Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Was MCAS needed?

Tech Log The very best in practical technical discussion on the web

Was MCAS needed?

Old 13th Jan 2021, 20:27
  #21 (permalink)  
 
Join Date: Feb 2010
Location: attitude is nominal
Posts: 1,192
OT: With some new from scratch design Boeing would have been able to match or top the A321neo.
Less Hair is offline  
Old 13th Jan 2021, 20:46
  #22 (permalink)  
 
Join Date: Jan 2021
Location: Waterbury, CT, USA
Posts: 1
Thumbs up

Wonder how much longer "blancoliori" will continue to defend Boeing's negligence and tortious actions? Hiding the existence of MCAS until after the first of two crashes? Sounds legit.
chriscrepon88 is offline  
Old 13th Jan 2021, 20:59
  #23 (permalink)  
 
Join Date: Jun 2009
Location: florida
Age: 78
Posts: 1,279
Salute!

Thanks, TD

The assumption that MCAS loss of sanity would be seen as runaway trim is one thing that bugs me. Most runaway trim would not be corrected by beeping the trim switches on the yoke, unless there is alot of folks out there that never had to trim using switches on the stick or yoke.

I do not put a lot of credence to the four second assumption of a big problem because the MCAS activation stopped briefly if the pilot just beeped the trim switch. Added to the implementation was undocumented changes to the trim cutout switches. Oh oh oh, how about telling the pilots that they had this thing called MCAS? How about telling them what it was supposed to do? As a pilot, I am pissed about the hold thing, and feel betrayed.

I had my share of "firsts" in new planes, and some hairy moments in others. But this MCAS implementation in both aero design and procedural implementation simply scares me. Imagine if you were on nuclear alert back in the sixties and they changed the pre arming and actual arming of our weapons without telling us and having us practicing a few sim missions?

I relinquish the floor.

Gums sends...








Last edited by gums; 14th Jan 2021 at 15:39. Reason: typo
gums is offline  
Old 13th Jan 2021, 21:46
  #24 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 65
Posts: 3,059
Gums
Shortly after the second 737 MAX crash, I was at an event at the Seattle Museum of Flight where I ran into some old friends from Boeing (including a test pilot) who'd been involved in the MAX. One thing they all agreed on was that they'd all assumed that MCAS would be covered in the differences training from the NG.
That it wasn't was admittedly bad, but may not have made a whole lot of difference in the long run - the Ethiopian crew certainly should have known about MCAS yet still couldn't handle it.
tdracer is offline  
Old 13th Jan 2021, 22:14
  #25 (permalink)  
 
Join Date: Mar 2006
Location: England
Posts: 907
gums, re your post #19,
Apologies for my my cryptic #13 which was a reference to your previous post '13' in this thread, minimising thread clutter with endless quotes.

We are dancing around the same pole; but without the details of the various factors which could have influenced the goals of the people involved we cannot know their reasoning.

A minor deficiency in certification stick-force requirement could be argued with the regulator, normally the first choice - low cost. We don't know the extent of the deficiency, likely the wrong side of the line with Mach effects.

However, the second goal - NG compatibility, minimum training, then at $1M per aircraft there would be a strong incentive to improve the MAX. Particularly where the cost of MCAS as an extension of the existing STS would be small beer in the overall certification costs.

Amongst these goals it is feasible that MCAS might not be required for certification, but for commonality - training, MCAS was essential. A typical situation of conflicting goals, commercial pressures, and time constraint, cobbled together and thrown at the regulator.
Maybe the 'MAX did not required MCAS, but it had it.'

Yes Boeing are paying for this misjudgement - hard cash; the FAA can only 'pay' with loss of reputation, credibility, and worldwide trust. Which of these two, Boeing / FAA, will be back in 'profit' first ?

