B737 QRH Loss of Thrust on Both Engines - interpretation question.

[Centaurus]

As always, different simulator/check captains have personal opinions on QRH interpretation.

The B737 QRH Loss of Thrust on Both Engines memory items are a case in point.
The stated objective according to the QRH is to restart at least one engine.

The actions include placing both engine start switches to the Flight position, and placing both start levers to cutoff. When EGT decreases, both engine start levers are set to idle detent. Hopefully, one or both engines will start depending on airspeed attained during the procedure. If one engine starts using that procedure, then simply follow the QRH instructions.

But if neither engine starts, the QRH then says if EGT reaches 930C or there is no increase in EGT within 30 seconds, the engine start lever for the affected engine (or, in my words, both start levers, if neither engine starts) are set to cutoff and then to idle detent again. If EGT again reaches 930C or there is no increase in EGT, repeat as needed. End of memory items

Advice on how many times that process is repeated is not given in the QRH and this then becomes wide open to personal opinion of the check pilot and or the candidate. It becomes a no brainer who wins that argument:ugh:

One proponent took the view that only one attempt should be made using both start levers as above; even though the QRH statement was clear when it says "repeat as needed."

It was suggested if the first attempt is unsuccessful in getting a start on either engine, the same process should be repeated but only on one engine at a time instead of both engines simultaneously. The QRH does not say that and does not elaborate. It just states "If EGT again reaches 930C or there is no increase in EGT within 30 seconds repeat as needed. In other words repeat the original memory items.

So it seems a matter of personal interpretation. I know what I think. What do you think? :ok:

[Ozdork]

Keep trying, until you've got one going. What have you got to lose?:ugh:

[mustafagander]

It seems to me that "repeat as needed" means just that. I fail to see where any interpretation is required.

Beware CP, TRI et al who add their own little twists to Boeing procedures. If you ever find yourself standing before a group of bewigged ladies and gentlemen, any deviations from QRH, FCTM etc will not be well received or easily explained away.

[B737900er]

I personally would try two attempts, after that, start pitching for required speed and attempting again whilst doing the QRH.

I would consider starting the APU as soon as possible.

[archer_737]

Hi there.

Remember when LOSS OF SYSTEM A/B had nothing on it, like 6-7 years ago. Then someone decided to give you a list of inoperative items.
Yeah I know we all study hard and we will remember them by heart by... you know what I mean, was a must IMO.

I've always wondered why they aren't adding something like "you're screwed with no engines so remember you can still do...".
If you see the QRH is always assuming that you're recovering at least 1 engine. What if not? Why not a short heads up on what's next? Will I be able to extend any flaps? Lower the gear? Etc..

Regarding your question, IMO I'll keep up and down with the start levers. As someone pointed up in the post, why not? Just do it until you get back one of the engines at least.

[Centaurus]

I personally would try two attempts, after that, start pitching for required speed and attempting again whilst doing the QRH.


Another point of view is that the attaining of the correct speed as per QRH figure should be carried out at the same time as completing the memory items. There would be no logical reason to try "two attempts" and only then "start pitching for required speed."

[flyingchanges]

I would wait to start the APU until at a FL that is more conducive to a battery start, why waste your electrons. Pretty much a MMO descent to get the speed, and you need to get down anyway. I would much rather enter the start envelope in a high energy state than waste that altitude getting to a high energy state.

[B737900er]

Centaurs- i see your point but, Heres a question - Why isn't the speed criteria a memory item? Surely you would want to take advantage of the excess speed you have, right?

The FCOM states a guaranteed start can be attempted at FL250 for the APU, it doesn't say you cannot attempt a start at a higher altitude nor will it start.

[Skyjob]

Think the OP needs reminding that:
- When 1 engine starts, you are NO LONGER in the "Loss of Thrust on Both Engines" scenario;

Thus, repeat of procedure is only required using BOTH levers if NO engine has successfully started. Until an engine has relit, the procedure loops itself indefinitely.

Why would you only try and repeat a few times? The lower you get, the thicker the air, the more higher concentration of O2 and the more likely it is to have a successful restart attempt. For those who need reminding, Speed bird 9 (http://en.wikipedia.org/wiki/British_Airways_Flight_9) was successful relighting the first of 4 engines only below 13,000' as the crew kept trying to relight the failed engines (due volcanic ash). Had the not been able to it would have been the first 747 to ditch. It pays to keep trying until the very last moment, one engine is all it takes to avert disaster.

