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 youŽve lost both your engines at FL410, at the same time, youŽve either ran out of fuel, or they put water in your tanks, so it wonŽt 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. IŽd 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]

Originally Posted by Jwscud

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 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

[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'

[ImbracableCrunk]

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

Hopefully I'm done doing interview checks. 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.