Flown the F101 Voodoo?! But for the toss of a coin I would have. However, the long-stab characteristics were closely studied, being typical of that generation of transonic aircraft. Extensive experience in 'the' Lightning which had similar, mild characteristics, showed how tolerant or unaware pilots can be of adverse characteristics.
These aircraft required 'MCAS', but didn't have it.
PEI_3721 is offline  
Old 14th Jan 2021, 00:20
  #26 (permalink)  
 
Join Date: Feb 2018
Location: Oxford
Posts: 20
Originally Posted by Banana Joe View Post
I fly a 737 manually for a lot longer than 30 seconds every sector...
And FD and AP are MEL items.

Back to your Cessna 150.
I fly the 737 too actually, the only hand flying we ever do is to 1,000' AGL and it comes off at the 500 foot stabilisation gate... what's the point in having FBW for stages of flight where everything is already trimmed out and all done in straight lines?
CessNah is offline  
Old 14th Jan 2021, 02:27
  #27 (permalink)  
 
Join Date: Jun 2009
Location: florida
Age: 78
Posts: 1,279
Salute!

For all to see, PEI and Gums can discuss some of the fine points about design and aero without calling names and raising cultural aspects of aviation.

We both share some "exciting:" times in various planes, and are still here to talk about it.

I am not sure PEI has as much experience training and learning from foreighn countries as I have, but I can unnerstan those here who have flown with many of the foreign carriers and all that that involves.

I sure hope we can contribute to a great resolve not to repeat the MCAS debacle.

Gums sends...
gums is offline  
Old 14th Jan 2021, 08:09
  #28 (permalink)  
 
Join Date: Jan 2014
Location: Melbourne
Age: 65
Posts: 381
I think this has all been done to death on other threads but it is worth reiterating the simple facts.

- MCAS was created to meet certification requirements of control column pitch force at the extreme edge of the performance envelope.
99.999 % of Pilots in normal operations would never expect to get anywhere near those conditions in 99.999 % of their total time on the aircraft.

- The inadequacy of the design was exposed ONLY after two subsequent events occurred;

- an angle of attack sensor failure
PLUS
- the incorrect application of the Non- Normal checklists expected by Boeing to resolve the issue.

Boeings assumption was that the procedures it had in place were adequate to mitigate the risk.
Subsequent events proved them wrong.
But not unreasonably so.
Took lots of cheese slices to line up to reach the outcome.

Last edited by George Glass; 14th Jan 2021 at 08:20.
George Glass is offline  
Old 14th Jan 2021, 08:57
  #29 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 12,482
Originally Posted by George Glass View Post
the incorrect application of the Non- Normal checklists expected by Boeing to resolve the issue
Boeing had a NNC to address MCAS failure ?
DaveReidUK is offline  
Old 14th Jan 2021, 09:27
  #30 (permalink)  
 
Join Date: Jan 2021
Location: Washington State
Posts: 1
MCAS was necessary though....

Originally Posted by Bergerie1 View Post
Perhaps MCAS was not needed to all on the 737Max. Patrick Ky of EASA has said that "they pushed the aircraft to its limits during stall tests, assessed the behaviour of the aircraft in failure scenarios, and confirmed that the aircraft is stable and has no tendency to pitch up even without MCAS."
From my reading of the Boeing email in the AirCurrent article, flight test data indicated that there was not sufficient warning to the pilot that one would be entering a stall condition. The issue thereby appears to not be one of control column feel but instead that the aircraft must provide tactile feedback that a stall is imminent. If this is the actual physical behavior of the aircraft than by all means MCAS would be required.

I always wondered why it took until flight test to identify the need to use MCAS in low speed flight. This observed behavior would explain why wind tunnel data and simulation would not have predicted this beforehand.

With regards to the criminal citation, my understanding of the law is that even if failure to comply is an honest mistake, e.g. Forkner did not know of the decision to change functionality, that it would still be criminally prosecutable. This would explain why the Company is criminally liable but not the individual. It would also explain why the criminal penalty was not as severe in only ~$200 million.

Does this seem like a reasonable interpretation?
Rainier is offline  
Old 14th Jan 2021, 12:46
  #31 (permalink)  
 
Join Date: Jan 2014
Location: Melbourne
Age: 65
Posts: 381
Yup.

Initial failure of Angle of Attack sensor leads to NNC “Airspeed Unreliable.”

