B737 RUNAWAY STABILIZER NNC
Thread Starter
B737 RUNAWAY STABILIZER NNC
Can I trouble any former or current B737 pilots to comment on this exchange in a separate forum please.
Comment 1
Comment 2
The two authors are apparently 'experienced pilots', one of them is meant to be a former Chief Pilot for a very large LCC.
None of what they've said strikes me as correct.
Was the first memory item for a Runaway Stab on a 737 ever to grab the trim wheel?
Comment 1
If it was a runaway trim condition, the first memory recall check list item is "trim wheel grasp and hold"
You are correct. It is a "recall check" to grab the trim wheel and stop its movement, followed by selecting the trim switch to the off position. Then consult the QRH. This has been the standard procedure since the B 737-200 and is practised in the simulator both in initial training and ongoing continuation checks.
None of what they've said strikes me as correct.
Was the first memory item for a Runaway Stab on a 737 ever to grab the trim wheel?
Control column. . . . . . . . . . . . . . . . . Hold firmly
2 Autopilot (if engaged) . . . . . . . . . . . . .Disengage
Do not re-engage the autopilot.
Control airplane pitch attitude manually with
control column and main electric trim as
needed.
3 Autothrottle (if engaged). . . . . . . . . . .Disengage
Do not re-engage the autothrottle.
4 If the runaway stops after the autopilot is
disengaged:
■ ■ ■ ■
5 If the runaway continues after the autopilot is
disengaged:
STAB TRIM CUTOUT
switches (both) . . . . . . . . . . . . . . . . CUTOUT
If the runaway continues:
Stabilizer trim wheel...grasp and hold
——————
Stabiliser...trim manually
Thread Starter
737NG
Control column. . . . . . . . . . . . . . . . . Hold firmly
2 Autopilot (if engaged) . . . . . . . . . . . . .Disengage
Do not re-engage the autopilot.
Control airplane pitch attitude manually with
control column and main electric trim as
needed.
3 Autothrottle (if engaged). . . . . . . . . . .Disengage
Do not re-engage the autothrottle.
4 If the runaway stops after the autopilot is
disengaged:
■ ■ ■ ■
5 If the runaway continues after the autopilot is
disengaged:
STAB TRIM CUTOUT
switches (both) . . . . . . . . . . . . . . . . CUTOUT
If the runaway continues:
Stabilizer trim wheel...grasp and hold
——————
Stabiliser...trim manually
Thread Starter
B737 RUNAWAY STABILIZER SIM TRAINING
To expand on my initial question, could any former or current B737 pilots please describe how the Runaway Stabilizer simulator training was/is conducted at your airline .
To the extent that you could address any or all of the following, that would be appreciated:
Thanks in advance.
To the extent that you could address any or all of the following, that would be appreciated:
- In what phase of flight is the problem usually presented?
- How was the runaway manifested (eg trim wheel suddenly starts running and control column forces build)?
- What (if any) alarms or cautions present themselves?
- Typically, does the runaway respond to the control wheel trim switch inputs?
- Typically was the Runaway Stabilizer thrown at you in isolation or concurrently with other significant non-normals?
- And perhaps most importantly, could you please comment on how frequently crews are normally exposed to Runaway Stabilizer in the sim? Elsewhere I've read that it might be as infrequently as once every two years.
Thanks in advance.
Last edited by MickG0105; 21st Mar 2019 at 07:47. Reason: Formatting tidy up
MickG0105,
See thread Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim
For training; consider an unannounced (surprise) situation such as manual flight, flap retract acceleration requiring normal forward trim.
Insert nose down trim runaway coincident with normal workload issues, checks, ATC, cabin.
Debrief situation perception (how formed and why), timing, ability, choice of action, etc.
See thread Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim
For training; consider an unannounced (surprise) situation such as manual flight, flap retract acceleration requiring normal forward trim.
Insert nose down trim runaway coincident with normal workload issues, checks, ATC, cabin.
Debrief situation perception (how formed and why), timing, ability, choice of action, etc.
Thread Starter
safetypee, thank you for that.
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Clearly a mix up with HOLD FIRMLY (control column, first action) with GRASP and HOLD (trim wheel, last action); similar talk but different times.
Q for SIM boys: can you initiate a "runaway stab" as a individual "press button selection" in the SIM??
Friend who was classic SIM instructor said cannot do, have to build up to it through gradual failures.
