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  • 22

FAA chief tells Congress 737 manuals should have mentioned MCAS

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Lawmakers grilled the head of the Federal Aviation Administration on 15 May, hammering acting administrator Dan Elwell with questions about the FAA’s certification and oversight of both Boeing and the troubled 737 Max. (www.flightglobal.com) المزيد...

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navigator2013
John Ward 1
I read on BBC news today that MCAS can be switched off. So I can’t understand, if that was the cause of the two crashes, why the aircraft is still grounded!
vector4traffic
vector4traffic 1
Because increasing/decreasing thrust can cause the plane to pitch significantly and makes hand flying more difficult.
navigator2013
John Ward 1
Sorry Vector4traffic but, weren’t the pilots endeavouring to control the plane by hand, but, the MCAS was over-riding their actions?
vector4traffic
vector4traffic 1
You misunderstand, with MACS OFF ".... increasing/decreasing thrust can cause the plane to pitch significantly and makes hand flying more difficult."

Are you not aware of why MCAS was created?
navigator2013
John Ward 1
Again, wasn’t MCAS, the the pilots were unaware of, was misreading the situation and forcing the plane to do actions that were not safe?
vector4traffic
vector4traffic 1
Boeing says follow the checklist but until you conclude it's stabilizer trim rather than hydraulic or jack-screw or whatever you have a bunch of lists to go thru as the plane pitches every 10 seconds. If you paid for "insider" training Boeing changed any potential trim issue to a MEMORY ITEM. Nice try Johnny.
navigator2013
John Ward 3
I repeat.....according to reports Boeing did not include MCAS in their aircraft manual thus the pilots were not only unaware of the equipment, but, were also fighting against an unknown force.......or are all the reports wrong?
vector4traffic
vector4traffic 1
I've been telling you this for last 2 weeks.
navigator2013
John Ward 1
Can’t see how you have been telling ME this for two weeks as I only got the original email listing the story today and thus I have only been commenting on it for the past twelve hours! But, don’t worry about it as it is ONLY a comment and thus, along with all the other comments, will have absolutely no effect on whatever takes place!
vector4traffic
vector4traffic 1
Look, i'm not gay so you're wasting your time.

mercsport
Frederick Mills 1
On the BBC News website today there is a rather fine step by step rundown upon the reasons for Boeing's Max groundings.
Hope the url works for all: https://www.bbc.co.uk/news/resources/idt-sh/boeing_two_deadly_crashes
vector4traffic
vector4traffic 1
Imagine what the FAA would tell Congress if Trump managed (it was ultimately defeated) to get his personal pilot to run the FAA...
Paulcorder
Paul Corder 1
So now Boeing and the FAA are trying to blame the Ethiopian pilots for the crash by saying that they were flying too fast!!!
What a whitewash! Just hope that other countries Aviation Authorities won't be swayed by American attempts to minimalise the poor design that prevented an override of an aggressive maneuver created by faulty hardware and software!
hopskip
Trent Hopkinson 1
400 knots at 8000ft (above mean sea level over ground nearly 7000ft high) is too fast. MCAS software took no account for system redundancy and failed in a dangerous configuration, wasn't documented or trained for, and was botched as heck. Oddly enough, both can be true. The pilots flew too fast (true) - and the MCAS system was implemented incompetently (also true)
Highflyer1950
Highflyer1950 1
And the maximum Calibrated Air Speed is 340 kts, so they were well over the never exceed speed.
FrankHarvey
Frank Harvey 1
Hi Highflyer

I am under the impression that on some 73Xs VNE below 10,000 is 250 kts. If ETH302 was actually doing 340 kts CAS is there any possibility in anyone's mind, prior to completion of the full investigation, that Max's computers might have been overriding crew efforts to reduce throttle settings, ie is it possible that the computer "stuck" the throttles open.

Do we know exactly what MCAS is programmed to do ? Does anyone this side of Chicago (or Bangalore, or wherever Boeing finds its programming expertise) know with absolute certainty that the MCAS program does not increase the throttle settings as well as stick Max's nose into the dirt ?

