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MAXs Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAXs Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 25th Aug 2019, 09:17
  #2021 (permalink)  
 
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airlaw question : If the American FAA certified the B737-MAX but say Canada,EASA, Mexico didn't, could a MAX operate into those territories to/from the US? How about overflights?

G

Last edited by groundbum; 25th Aug 2019 at 10:13.
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Old 25th Aug 2019, 09:27
  #2022 (permalink)  
 
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Originally Posted by groundbum
airlaw question : If the American FAA certified the B737-MAX but say Canada,EASA, Mexico didn't, could a MAX operate into those territories from/from the US? How about overflights?

G
A MAX has been turned back on a ferry flight over I think Germany during the grounding.

So I expect it would be just USA (airspace) domestic restricted.

It would also put FAA in a class of it's own - new type certifications will be a very long process in every other country forevermore.

It has been a long path since the moon landing 50 years ago, not all steps since have been forward ones.
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Old 25th Aug 2019, 09:27
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Regarding over RTOW: Its not a PA-32, its a jet. 2 tonnes over is 1.5% more mass and not significant on two engines. At all.

Re air law. Historically regulators accept country of origin certification. I can’t recall a type for which approval was withheld by a regulator apart from some ex Soviet types. I think if approval were to be specifically withheld then overflights would be disallowed. I guess we just might see what happens if the Trump/China foolishness gets anymore out of hand.
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Old 25th Aug 2019, 10:23
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Originally Posted by MurphyWasRight
One can hope that the Lion air and Ethiopian investigators did such testing early on before it became widely known and discussed.
In fact the Ethiopian accident suggests that the crew was not fully aware and ready to pounce on MCAS, although in that case partial knowledge may have been deadly if it led to disabling electric trim before achieving neutral trim.
Without having to THINK, an experienced captain with sufficient manual flying skills would not need to know if MCAS, ordinary runaway stab trim or ambiguous autopilot stab trim inputs were causing the uncommanded nose-down trim. Such trim anomaly at low altitude would automatically trigger a self-preserving INSTINCTIVE response of stopping the trim-in-motion forward moving stabilizer wheel either with his knee, right thigh or right hand and simultaneously ordering the F/O to cut off the electric stab trim switches, or doing that by himself, while simultaneously clicking off the A/P and A/T.
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Old 25th Aug 2019, 10:53
  #2025 (permalink)  

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I can’t recall a type for which approval was withheld by a regulator apart from some ex Soviet types.
I seem to recall that D.P. Davies, the then Chief test Pilot of the CAA predecessor, the Air Registration Board (ARB), found the control loads unacceptable for an average pilot suffering an outboard engine failure at a critical time. He was backed by the head of the ARB, Lord Brabazon, and the ARB would not grant the B707 approval.

Boeing fitted a larger fin and rudder in consequence.
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Old 25th Aug 2019, 10:54
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Originally Posted by GlueBall
Without having to THINK, an experienced captain with sufficient manual flying skills would not need to know if MCAS, ordinary runaway stab trim or ambiguous autopilot stab trim inputs were causing the uncommanded nose-down trim. Such trim anomaly at low altitude would automatically trigger a self-preserving INSTINCTIVE response of stopping the trim-in-motion forward moving stabilizer wheel either with his knee, right thigh or right hand and simultaneously ordering the F/O to cut off the electric stab trim switches, or doing that by himself, while simultaneously clicking off the A/P and A/T.
Seems the simulator only passed the military test pilots on this not the "airline pilot" and Sully agrees.

If that simple, the fix was months ago - not still in the waiting or the need to think! The problem is bigger than an experienced captain.
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Old 25th Aug 2019, 12:12
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Originally Posted by GlueBall
Without having to THINK, an experienced captain with sufficient manual flying skills would not need to know if MCAS, ordinary runaway stab trim or ambiguous autopilot stab trim inputs were causing the uncommanded nose-down trim. Such trim anomaly at low altitude would automatically trigger a self-preserving INSTINCTIVE response of stopping the trim-in-motion forward moving stabilizer wheel either with his knee, right thigh or right hand and simultaneously ordering the F/O to cut off the electric stab trim switches, or doing that by himself, while simultaneously clicking off the A/P and A/T.
And if the stick shaker wasn't the most prominent feature - shaking violently, and noisily - taking their full attention, warning as it does of too high angle of attack, which requires an immediate nose down input, then, yeah, probably they might have started to question what unknown system might be secretly moving a highly effective, primary control, without their knowledge, without them even knowing of its existence. That's a very big 'IF'. Just like if my auntie had a d!(k she'd be my uncle!

