How to ground loop a 737. Full power one side. Full reverse on other side.
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How to ground loop a 737. Full power one side. Full reverse on other side.
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
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
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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
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
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.
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More hilarious is this letter by his colleague trying to sell dummy of automatic reverse thrust deployment on one side and ridiculing passenger's ignorance about reverse thrust.
https://www.dailyo.in/variety/jet-airways-flight-skids-off-goa-mumbai-runway-pilot-writes-strong-letter/story/1/14769.html
https://www.dailyo.in/variety/jet-airways-flight-skids-off-goa-mumbai-runway-pilot-writes-strong-letter/story/1/14769.html
Last edited by vilas; 12th Dec 2018 at 12:34.
Do note in the report that the reverse on right side was only selected in the last few seconds, so probably did not do much to contribute to anything. Not in defense of anything, just for the sake of accuracy. Quite obvious mishandling of the aircraft here.
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Rightly (or wrongly), I used always to set the spool up 40% manually, then run the throttles in parallel up to a bit below the nominated thrust .. and then select the buttons to finish the final setting for checking by the crew. I saw two advantages .. maintenance of a practiced skill and I can never recall any untidy acceleration such as one sees, occasionally with the automatics. I don't see that my approach was inconsistent with the manual's requirements and, certainly, no-one ever queried me.
Quite happy to field any comments ...
Quite happy to field any comments ...
Thread Starter
Well, the manuals usually says "minimum 40%", so if you want your engines stabilized at 40, 45, 50, 65 or whatever that's up to the flightcrew, before pressing TOGA.
Idle thrust is about 22% N1. The wording could be better as it could be construed that 40% N1 was idle N1.
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FCTM : The exact initial setting is not as important as setting symmetrical thrust.
I wouldn't bother eating runway by fiddling too much with the thrust levers to set exactly 40% N1.
I wouldn't bother eating runway by fiddling too much with the thrust levers to set exactly 40% N1.
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Agreed. My understanding is that the symmetry of thrust at TOGA application is the key. Boeing/CFM have obviously determined that application of TOGA with N1 below 40% can have unpredictable results, so logically 40% is the minimum. I don’t see any problem setting thrust higher than 40% and then pushing TOGA. For example if the thrust was set symmetrically at 70% and then TOGA applied, the maximum possible differential thrust would be approximately 20%. ( or Takeoff N1-70). If takeoff thrust was set manually and TOGA applied then maximum possible differential thrust would be zero. If 40% was manually set and TOGA pushed, max differential thrust would be 50%.
With FADEC engines, nearly all the differences in accel rates are when coming off idle. There are various control laws that limit the engine accel rate coming off idle - depending on engine health (mainly compressor efficiency) and even subtle differences in idle speed, you can see meaningful differences in accel off idle (we investigated a few 747-8 differential accel RTOs where not all the throttles where on the idle flat when they initiated the throttle push) Once above idle, the FADEC control laws revert to what's called "N1dot" (rate of change of N1) - or EPRdot - which relate directly to thrust - so thrust asymmetry is minimal.
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One Asian airline introduced a call by the PM of "Stable" when the N1's were stable at 40% N1. This was not a Boeing SOP call but someone in management who thought it was a good idea at the time. On this occasion the PM was quietly advised by the simulator instructor on the private intercom, not to call "Stable."
The captain released the brakes and pushed the thrust levers to the 40% N1 position in preparation for hitting the TOGA button. T he 737 trundled down the runway at 40% N1 slowly gathering speed while the captain waited for the PM to call "Stable" which never occurred.
Passing the 1000 feet runway marker still at 40% N1, the captain looked accusingly across the cockpit to the PM and said "You forgot to call Stable."
This proved without any doubt some pilots rely 100% on an SOP call to initiate an action rather than using common sense.
l
The captain released the brakes and pushed the thrust levers to the 40% N1 position in preparation for hitting the TOGA button. T he 737 trundled down the runway at 40% N1 slowly gathering speed while the captain waited for the PM to call "Stable" which never occurred.
Passing the 1000 feet runway marker still at 40% N1, the captain looked accusingly across the cockpit to the PM and said "You forgot to call Stable."
This proved without any doubt some pilots rely 100% on an SOP call to initiate an action rather than using common sense.
l
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Airbus Safety First - Thrust Setting at Take Off
