Critical engine

[Redflyin]

I have never flown a four engine jet, so I'm a little confused about which engine is critical. I have read that the upwind outer engine is critical on a four engine jet, but I also read that its more advantagous to lose the upwind engine on a jet because of yaw reduction with the crosswind input counteracting the engine failure.

Which is it?

[barit1]

If all four are running, which way does the bird want to yaw? Into the wind, right?

So which engine does the most good in countering the yaw? The upwind engine, right?

Therefore the upwind engine must be critical, at least until you break ground.

(Same principle must apply to a twin, right?)

[Redflyin]

That does make sense. I just have a book that says its best to lose an upwind engine.

If the wind is from the left on takeoff then you would be applying right rudder to keep the nose straight, if you lost the left engine (upwind) then it would naturally want to yaw left, adding to the yaw to the left (wind plus lost of thrust on the left)

Its a little different on a turbo-prop where the critical engine is always the left engine because of the high amount of torque and P-factor. The wind never seemed to make that much difference to me.

Just trying to figure it out, thanks for the help.

[TruBlu351]

That's right Redflyin, a jet aircraft only has a critical engine whilst on the ground, for the reasons you just mentioned. When airborne there's no additional yaw due to weather cock as there is on the ground.

Instead of saying a multi prop's critical engine is always the left side, I'd say's it's always the outbord engine who's prop is going down closest to the fuselage (fpr p-factor like you mentioned).....then it covers you incase the prop rotates a different way.

[Rainboe]

If you abandon take-off with a fire in an engine, then the upwind engine is the most critical! It is officially advised that even a few knots blowing the fire towards the fuselage may have a disastrous effect if fuel leakage occurs, so ever since the MAN 737 incident, I've found it's worth briefing which engine/s is upwind and whether you will try and turn as you stop to prevent fire moving towards the fuselage.

[Pilot Pete]

Originally Posted by Rainboe

... whether you will try and turn as you stop to prevent fire moving towards the fuselage.

All well and good in theory, but in practice many carriers do not condone ANY attempt to turn the aircraft in the scenario you describe. Why? Firstly, at what point are you going to try to turn with the aircraft RTO function bringing you to a very rapid stop? If you stop and then consider a turn you are wasting time. If you try to turn to stop whilst still decellerating under RTO then you are probably attempting to do a manoevre that you haven't done in a sim (or do your company practice this?)

Another factor is the aircraft type. After considerable discussion on this subject my airline decided not to go with the turn after engine fire on the ground as your positioning of the aircraft (especially on a narrow runway) can mean that the fire trucks have less unimpeded access to both sides of the aircraft. If the ground is very wet and they have to end up on the grass (which is not a problem, but less desirable), then this is not ideal for them. Add to this any extra time taken to stop the aircraft, or move again to turn it and the company decided you would be better off stopping straight ahead using centreline guidance (especially in very wet crosswind conditions), applying the parking brake and carrying out the recall items, initiating evacuation in an expeditious manner.

I have worked in previous airlines where the 'turn' was advocated, but having worked under both 'regimes' I think the pulling up straight ahead option is the better.

There never is a black and white though. It's always a compromise and what is best on the day.

PP

[Rainboe]

Point taken, but I think I agree with the common view at the moment that any turn keeping fire from blowing onto the fuselage is beneficial. On the flight deck, especially with the current locked door policy, we really have no idea what is going on in the cabin, and whilst the pilots are making their mind up, there may be drama going on already at the rear they don't know about. This was the situation in Manchester where fire was being blown onto the fuselage from the severe fuel burst. If you have the capacity before you stop to work it out, it won't hurt doing it, and may take a couple of seconds- maybe not quite like the spectacular handbrake turn I did the other day in the sim! The mantra is 'in a headwind, any turn towards the fire, in a tailwind, any turn away'. I've been briefing at the start of roll which is the critical in the event of fire and asking for a reminder. I think it works.

[Gary Lager]

whilst the pilots are making their mind up, there may be drama going on already at the rear they don't know about.

Hopefully the drama unfolding in the rear will contribute to the making up of the pilots' collective mind.

I have RTO'd from 110kts in a heavy (87T) A321 as an FO - the autobrake did not allow any time for the 'briefed' call to ATC, let alone any steering input from the Captain at low enough speeds to avoid leaving the concrete.

The MAN accident was exacerbated by the pilots failing to consider wind direction after they had taxyed off the active, not during the RTO itself.

Mental capacity is a whole other consideration - I would go so far as to suggest that if you have time to remember to turn the burning engine out of the wind, remember which way the wind was coming from and then actually work out which way to turn the aircraft, especially considering that no concrete identification of the engine concerned ought have been completed yet, then the control of the aircraft/monitoring of the PF is not been attended to with adequate vigilance. Unless you're a test pilot and do RTOs every day, instead of every six months in the sim when an RTO is not unexpected.

Sorry for thread creep, but I firmly believe on my recent types (B737, A320/321) this 'burning engine downwind' stuff is ared herring.

[Rainboe]

Shouldn't be too quick to dismiss it. Since that MAN accident, BA and my current emloyer have been putting into practice the turn. All it takes is a final reminder before you go that 'this is the upwind engine, so if it is on fire, we must try and remember to turn left/right before we stop, and if you can, try and remind me before we stop' ie 'wind is from there, so if the left engine is on fire, we turn left OK?'. So it then doesn't take any mental capacity on the take-off. If it blows a fire away from the slides, it must be worth a try.

[Gary Lager]

So it then doesn't take any mental capacity on the take-off

I'd disagree, but only perhaps by saying it need only take a little extra thought. However anyone who has experienced a full-on RTO in a modern Autobrake-equipped airliner will probably recognise that the time available to do anything with that extra thought is very limited indeed.

Consider it a bonus if acheivable, then, but I remain doubtful as to whether I personally would be able to put it into practice (not for want of trying).

BA and my current emloyer have been putting into practice the turn

For real? Or do you just mean in the sim, when RTOs (and the subsequent points which 'score' in the debrief are expected and prepared for)? It is a frequent "why not" debrief point for my current and previous employer during Prof checks too, but that doesn't necessarily make it practical.

Don't get me wrong: I do try to remember, but should it come to it I shall not automatically consider it a priority.

I think there is a great deal of difference between:

a) stopping on the runway C/L post-RTO and conducting an evacuation after proper diagnosis of the aircraft condition, and

b) slowly taxying off the runway to actively park in a position which blew the flames onto the fuselage.

A tragic lesson in failure management - but ultimately it wasn't 'not turning into the upwind burning engine' which killed those people that day.

[Rainboe]

For real, and expected, and commented on if not done, and, I have to agree, rightly. The whole point of autobrake is to unload you and provide max deceleration, so all you have to do is get reverse in and then give it a quick think. having already stressed the point before roll, it comes easily. It can be done, and it will help.