Autothrottle on takeoff

[kylegavin11]

I've noticed that when pressing the TOGA buttons sometimes it will only increase the thrust to 84% and not the set N1 in the fmc, and other times it works fine? Is there something I'm doing wrong or is that just a small bug. I know that it briefly pauses at 84% N1 to stabilize the engines before proceeded to takeoff N1, but sometimes it will just stop at 84

Edited June 4, 2016 by kylegavin11

[Tchou]

Hello, 

If I may say so : 

If the day is hot, thrust will decrease, not increase.

That's how reduced power take off works (you assume you are on a hot day when it is not;)

Richard.

 

[Eddie]

Hello, 

If I may say so : 

If the day is hot, thrust will decrease, not increase.

That's how reduced power take off works (you assume you are on a hot day when it is not;)

Richard.

 

That's based on a fixed thrust level, not a fixed N1.

[Litjan]

Hi and thanks for the report -- I have never seen this, but could think of a few causes:

The N1 should go to the value specified on the TAKEOFF REF page - depending on environmental factors, a derate or thrust reduction selected this could be between 83 and 93% (or so).

If the A/T is not achieving this N1 after pushing the TO/GA buttons, it is most likely because either the THR HOLD speed is reached before the A/T is done (this is at 84kts), or because the users joystick is interfering. This would happen if you move the joystick thrust lever down a bit during the takeoff run. The logic interprets this as an attempt to reject the takeoff, and the thrust control is handed back to the joystick thrust lever.

To avoid this, follow the procedure that we suggest in the tutorials: After pushing TO/GA buttons, advance your joystick thrust lever ALL THE WAY FORWAR TO THE STOPS immediately. Don´t try to follow the "ghost throttles" or try to adjust to the correct position. All the way forward very rapidly, then don´t touch them.

Let me know if this helps, Jan