Ethiopian airliner down in Africa
Joined: Aug 2018
Posts: 1
Likes: 1
From: Hyderabad
The single most powerful control surface on a transport jet is the THS.
Why Boeing would give control of it to a subsystem, like the MCAS is hard to understand.
No amount of hauling (or pushing) on the elevator is going to save you if the THS isn't where it should be.
Why Boeing would give control of it to a subsystem, like the MCAS is hard to understand.
No amount of hauling (or pushing) on the elevator is going to save you if the THS isn't where it should be.
Joined: May 2008
Posts: 31
Likes: 9
From: El Paso, Texas
Does anyone know? If you have a 737 Max , airborne, flaps up, really high speed, full nose down trim, electric stabilizer trimming motors shut off, how much back pressure does it take to raise the nose with the elevator? While applying this large force to the elevator, how much force is required to turn the stabilizer trim hand wheel? How many turns of the hand wheel per degree of stabilizer trim. In other words, is it possible to get into a position in which it is impossible to recover, not enough elevator authority due to force required and or inability to retrim the stabilizer manually due to it binding from a combination of speed and forces being applied through the elevator.
Joined: Dec 2006
Posts: 1,350
Likes: 0
From: Florida and wherever my laptop is
Does anyone know? If you have a 737 Max , airborne, flaps up, really high speed, full nose down trim, electric stabilizer trimming motors shut off, how much back pressure does it take to raise the nose with the elevator? While applying this large force to the elevator, how much force is required to turn the stabilizer trim hand wheel? How many turns of the hand wheel per degree of stabilizer trim. In other words, is it possible to get into a position in which it is impossible to recover, not enough elevator authority due to force required and or inability to retrim the stabilizer manually due to it binding from a combination of speed and forces being applied through the elevator.
Joined: Nov 2007
Posts: 24
Likes: 0
From: Canada
Clearly MCAS is not a runnaway trim condition, otherwise we would be reaching for the cut-out switches every time the speed-trim operated. I think some people here do not realise that the trimmer doing its own thing is operations normal.
And the auro-trim systems are always mis-trimming the aircraft (the trim inputs by the speed-trim system are always wrong, and you always have to re-trim manually). So at what point does ‘operations normal’ become ‘operations abnormal’? At what point do you assume that the trimmer has gone awry..??
Silver
I don’t think this would happen as the MCAS does not activate the brake. All that sim training on runaway stab wouldn’t help because it’s not a runaway.
The stall horn and stick shaker would make pulling back and trimming nose up counter to all training that a pilot receives from initial stall recovery in a Cessna with a stall horn through to transport aircraft.
Two responses to two different stimulus. One Stall Recovery and one Unreliable Airspeed mask the third undocumented MCAS.
To learn anything from any accident you need to have empathy for those involved. Not just the pilots but the line mechanics, Boeing and FAA engineers. The true villains, senior management, board members and yes, even politicians will never be held accountable
The USA government shutdown that both political parties participated in was also a factor.
... and hence, the voters like you
Joined: May 2008
Posts: 31
Likes: 9
From: El Paso, Texas
I haven’t flown a 73 but on the 72 (if I recall correctly) during a runaway, the first instinctual response was to apose the runaway with opposite elevator. This ingaged the trim brake. The noise of the brake verses the runaway trim was a giveaway to use the cutout switches.
I don’t think this would happen as the MCAS does not activate the brake. All that sim training on runaway stab wouldn’t help because it’s not a runaway.
The stall horn and stick shaker would make pulling back and trimming nose up counter to all training that a pilot receives from initial stall recovery in a Cessna with a stall horn through to transport aircraft.
Two responses to two different stimulus. One Stall Recovery and one Unreliable Airspeed mask the third undocumented MCAS.
To learn anything from any accident you need to have empathy for those involved. Not just the pilots but the line mechanics, Boeing and FAA engineers. The true villains, senior management, board members and yes, even politicians will never be held accountable
The USA government shutdown that both political parties participated in was also a factor.
... and hence, the voters like you
I understand all that, and yes, I vaguely remember the trim brake. but the question is still this. Is there a conceiveable way to load the stabilizer to the point that it cannot manually be trimmed back to a point were elevators will work again?
Joined: Dec 2011
Posts: 11
Likes: 0
From: Czech Republic
I know it may look a bit stupid but I need to clarify that. I would like if someone who flies 737 could reply.
Why Boeing put MCAS to MAX? As I understood there was problem with pitch moment created by engines at some occasions. But is it possible to fly without it and it will be just difficult or it is impossible to handle the aircraft without MCAS? I though it is there just to be safer and easier for pilots but I have read many strange things about that. But I think that is just mess made up by media.
Why Boeing put MCAS to MAX? As I understood there was problem with pitch moment created by engines at some occasions. But is it possible to fly without it and it will be just difficult or it is impossible to handle the aircraft without MCAS? I though it is there just to be safer and easier for pilots but I have read many strange things about that. But I think that is just mess made up by media.
