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B737 Mis-set T/O Power at BRS - 4 Mar 2024

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B737 Mis-set T/O Power at BRS - 4 Mar 2024

Old 3rd Jun 2024, 08:12
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B737 Mis-set T/O Power at BRS - 4 Mar 2024

Not sure if this has made it here - a search suggests not but happy to be corrected! Anyway, ..............

https://www.gov.uk/aaib-reports/aaib...737-8k5-g-fdzs

I'll leave it to the jet-jocks out there to comment as they see fit. Posted FI.
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4th Jun 2024, 10:32
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Having read this report I couldn’t help but ask what happened to the call of “Thrust set” after checking that the N1 is actually what it should be. I’ve flown for five 737 operators in the last eighteen years, and it’s been an SOP at all of them, I believe it comes from Boeing so can’t imagine it’s not in TUI’s manuals as well.

The other thing that surprises me on most days I go flying is how many F/Os at my current operator (not TUI) don’t bother to follow up the thrust levers as the A/T sets the thrust. Before anyone says anything maybe Captains aren’t checking as well, but I don’t fly with them. It’s something so basic to airmanship that it’s taught on a first take-off in a Cessna 150 (“Airspeed increasing RPM rising/correct),
and should be checked in some form on every take-off in any aircraft I’ve ever flown.
Old 4th Jun 2024, 04:40
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Unfortunately pilots are so reliant on the automatics taking care of things like the thrust setting that when it doesn't work properly it goes unnoticed. Both pilots probably thought that reselecting the A/T button fixed the issue. The fact that it was a command training flight just shows that even experience doesn't counter an important automated system not working as the crew expected it to. I remember the first time I flew a classic 737 when the A/T had been MEL'd. It required a lot of extra concentration and we still missed the throttles not being set to the correct position when we leveled off on the STAR. One of the issues with MELing systems like A/T is that the backup to it not working is atrophied pilot skills. As for pilots kicking out the A/T more often to not let those skills atrophy, good luck with the Flight Ops department of any airline permitting that as a regular practise.
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Old 4th Jun 2024, 08:08
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With the end of the runway coming up at an alarming rate and way past V1, the expression ‘firewall the bastard’ comes to mind.

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Old 4th Jun 2024, 10:32
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Having read this report I couldn’t help but ask what happened to the call of “Thrust set” after checking that the N1 is actually what it should be. I’ve flown for five 737 operators in the last eighteen years, and it’s been an SOP at all of them, I believe it comes from Boeing so can’t imagine it’s not in TUI’s manuals as well.

The other thing that surprises me on most days I go flying is how many F/Os at my current operator (not TUI) don’t bother to follow up the thrust levers as the A/T sets the thrust. Before anyone says anything maybe Captains aren’t checking as well, but I don’t fly with them. It’s something so basic to airmanship that it’s taught on a first take-off in a Cessna 150 (“Airspeed increasing RPM rising/correct),
and should be checked in some form on every take-off in any aircraft I’ve ever flown.
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Old 4th Jun 2024, 14:14
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Originally Posted by excrab
Having read this report I couldnít help but ask what happened to the call of ďThrust setĒ after checking that the N1 is actually what it should be. Iíve flown for five 737 operators in the last eighteen years, and itís been an SOP at all of them, I believe it comes from Boeing so canít imagine itís not in TUIís manuals as well.

The other thing that surprises me on most days I go flying is how many F/Os at my current operator (not TUI) donít bother to follow up the thrust levers as the A/T sets the thrust. Before anyone says anything maybe Captains arenít checking as well, but I donít fly with them. Itís something so basic to airmanship that itís taught on a first take-off in a Cessna 150 (ďAirspeed increasing RPM rising/correct),
and should be checked in some form on every take-off in any aircraft Iíve ever flown.
Adding to this when I flew the 737 (admittedly the classic) part of our performance calculation was to cross check the expected N1 setting, which was displayed on the MCDU and as part of the perf calculation - indeed the AT on the classic normally needed some fettling to get this correct, so you needed to know the figure to be set.
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Old 4th Jun 2024, 15:06
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Mmm, having had to deal with PIREPS of throttle stagger, as an LAE on the classic B737, I am surprised that anyone would quote using the AT, it was so crude a set up and the same with the B727 where all 3 throttles were clutched together dah!
At least on the B727 the F.E would enjoy the task of throttle management
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Old 4th Jun 2024, 15:10
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Good report. I like the graph showing what an outlier in terms of acceleration it was compared to other flights from BRS, along with the rider that it is notoriously difficult to detect.

