Ethiopia crash

[rmeier 473]

I read the reply above and started to think about the term "FBW".

For those of us old enough to recall the United Airlines Flight 232 incident, I don't recall the Douglas DC-10 having been designed as a "FBW" aircraft.

In credit to those UA 232 pilots, they did (arguably) manage to "fly" the plane with severe handicap (with the benefit of altitude!). I think this theory is what the latest conversation centers around...the DC-10 was "balanced".

Indications/reports are becoming available that the MCAS was in fact supplemented due to unfavorable flight characteristics of this airframe.

Time (and professional investigation) will determine the root cause.

RIP to the victims.

Rob

[sloppysmusic 242]

10 minutes ago, KevinAu said:

The greater thrust and location of the max’s engines enhanced this characteristic to the degree that boeing decided a software response was required.

Thanks for the very useful info.The above implies Boeing patched up a poor design rather than admit they messed up. Surely no-one would plan ahead a structural design that would require software to make safer in stall recovery? Been reading an engineer's test manual recently the first chapter is full of longitudinal, horizontal and vertical references when increasing /decreasing thrust. Very interesting was reading on how increasing thrust was NOT always the best way to get out of a stall as it can acerbate the existing over pitching condition depending on engine placement. For and aft of the CG as well as up or down in vertical position from the longitudinal axis. Excuse me, I'm very much still trying to learn this!

"Indications/reports are becoming available that the MCAS was in fact supplemented due to unfavorable flight characteristics of this airframe."

If this is found to be true the 737 Max is dead. No one will fly it again. If it is not wiped from service ASAP then the 737 itself will be tainted as well as Boeing's reputation for decades. Remember the Comet.

Edited March 16, 2019 by sloppysmusic
added quote

[KevinAu 441]

Increasing thrust has never been the best way to recover from a stall. Decreasing angle of attack is the best and only way to recover from a stall.

Pretty much every modern airliner you will fly on has numerous flight control software ‘fixes’ for something or another.

[Bob Scott 7,721]

49 minutes ago, sloppysmusic said:

Thanks for the very useful info.The above implies Boeing patched up a poor design rather than admit they messed up. Surely no-one would plan ahead a structural design that would require software to make safer in stall recovery? Been reading an engineer's test manual recently the first chapter is full of longitudinal, horizontal and vertical references when increasing /decreasing thrust. Very interesting was reading on how increasing thrust was NOT always the best way to get out of a stall as it can acerbate the existing over pitching condition depending on engine placement. For and aft of the CG as well as up or down in vertical position from the longitudinal axis. Excuse me, I'm very much still trying to learn this!

No it does not imply anything resembling a poor design, patched-up or otherwise.  At least while you're trying to learn this stuff, try to avoid drawing conclusions you're not qualified to make.

Every multi-engine jet transport aircraft ever made encounters a pitch and yaw moment (that varies with thrust) due to the engines' position away from the CG and longitudinal centerline.  Most multiengine aircraft have, for example, a defined minimum control airspeed (Vmca), below which application of full power with one engine out will produce an uncontrollable yaw/roll due to insufficient rudder and aileron authority to counteract the asymmetric thrust.  Many, many aircraft accidents have been attributed to pilot error in not observing this limitation.  By your reasoning, every multi engine jet ever made is a poor design since an engine failure can put the aircraft into an unrecoverable state if poor crew technique results in allowing airspeed to drop below Vmca during engine-out flight.  Crews are trained in the operating characteristics and limitations of their aircraft...failure to properly analyze and correct a malfunction when it occurs can very well put even the best-designed aircraft into an unrecoverable state.

Runaway trim (actually in this case a runaway stab) is a serious malfunction, but it's absolutely controllable by a properly trained and proficient crew.  If something is causing stab runaways (and it could be the new MCAS, the autopilot, wiring or other electrical malfunction in the stab trim system) then yes, Boeing needs to figure it out and fix it post-haste.  But a runaway stab, like an engine failure, should never result in an airplane-shaped hole in the dirt because we train crews to handle those problems.  We would not ground the fleet for a couple of engine failures where the crew botched the single-engine approach and crashed the jet.  We certainly wouldn't blame the manufacturer if one of those crashed jets was flying with engine problems identified but uncorrected over several previous flights.

