PPRuNe Forums - Engine Thrust Rating on TOGA Double Push (B737)

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mmrassi

29th Nov 2018 17:02

Engine Thrust Rating on TOGA Double Push (B737)

Hello Guys,

If we perform a takeoff with 22K Derate and Assume Temperature of 40, What will happen to Engine thrust ratings if we double push the TOGA, Does the thrust increase to Full 26K or only 22K?!

Thanks

JCO7	29th Nov 2018 20:10

When doing a combined ATM and fixed derate, Vmcg and Vmca are based on the full derated thrust value so you generally shouldn't go beyond the fixed derate value. You can however manually advance thrust to the full derated thrust (indicated on the bugs) at any time in the take-off roll. The ATM reduction is thrust in your back pocket but the fixed derate value becomes your new max thrust. If you do need up to max (26k) thrust in an emergency you can still manually advance the thrust levers but an engine failure at low speed may lead to loss of directional control.

A second press of the TOGA switches during take-off whilst in THR HLD mode (below 800 feet) will cause the TMA to change to GA and max GA (26k) thrust to be indicated on the N1 bugs. However the A/T will not advance the thrust levers automatically - you will have to do so manually (different story above 800 feet).

Hope that answers.

mmrassi

30th Nov 2018 21:11

Quote:

Originally Posted by JCO7 (Post 10323941)

The ATM reduction is thrust in your back pocket but the fixed derate value becomes your new max thrust. If you do need up to max (26k) thrust in an emergency you can still manually advance the thrust levers but an engine failure at low speed may lead to loss of directional control.

Many thanks for for the answer,

Refere to the bolded part of your reply, I understand that pressing TOGA for the second time (above 800) should give us full derated thrust. But FCOM statement as you mentioned is talking about full GA thrust which you said is 26k in this case. I’m still confused!

Denti

1st Dec 2018 14:29

When we started to use the derate thingy together with AT, we were advised that a second push on the ground before THR HLD or in the air above 800 would result in full rated thrust, up to the max limit of the engine, which would invalidate Vmcg/a. Therefore, it was not rcommended.

JCO7	2nd Dec 2018 13:10

Quote:

Originally Posted by mmrassi (Post 10324878)

GA thrust is full thrust, i.e. 26k. So pressing TOGA above 800' will result in max thrust being set by the A/T. Pressing it below 800' will result in GA (26k) thrust being indicated on the N1 bugs and GA annunciated on the TMA, but thrust levers will not move automatically.

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