B737 Loss of Thrust on Both Engines

[ImbracableCrunk]

I'm taking opinions on the Loss of Thrust on Both Engines drill.

Let's say you're at FL410 and you lose both engines. Let's say you believe you should attempt to restart the engines. There are many suitable fields right below your flight path, just for your choosing and the other pilot is doing an excellent job flying to one. You're starting the APU, but's it's about 2 minutes from coming online due to the altitude. So, you are following the checklist when you get to item 5.

Item 5 from the drill

5 At or above FL270, set airspeed to 275 knots. Below FL270, set airspeed to 300 knots. Do you:

A. Pitch over and accelerate to 275 and exceed MMO;

B. Pitch over and accelerate to MMO or 275, whichever is less; or

C. Pitch over and accelerate to 275 - you probably won't get to MMO by the time you descend to 36,000ft

Pick one A, B or C. Provide a reason for A or B or C, if you like, but pick from A or B or C.

[cosmo kramer]

To me it would depend how far to nearest suitable airport. If over water and 120 miles away, I would start a slow descend with oxygen masks on. The cabin will slowly depressurize and the pax would have to do with the 12 min oxygen, once cabin exceed 14.000 feet. The glide towards nearest suitable airport (while doing the memory items for as long a time a they make sense, with regards to RPM). If no success an when below 30.000 feet attempt start APU and hope to get one engine restarted. Otherwise, hope to be able to repeat one of the glider success stories!

If no suitable airport within 120, it would be a ditching anyway, so might as well start an emergency descent and attempt windmill restart. MMO, would quickly transition into 275, I think before you had time to do the memory items and get the QRH out (275 is not a memory item).

If suitable airport available close up, same as above and start head in that direction.

Any other ideas? Interesting subject.

[lomapaseo]

If you set up for max glide rather than entering an engine restart envelop you are very high on the probability for an unsatisfactory outcome.

If you set the restart envelop as primary the historical odds are that at least one will restart, albeit may not operate at full thrust. However if you screw up the restart outside the envelop your odds swing to poor or nil.

[latetonite]

First you fly the airplane. That means you fly a speed within amber limits.
Get a working flight director in level change. Do not look at your FMC: there is nothing useful in there, besides maybe alternate airfield distances.
You have no APU bleed, so you wait for adequate airspeed. Then keep trying a windmill start while getting a QRH out. Does not cost anything.
At a start level of 410, at least time is on your side.

If the engines are not damaged, and you have fuel onboard, chanches are big at least one will start and run later on, once you fly through denser air

One of the proposed answers was to exceed VMO. Please restate your objective.

[sudden Winds]

if you´ve lost both your engines at FL410, at the same time, you´ve either ran out of fuel, or they put water in your tanks, so it won´t really matter what speed you use. Another (more realistic) possibility is a volcanic ash encounter. If that is the case make sure you conduct a 180 degree turn out of it, then worry about the engines.
Regards.

[Jwscud]

Another possibility is loss of AC power leading to suction feeding of the engines and flameout.

[John Farley]

I have no experience of the B737 but I have relit a lot of different engines for trials purposes (and a few for real failures) so I make these comments:

While it may be possible to get high altitude relights the most reliable relights are to be had below 25,000ft.

It is possible to actually damage engines trying to light them too high if they go into surge and you do not turn the fuel off within a second or so.

So I would forget relighting drills and concentrate on gliding for range, sorting out ATC and deciding which airfield to aim for.

Because of your height you have ages before you will get down to 25k so things should be quite calm when you do eventually do a relight drill on one engine. If it fails to light I would stick to that engine until passing 20k when I would try to light the other one.

If neither lights by 15k concentrate on flying to your force landing diversion.

Once below 10k the non handling pilot should try more relights but the pilot flying should not be distracted from the force landing attempt.

[Jwscud]

The memory items from the QRH are as follows:

1 ENGINE START switches (both) . . . . . . . . . . .FLT

2 Engine start levers (both) . . . . . . . . . . . CUTOFF

3 When EGT decreases:

Engine start levers (both) . . . . . . .IDLE detent

4 If EGT reaches 950°C or there is no increase in EGT within 30 seconds:

Engine start lever (affected engine) . . . . Confirm . . . . . CUTOFF, then IDLE detent

If EGT again reaches 950°C or there is no increase in EGT within 30 seconds, repeat as needed. - - - - - - - - - - - - - - - - - - - - - - -

5 At or above FL270, set airspeed to 275 knots. Below FL270, set airspeed to 300 knots.

Note: Engines may accelerate to idle very slowly, especially at high altitudes or in heavy precipitation. If N2 is steadily increasing and EGT stays within limits, do not interrupt the start.