You are a perfect example of an armchair expert, now you know all the facts, with 20:20 hindsight. And dare I say it, quite likely with a strong vested interest. How very convenient to come on here and be the expert about what they all should have done.

Last edited by pilotmike; 25th Aug 2019 at 17:48.
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Old 25th Aug 2019, 13:10
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Originally Posted by GlueBall
Without having to THINK, an experienced captain with sufficient manual flying skills would not need to know if MCAS, ordinary runaway stab trim or ambiguous autopilot stab trim inputs were causing the uncommanded nose-down trim. Such trim anomaly at low altitude would automatically trigger a self-preserving INSTINCTIVE response of stopping the trim-in-motion forward moving stabilizer wheel either with his knee, right thigh or right hand and simultaneously ordering the F/O to cut off the electric stab trim switches, or doing that by himself, while simultaneously clicking off the A/P and A/T.
My bold in above.
The above does not mention the need to first get the aircraft in trim -before- cut off of electric trim which appears to be the fatal action by Ethiopian crew. Although not confirmed yet it appears that they were unable to use the manual trim wheel once they activated the cutouts.
Not trying to re-open a long running discussion just pointing out that things are never as simple as one might hope.
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Old 25th Aug 2019, 14:40
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Originally Posted by GlueBall
Without having to THINK, an experienced captain with sufficient manual flying skills would not need to know if MCAS, ordinary runaway stab trim or ambiguous autopilot stab trim inputs were causing the uncommanded nose-down trim. Such trim anomaly at low altitude would automatically trigger a self-preserving INSTINCTIVE response of stopping the trim-in-motion forward moving stabilizer wheel either with his knee, right thigh or right hand and simultaneously ordering the F/O to cut off the electric stab trim switches, or doing that by himself, while simultaneously clicking off the A/P and A/T.
... What?!
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Old 25th Aug 2019, 16:08
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Originally Posted by GlueBall
Without having to THINK, an experienced captain with sufficient manual flying skills would not need to know if MCAS, ordinary runaway stab trim or ambiguous autopilot stab trim inputs were causing the uncommanded nose-down trim. Such trim anomaly at low altitude would automatically trigger a self-preserving INSTINCTIVE response of stopping the trim-in-motion forward moving stabilizer wheel either with his knee, right thigh or right hand and simultaneously ordering the F/O to cut off the electric stab trim switches, or doing that by himself, while simultaneously clicking off the A/P and A/T.
Have you ever flown a 737?
The stabilizer manual trim wheels rotate at a rapid rate when there is a runaway stab condition. I doubt a knee or hand would be able to hold the stab trim wheel. Moreover, there isn't really a sufficient gap between the pedastal and the wheels to get any grip on the wheel. Most certainly a pilot could get a severe hand injury in trying to hold the wheel, without using the handles which are folded into a section of the wheel (s).

Last edited by 568; 25th Aug 2019 at 16:10. Reason: text
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Old 25th Aug 2019, 16:32
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Originally Posted by GlueBall
Such trim anomaly at low altitude would automatically trigger a self-preserving INSTINCTIVE response of stopping the trim-in-motion forward moving stabilizer wheel either with his knee, right thigh or right hand...
Someone liked Flying Wild Alaska too much.
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Old 25th Aug 2019, 18:17
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Originally Posted by CurtainTwitcher
Is 2000 lbs / 900kg over RTOW on two engines going to have a dramatic impact on the climb performance to the extent it is discernible in a newspaper graphic (Reuters link to graphics), especially given the scale? Single engine, yes, but that wasn't the scenario.
No idea how exactly Reuters created that graph, but it doesn't seem to match what happened accurately at all:



The Reuters graph is labeled "GROUND Altitude From Addis Ababa’s altitude of 7,625 feet" and they claim it's based on "altitude data from the flight, released by Flightradar24".

