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Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

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Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

Old 13th Mar 2019, 20:06
  #161 (permalink)  
 
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Originally Posted by Lonewolf_50 View Post
Once that I know of, during an early test flight of a V-22, but that seems to have been set up by a wiring problem that was identified and corrected.
In computer engineering we call this a 'byzantine failure', which could be discussed until the cows come home without a resolution. Seems to me that the only protection is a pilot that has done a lot of flying without the automation and a strong 'feel' for the aeroplane.

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Old 13th Mar 2019, 21:17
  #162 (permalink)  
 
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Originally Posted by DaveReidUK View Post
The Canadians referred to new "satellite tracking data", which may just be a roundabout way of saying more granular ADS-B data hoovered up by satellite.
sounds like it...

https://edition.cnn.com/world/live-n...ash/index.html

Satellite company provided data to FAA and NTSB 2 days ago

From CNN's Ellie Kaufman
The company that provided the satellite data that informed the FAA's decision to ground Boeing's Max 737 planes did so on Monday, according to Jessie Hillenbrand, director of Public Relations at Aireon.

Transport Canada received it Tuesday evening.

Hillenbrand said Aireon provided the data, which shows Ethiopian plane's flight position data, to authorities who requested it. The company does not analyze the information, she said, they just provide it.

Hillenbrand said they don't have any information about the crash itself. But the data sent shows the flight's path as captured by satellites as it travels. She said the "aircraft transmits its position twice a second, our satellites catch it. We have caught that data in real time and provided that to authorities."
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Old 13th Mar 2019, 23:01
  #163 (permalink)  
fdr
 
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Originally Posted by gums View Post
Salute!

@FCeng from my post


What I am implying is that the MCAS was put in the plane in order to satisfy certification requirements and just old basic aero you would expect from an airliner. i.e. it was not installed or required in previous 737 models.

I have a good plot of the longitudinal pitch authority of the plane I flew 30 years ago. At one point (AoA) the stab looses nose down control authority with a "neutral" stick command. Ditto for my VooDoo, and most of us could feel the stick getting lighter if we were pulling hard. No feedback of any kind in the Viper or Airbus to let you know how close you wereto losing it.

So what I am hearing about the new 737 is that as we get close to a certain high AoA that the plane looses some amount of pitch authority that is normally commanded by the pilot. Worse, it may even enter the "pitch up" mode where no pilot command will lower the nose.

Gums sends...
In respect of the MCAS/certification requirement.

Gums, the 101 had a particular issue related to the T tail configuration, which gave endless entertainment and some great movies. The Max's issue stems from the nacelles of the LEAP donks, and they are destabilising at higher AOA. The engine weight is beneficial to static stability, lift from the nacelle forward of the Cp (sans nacelle) is not.The nacelle lift is fairly non linear to AOA, a substantial portion is induced by the vortex flow off the nacelle body at higher (not high for a 16 or 18 etc...). I suspect that the MLA is also playing into the equation, but don't have info on the criteria for the triggering of that, however the MLA whenever active reduces the static stability of the aircraft.

The Max is not the first Boeing or 737 to have some quirks, the classic STS is understood, but the NG did as well but was cured with good revision. The B767 had its own variant of quirks with 25.173 compliance which was cured aerodynamically by add ons and then by refined design.

The unfortunate state of affairs is that the envelope area that is protected by 25.173 that resulted in MCAS which has the potential to cause more serious handling problems is as much a compliance/box ticking exercise as it has to do with acceptable safety of flight. Without direct knowledge on the PSCP that was undertaken, that being proprietary to TBC, one can assume from the information released that the issue arises during a wind up turn profile at aft CG, which doesn't happen as often as takeoffs and landings occur with a single AOA vane as a sensor in the current system architecture. Put the reg in perspective, a century after Sperry starting handing out instruments for IMC flight... a Pitts usually has a little trim requirement, not much and is nice to fly; it sits where you point it until disturbed, dynamic stability is not an issue, VFR is fine, IFR is not too bad. Another single engine jet I fly only has a trim change for the gear and flap change; from 100KCAS to 450KCAS there is no appreciable trim change, and that is a delight to fly, VFR or IFR, it is statically weakly positive, but has good dynamic stability. Static stability was important in the days of lousy instruments, and hand flying, as a cue to what the driver was doing.

In a perfect world the planes would have linear responses that are just so, meeting the regs. To do that needs assistance or FBW, and the latter comes with it's own set of benefits and attendant risks. The B777 and 787 FBW systems are nice to fly, but are more importantly simple to revert to Cessna 150 state, but then MAS had a wild ride with even that system once upon a time. The Airbus FBW is nice for a pilot to fly when it is working properly, when it is not, it can be pretty entertaining getting the right result. [A logical weirdness in the 777 and 787 is that the plane is hand flown with a speed (AOA) referenced through the trim switch, but with the autothrottle in SPD mode as well... and underneath it all the planes still have a phugoid that is not taken out by the control law. That is just curious and makes the A320/330/340 etc nice to fly in comparison, other than in a crosswind].

