|
At what altitude? Since the aerodynamic effects differ with air density. |
AF447 is another example where sensor failure produced a cascade of faults where the crew did not find a way to recover.
The flight computers dependent on these sensors can add to the confusion with unsuitable outputs. |
Originally Posted by ST Dog
(Post 10580896)
Maximum? Within the normal flight envelope or at the edges (or even beyond) of the certified envelope? Just to Vmo or all the way to Vne? At what altitude? Since the aerodynamic effects differ with air density. |
Getting the 737 Max flying again will require Boeing to make its MCAS system less confusing for pilots
Points
|
Assumptions Used in the Safety Assessment Process and the Effects of Multiple Alerts and Indications on Pilot Performance
https://www.ntsb.gov/investigations/...ts/ASR1901.pdf |
[QUOTE=Longtimer;10581169]when the new MCAS anti-stall software kicks in.....[QUOTE]
I guess it doesn't matter how many times it's been stated: MCAS is not an anti-stall system. But what do I know with all these experts around.... |
[QUOTE=wrench1;10581188][QUOTE=Longtimer;10581169]when the new MCAS anti-stall software kicks in.....
I guess it doesn't matter how many times it's been stated: MCAS is not an anti-stall system. But what do I know with all these experts around.... Doesn't matter how many times it's been stated... its still fundimentally there to prevent a stall.... if people see something that walks like a duck , quacks, and ****s all over the place , they gonna say "there's a duck" . We all know that "not an anti-stall system" was and is word play for certification purposes. It does not reflect the reality of an agressive primary control movement in response to a high AOI. It works against any re-establishment of trust to continue the charade. |
Rather scathing NYT article today..
https://www.nytimes.com/2019/09/26/b...sultPosition=1 |
Originally Posted by Octane
(Post 10581231)
Rather scathing NYT article today..
https://www.nytimes.com/2019/09/26/b...sultPosition=1 (Paraphrased) "Boeing did not realize that all the alarms might cause some crews to not carry out the perfectly reasonable and functional standard emergency procedure" But on one level I agree with them. I do not think nearly enough emphasis is put on the need to eliminate erroneous alarms and the direct part these play in many accidents. and as long as we are continuing the fiction that MCAS exists only as pilot feedback then it also can be considered an alarm. |
https://www.nytimes.com/2019/09/26/b...sultPosition=1
The National Transportation Safety Board said Thursday that Boeing made faulty assumptions during the development of its 737 Max jet.CreditCreditRuth Fremson/The New York Times By Natalie Kitroeff · Sept. 26, 2019 A monthslong federal investigation into Boeing’s 737 Max plane has called into question some of the most fundamental assumptions used by manufacturers and regulators when certifying aircraft, and challenged Boeing’s repeated assertions that pilots should have been able to easily handle a malfunction on its jet. The National Transportation Safety Board, which released the results of its review of potential lapses in the design and approval of the 737 Max on Thursday, faulted the company for making erroneous assumptions during the development of the jet and pushed for broader changes in the way airplanes are certified. The agency said Boeing had underestimated the effect that a malfunction of new automated software in the aircraft could have on the environment in the cockpit. When activated, the system, known as MCAS, automatically moves the Max’s tail and pushes its nose down. The system contributed to two crashes in less than five months that killed 346 people and caused regulators around the world to ground the plane. Boeing did not fully inform pilots about how MCAS functioned until after the first accident. The safety board calls for Boeing and federal regulators to revamp the way they assess the risk of key systems on airplanes, by giving more weight to how a cacophony of alerts could affect pilots’ responses to emergencies. The safety board’s suggestions are not binding, but the Federal Aviation Administration has accepted the vast majority of its recommendations in the past. In conversations with airlines and aviation unions following the crashes, Boeing executives said that the accidents could have been avoided if pilots had simply run a standard emergency procedure. But officials with the safety board suggested that Boeing was too confident the average pilot could easily recover the plane in that situation, because the company had not considered the chaos that ensued inside the cockpit. Dennis Tajer, the spokesman for the American Airlines pilots union, agreed with the investigators. “They completely discounted the human factor component, the startle effect, the tsunami of alerts in a system that we had no knowledge of that was powerful, relentless and terrifying in the end,” Mr. Tajer said of Boeing. Boeing continues to grapple with fallout from the two fatal crashes. The Max remains grounded, as the company and federal regulators face multiple federal investigations into how the plane was built and certified in the first place. In a meeting last month, Boeing struggled to answer a raft of questions from international regulators and the F.A.A. about a software fix it has been working on to make the plane safer. Two investigators handled the bulk of the work for the N.T.S.B., reviewing thousands of pages of documents, interviewing officials at Boeing and the F.A.A. and studying black-box data from the two crashes, in Indonesia and Ethiopia. They focused on MCAS, which sent both planes into nose dives. When Boeing developed the Max, it assumed that if MCAS activated erroneously, pilots