It seems to suggest that the aircraft reached only about 500 feet AGL before MCAS activated, and it almost touched the ground as a result. Everything I've seen so far contradicts that.

The FR24 data is the ADS-B reported pressure altitude, and needs to be corrected based on the actual pressure at the time of the flight, otherwise the graph will show the plane departed from 425 feed below ground level.

If you do that, the FR24 data looks like this, quite different from the Reuters graph:



I'm not sure if the ADS-B reported pressure is corrected based on the AOA and airspeed. If it is, then even my graph would not be accurate, showing lower altitudes, the actual altitude would be higher. On the DFDR traces from the preliminary report the computed left and right pressure altitudes diverge progressively, reaching more than 1000 feet difference as the speed increases. This could make even the altitude loss from my graph show as worse than it actually was. The aircraft could be at 1500 feet AGL, when ADS-B would show it at 500 feet AGL.

In any case, it shows that at 05:40:00Z, when MCAS first activated, the aircraft was already descending.

Finally, I scaled the altitude graph from the preliminary report, compressing the time axis 10 times, to get a scale factor more similar to the Reuters graph and my graph:




The blue trace is the corrected pressure altitude from the right side, with the functional AOA sensor, the red trace is from the left side, with the broken AOA sensor.

Each vertical division is 1000 feet. The red trace seems to match the FR24 data, so it seems the ADS-B information was incorrectly adjusted due to the broken AOA sensor. According to the trace from the right side, with the functional AOA sensor, the aircraft actually reached about 1500 feet AGL before it started descending, and only lost about 250 feet of altitude, instead of 450 feet like the FR24 data shows.

Last edited by MemberBerry; 25th Aug 2019 at 18:40. Reason: corrected scaling factor to 10 from 5
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Old 25th Aug 2019, 18:52
  #2033 (permalink)  
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Originally Posted by GlueBall
Such trim anomaly at low altitude would automatically trigger a self-preserving INSTINCTIVE response of stopping the trim-in-motion forward moving stabilizer wheel either with his knee, right thigh or right hand . . .
Is there somewhere we can see video of this maneuver?

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Old 25th Aug 2019, 19:46
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Not a pilot here but a quick search reveals this - (acknowledgements to Youtube)


Only bit missing was an exclamation of 'just fly the darn plane'
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Old 25th Aug 2019, 19:50
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Originally Posted by GlueBall
Without having to THINK, an experienced captain with sufficient manual flying skills would not need to know if MCAS, ordinary runaway stab trim or ambiguous autopilot stab trim inputs were causing the uncommanded nose-down trim. Such trim anomaly at low altitude would automatically trigger a self-preserving INSTINCTIVE response of stopping the trim-in-motion forward moving stabilizer wheel either with his knee, right thigh or right hand and simultaneously ordering the F/O to cut off the electric stab trim switches, or doing that by himself, while simultaneously clicking off the A/P and A/T.
Actually, it's quite a bit more instinctive than that. And it doesn't involve any "Wild Alaska" maneuvering. All the Captain has to do is pull back on the yoke, and forward trim stops. The Control Column Cutout Switches stop "opposing trim inputs." This is true on every manual flight controlled Boeing since the "Dash-80". The pilots FRM for the MAX still says it is true for the MAX, even though it is not. Boeing removed a foundational, instinctive way for the pilot to over-ride undesirable trim trim inputs, put it under the control of some junior level automation programming, and didn't tell anyone.
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Old 25th Aug 2019, 20:58
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Originally Posted by Takwis
Actually, it's quite a bit more instinctive than that. And it doesn't involve any "Wild Alaska" maneuvering. All the Captain has to do is pull back on the yoke, and forward trim stops. The Control Column Cutout Switches stop "opposing trim inputs." This is true on every manual flight controlled Boeing since the "Dash-80". The pilots FRM for the MAX still says it is true for the MAX, even though it is not. Boeing removed a foundational, instinctive way for the pilot to over-ride undesirable trim trim inputs, put it under the control of some junior level automation programming, and didn't tell anyone.
You win the internet trophy for simplest explanation of this matter.