FC84, great input.

§25.173 Static longitudinal stability.

Under the conditions specified in §25.175, the characteristics of the elevator control forces (including friction) must be as follows:
(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC/MFC,whichever is appropriate, or lower than the minimum speed for steady unstalled flight.
(b) The airspeed must return to within 10 percent of the original trim speed for the climb, approach, and landing conditions specified in §25.175 (a), (c), and (d), and must return to within 7.5 percent of the original trim speed for the cruising condition specified in §25.175(b), when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.
(c) The average gradient of the stable slope of the stick force versus speed curve may not be less than 1 pound for each 6 knots.
(d) Within the free return speed range specified in paragraph (b) of this section, it is permissible for the airplane, without control forces, to stabilize on speeds above or below the desired trim speeds if exceptional attention on the part of the pilot is not required to return to and maintain the desired trim speed and altitude.
[Amdt. 25-7, 30 FR 13117, Oct. 15, 1965]



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Old 13th Mar 2019, 23:18
  #164 (permalink)  
 
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Boeing apparently issued this ;

Stabilizer incremental commands are limited to 2.5 degrees and are provided at a rate of 0.27 degrees per second. The magnitude of the stabilizer input is lower at high Mach number and greater at low Mach numbers. The function is reset once angle of attack falls below the Angle of Attack threshold or if manual stabilizer commands are provided by the flight crew. If the original elevated AOA condition persists, the MCAS function commands another incremental stabilizer

With refence to BOLDed statement (emphasis mine) can someone tell me what that means? By MAGNITUDE do they mean rate of MCAS trim input ( I though fixed rate of .27ish per per second.)?
Does it mean a range where it begins and stops?
What would be the upper and lower MACH numbers they are refering to?

I assumed it just ran pending the other conditions and the rate of trim input did not change

Last edited by GFCH; 13th Mar 2019 at 23:20. Reason: editorial
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Old 14th Mar 2019, 06:06
  #165 (permalink)  
 
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Isn’t it simply time for Boeing to design a ground up ‘modern’ replacement for the 737? Surely you can only retrofit so many systems before it’s time to pull the plug?

But it that would cost money - lots. The cynic in me says $$$ before safety.
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Old 14th Mar 2019, 07:31
  #166 (permalink)  
 
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Originally Posted by c53204 View Post
Isn’t it simply time for Boeing to design a ground up ‘modern’ replacement for the 737? Surely you can only retrofit so many systems before it’s time to pull the plug?

But it that would cost money - lots. The cynic in me says $$$ before safety.

Worth reading this article by Jon Ostrower who explains, in typical pithy fashion, how Boeing were backed into a corner and had to choose between doing a warmed-up 737 or having Airbus eat their lunch.
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Old 14th Mar 2019, 07:47
  #167 (permalink)  
 
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Originally Posted by GFCH View Post
MAGNITUDE
Magnitude is Mathematics jargon meaning size irrespective of direction.

The magnitude of 2 is 2.

The magnitude of -4 is 4.

In this case it means an amount of trim applied either up OR down.
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Old 14th Mar 2019, 07:58
  #168 (permalink)  
 
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Isn’t it simply time for Boeing to design a ground up ‘modern’ replacement for the 737? Surely you can only retrofit so many systems before it’s time to pull the plug?
Longer undercarriage to hold more wheels/brakes and to give more tail clearance? Room for big round engine UNDER the wing? Call it the Boeing 757?
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Old 14th Mar 2019, 08:26
  #169 (permalink)  
 
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I am so grateful for all the data Lion Air and the Indonesian Aviation authorities have provided so far. The world is a better place with their assistance.
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Old 14th Mar 2019, 08:49
  #170 (permalink)  
 
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But it that would cost money - lots. The cynic in me says $$$ before safety.
Cost money compared to what?

What value did they put on grounding a fleet of aircraft, losing public confidence, 300 something deaths, subsequent lawsuits etc etc?

I suspect the heart of this issue is short term thinking and noone thinking about the long term because they only get paid in the short term.

I'd bet right now that a cleansheet 737 with 2019 technology/system suite and aerodynamics is looking alot cheaper than the mess they find themselves in today.
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Old 14th Mar 2019, 08:56
  #171 (permalink)  
 
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Originally Posted by c53204 View Post
The cynic in me says $$$ before safety.
Hardly an exception, it's still too often a rule. But sweeping under the carpet can prove expensive.


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Old 14th Mar 2019, 09:02
  #172 (permalink)  
 
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Sorry, couldn't resist.
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Old 14th Mar 2019, 10:22
  #173 (permalink)  
 
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Originally Posted by neville_nobody View Post
Cost money compared to what?

What value did they put on grounding a fleet of aircraft, losing public confidence, 300 something deaths, subsequent lawsuits etc etc?

I suspect the heart of this issue is short term thinking and noone thinking about the long term because they only get paid in the short term.