 

[HighBypass 2,339]

Thank you for the insights, gentlemen. I am less confused now. 

I am still slightly worried that Boeing felt a need to include a software "patch" to automatically counteract something which a type-rated pilot would surely know about. Namely, applying lots of power results in a pitch up moment.

Much like a Spitfire or Mustang pilot (or any other high powered single engined piston powered plane) knows not to slam open the throttle on takeoff lest the resulting torque roll flips the plane onto her back.:D No one has seen fit to retrofit a computer controlled governor to prevent the pilot applying too much throttle... so that wise words and physics can be ignored.

What I'm trying to say, at least from a layman's point of view, is that different planes all have different flying characteristics - modifications to a particular type can also alter the characteristics of that type. Pilots trained on a particular type will (should...) know the characteristics:-  "do this and she will bite you in the word not allowed, hard!", or "she's a pussycat and gives you chances and warnings to let you get out of the mess you're causing".

[skelsey 765]

1 hour ago, w6kd said:

find me a western airline crewing its passenger jets with 200 hour neophyte pilots

Let's see:

• British Airways
• Lufthansa
• Ryanair
• Easyjet
• Flybe
• TAP
• Icelandair
• Virgin Atlantic
• BA CityFlyer

...the list goes on. In the case of BA (at least) this has been the case for more than 50 years. Heck, the military put "200-hour neophyte pilots" in to single-seat fighter jets.

So either all these airlines have been miraculously lucky... or perhaps it's not quite as simple as how many hours the FO has.

Likewise, pilots at Ethiopian (and other airlines across the world) seem to have been dealing with other issues in other aircraft reasonably successfully without large numbers of aircraft ending up crashing vertically in to the ground with full nose-down trim.

54 minutes ago, KevinAu said:

The mcas, as I explained already, is meant to correct a greater nose up moment when increasing thrust during a stall recovery

Not quite true; it is NOT a thrust couple issue. It is to do with the positioning of the new engines which results in a reduced amount of 'pull' force at high AoA (with constant thrust).

In other words -- if you imagine a standard approach to stall entered from level flight with idle thrust -- conventionally you would expect the backpressure required to increase as AoA increases (and this is a certification requirement).

Because of the new engines, the Max does not exhibit this characteristic: the backpressure required reduces at higher AoA so the 'pull' would be reduced or even reversed to a push to maintain a constant rate of increase in AoA. This does not comply with the certification requirements, so Boeing introduced MCAS as an artificial fudge -- when the AoA is indicated to be in the affected region, some nose-down trim is applied to artificially provide a nose-down force to pull against.

It is an aerodynamic effect caused by the lift produced by the new engine cowlings at high AoA and nothing to do with thrust-pitch coupling (so the suggestion mooted earlier of derating the engines to limit this effect would not be applicable). So yes, it is fair to describe MCAS as a software patch to fix an aerodynamic issue which was not present in previous versions of the 737.

1 hour ago, w6kd said:

Again, that begs the question of why the crew didn't shut off the stab trim and trim manually with the trim wheels...had they done so, the jack screw would not have been at its nose-down limit.  Also, one has to ask why the acft was allowed to keep accelerating (and thus progressively exacerbating the out-of-trim control forces) through the entire mishap, suggesting either task saturation on the part of the crew or a grossly incorrect analysis of the problem.

This is the nub of the question. From what I can establish, at least some of the problems here are:

• MCAS does not look like a 'typical' stab runaway: it trims a bit, then stops, then trims a bit more, then stops for a few seconds etc. The 737 has a speed trim system which does a lot of 'uncommanded' trimming in the opposite direction to that which one would expect (i.e. against the column force) around this point in the flight anyway.
• If the AoA sensor is the problem then it is highly likely that one or both stick shakers is going off and that is quite distracting, to put it mildly. Worse, the potential exists for be conflicting warnings -- an overspeed warning and a stall warning going off simultaneously, for instance.
• In to this environment already loaded with activity and sensory overload, throw in the potential for sensory illusions (somotogravic illusion, for example -- as the aircraft accelerates it is possible that the crew may have sensed this as a pitch up. With the stick shaker going off...

The problem is that as far as the evidence at the moment shows, the system is very far from being 'fail safe' -- in a situation where one single input to the system is in error, not only is the system incapable of recognising that erroneous data, it will use that data to (insidiously) trim the aircraft full nose down.