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Old 25th Aug 2019, 21:08
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I realized how confusing the situation would have been for the Ethiopian captain after working on my comment comparing the differences between the pressure altitudes computed on the left side and the right side.

The broken AOA indicator messed up the computed pressure altitude on the captain side so severely that it was showing the aircraft much lower than it actually was, more than 1000 feet lower as the speed increased, reaching almost 3000 feet difference during the final dive. At some point after the MCAS activation the aircraft was slightly climbing, but the captain pressure altitude was showing the aircraft as failing to climb, despite the increasing speed. Also the indicated airspeed was lower on the left side than on the right side by up to 25 knots.

So overall the instruments were presenting to the captain a situation much worse than it actually was. It's not the same thing if you are at 1500 feet, you lose 250 feet of altitude, and then the aircraft slowly starts climbing, compared with what the captain was actually seeing: being at around 950 feet and losing 450 feet of altitude, then the aircraft not climbing at all, despite the increasing speed.

With that in mind, even ignoring other factors, it becomes more understandable why the captain didn't reduce thrust. And I think determining quickly which side had the unreliable airspeed and altitude information, and using the information from the other side, is one thing that could have prevented the accident.

Last edited by MemberBerry; 25th Aug 2019 at 21:32.
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Old 25th Aug 2019, 23:10
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Originally Posted by MemberBerry
And I think determining quickly which side had the unreliable airspeed and altitude information, and using the information from the other side, is one thing that could have prevented the accident.
Quite a few votes for "It's an unreliable airspeed problem." Also quite a few votes for "It's a stab trim runaway problem." I haven't kept track of which has more votes, but I will note that at one time or another, Boeing has made both of those statements.

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Old 25th Aug 2019, 23:14
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Meber Berry referring to the height the PF was seeing.

it becomes more understandable why the captain didn't reduce thrust.
Very good point.


Re Takwis' post.
You win the internet trophy for simplest explanation of this matter.
Yes, it was a good post, but way back there was an even more simplistic way of putting it.

This and that, followed by,
but pulling back, MCAS wins.
It's utterly bewildering that people would be in command of an aircraft not knowing something so fundamental and so vital.
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Old 26th Aug 2019, 00:27
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Originally Posted by Takwis
Quite a few votes for "It's an unreliable airspeed problem." Also quite a few votes for "It's a stab trim runaway problem." I haven't kept track of which has more votes, but I will note that at one time or another, Boeing has made both of those statements.
Still, even with the aircraft severely out of trim, with unreliable airspeed and altitude information, the airspeed around VMO, stick shaker and other distractions, the pilots managed too keep the aircraft in the air, fly it, and even gain significant altitude. The preliminary report for the Ethiopian flight mentioned reaching 13400 feet, so more than 5000 feet AGL.

At this point they decided to re-enable electric trim and they made two ANU adjustments. Until today I assumed that, since they found it impossible to trim manually with the trim wheels, their plan was to slowly bring the aircraft back into trim using the thumb switches, then disable electric trim again, which doesn't sound like such a bad idea.

However, when looking today at the DFDR traces, I noticed that, immediately after re-enabling electric trim and making the two manual ANU adjustments with the thumb switches, there is a blip on the AP Warn Capt. trace.

So it seems that their plan was actually to re-enable electric trim, then test if it works for a bit using the thumb switches, then re-enable the auto-pilot. Unfortunately the auto-pilot failed to activate, and instead MCAS made the final AND trim adjustment dooming the flight.

If that was indeed their plan and that's what they did, it sounds like a really bad idea.

Later edit: from what I'm reading the A/P can't be engaged while there is force applied to the control wheel or column, which makes this even stranger. Because I don't see anything indicating they released the pressure on the column around the time of that blip. The column remained in the aft position according to the DFDR trace from the preliminary report.

Last edited by MemberBerry; 26th Aug 2019 at 03:44.
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