Continued motion of Stab Trim leads to NNC “ Runaway Stabilizer.”

Challenging, but doable. Fly thrust and attitude.
But if you leave the autothrottle engaged at T/O thrust , try to re-engage the autopilot AND try to re-engage stab. trim you are screwed.
As a matter of interest , the flight data recordings from the initial Ethiopian report seem to have disappeared from the internet.
Why ?
George Glass is offline  
Old 14th Jan 2021, 12:54
  #32 (permalink)  
 
Join Date: Feb 2010
Location: attitude is nominal
Posts: 1,192
However it used to be some intermittent motion of stab trim. Starting over and over again. MCAS had been kept unknown to the pilots. And those AoA indicators were not displayed as advertised.
Not only the training got changed but the hardware and software.

Last edited by Less Hair; 14th Jan 2021 at 13:31.
Less Hair is offline  
Old 14th Jan 2021, 14:15
  #33 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 2,779
Originally Posted by George Glass View Post
Yup.

Initial failure of Angle of Attack sensor leads to NNC “Airspeed Unreliable.”

Continued motion of Stab Trim leads to NNC “ Runaway Stabilizer.”

Challenging, but doable. Fly thrust and attitude.
But if you leave the autothrottle engaged at T/O thrust , try to re-engage the autopilot AND try to re-engage stab. trim you are screwed.
As a matter of interest , the flight data recordings from the initial Ethiopian report seem to have disappeared from the internet.
Why ?
The question was did Boeing had NNC for MCAS? When MCAS itself was not disclosed how will they have a procedure for its abnormality?
vilas is offline  
Old 14th Jan 2021, 16:39
  #34 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 12,482
Originally Posted by George Glass View Post
As a matter of interest , the flight data recordings from the initial Ethiopian report seem to have disappeared from the internet.
I'm not sure exactly what you mean - the Preliminary Report, complete with the FDR traces that were widely discussed here on PPRuNe, is still downloadable from the Ethiopian CAA website.
DaveReidUK is offline  
Old 14th Jan 2021, 19:05
  #35 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting home
Age: 43
Posts: 3,101
For the record, as well I find G.G.'s summary markedly off the centre-line. That's from a person who agreed on all observations made by 737driver and fdr. For the latter it is certainly not a surprise, however, the former had received a lot of friendly and undeserved fire IMHO. With so many lives lost unnecessarily, the aim for everyone is taking as many lessons as possible for their own job.

At the edge of the envelope, an aeroplane must behave in a predictable manner and provide tactile resistance of sufficient and increasing magnitude.
Encountering unreliable airspeed event at take-off, a pilot shall assure for the necessary power + pitch to continue climbing safely.

Each of them being correct does not make the other one less true. Two gas pedals, two feet.



FlightDetent is offline  
Old 14th Jan 2021, 23:02
  #36 (permalink)  
 
Join Date: Jan 2014
Location: Melbourne
Age: 65
Posts: 381
Originally Posted by DaveReidUK View Post
I'm not sure exactly what you mean - the Preliminary Report, complete with the FDR traces that were widely discussed here on PPRuNe, is still downloadable from the Ethiopian CAA website.
Is it ?
Last time looked the link wasn’t there.

For those that are wondering I have personally experienced an “ Airspeed Unreliable” event in flight.
After the initial “what the f#ck “ moment the NNC worked just fine.
It will NOT work if you leave the autothrottle engaged.

My understanding is that MCAS was certified on the basis that the existing checklists and procedures would be carried out by a properly trained crew and would mitigate any risk.