I'd bet right now that a cleansheet 737 with 2019 technology/system suite and aerodynamics is looking alot cheaper than the mess they find themselves in today.
Not as simple as that. MAX total order book value is somewhere around $600 billion - that is the size of the opportunity at risk long term if they didn't do the MAX.

These accidents, the groundings the lawsuits, the fallout, whatever subsequent band-aid they patch the plane up with (make no mistake, there will be one, and probably a political price with the rest of the world's regulators along with it), might cost several billion, or maybe into the tens or even towards a hundred (with lost orders), but that is still cheaper than abandoning the market to Airbus.

Fact is that the timing was probably the biggest factor - the neo came along right when Boeing were putting everything into fixing their 787 screw up, if they had gone for a cleansheet 737 they faced a huge execution risk and concurrently failing at 787 and new737 would have been very very bad.

Considering that they opted for the quick-cheap-easy solution (compared to cleansheet design) and still seem to have managed to mess it up, avoiding the cleansheet may yet prove to have been a wise decision.
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Old 14th Mar 2019, 14:45
  #174 (permalink)  
 
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I don't want to be in the shoe's of the Boeing guy who is going to sign off on this.

If they think they can fix what is clearly a hardware/sensor issue with an MCAS software update must live in dreamland.

But , tja, we live in an IT is GOD period.

This is clearly a HARDWARE issue, the software is secondary.
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Old 14th Mar 2019, 14:54
  #175 (permalink)  
 
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Originally Posted by gums View Post
Salute!

Thank you Ridges.

The MAX would not meet the applicable requirement in "Part 25" for control force/command per AoA ( several reputable references). The controls got "lighter" at high AoA whether banking or not. Whether the plane would have kept increasing AoA all by itself without moving the yoke, we'd have to ask one of the cert test pilots or evaluators.

Personal opinion is 1) new type cert with basic aerodynamic characteristics meeting the requirement without kludge add-on crapola like STS and MCAS 2) If FAA buys off on the kludge MCAS, then at least smooth the thing out and have some warning that it is acting and not STS. Good grief, 10 seconds of down trim and moving the stab over 2 degrees? Sheesh. Sure, if I was a "trim-aholic" I could beep nose up after one second of uncommanded nose down trim and keep doing it every 5 seconds. I could also ascribe the uncommanded trim to the STS, just as the previous crew in Indonesia accident sequence did. That crew may not have realized they even had MCAS installed, and simply turned off the electric trim motor, used the wheel and flew on. Oh yeah, no clear AoA failure indication and the single point failure and ......

Gums sends...
You do realize there is kludge on crapola in virtually every airliner flying today.
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Old 14th Mar 2019, 15:25
  #176 (permalink)  
 
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Salute Salvi !!!

I would laugh, but this is a sad time for commercial flying, and I have a hard time not screaming and throwing things.

Only time I was ever surprised in peacetime flying when something happened was when one leading edge flap folcded up but I could keep going straight ahead and finally got the sucker around to land it. Well, I did have a reversed aileron-rudder interconnect wire connection in the VooDoo one day over a decade before , but the nose moving opposite the roll command is an easy one to detect.

Gums....
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Old 14th Mar 2019, 15:46
  #177 (permalink)  
 
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Regarding how to ' handle' faulty sensors re inertial/GPS systems

See pages 40 and 41 on 787 v 777 features. One wonders why such was not incorporated in MAX ?

http://www.ata-divisions.org/S_TD/pd...ngtheB-787.pdf

•Calculated from angle of attack and inertial data
-AOA –voted dual sensors plus inertial data
-Accurate Coefficient of Lift (CL)
-Airplane Mass from FMC -Validated after Takeoff
•Algorithm developed for enhanced stall protection
•Avoid displaying data known to be bad
-Loss of valid voted VCAS
= Display synthetic airspeed VSYN
-Loss of valid voted PSTATIC= Display GPS altitude
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Old 14th Mar 2019, 16:41
  #178 (permalink)  
 
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AOA from inertial data?

Originally Posted by CONSO View Post
-AOA –voted dual sensors plus inertial data
This keeps coming up... I don't understand how inertial data can tell you anything about AOA, unless you make the assumption that the air outside the aircraft is stationary with respect to the inertial frame of reference, which seems like a particularly bad assumption to make.

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Old 14th Mar 2019, 16:57
  #179 (permalink)  
 
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Originally Posted by Gauges and Dials View Post
This keeps coming up... I don't understand how inertial data can tell you anything about AOA, unless you make the assumption that the air outside the aircraft is stationary with respect to the inertial frame of reference, which seems like a particularly bad assumption to make.
Click on the link in the post you quoted from. It doesn't say what you think it does.
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Old 14th Mar 2019, 16:58
  #180 (permalink)  
 
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Originally Posted by Gauges and Dials View Post
This keeps coming up... I don't understand how inertial data can tell you anything about AOA, unless you make the assumption that the air outside the aircraft is stationary with respect to the inertial frame of reference, which seems like a particularly bad assumption to make.
Possibly using pitch rate information to smooth and/or interpolate the sensor readings? The IVSI does something like that.
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