A classic Vs NG Vs (dare I say it) MAX SIM design??
Cheers.
Q for SIM boys: can you initiate a "runaway stab" as a individual "press button selection" in the SIM??
Friend who was classic SIM instructor said cannot do, have to build up to it through gradual failures.
A classic Vs NG Vs (dare I say it) MAX SIM design??
Cheers.
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Runaway! Stop and think what that's really meant to 737
pilots over time. Whrrr...Whrr... of the trim wheels
spinning away without input. EASY, we have a recall to
fix that.
This is DIFFERENT! Because of the component fault situation
AOA, the stick is shaking.... a whole different and scary event,
especially because the plane seems to be in a routine flight
condition. Nobody would really notice that in such an unexpected
time the trim wheels are ever so discretely moving, and PAUSING...
due to inputs, but then relentlessly resuming their travel. Very
sneaky while a another perceived crisis is unfolding.
No reasonable person should just casually roll off their tongue,
This is a runaway stab, they should have selected cut out.
Don't know about the Boeing factory, but out in the real world there
are NO 737 Max flight simulators where this could have been
observed/trained. (and in some airlines NO pilots knew their
familiar 737 had been changed enough to include an unknown
automatic flight control input)
It's NOT a runaway stab... for most normal 737 pilots out there!
The stick shaker is still going, with the attitude and power this
should not be possible. Who would be thinking stab trim at this
time? Remember that in daily life those Whrr.. wheels are so
often doing their thing in the background. It's not abnormal if
one is otherwise stressed out.
pilots over time. Whrrr...Whrr... of the trim wheels
spinning away without input. EASY, we have a recall to
fix that.
This is DIFFERENT! Because of the component fault situation
AOA, the stick is shaking.... a whole different and scary event,
especially because the plane seems to be in a routine flight
condition. Nobody would really notice that in such an unexpected
time the trim wheels are ever so discretely moving, and PAUSING...
due to inputs, but then relentlessly resuming their travel. Very
sneaky while a another perceived crisis is unfolding.
No reasonable person should just casually roll off their tongue,
This is a runaway stab, they should have selected cut out.
Don't know about the Boeing factory, but out in the real world there
are NO 737 Max flight simulators where this could have been
observed/trained. (and in some airlines NO pilots knew their
familiar 737 had been changed enough to include an unknown
automatic flight control input)
It's NOT a runaway stab... for most normal 737 pilots out there!
The stick shaker is still going, with the attitude and power this
should not be possible. Who would be thinking stab trim at this
time? Remember that in daily life those Whrr.. wheels are so
often doing their thing in the background. It's not abnormal if
one is otherwise stressed out.
Thread Starter
Runaway! Stop and think what that's really meant to 737
pilots over time. Whrrr...Whrr... of the trim wheels
spinning away without input. EASY, we have a recall to
fix that.
This is DIFFERENT! Because of the component fault situation
AOA, the stick is shaking.... a whole different and scary event,
especially because the plane seems to be in a routine flight
condition. Nobody would really notice that in such an unexpected
time the trim wheels are ever so discretely moving, and PAUSING...
due to inputs, but then relentlessly resuming their travel. Very
sneaky while a another perceived crisis is unfolding.
No reasonable person should just casually roll off their tongue,
This is a runaway stab, they should have selected cut out.
Don't know about the Boeing factory, but out in the real world there
are NO 737 Max flight simulators where this could have been
observed/trained. (and in some airlines NO pilots knew their
familiar 737 had been changed enough to include an unknown
automatic flight control input)
It's NOT a runaway stab... for most normal 737 pilots out there!
The stick shaker is still going, with the attitude and power this
should not be possible. Who would be thinking stab trim at this
time? Remember that in daily life those Whrr.. wheels are so
often doing their thing in the background. It's not abnormal if
one is otherwise stressed out.
pilots over time. Whrrr...Whrr... of the trim wheels
spinning away without input. EASY, we have a recall to
fix that.
This is DIFFERENT! Because of the component fault situation
AOA, the stick is shaking.... a whole different and scary event,
especially because the plane seems to be in a routine flight
condition. Nobody would really notice that in such an unexpected
time the trim wheels are ever so discretely moving, and PAUSING...
due to inputs, but then relentlessly resuming their travel. Very
sneaky while a another perceived crisis is unfolding.