So split the flight deck duties:
LHS flies/glides, keeping aloft as long as possible until a (no engine available) landing spot has been successfully been identified and is within reach;
RHS continues to try and restart engines, read QRH, actions drills and advises if there is a requirement to "dive for speed" only when QRH dictates...
Don't rush, give yourself more time by staying aloft longer and preparing for the worst rather then diving down.

[de facto]

flyingchanges I would wait to start the APU until at a FL that is more conducive to a battery start, why waste your electrons. Pretty much a MMO descent to get the speed, and you need to get down anyway.

Loss of thrust on both engines can happen at any altitude,not only at your cruising level:}

[flyingchanges]

Then you would start the APU and use GND not FLT to get em going again...

[ImbracableCrunk]

The FCTM clearly states to keep the airspeed up so as to keep energy in the engine core.

[Tee Emm]

Keep trying, until you've got one going. What have you got to lose?

Interesting that because there is no specific mention to close the thrust levers first, before you start the Loss of Thrust on Both Engines memory items, should one assume that you don't move the thrust levers from their current position at the time of double engine failure and during the memory items process?

Normally before effecting a relight on a failed engine, part of the procedure is to close the thrust lever first. But apparently not so in the dual engine failure case. I wonder why?

[framer]

SkyjobRHS continues to try and restart engines, read QRH, actions drills and advises if there is a requirement to "dive for speed" only when QRH dictates...
Don't rush, give yourself more time by staying aloft longer and preparing for the worst rather then diving down.

900-ERI personally would try two attempts, after that, start pitching for required speed and attempting again whilst doing the QRH.

I disagree with both the above statements.
Jet engines are all about mass airflow.
I would be taking control and pitching to just below the barbers pole ( assuming we're in the cruise) while the F/O carried out the memory items. I would be doing that in fairly quick order once the identification process was complete in order to keep the 'energy in the core' as Imbracable put it.

[JeroenC]

Makes sense. But why didn't Boeing put the speed in the memory items then, and (most likely deliberately) put that in the reference items?
Any ideas on the TL position? I was wondering myself as well.

[Skyjob]

I would be taking control and pitching to just below the barbers pole ( assuming we're in the cruise) while the F/O carried out the memory items. I would be doing that in fairly quick order once the identification process was complete in order to keep the 'energy in the core' as Imbracable put it.

Interesting philosophy.
Let's put us in a scenario operating e.g. on T9/T16 or even in middle of Bay of Biscay, diving would potentially put you in the water quicker and less prepared, gliding could put you near/on land... What would you choose given anecdotal history of events and successful landings on water? We are not all as good as Captain Sullenberger...

[InSoMnIaC]

If Fuel is available and a relight is possible, forget about gliding distance initially.

The main priority is to start the engines. So pitch down to the windmilling start IAS and turn to somewhere sensible while the FO simply concentrates on starting the engines (repeatedly).

Once able, start the APU, use APU bleed for further start attempts and slow to greendot speed.

[mustafagander]

Thrust lever position (PLA) is irrelevant during the start sequence. Until the red start limit temp lines disappear from the EGT readout, PLA has no influence.

On the B744 a Multiple Engine Fail checklist can be quite alarming when the engines spool up to match the PLA after start achieved without further warning.

[Centaurus]

But why didn't Boeing put the speed in the memory items then, and (most likely deliberately) put that in the reference items?

Speculation only but maybe if speed was in memory items (depending on where it was in the sequence), the crew may be tempted to concentrate on getting the speed up to the desired figure rather than try for a quick relight while RPM is still high as per QRH intention?

[cosmo kramer]

I think this question has so many variables, that trying to make a "canned solution" doesn't make sense.

It is being assumed that the memory items are being done rapidly after the engines have failed, to take advantage of the engines still having a high rpm.

Simultaneously, an evaluation of the situation should take place.
1) First of all, where are we? (situational awareness/fly the airplane)
2) WHY did the engines quit? (analyse the problem/airmanship)

a) If the engines got filled with Canadian geese in 7000 feet, there is not much point in keeping the energy focused on a restart too long (Hudson).

b) If both fuel filter bypass lights are on and you are at cruising altitude, it might make sense to prioritise to stay aloft in what ever way will ensure you can glide to some tarmac.

c) If you just had a weird icing phenomena/heavy precipitation/turbulence and plenty of altitude, you might want to focus on restarting even on the trade of altitude to keep in a sensible start envelope.

d) insert one of 1000 other possibilities.


