Originally Posted by
Centaurus
See link below. A spectacular event indeed. Some may even laugh and say SNAFU. B737-800 pilot hits TOGA before both engines momentarily stable at 40% N1. Due to asymmetric thrust, directional control is lost.
Take off was rejected at low speed but pilot inadvertently omits to close left thrust lever from full power while full reverse was selected on the other engine, despite not being needed. End result, not so graceful low speed 180 degree ground loop. Severe damage to 737 but fortunately only minor casualties. Read Final Report for more details.
Momentarily stabilisation at approximately 40%N1 is there for a good reason. According to handling notes for the CFM 56 series engine, from ground idle N1 to 40% N1, there is a 3 second tolerance in rate of increase of thrust for same rate of throttle movement. However, from 40% N1 to full power the tolerance is only one second. That is why you don't hit TOGA autothrottle until both engines are momentarily stable at 40% N1. Otherwise uneven power build up at beginning of take off run can cause unwanted swing.
It is quite common to observe pilots impatiently pushing the throttles half way up the quadrant (well beyond the 40% N1 throttle position) and thus significantly overshooting 40% N1 position before pressing TOGA. An engine taking up its 3 second tolerance in this case may result in significant asymmetric thrust possibly leading to a directional problem very early in the take off roll.
https://aviation-safety.net/database/record.php?id=20161227-0
Double whammy!
First error was not stabilizing the engines before TOGA.
Second error was selecting reverse thrust instead of just closing the throttles in a low speed abort.
Yes, I have seen different, incorrect ways to set thrust. Straight to 60%, TOGA. 40% then 60%, TOGA. Slowly all the way up, TOGA.