Note: Do not wait for successful engine start(s) before starting the APU


One would want to start the APU ASAP as you are also on standby power assuming the engine speed has dropped low enough to lose the IDG, but APU start attempts aren't recommended above 25,000 feet.

Does anyone have any practical experience starting the APU above that?

[ImbracableCrunk]

Do you guys do this on your exams? ;)

The question is limited to following the Loss of Thrust on Both Engines drill, specifically the airspeed - not where you're going for breakfast or whether the APU will start. (Yes - it starts up there - I've done it myself.)

A or B or C?

[CHfour]

Do you guys do this on your exams?

The question is limited to following the Loss of Thrust on Both Engines drill, specifically the airspeed - not where you're going for breakfast or whether the APU will start. (Yes - it starts up there - I've done it myself.)

A or B or C?
Sorry you didn't get the answers you wanted but maybe it was a poor/incomplete question (you didn't say if there were any suitable airports nearby, for instance) The advice about damaging engines by trying to relight too soon (too high) is worth remembering. When people are kind enough to respond it is probably better to thank them rather than to give a rude reply.

[sudden Winds]

jwscud,

sometime ago while balancing fuel I accidentally turned off both fuel pumps from one tank prior to opening the fuel crossfeed valve. This was at 41k. I realized immediately and opened the x feed valve while staring at the engine parameters for the longest 2 seconds of my life it took the crossfeed to open completely. The left engine did not show the slightest sign thrust deterioration. The suction feed is quite reliable.

And again, if you lose both your AC sources at the same time, either someone is trying a new electronic weapon nearby or you are a very unlucky fellow. I´d go for the 2nd.

[ImbracableCrunk]

Sorry you didn't get the answers you wanted but maybe it was a poor/incomplete question (you didn't say if there were any suitable airports nearby, for instance) The advice about damaging engines by trying to relight too soon (too high) is worth remembering. When people are kind enough to respond it is probably better to thank them rather than to give a rude reply.

I was trying to be funny, that's why I put a ;) in the post. I guess it didn't work. Oops.

Maybe the fact that people don't have an easy answer is telling. I'm simply looking to see what airspeed most pilots would fly when following the checklist.

I guess I'll edit the original again. Thanks!

[FlyingStone]

Does anyone have any practical experience starting the APU above that? (FL250)

Tried starting APU 1 hour into the flight at FL360 (on Classic though) with no luck. It only started when passing FL260 - mind this was with full battery and AC power available from one generator!

[de facto]

Pick one A, B or C. Provide a reason for A or B or C, if you like, but pick from A or B or C.

Id go for answer B.
I wouldnt exceed VMO/MMO:E but stay close to it until the change over to 275 kts and while approaching to FL 270 adjust pitch towards 300 kts while keeping an eye on N2 to get about 11%.
In any case starting the APU should not be delayed.
If no luck on a windmill restart and a starter assist is the only way, then start to pitch for a speed equal to 100kts above vref40 if above FL270 and a speed equal to vref40+80 kts when below fl 200.
500ft/NM i believe is the NG glide.

[ImbracableCrunk]

So far it sounds like Cosmo Kramer, Latetonite, and DeFacto are all chosing B - don't exceed MMO.

In other checklists, Boeing specifically say, "DO NOT EXCEED . . ." Gear extend limit, leading edge device limit, emergency descent. This checklist says not one thing about "DO NOT EXCEED." It's simply 275.

My thought is that maybe Boeing wants you to keep the engines moving and forget about the MMO. i.e. You're more concerned with high airflow than high true airspeed - you're not worried about an overspeed at this point.

[de facto]

My thought is that maybe Boeing wants you to keep the engines moving and forget about the MMO. i.e. You're more concerned with high airflow than high true airspeed - you're not worried about an overspeed at this point.

Try that at your next inteview sim check and let us know how it went:E:p

[de facto]

Valid point though.
Eventhough i wouldnt do it(exceed Mmo) that is,if it happened to me tomorrrow.
However exceeding Mmo is not the end of the world as i believe the NG is certified to overshoot MMO by 0.07 and VMO by 50 kts with 1.5 G load with no significant controllability issue.