There's no question that a sharp crew under good conditions could catch the issue. Whether or not there is a checklist, the question is whether an average crew, under less than ideal conditions (dark stormy night, lack of sleep, startle factor, lots of other conflicting warnings going on etc) could be reasonably expected to identify the problem and apply the appropriate actions at low level before it develops in to a full-blown loss of control.

The evidence we have so far (and that may change as the investigations progress of course) seems to suggest not, and aviation authorities worldwide seem to have reached that view as well for now.

We shall see.

[Bob Scott 7,721]

1 minute ago, skelsey said:

Let's see:

• British Airways
• Lufthansa
• Ryanair
• Easyjet
• Flybe
• TAP
• Icelandair
• Virgin Atlantic
• BA CityFlyer

...the list goes on. In the case of BA (at least) this has been the case for more than 50 years. Heck, the military put "200-hour neophyte pilots" in to single-seat fighter jets.

So either all these airlines have been miraculously lucky... or perhaps it's not quite as simple as how many hours the FO has.

 

Source?

[skelsey 765]

6 minutes ago, w6kd said:

Source?

Errm...

Well BA started training recruits at Hamble in the 1960s and I can think of at least a couple of Avsim members here who I know personally that were students there. They've been running ab-initio cadet schemes in one form or another ever since.

If you head over to the artist formerly known as CTC (now L3) you will see plenty of very respectable airlines recruiting ab-initio through them.

Virgin have been running an ab-initio scheme for some time.

Lufthansa have a long-established ab-initio programme and have done for as long as I can remember.

[n4gix 4,947]

8 hours ago, charlie130 said:

These are all the questions I asked myself! Especially the question of turning off MCAS manually? If it's not an option to turn it off, then I can imagine why the poor chap trying to fly the plane had a panicky radio voice when asking for a return.

Here is the answer to your question. First a picture of the three controls needed to stop a trim runaway: 1) see the big wheels on either side? Those are the mechanical wheels to adjust the elevator trim. 2) notice the two switches within the red box? Those two switches cut off electrical power to the elevator trim motor.

Step one would be for either pilot to simply grab one of the trim wheels to stall all movement immediately. Step two would be for the pilot not flying reach over and flip those two switches off. Step three would be for the pilot flying to manually restore proper trim using the wheel. Not seen in this picture is a handle that can be use to more quickly adjust the trim. You'll see that in the linked video with a full explanation.

 

[Bob Scott 7,721]

 

43 minutes ago, skelsey said:

Errm...

Well BA started training recruits at Hamble in the 1960s and I can think of at least a couple of Avsim members here who I know personally that were students there. They've been running ab-initio cadet schemes in one form or another ever since.

If you head over to the artist formerly known as CTC (now L3) you will see plenty of very respectable airlines recruiting ab-initio through them.

Virgin have been running an ab-initio scheme for some time.

Lufthansa have a long-established ab-initio programme and have done for as long as I can remember.

We have similar training programs here, but we sure don't put their graduates directly into the right seat of a jetliner flying international routes at a major airline.  If that's really what they're doing in the EU, all I can say is "Thank God for our cabotage rules!"

A pilot with such low experience, then placed into a right seat where he's watching the autopilot the vast majority of the time, and playing second fiddle to the captain most of the rest is a simply dreadful proposition.  He'll have been at his peak hands-on proficiency graduating from the school, and then after that he enters a decline, building next to no hands-on proficiency and with almost no base of experience to back up his dearth of recent hands-on flying.  I'll be very interested to see the human factors analysis of the Ethiopian crash...how much help that FO really was to the captain when it mattered most.

Could be that this stab trim issue on the 737 Max proves to be the tip of the iceberg in exposing how far the industry has fallen with regards to crew flying competence and proficiency.  I talked to a recently retired check airman for an international airline maybe a year ago, and he was telling me how his airline insisted that crews fly on automation to the max extent possible in the interest of pax comfort and fuel savings...he actually got called on the carpet for insisting his FOs hand-fly departures and approaches from time to time.

Regards

[sloppysmusic 242]

11 minutes ago, w6kd said:

Could be that this stab trim issue on the 737 Max proves to be the tip of the iceberg in exposing how far the industry has fallen with regards to crew flying competence and proficiency

..and this will continue as long as mounting costs and fees persuade airlines to cut corners to achieve any reasonable profit. I'm wondering if it is even possible to be safe (adhering to all safety standards and required training procedures) AND profitable these days. People demand low prices and at the same time want to be safe whoever they fly with or wherever they fly.

