View Full Version : B737 N1 limit

11th May 2003, 02:25
ENG failure at take off: if I push N1 on the MCP will I get CLIMB thrust or MAX CONTINUOUS?
Is it more correct to reduce the limit via the N1 limit page on the FMC?

11th May 2003, 04:44
As Im not a "MCP licensed", Ill give some information regarding the 737-200 (but you can derivate a bit).
For my kind of acft, in this case it wont be correct to select MAX CONT thrust. It would be better to choose G/A thrust. Needless to say that Im assuming that the failure occurred above 60Kt - otherwise, you would be supposed to select TO power.
G/A provides a little more thrust than Max Continuous. But remember that, after 5 min using this eng setting (its a limitation), youll need to ask for Max Cont thrust.
I hope you understood my point of view.


11th May 2003, 07:25
After TOGA is pressed during a takeoff roll at 64 kts the auto throttle will go into throttle hold. During this time power is removed from the auto throttle therefore the auto throttle is basically inactive therefore pressing N1 will not accomplish anything. Throttles can be repositioned manually to full takeoff power if needed any time throttle hold is annunciated.
At the completion of 18 second period and above 400 RA the autothrottles annunciate Arm; the autothrottle is now ready to accept commands.
Pressing the N1 button will allow the auto throttle computer to set climb power, this is the correct procedure for selecting climb power.
If MAX Continuous power is needed due to an engine failure this is selected off the N1 page.

I hope this helps you.

11th May 2003, 18:31
Hi guys,
what I meant was not changing thrust during t/o roll, of course, but reducing thrust after cleanup, before the 5 minutes limit:
Joey you are right, but just as a curiosity, what will happen if I push N1 on the MCP?


12th May 2003, 00:18
Hello LEM,

If I understand cit rrectly, pushing N1 on the MCP will bring the thrust lever back to climb thrust....Try it in the SIM, set engine flame-out, don't do anything at 600ft and press the N1... thrust will come back to either CLB, CLB1 or CLB2, depending on the assumed temperature set in the Takeoff Ref pg...

12th May 2003, 01:09
Ok, CI54, that was my point: the N1 button is not so clever to give me CONT instead of CLB after an eng failure!

Would be great to be in the sim everyday!

12th May 2003, 16:31

On some Boeings, the FMC IS so clever to provide Max Cont thrust following engine failure, but unfortunately not the B737. The Flight Director still provides the proper engine out guidance.

On later A/T computers, the hold mode starts at 84 knots and the A/T re-arms at the airline default height (may be higher than 400 RA).

After flap retraction, the other pilot selects CON on the N1 page which moves the bug to Max Cont thrust (until another mode is selected or engaged). The thrust must be manually set. Disconnect the A/T and select level change for further climb.

(The thrust may be left at max N1 for up to 10 minutes for terrain clearance, otherwise 5 minutes).

12th May 2003, 19:56

:ok: :ok:

13th May 2003, 00:15
But don't forget:
At flaps-up maneuvering speed select LVL CHG mode before pushing CON on the N1 page otherwise N1 limit will revert to climb thrust again.

13th May 2003, 04:29
This point is not highlighted sufficiently on the books.
Thank you, Bokomoko!