No reasonable person should just casually roll off their tongue,
This is a runaway stab, they should have selected cut out.
Don't know about the Boeing factory, but out in the real world there
are NO 737 Max flight simulators where this could have been
observed/trained. (and in some airlines NO pilots knew their
familiar 737 had been changed enough to include an unknown
automatic flight control input)
It's NOT a runaway stab... for most normal 737 pilots out there!
The stick shaker is still going, with the attitude and power this
should not be possible. Who would be thinking stab trim at this
time? Remember that in daily life those Whrr.. wheels are so
often doing their thing in the background. It's not abnormal if
one is otherwise stressed out.
Regarding MAX sims from what I've been able to find Boeing Flight Services at Gatwick, Miami, Shanghai and Singapore all have got MAX FFSs.
Deepinsider, #9
You appear to have misunderstood the thread theme - title.
Whilst your views have merit in discussions on recent accidents, the point here relates to all 737s.
In part this confusion has been heightened by FAA / Boeing’s (mis)use of the the term in their interim checklist for the 737 Max.
Terminology, language is a major factor in aviation; see a related discussion Plain English in incident reports, please
The context of the training situation is critical; just a normal days flying, without warning - attempting to generate surprise. A need to determine and act on the perceived situation, do crews have the same perception, if not why. Choice and use of checklist - the nature of this fault warrants immediate recall actions, again if one pilot acts what do the other crew do.
As much as grabbing the trim wheel is required ‘in theory’, the practice might - should be flying the aircraft … pull. A interesting point could be if the PM is empowered to take memory items - hold the wheel, or after what time does the failure require both pilots to PULL. Simulator; is the simulator representative.
‘Can we ever imagine how work is done’ - Work as done is not Work as imagined https://www.eurocontrol.int/sites/de...ing-room-1.pdf Hollnagel,
Then again why would an operator train for this failure if it were judged sufficiently remote in relation to some other, current, salient, feature, e.g. LoC or UAS.
We are only as good as the last accident - and our thinking about it - determining the context.
You appear to have misunderstood the thread theme - title.
Whilst your views have merit in discussions on recent accidents, the point here relates to all 737s.
In part this confusion has been heightened by FAA / Boeing’s (mis)use of the the term in their interim checklist for the 737 Max.
Terminology, language is a major factor in aviation; see a related discussion Plain English in incident reports, please
The context of the training situation is critical; just a normal days flying, without warning - attempting to generate surprise. A need to determine and act on the perceived situation, do crews have the same perception, if not why. Choice and use of checklist - the nature of this fault warrants immediate recall actions, again if one pilot acts what do the other crew do.
As much as grabbing the trim wheel is required ‘in theory’, the practice might - should be flying the aircraft … pull. A interesting point could be if the PM is empowered to take memory items - hold the wheel, or after what time does the failure require both pilots to PULL. Simulator; is the simulator representative.
‘Can we ever imagine how work is done’ - Work as done is not Work as imagined https://www.eurocontrol.int/sites/de...ing-room-1.pdf Hollnagel,
Then again why would an operator train for this failure if it were judged sufficiently remote in relation to some other, current, salient, feature, e.g. LoC or UAS.
We are only as good as the last accident - and our thinking about it - determining the context.
Some thoughts on runaway stabilisers:
The condition statement at the top of the non-normal checklist that I posted reads this:
Condition:
Uncommanded stabilizer trim movement occurs continuously. (My bold)
That seems like a pretty definitive statement to me, but it is at odds with the MCAS actions as we now know them. Oddly, it is also at odds with at least one failure mode of the stabiliser actuation mechanism.
Perhaps the word continuously is the problem. Does it mean constant, or does it mean “continued, intermittent”, or perhaps “regular, persistent” ?
I cannot remember any runaway stab training in 24 years on 737-200 -300 -400 -800*, but I did do a return from FL240 on climb because the stab trim brakes failed and air loads were back-driving the stab, just like an STS normal actuation, but at an inappropriate phase of flight. I believe they found wear on the acme screw/nut in the stab jack too.
The 737 speed trim system is another stability characteristics kludge, and 737 pilots get used to the system trimming in opposition to pilot inputs.
The Lion Air crew the day before the accident described their (then undocumented) MCAS woes as a fault in the speed trim system in fact.