I hope someone somewhere is going through the pre-revision MCAS code line by line to determine exactly what it was commanding the a/c computers to do, and the investigators are not relying on what Boeing or their programmers are telling them it did.
Highflyer1950
Highflyer1950 1
Frank, 250 Kts below 10,000’ is an ATC speed restriction unless authorized to go faster. Some countries allow climb airspeeds as high as 320/330 knots. Vne is the speed at which the aircraft should never exceed in normal flight. Mmo is the Maximum Mach Operating speed number which the aircraft should not exceed in normal flight. The auto throttle system can just be selected off or disengaged by manual throttle movement. In fact an engine failure or partial power loss will disengage auto thrust systems. Your last sentence is interesting in that the MCAS was doing exactly what it was intended to do, lower the nose attitude. However, the input MCAS received was from a faulty sensor either from computer code issues or a physically damaged AOA probe located at the side of the nose of the aircraft. again just my 2 cents worth.
FrankHarvey
Frank Harvey 1
Hi Highflyer

Thanks for the explanation of 250 Kts below 10,000' being an ATC restriction and definitions of Vne and Mmo. I had somewhere read the 250 Kts as if it were Vne and had misunderstood it as a 73X airframe restriction. Thanks for clearing that up. (I was puzzled as 250 Kts seemed very low for a 73X!).

Thanks also for explaining the ability of the crew to disengage the auto-throttle in prior 73X models. Hopefully that still functions in all situations, even under MCAS, which is what I was alluding to in the rest of the post. A lengthy explanation of my reasoning follows.

When I was involved in testing software, and more so in testing revised software, I sometimes encountered deviations from the specified/desired functioning, and even unexpected, unwanted, differences with previous software releases. This sometimes occurred in communication between modules and/or under unusual combinations of circumstances. Sometimes changes in programming inadvertently bypassed a section of code which put data into a "record" being passed between modules to invoke an action, or sent the wrong data, which resulted in undesirable functioning of the secondary module. Some situations were so unanticipated that they were not always covered by the test scripts. Program code as installed does not always do what it is supposed to do, especially using today's software generation methodologies and tools. The only way to determine exactly what code was operative is to meticulously go through line by line what the machine code actually said. And there are very few people who can competently do this, most "coders" cannot, and more so now that so much is firmware on a chip.

For example, from a real life, and relevant to the 737 single sensor input. When an early AEGIS cruiser was on an exercise in the Caribbean, an intake cooling water temperature sensor failed. The computer shut the engines down and would not permit restart. Amazingly there was no override ! The ship was towed back to Norfolk. This cruiser is the heart of integrated air defence for an aircraft carrier battle group. Had it occurred in actual combat or during a severe storm there could have been disastrous repercussions.

The reason for my speculation regarding possible links between throttle controls and stall recovery is based on my very limited flying experience but my much more extensive time in software development. When I flew a glider into a stall, I recovered by sticking the nose down, but in a powered aircraft I can aid recovery by increasing power. I was speculating on the possibility that the MCAS software in addition to taking over the electrical trimming system might have misguidedly also taken over the throttle control system and increased power while locking out the pilots under the mistaken assumption that stall recovery could be enhanced by increased power. This might explain the Ethiopians pilots' 400 Kts IAS.

Highflyer1950
Highflyer1950 1
Cool explanation. The auto thrust system will only command what ever speed is selected, even when flying manually. So, If the thrust levers were at take-off setting and the the gear and flaps are up and the pilot rolls the aircraft into say a 30 degree bank and allows the nose attitude to get excessively high , MCAS is supposed to add a few units of nose down stab trim so the AOA does not exceed a high setting and the “feel” of the aircraft mimics that of earlier versions. My guess is if the auto thrust was turned off the thrust levers would have stayed in the same high power position. We are all trained that when the automation fails, turn off everything and hand fly a known attitude and power setting. If it is a flight control issue then slower is usually better. remember the aircraft was nowhere near an aerodynamic stall, just the malfunction/damaged sensor thought it was. Machines can react to input but when the input is bad......you need reasoning, something A.I. hasn’t perfected yet?
Paulcorder
Paul Corder 1
Maybe technically too fast, but it wouldn't cause the plane to dive into the ground. Not sure that your reply is particularly measured!
Highflyer1950
Highflyer1950 0
years ago Learjet had a few accidents where the crew disabled the Stall Warning switches so they could fly faster in level flight without the stick puller going off. When they exceeded MMO in turbulence, in some cases the aircraft entered a mach tuck region and nosed over. When the crew reduced power and tried to raise the nose the aircraft continued to descend, going faster and faster. They pulled harder and harder and as one atc controller responded, it went from FL450 into the ground “like a lawn dart” Others had the tail distort from pulling so many “(g’s)” that the tail section failed when the aircraft entered thicker air. Those aircraft had a stick puller, pusher & shaker and an aural overspeed warning. Yes, the faster you go, the more the nose wants to fo down.
vector4traffic
vector4traffic 3
Wait, those were American pilots. They aren't foreigners. You just ruined the narrative.

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