Anyway, the memory items assumes that at least one of the engines will relight more or less immediately, as can be seem from the rest of the checklist. With all engines failed you are in ****s creek in any case, and only thing that will save you is thinking out of the box.

Why are you practicing this in the simulator anyway? A waste of time in my humble opinion!! Except if the goal of the practice is clearly stated e.g.:

1) "today we will practice doing the checklists and how we do an inflight restart I.e. both engines fail, one immediate restart on doing the items and afterwards practicing starting the other one using the "Engine inflight start" checklist".

2) "today we will practice doing a glider approach from FL200, simulating contaminated fuel".

Making the session without any description or goal, is just a valuable as saying: "today we will practice doing an approach into Bagdad, someone shoots a missile at your right wing - see if you can survive that". Both engines quitting is not a scenario where it can be expected the trainee to survive consistently. Trying to force the trainee to use a "canned solution" makes even less sense.

Doing TRAINING exercises should have clear stated goals about what is expected to be achieved. Doing checking, should be for failures where it is expected to survive consistently.

[RAT 5]

C.K.
Spot on. I wish there were more like us. Trapping, went out years ago, (should have). Training in TQ's is just that; introduce an experience to learn from, well briefed and pattered during. Training in recurrency; introduce an experience that has been discussed briefly, but not in depth, and 'have a go' and see what happens. Perhaps try again, if necessary, after a short de-brief. Oh that there was time. Let's put the value back into training and less ticking boxes, or crazy scenarios.
Rather than show a scenario that is so unlikely to happen I'd rather spend time educating the pilots properly about how the damn thing works, so that when the unlikely happens they can think for themselves and sort it out as best they can. Searching the SOP manual won't help, and saying prayers won't either. Cursing the day you spent €150,000 on a type rating won't do diddly squat. Having a fundamental understanding of the beast you are trying to control in an environment you have a vague appreciation of will give you a fighting chance.

[RVF750]

CK, Rat5 I also agree. The scenario needs to be appreciated every time for the correct decision.

The Fundementals are if you are in the cruise, you'll need to get down for the Pressurization anyway, so get the speed up and see if one will start. Once you're lower, then the APU and bleed starting is an option. DO you dive for 10,000ft? Nah, I'd start trading speed for range soon after the APU starts up as There's 10-12 minutes of time in the 02 systems for the pax.

Having said that, I did try dead sticking in the SIM mid North Sea, and struggled to get down after circling AMS. Best glider I've flown for years....

[de facto]

Once you're lower, then the APU and bleed starting is an option.

Interesting point of view....id get it to start ASAP for obvious electrical reasons no?

[RAT 5]

One shot immediately then, if no success, wait until FL250 IMHO. Save battery; it's all you've got. Concentrate on aiming at a suitable landing site within a comfortable radius. Note I didn't say airfield. Keep your options open. Having just seen a documentary about the Bonneville Flats I might choose that over any airfield. Biggest multi directional runway in the world. I'd hope not to need the fire trucks, but walk away from it.

[Australopithecus]

It pays to have at least a nodding acquaintance with the airstart envelope. Pick a speed target at 25,000 and 10,000' so that you can interpolate mentally during the otherwise placid procedure. :cool:

Energy bled off at a high speed cannot be recovered completely in a subsequent speed reduction to min drag. Min drag isn't always the best range number wither, depending on wind. But you guys know that, obviously.

When I flew 737's the TREs would take great pains to point out the start EGT limits applied for the second start. I would always get them to clarify that if the first engine took, say 900° to start up, then I couldn't have the second engine back if it exceeded 725° during its start? (This was always preceded by an ash encounter, by the way). There is often an urge to invent arbitrary limitations based on something unrelated mentioned in the FCOM, I have found.

To summarise...in a loss of both engines, you are keeping some engine restart attempts in reserve for what? There is no duty cycle for non starter assisted starts, and hence no limits published, reasonably imagined, nor, by any measure, logical. Die busy.

[Oakape]

When I flew 737's the TREs would take great pains to point out the start EGT limits applied for the second start. I would always get them to clarify that if the first engine took, say 900° to start up, then I couldn't have the second engine back if it exceeded 725° during its start? (This was always preceded by an ash encounter, by the way). There is often an urge to invent arbitrary limitations based on something unrelated mentioned in the FCOM, I have found.

The way the checklist is written you have no choice, unless you want to go outside the QRH. It directs you to the Engine In-Flight Start checklist for the second engine start & that requires you to respect the EGT start limit of 725 degrees.