On a short field like BRS, rejecting at low speed for an A/T malfunction makes a lot of sense, as by trolling down the runway attempting to get it working you have already reduced the margins or even invalidated the performance calculations. When I flew the 737 like Speed_Trim_Fail above, it was very much SOP to do a sanity check on the required N1 and to make sure you achieved it - still the same on what I operate now. By doing that all the time you got a feel of what numbers made sense for a particular runway + WAT.
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Old 4th Jun 2024, 15:16
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Originally Posted by aeromech3
Mmm, having had to deal with PIREPS of throttle stagger, as an LAE on the classic B737, I am surprised that anyone would quote using the AT, it was so crude a set up and the same with the B727 where all 3 throttles were clutched together dah!
At least on the B727 the F.E would enjoy the task of throttle management
Noting throttle stagger with the old hydromechanical engine control on the classic isn't really applicable when talking the 737-800 (FADEC) - throttle stagger is less than 1/4 knob unless something is seriously wrong.
BTW, when you say classic, do you mean the -3/4/500 (Boeing calls that the 'classic') or the -1/200 (aka the 'Jurassic').
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Old 4th Jun 2024, 15:38
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guess I am back in the "Jurassic" -200 along with B727, as if you did not notice.
I should have known the ref to MCDU sets the type above -200 but it appears that A/T is still not to be trusted.
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Old 4th Jun 2024, 15:48
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Originally Posted by aeromech3
guess I am back in the "Jurassic" -200 along with B727, as if you did not notice.
I should have known the ref to MCDU sets the type above -200 but it appears that A/T is still not to be trusted.
Yea, I suspected you were talking "Jurassic"
The A/T on the newer 737s is a huge improvement over that on the Jurassic 737 - but that doesn't mean the pilots shouldn't always verify thrust set by 80 knots - it's their job!!! The A/T is not considered a flight critical system - it's allowed to occasionally fail - and the pilots need to remember that.
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Old 4th Jun 2024, 18:31
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Originally Posted by excrab
what happened to the call of ďThrust setĒ after checking that the N1 is actually what it should be.
Reciting the callout without actually checking the thing, a tale as old as time.
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Old 5th Jun 2024, 09:09
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Originally Posted by excrab
The other thing that surprises me on most days I go flying is how many F/Os at my current operator (not TUI) donít bother to follow up the thrust levers as the A/T sets the thrust. Before anyone says anything maybe Captains arenít checking as well, but I donít fly with them.
Do you mean pressing a TO/GA switch and taking their hands off the thrust levers? An engine failure at 20kts will solve that tendency pretty quickly.

Perhaps itís linked to their policy of not allowing FOs to handle an RTO?
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Old 5th Jun 2024, 10:05
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When I flew the 737 300/400 for a season, PM was not trained to follow up the thrust levers. But we most definitely WERE trained to check and adjust the Take-off N1s after PF had set them for T/O. And to call thrust set at 80kts. (and I think PF calls "set thrust" after taking their hands off the levers?).


Originally Posted by Lookleft
Unfortunately pilots are so reliant on the automatics taking care of things like the thrust setting that when it doesn't work properly it goes unnoticed. Both pilots probably thought that reselecting the A/T button fixed the issue. The fact that it was a command training flight just shows that even experience doesn't counter an important automated system not working as the crew expected it to. I remember the first time I flew a classic 737 when the A/T had been MEL'd. It required a lot of extra concentration and we still missed the throttles not being set to the correct position when we leveled off on the STAR. One of the issues with MELing systems like A/T is that the backup to it not working is atrophied pilot skills. As for pilots kicking out the A/T more often to not let those skills atrophy, good luck with the Flight Ops department of any airline permitting that as a regular practise.
The cross-check of actual-versus-required N1, as set on T/O, is very important and fundamental. This was an ASM (auto-throttle servo motor) fault, but the auto-throttle system on some Boeings can be a bit sketchy, and not necessarily very intuitive, so it always needs to be very carefully double checked.

And even now there are posters like this for another "auto-throttle trap" under the green heading seen in SIM classrooms:
(sorry it has come out sideways; perhaps the Mods could re-orientate it - some forum software cannot read the orientation info of photos).



