500 engine stalled and surged passing 5500' in the climb. There was a mighty great bang with the attendent flames from the jet pipe, the engine went to idle and stayed there. At no time was there any ECAM warnings at all!

IAE have never given an explanation other than to say that it was a bleed valve problem.

As one old pilot of my acquaintance said to me one day.."guess the aircraft has never read the FCOM"!!;)

[lomapaseo]

A very interesting thread! I would also like to hear of any stats on engines that successfully relit having just 'failed'. I suspect not many but am open to correction. I agree with the view that modern engines don't 'fail' for any reason.

I'm perplexed by your post. How on earth are you defining a failure .

Of course engines malfunction for a variety of reasons and some of these malfunctions require the pilot to secure the engine in other words shut off the fuel In spite of this the pilot always has the discretion to restart an engine which he has secured although he would rarely do this unless he has had other engines losing power as well.

All told the multiple engines out that had the time to be restarted have been very few. A couple of accidental fuel shutoff events, a couple of mistaken shutdowns at altitude and a couple of volcanic ash events. Perhaps we might also include the Kegworth event.

There have been numerous events with multiple engines out but no attempt or time was available to restart.

As long ast the high pressure compressor will spin and still has a turbine behind it, most engine will restart and run at idle if fuel is still available..

Running at high power is another thing however.

[idg]

LP,

I put the fail in "" because there are indeed a number of ways an engine can fail ie stops creating thrust.

It seems to me however that there have been very few times (as was mentioned earlier in the thread) when an engine just stopped producing thrust with no apparent damage and was able to be restarted.

The situations that I can think of are the volcanic ash encounters, icing and fuel starvation. Modern engines are extremely reliable and for the most part there is some sort of damage that precipitates the failure.

This is my conjecture of course, which is why I asked if there were any statistics of engine failures as LK had done earlier on with no responses.

[b777pilot]

i think it is always good training that a re-start follows a flame-out after checking that all parameters are ok and it is still spinning.

on the classics we had a chart that gave N1 rpm at altitude to see if the spinning was bonafide.

i will agree that if you have any doubts at all, then do not attempt one. particularly if the field is over your left shoulder.

[lomapaseo]

Well IDG as we parse your question(s) down did you feel that they were answered?

If not try again:O

[JW411]

There was of course the case of the Eastern L1011 en route from the Bahamas to Miami. All of the O rings had been left out by maintenance. The crew ended up relighting the first engine that they had shut down when the oil disappeared from the other two. Luckily there was just enough oil left in it to get them to Miami.

I also heard the tale of an AA crew who got airborne from LAX in a DC-10. Shortly after take-off they got a fire warning in one engine which they shut down. Then they lost another engine (can't remember why). They saved the day by relighting the original engine.

It transpired that the original fire warning was spurious but, in any event, a burning engine will at least produce some thrust when things become critical.

[Captain Phaedrus]

Generally, I would look back to my initial thoughts when we shut the thing down, and use that as a guide. But, bear in mind that some engines (notably CFM-56) suffer occasional in-flight run-downs/failures for no apparent reason. This might have happened to you. (I still wouldn't relight and carry on to destination, though! - to do so indicates that the thinking is skewed, probably by lack of confidence in the company's management).