Joined: May 2008
Posts: 12
Likes: 0
From: Stafford uk
I also wonder if the forward position of the engines, which gives a pitch up moment at high angles of attack, and led to the addiction of MCAS, could possibly give a pitch down moment at low angles of attack?
Joined: Feb 2009
Posts: 379
Likes: 0
From: Seattle
Does anyone know? If you have a 737 Max , airborne, flaps up, really high speed, full nose down trim, electric stabilizer trimming motors shut off, how much back pressure does it take to raise the nose with the elevator? While applying this large force to the elevator, how much force is required to turn the stabilizer trim hand wheel? How many turns of the hand wheel per degree of stabilizer trim. In other words, is it possible to get into a position in which it is impossible to recover, not enough elevator authority due to force required and or inability to retrim the stabilizer manually due to it binding from a combination of speed and forces being applied through the elevator.
Also with regard to your reference to "very high speed" specifics make a difference as Mach effects come into play along with dynamic pressure. At cruise speeds and faster elevator travel is limited by actuator force capability. The faster you go the less the elevator can be deflected and thus the more critical it is to have the horizontal stabilizer near its trim position.
Joined: Dec 2003
Posts: 2,338
Likes: 821
From: Tring, UK
Clearly MCAS is not a runnaway trim condition, otherwise we would be reaching for the cut-out switches every time the speed-trim operated. I think some people here do not realise that the trimmer doing its own thing is operations normal.
And the auro-trim systems are always mis-trimming the aircraft (the trim inputs by the speed-trim system are always wrong, and you always have to re-trim manually). So at what point does ‘operations normal’ become ‘operations abnormal’? At what point do you assume that the trimmer has gone awry..??
Silver
And the auro-trim systems are always mis-trimming the aircraft (the trim inputs by the speed-trim system are always wrong, and you always have to re-trim manually). So at what point does ‘operations normal’ become ‘operations abnormal’? At what point do you assume that the trimmer has gone awry..??
Silver
That’s one of the biggest elephants (gorillas?) in the room. By the time you’ve thought “hmm, that’s not quite right” at low-level the situation has gone from nuisance to critical. The 737 trim is on the move all the time, be it from pilot inputs or STS/MCAS/Autopilot. Clickety-clack is the most heard noise on a 737 flight deck as the trim wheel spins it’s merry way backwards and forwards. Add an unreliable airspeed scenario to the above and no wonder things go from bad to worse. I really feel sorry for the crews who were dumped in this situation.
Joined: Oct 2017
Posts: 143
Likes: 0
From: Vienna
However, when an AoA is faulty, it will continously indicate high AoA to MCAS. MCAS kicks in, but still get high AoA input so it kicks again.. and again.. and again....
Joined: Feb 2005
Posts: 2,411
Likes: 2
From: USA
I haven’t flown a 73 but on the 72 (if I recall correctly) during a runaway, the first instinctual response was to apose the runaway with opposite elevator. This ingaged the trim brake. The noise of the brake verses the runaway trim was a giveaway to use the cutout switches.
I don’t think this would happen as the MCAS does not activate the brake. All that sim training on runaway stab wouldn’t help because it’s not a runaway.
The stall horn and stick shaker would make pulling back and trimming nose up counter to all training that a pilot receives from initial stall recovery in a Cessna with a stall horn through to transport aircraft.
Two responses to two different stimulus. One Stall Recovery and one Unreliable Airspeed mask the third undocumented MCAS.
To learn anything from any accident you need to have empathy for those involved. Not just the pilots but the line mechanics, Boeing and FAA engineers. The true villains, senior management, board members and yes, even politicians will never be held accountable
The USA government shutdown that both political parties participated in was also a factor.
... and hence, the voters like you
Joined: Dec 2011
Posts: 11
Likes: 0
From: Czech Republic
How the engines do that? What is supposed to be a problem? I expected that power and placement of engines creates this pitch up moment. Is it something aerodynamics related?
Joined: May 2008
Posts: 12
Likes: 0
From: Stafford uk
Yes its aerodynamic - my understanding ,from reading the whole thread, is that the engine nacelles being in front of the C of G exert aerodynamic forces - a positive angle of attack gives a pitch up moment - and subsequent reduction of stick back pressure approaching the stall - hence MCAS. I was just speculating if a low angle of attack would produce a nose down moment as the engines are presumably mounted to be zero A of A when the wing is at cruise A of A.
Joined: Feb 2009
Posts: 379
Likes: 0
From: Seattle
This is a very large thread, but if you want to know what is going on here you need to read from the beginning or at least skim through. Your question has been covered in numerous posts. You are welcome to search on my user name to see what I have contributed, but I suggest you read other's entries as well.
