Loss of Thrust on Both Engines - 737ng Checklist
 

Hi everyone,

Why there is no mention to close the thrust levers during this procedure? Is it considered obvious that you have to close it, or they just forgot to mention at the checklist? If you don't close them and the engines light up at different times, you will have a great yaw movement and need to compensate. No big deal, but the checklist mention that if one or both engines light up, you should advance the thrust lever slowly...
In a simulator lesson, the pilots didn't close the levers and had to correct the yaw later.

Something seems to be missing here?

Needs a more in depth explanation of the scenario.

Flameouts of multiple engines at the same time are quite rarely confirmed even tjhough reported. However, loss of thrust repsonse of multiple engines are far more common. Most of the dichotomy is due to the crew failing to take into account the engine(s) actually still being lit but so slow to response that they give up on them and engage a restart procedure which may be problematic to begin with.

The idea is that the best odds of recovery is doing only one engine at a time.

Nothing really missing (apart from any mention of closing the thrust lever :)). The original poster is using the correct title of a particular Boeing checklist. My slightly old version says:


737 Flight Crew Operations Manual
Copyright © The Boeing Company. See title page for details.


Loss Of Thrust On Both Engines

Condition: Both of these occur:
•Both engines have a loss of thrust
•Both ENG FAIL alerts show.
Objective: To restart at least one engine.

ENG FAIL (both)
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.


How, and why, a crew decide they need this checklist is best left to their decision making process. But if they need it, then there is no mention of the thrust lever (or throttle in another language). I can't give any reasons why this should be.

I presume the point of the checklist is to attempt a start as a matter of urgency, before the residual fan speed decays. If you reduce the thrust lever to idle you may excacerbate the problem. If one or both engines fail to start, the reference items call for the thrust lever(s) to be closed.

there's the sim and there's the real life

in the sim, having the engine relight at idle setting makes things easier

in real life, well...MORE POWER SCOTTY!

Precisely. When in doubt read the manual and all will be revealed. For example try Boeing FCTM Page 8.8 Loss of Thrust on Both Engines, which amplifies the subject.

Dual engine failure is a situation that demands prompt action regardles of altitude or speed. Accomplish recall items and establish the appropriate airspeed to immediately attempt a windmill start. There is a higher probability that a windmill start will succeed if the restart attempt is made as soon as possible (or immediately after recognizing an engine failure) to take advantage of high RPM
By closing the thrust levers as you would normally do for most engine starts the N1 reduces very quickly which contradicts the Boeing advice of taking the advantage of high N1