Ill check and ask my 'sources':E

[ImbracableCrunk]

Try that at your next inteview sim check and let us know how it went:E:p

Hopefully I'm done doing interview checks. :bored: The last one was a bear. Right now, I'm more worried about what to do if my life and limb are on the line.

[de facto]

The LOSS OF THRUST ON BOTH ENGINES NNC is written to ensure that flight crews take advantage of the high RPM at engine failure regardless of altitude or airspeed.
Taken from the FCTM.

It seems that at high level Boeing is saying that (already) high rpm is essential for relight and below FL300, speed is.

[ImbracableCrunk]

That is the excerpt that made me start asking around in the first place.

To me, the FCTM implies that you should follow the KCAS 275, and disregard MMO.

You need air through the engine core, forget about M0.82 for today. I think worrying about overspeed at this point would be like worrying about shutting off the IRS after a ditching.

[de facto]

Strange, to me it implies that the actions of a relight are primary (hence recall items) to restart while the engine is already at high rpm regardless of aircraft altitude and airspeed (as stated in the FCTM quote).
Speed setting being secondary.

If speed were so important for a relight then it would have been positionned at the beginning of the memory part of the checklist.

Therefore i still doubt boeing expects crews to go into an overspeed to achieve that speed and still vote for B:E

Also the inflight relight,windmill enveloppe speed is shown to be at a minimum of 140 kts and maximum of 340 kts ..would it mean something?.

[ImbracableCrunk]

Loss of Thrust on Both Engines
Dual engine failure is a situation that demands prompt action regardless of altitude or airspeed. Accomplish memory items and establish the appropriate airspeed to immediately attempt a windmill restart.de facto, here's how I see it:

The first sentence tells you take prompt action. What action? The second sentence tells you: Complete the Memory Items and establish the appropriate airspeed.

Keep the high RPM you have in the engine and try to relight as soon as possible - just as you said. Also, keep the high RPM by getting to a higher airspeed.

One pilot is running the restart, the other is pitching for the airspeed.

Also the inflight relight,windmill enveloppe speed is shown to be at a minimum of 140 kts and maximum of 340 kts ..would it mean something?.

I'd say no:

FCTM:

The in-flight start envelope defines the region where windmill starts were
demonstrated during certification. It should be noted that this envelope does not
define the only areas where a windmill start may be successful.

[de facto]

One pilot is running the restart, the other is pitching for the airspeed

I cant disagree with that:O

[lomapaseo]

The engine cares about burner pressure in order to relight. What Boeing has to say is about how to achieve this burner pressure in an altitude vs airspeed mode..


You can have lots of pressure at low altitude but unless you can get this to the combustor it aint gonna light. You can have lots of airspeed at high altitudes but the total pressure at the burner may be too low to stay lit.


As you can guess you need some help from the spinning engine to convert some of the speed to pressure. This balance is what defines the inflight restart envelop.


Yes you may be lucky and get it started outside this envelop but if you cook the turbine in a bad start it's all over. Not to mention it seriously impacts your ability to hang around in a proper restart envelop. Too many accidents have this in their causal chain

[Judd]

Get a working flight director in level change
Why the need for a "working FD"? Is this yet another case of blind reliance on FD information when the ADI is working normally and the crew should know the required attitudes?


It should be remembered that if the thrust levers are in cruise setting when the dual engine flameouts occur you do not close them as part of the attempt at initial re-start. See QRH.

[latetonite]

Judd.
Level change has nothing to do with closed trust levers. It simply opens now your speed window, and the FD shows you how to fly present speed between the two speed limits.
As your VNAV will probably disconnect by itself upon loosing the two engines, the pitch mode will revert to ALT HOLD, showing you a stall in the making.
Of course you can do all this raw data, but the FD makes it easier, especially turning in a safe direction, and decending just enough to maintain safe speed.

[Travelling_Gav]

My thought is that maybe Boeing wants you to keep the engines moving and forget about the MMO.

No. I just searched my entire QRH and the only time Boeing states specifically "Do not exceed" is when the particular limit is not on the PFD. (ie. Gear disagree - Do not exceed the gear limit).