[Image given a stern talking to and told to shape up and stop lying down on the job - SD]

Last edited by Saab Dastard; 5th Jun 2024 at 14:42. Reason: Corrected image
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Old 5th Jun 2024, 11:03
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I like the use of the word "quirk". Another term would be design flaw.
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Old 5th Jun 2024, 12:34
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Originally Posted by Uplinker
When I flew the 737 300/400 for a season, PM was not trained to follow up the thrust levers. But we most definitely WERE trained to check and adjust the Take-off N1s after PF had set them for T/O. And to call thrust set at 80kts. (and I think PF calls "set thrust" after taking their hands off the levers?).

The cross-check of actual-versus-required N1, as set on T/O, is very important and fundamental. This was an ASM (auto-throttle servo motor) fault, but the auto-throttle system on some Boeings can be a bit sketchy, and not necessarily very intuitive, so it always needs to be very carefully double checked.

And even now there are posters like this for another "auto-throttle trap" under the green heading seen in SIM classrooms:
(sorry it has come out sideways; perhaps the Mods could re-orientate it - some forum software cannot read the orientation info of photos).
It has been a very long time but I recall that PF would ask PM to “set thrust”. How this works when FO doesn’t handle their own thrust levers I am less clear on.
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Old 5th Jun 2024, 13:18
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Originally Posted by Speed_Trim_Fail
It has been a very long time but I recall that PF would ask PM to ďset thrustĒ. How this works when FO doesnít handle their own thrust levers I am less clear on.
If F/O is PF the captain as PM checks thrust is set, adjusts the thrust levers as needed, and then keeps their hand on the thrust levers into V1. If the F/O is PM they follow up the thrust levers and adjust as necessary whilst the captain keeps their hand on or slightly above the top of the thrust levers. Once thrust is set the F/O removes their hand in case the Captain slams the levers back for an RTO.

Different companies / trainers might have slightly different versions of it, but thatís how I was taught it. As has been mentioned the NG seems to work better (although not on this occasion, obviously); My memory, having not had the misfortune to fly the classic for 11 years, is that the thrust levers seemed to need ďtweakingĒ on almost every take-off, whereas I canít remember ever having to do it on the NG except when dispatching with the A/T u/s.
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Old 5th Jun 2024, 13:33
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Originally Posted by excrab
If F/O is PF the captain as PM checks thrust is set, adjusts the thrust levers as needed, and then keeps their hand on the thrust levers into V1. If the F/O is PM they follow up the thrust levers and adjust as necessary whilst the captain keeps their hand on or slightly above the top of the thrust levers. Once thrust is set the F/O removes their hand in case the Captain slams the levers back for an RTO.

Different companies / trainers might have slightly different versions of it, but thatís how I was taught it. As has been mentioned the NG seems to work better (although not on this occasion, obviously); My memory, having not had the misfortune to fly the classic for 11 years, is that the thrust levers seemed to need ďtweakingĒ on almost every take-off, whereas I canít remember ever having to do it on the NG except when dispatching with the A/T u/s.
Thank you - I thought it would be something like that but itís not how I operated so obviously wasnít about to put my foot in my mouth.

Your experience of setting thrust on the classic echoes mine - on every takeoff you had to manually fettle the thrust levers to make sure thrust was set correctly byÖ I seem to recall 60kts. Hence the need to know the N1 you were targeting.
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Old 5th Jun 2024, 16:32
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Thank you, SD, for rotating that photo
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Old 5th Jun 2024, 19:24
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Originally Posted by aeromech3
Mmm, having had to deal with PIREPS of throttle stagger, as an LAE on the classic B737, I am surprised that anyone would quote using the AT, it was so crude a set up and the same with the B727 where all 3 throttles were clutched together dah!
Well, now I'm curious. In your experience what autothrottle systems do not drive all the thrust levers through a single clutch pack? The MD-11 with FADEC controlled engines drives all three levers through a single clutch pack. The main difference for FADEC control is that the thrust levers send electrical signals representing lever position to the FADEC instead of actuating mechanical cables that drive the fuel control valves. FADEC, or pre-FADEC, thrust control systems typically include a limited authority trim system that compensates for throttle stagger.

Last edited by EXDAC; 5th Jun 2024 at 22:56.
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Old 6th Jun 2024, 07:22
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Originally Posted by Lookleft
the A/T had been MEL'd.
Most dangerous MEL in the book because of
Originally Posted by Lookleft
​​​​​​​atrophied pilot skills.
​​​​​​​Well said.
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