Clearly they were wrong.
George Glass is offline  
Old 14th Jan 2021, 23:40
  #37 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 12,482
Originally Posted by George Glass View Post
Is it ?
Last time looked the link wasn’t there.
Aircraft Accident Investigation Preliminary Report Ethiopian Airlines Group B737-8 (MAX) Registered ET-AVJ 28 NM South East of Addis Ababa, Bole International Airport March 10, 2019
DaveReidUK is offline  
Old 14th Jan 2021, 23:51
  #38 (permalink)  
 
Join Date: Dec 2003
Location: Tring, UK
Posts: 1,521
I thought that most of us had agreed over this one but the trigger for the runaway trim NNC was “continuous uncommanded movement”. For those who haven’t flown the 737, the trim moves quite a lot in bursts in normal operation, without a command from the pilots, as it is driven by STS, MCAS on the MAX and the autopilot. How could you tell that the trim moving then stopping was a) normal operation or b) a dangerous system failure? Answer: you couldn’t, without (secret) prior knowledge and continued observation. If you disconnect the trim every time it moved under its own accord you might as well pull the circuit breaker on the ground. It’s many years since I flew one but I still remember the “clunk clunk clunk” which was the most common sound on the flight deck.

It was asking too much of pilots dealing with a complex failure plus tactile and aural alerts, during a critical phase of flight where the trim was actually responding to their inputs, to immediately diagnose a failure of a system that wasn’t even documented and work out what to do. We now know that the sim trials were unrepresentative due to prior coaching.
FullWings is online now  
Old 14th Jan 2021, 23:58
  #39 (permalink)  
 
Join Date: Dec 2013
Location: US
Age: 62
Posts: 430
Originally Posted by vilas;10967152t
John Leahy ex CCO of Airbus said A380 was undone because when they launched in 2000 the engine manufacturers offered them engines which according to them was the most economical and anything better was atleast ten years away. But in three years the engine manufacturers turned out new engines for B787 which was 12% better in SFC. B737 was also undone by new engine technology in a different way. The 1960s low wing aircraft was unsuitable for high bypass engine era. Had Boeing anticipated this they should not have made 800 series itself but built a new aeroplane which being later generation aircraft may be even outlasted Airbus neo. Unfortunately they had gone for widebody 787 and by the time it turned profitable Boeing was left with no gumption to invest in another new aircraft. They hurriedly did another plastic surgery on the old lady which turned out very nasty and apart from financial damage has even destroyed their credibility and reputation.
Just a small point on the engine issue. The Airbus A320 and 321 NEO’s suffer from a similar if not the same issue and it’s actually worse on the Airbus because the aircraft could in fact become unstable. This was not caught until the aircraft was in service and it required the CG be restricted by blocking the last seat rows on many configurations. They were attempting to address this and remove the CG restriction via software. I am not sure if this has been completed. MCAS was primarily designed to insure the aircraft handled like the 800 and would not require any pilot simulator training for the transition. In fact Boeing promised SWA that no simulator differences training would be required. SWA wrote a 1 million dollar per aircraft penalty into their purchase contract if even 1 sim session would be mandated by the FAA. The rest is history.
Sailvi767 is offline  
Old 15th Jan 2021, 01:03
  #40 (permalink)  
 
Join Date: Jan 2014
Location: Melbourne
Age: 65
Posts: 381
A B737 simulator instructor at a carrier I used to work for used to do an exercise when we had some time left over.
He’d position us at about 7nm on final to a lit runway , at night , in flight freeze , and then turn all the lights off on the forward panel.
When we were happy he’d let us go.
After a while he would stop the sim. and ask us how we thought it was going.
”Bit fast and a fraction low” I said.
”Correct. Continue”
After a normal landing we discussed what had been an interesting exercise.
It demonstrated several things;
1) How well thought out the Boeing cockpit is and how visual cues and muscle memory can get you a long way.
2) That old [email protected] like myself know more than we think we do , just by virtue of years of experience.
3) What a confidence building exercise it was for new F/Os , particularly those coming from Airbus , as to what the aircraft can actually do.

Another exercise was to take the aircraft to 20,000 ft and turn off every unguarded switch on the overhead panel.
The aircraft still flies.

The point is that the B737 is an analogue aircraft with lots of nice to have , but not necessary , digital add ons.

Reading all that has been written about the MCAS debacle I now realise that the B737s time has passed , not because it is fundamentally unsafe , but because the world has moved on. I don’t think its going to far to say that the time of Piloting as a highly regarded , valued profession is over.
The accountants have won.
Airbus philosophy has won.
Time to retire the B737 ASAP.
Very sad.
George Glass is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.