Why would you consider the compounding of a very bad situation with also overstressing the airframe. Please don't quote the " there are margins built into this.." crowd. You would find yourself with two engines shutdown, the overspeed clacker going off and the PFD looking very disconcerting by being into the red.

The inflight start envelope caps out at 24000ft. If your goal is to get to 275 to maximise your chance of the restart then your argument is flawed because you are too high. If you want to maximise your chance of an inflight start you should do a emergency descent to 24000ft, set the speed to 281-340 and try there. There may be other reasons why you don't want to do that but yoru question does not expand on the exact scenario you are contemplating.

[WYOMINGPILOT]

Follow the QRH but do not overspeed the aircraft therefore answer B would be the logical choice. Most 737 simulators are programmed to not allow an engine to relight inflight unless the speed parameters are met. I routinely give this scenario in the sim as an Instructor but usually around FL 310. Many pilots attempt the QRH actions but they don't have 275 knots. The red line speed is mach .82 and about 290 knots at FL 310 depending upon simulator preprogrammed conditions. If the pilots do not get to 275 knots the engines will never relight. I actually had a crew dead stick it in to a vfr airport one time because they never achieved the required speed parameters ie 275 above FL270 and 300 knots below. They slowed to 250 knots at 10,000 feet so they never had a chance at low altitude as the sim won't allow you to relight unless you have the required parameters met. I debriefed them they had good pilotage gliding skills but poor checklist discipline.

[ImbracableCrunk]

So it sounds like a lot of us think that "at or above FL270, set airspeed to 275 knots" means many things. So here's what I've distilled (forgive me if I generalize):



Cosmo Kramer - L/D Max or 275/MMO
Lomapaseo - L/D Max
Latetonite - within the amber limits
Sudden Winds - "Doesn't Matter"
John Farley - L/D Max
De Facto - 275/MMO
Travelling Gav - VMO/MMO until you're in the certified envelope
WYOMINGPILOT - 275/MMO
ImbracableCrunk - 275


I like WYOMINGPILOT's story about not relighting because the pilots slowed to 250 below 10000. I just wonder if that staying below MMO is the same mistake.

[flyingchanges]

I vote for coming into the start envelope with the most energy and thus ability to stay in the start envelope the longest. Accelerating at lower altitudes makes the earth get larger at an alarming rate.

Remember, you get 30 minutes if battery plus one APU start attempt. Again, why waste more of your battery life waiting to get into the APU start envelope.

[latetonite]

It is actually at higher altitude the earth gets larger more quick, while picking up speed..

[lomapaseo]

It is actually at higher altitude the earth gets larger more quick, while picking up speed..


I think he meant the mountain goats appear larger

[flyingchanges]

I meant to not piss away your energy while in the start envelope.

[ImbracableCrunk]

It sounds like many of you would just ignore the checklist and FCTM entirely. Interesting.

[cosmo kramer]

It seems to me that people here confuse "Loss Of Thrust On Both Engines" with "Engine In-Flight Start".

In case of "Engine In-Flight Start", only one engine has failed, and you have tons of time to either start the engine that had a flameout or prepare for a one engine inoperative landing..

In the case of "Loss Of Thrust On Both Engines", the point is to get an immediate relight on at least one of the engines, by following the QRH memory items. The rest of the checklist is for a dire emergency and, as I see it, does not necessarily provide a successful outcome.

If the engines doesn't immediately relight, the chance is that they won't - most likely due to a fuel problem (ran out or contaminated). I think the most important thing is to get the start switch set to flight, and to cycle the start levers. If e.g. the dual flameout is cause by high altitude icing.

Give me one other good example why both engines would otherwise fail simultaneously...

[ImbracableCrunk]

Cosmo Kramer, I've wondered about how often this checklist has been or will be used. Maybe older engines that were less tolerant of upset, ice, etc. required this and is now a holdover from certification.

The question would be academic if it wasn't a something we're required to be able to demo or perform.

[cosmo kramer]

Not once have I done this in the sim. It's a bs exersice anyway, in my humble opinion (guess I had luck with sensible companies/instructors). What is there to learn from doing it in the sim? Except to learn how the sim was programmed. Memory items? You can practice those with your eyes closed, you don't need to waste costly sim time on that. There are no handling issue to learn, as you just have an aircraft descending.

Then rather use the time to learn how to dead stick it, and from low altitude, like severe damage on both engines after takeoff with two close airports. But this is not a requirement anyway...