* I work for a non-US major carrier that does not cut corners on safety or training. A 737 endorsement course here goes for three months and incorporates 22 sim sessions.
The condition statement at the top of the non-normal checklist that I posted reads this:
Condition:
Uncommanded stabilizer trim movement occurs continuously. (My bold)
That seems like a pretty definitive statement to me, but it is at odds with the MCAS actions as we now know them. Oddly, it is also at odds with at least one failure mode of the stabiliser actuation mechanism.
Perhaps the word continuously is the problem. Does it mean constant, or does it mean “continued, intermittent”, or perhaps “regular, persistent” ?
I cannot remember any runaway stab training in 24 years on 737-200 -300 -400 -800*, but I did do a return from FL240 on climb because the stab trim brakes failed and air loads were back-driving the stab, just like an STS normal actuation, but at an inappropriate phase of flight. I believe they found wear on the acme screw/nut in the stab jack too.
The 737 speed trim system is another stability characteristics kludge, and 737 pilots get used to the system trimming in opposition to pilot inputs.
The Lion Air crew the day before the accident described their (then undocumented) MCAS woes as a fault in the speed trim system in fact.
* I work for a non-US major carrier that does not cut corners on safety or training. A 737 endorsement course here goes for three months and incorporates 22 sim sessions.
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"These terms, along with their adjective forms continual and continuous, are often used interchangeably in speech and writing, but style guides urge writers to practice discernment when using continually and continuously. In formal contexts, continually should be used to mean “very often; at regular or frequent intervals,” and continuously to mean “unceasingly; constantly; without interruption.” To put this into context: reading grammar blogs continually, or at regular intervals, throughout the day might be a fun way to boost your knowledge about the English language, but doing so continuously, or without stopping, for the duration of a day would likely result in fatigue, hunger, and—dare we say—boredom."
https://www.dictionary.com/e/continu...-continuously/
https://www.dictionary.com/e/continu...-continuously/
GH5,
How long does it take for the pilot to noticed that the trim is not moving as might be expected. Is first sighting deduced as STS; no flap up. Is it MCAS (assuming that you know of / recall the feature) 10 -15 sec cycle time - second cycle (airspeed check) required to indicate abnormal.
More likely increasing stick force will focus attention on pitch control - speed - stick-shake, low speed awareness.
Second cycle increases stick force, nose down, speed and vertical speed increase; increacing stick force.
PM enquires what’s happening; the first crew member to deduce a trim problem calls the failure, then memory drill started, switch to cutout and ‘hold trim’ - 20 sec nose down trim high stick force. Next call, ‘help’, back trim required, and two - four hands on the stick.
How high, how long is your piece of ‘assumption’ string.
How long does it take for the pilot to noticed that the trim is not moving as might be expected. Is first sighting deduced as STS; no flap up. Is it MCAS (assuming that you know of / recall the feature) 10 -15 sec cycle time - second cycle (airspeed check) required to indicate abnormal.
More likely increasing stick force will focus attention on pitch control - speed - stick-shake, low speed awareness.
Second cycle increases stick force, nose down, speed and vertical speed increase; increacing stick force.
PM enquires what’s happening; the first crew member to deduce a trim problem calls the failure, then memory drill started, switch to cutout and ‘hold trim’ - 20 sec nose down trim high stick force. Next call, ‘help’, back trim required, and two - four hands on the stick.
How high, how long is your piece of ‘assumption’ string.
"These terms, along with their adjective forms continual and continuous, are often used interchangeably in speech and writing, but style guides urge writers to practice discernment when using continually and continuously. In formal contexts, continually should be used to mean “very often; at regular or frequent intervals,” and continuously to mean “unceasingly; constantly; without interruption.” To put this into context: reading grammar blogs continually, or at regular intervals, throughout the day might be a fun way to boost your knowledge about the English language, but doing so continuously, or without stopping, for the duration of a day would likely result in fatigue, hunger, and—dare we say—boredom."
https://www.dictionary.com/e/continu...-continuously/
https://www.dictionary.com/e/continu...-continuously/
I read this forum from time to time and have been listening to pilots opine for fifty years. Given the widespread incidence of
poor spelling and suspect logic I don’t believe that we, as a group, are well suited to parsing out the meaning of a checklist condition statement, especially in the heat of the moment. I don’t think that Boeing employs the AP style guide-they use the language of tech writers, evidently edited by the marketing department.