Regarding correct procedure for this condition, it may be explained exactly as the informative video shows above

Control column HOLD FIRMLY

A/P DISENGAGE and do not reengage

IF runaway stops then fine

IF runaway continues 

STAB TRIM turn both cut out switches off

IF still continues grab and hold trim wheel

Trim stabilizer manually

checklist complete.

All that is in the QRH for the 737 NG but no mention is made of what to do is this condition occurs straight after takeoff. IF the pilots learned the QRH off by heart for this particular checklist AND practiced in the sim before then from muscle and mind memory there is a reasonable assumption they would do this in a few seconds. If they had NOT practiced in the sim and the FO had to actually refer to the QRH they are probably doomed. We are talking during initial climb, the ground is very close and getting closer, the plane is speeding up the natural (rabbit in headlights) reaction for a human pilot would be for both pilots to grab control wheel and pull back as hard as possible and radio for immediate return. Sadly not the solution to runaway trim but as long as it's not drummed into pilots that runaway trim WILL kill you and all your passengers in less than a minute at low altitude then this would have happened again if the planes were not grounded.

The question I still have (sorry if I missed it) is IF you disengage AP with the yoke double click (leaving AT still connected) is MCAS now disabled as well or will that still make changes to stab trim?

The FCOM I quote above is for the NG I would love to see the MAX version and if it includes specific MCAS disabling instructions in the recovery logic.

[skelsey 765]

8 minutes ago, sloppysmusic said:

The question I still have (sorry if I missed it) is IF you disengage AP with the yoke double click (leaving AT still connected) is MCAS now disabled as well or will that still make changes to stab trim?

 

No, it is not disabled -- in fact quite the opposite, MCAS (as I understand it) is ONLY active in manual flight. This is the whole point - to provide a force for the pilot to pull against in MANUAL flight at high AoA (to provide additional warning that the stall is approaching). Furthermore, in a 'traditional' trim runaway there is a trim cutout switch on the control column which prevents trim opposite to control column movement (so in the event of a nose-down trim runway, pulling back should cut the trim out in itself). MCAS bypasses this because it would defeat the object (it has to trim 'against' the pull to provide that increased nose down force).

My understanding is that there was NO mention of MCAS anywhere in the books and certainly not the QRH. I am not sure if that has changed.

 

[charlie130 196]

5 minutes ago, skelsey said:

No, it is not disabled -- in fact quite the opposite, MCAS (as I understand it) is ONLY active in manual flight. This is the whole point - to provide a force for the pilot to pul against in MANUAL flight at high AoA (to provide additional warning that the stall is approaching). Furthermore, in a 'traditional' trim runaway there is a trim cutout switch on the control column which prevents trim opposite to control column movement (so in the event of a nose-down trim runway, pulling back should cut the trim out in itself). MCAS bypasses this because it would defeat the object (it has to trim 'against' the pull to provide that increased nose down force).

My understanding is that there was NO mention of MCAS anywhere in the books and certainly not the QRH. I am not sure if that has changed.

 

So if you can't disable the computer sitting between your stick and throttle and the moving parts, you ( the pilot flying) don't have full control of the aircraft?  A silicon chip and some program has the final say?

Blimey! That's too much for my 1950's mentality! 

Regards.

[skelsey 765]

5 minutes ago, charlie130 said:

So if you can't disable the computer sitting between your stick and throttle and the moving parts, you ( the pilot flying) don't have full control of the aircraft?  A silicon chip and some program has the final say?

Blimey! That's too much for my 1950's mentality! 

Regards.

You can (in fact, the only way) disable MCAS through the trim cutout switches on the pedestal. 

If of course you realise what's going on and can reach the things whilst being bounced around/nosed over under negative G/pulling back on the control column with both hands and feet up on the panel for leverage etc.

[sloppysmusic 242]

12 minutes ago, Bobsk8 said:

Boeing will have a major job trying to fix this issue and get the aircraft back in the air. 

If this is so Boeing will have more to worry about than getting the plane back up. Class action attorneys will be rubbing their hands together in glee.