would immediately react by performing a standard emergency procedure. But the company had tested the possibility of an MCAS failure only in isolation, failing to account for just how chaotic the cockpit would become when the activation caused other malfunctions. On the doomed Lion Air and Ethiopian Airlines flights, a faulty sensor triggered MCAS, which produced a cascading number of warnings that may have overwhelmed the pilots. “They did not look at all the potential flight deck alerts and indications the pilots might face,” said Dana Schulze, the director of the Office of Aviation Safety at the safety board. “Multiple alerts and indications have been shown through years of research to have potentially an impact where pilots will not respond as perhaps you might have intended.” Ms. Schulze said the agency would like the F.A.A. to review Boeing’s safety assessment of MCAS before allowing the plane to fly again. The plane is grounded while Boeing works on the software update and other changes intended to make it safer. The safety board recommended that the F.A.A. require Boeing and other manufacturers to consider the effect of multiple cockpit warnings when assessing how quickly pilots will respond to a malfunction. It also suggested that the agency direct plane makers to develop technology that could diagnose a problem during flight and tell pilots what procedure to follow. “We are committed to working with the F.A.A. in reviewing the N.T.S.B. recommendations,” a Boeing spokesman, Gordon Johndroe, said. An F.A.A. spokesman, Lynn Lunsford, said the agency “will carefully review these and all other recommendations as we continue our review of the proposed changes to the Boeing 737 Max.” Results of an internal review by Boeing, which its board made public on Wednesday, recommended changes to the design of cockpits and the company’s organizational structure to improve safety. The F.A.A. also continues to face criticism for its handling of the Max certification. In a hearing on Capitol Hill on Wednesday, the deputy director of the F.A.A. faced questions from senators about allegations that it misled Congress about the qualifications of inspectors who helped determine the training that pilots received. A task force composed of several international regulators is expected to submit a report this month on how the plane was certified. This week, the United States Office of Special Counsel sent a letter to President Trump and Congress saying that the F.A.A. provided incomplete information about a complaint made by a whistle-blower who claimed that inspectors at the agency weren’t fully qualified to determine pilot training on the Max. In response to a request this year by Senator Roger Wicker of Mississippi, Republican chairman of the Senate Commerce Committee, the F.A.A. said that the complaint concerned officials working on a Gulfstream aircraft, not the Max, and that it had determined that inspectors evaluating pilot training on both planes were competent. At the Wednesday hearing, top F.A.A. officials defended their comments. “Any insinuation that the F.A.A. misled Chairman Wicker in our reply to his inquiry is not what happened,” said Daniel K. Elwell, the deputy director of the agency. He called the special counsel’s allegation “simply inaccurate.” A version of this article appears in print on Sept. 27, 2019, Section B, Page 1 of the New York edition with the headline: Boeing Miscalculated Pilot Reaction, Report Says. Order Reprints Today’s Paper Subscribe |
"The accident was truly caused by the crew in both cases"
"It amounted to just a runaway trim" "There was never a reason to ground [the MAX]" "[Boeing's] largest mistake was to overestimate the quality of the pilots it was selling its airplane to" Video: CNBC interview with William Langewiesche |
Originally Posted by Speed of Sound
(Post 10580898)
The torque must have been measured (or calculated) when the original trim wheel gearing was designed. I assume that when the wheel diameter was reduced they left the rest of the system unaltered, hence the retractable handle to increase leverage |
Originally Posted by ZFT
(Post 10581281)
That handle has been a feature since the B737-100 and was also on the 707 and 727
|
Originally Posted by DaveReidUK
(Post 10581278)
"The accident was truly caused by the crew in both cases"
"It amounted to just a runaway trim" "There was never a reason to ground [the MAX]" "[Boeing's] largest mistake was to overestimate the quality of the pilots it was selling its airplane to" Video: CNBC interview with William Langewiesche Brings to mind:
That size "roman" font.. written with a camel hair brush |
Indulge me for a moment I'd like to suggest the following:- As a matter of design principle the trim wheels are intended to be able to overcome a runaway stabiliser (i.e. If the stab motor is still operating) Figure 2 of the FAA AD#2018-23-51 says "If runaway continues, hold the stabilizer trim wheel against rotation and trim the airplane manually" What this means is that the force (torque) stab motor can exert on the jackscrew must be less than that a pilot using the trim wheel is expected to be able to apply. The troubling conclusion of this might be that:- IF stab air loads are very high and, as reported, trim wheel forces so high that it is not possible for the pilot to move the stabiliser THEN the stab motor will also not be able to move the stabiliser if column switch electric trim is applied. I'm happy to be corrected but this would be a very bad place to be and might be relevant to understanding the final moments of ET302. |
Originally Posted by Europa01
(Post 10581481)
Indulge me for a moment I'd like to suggest the following:- As a matter of design principle the trim wheels are intended to be able to overcome a runaway stabiliser (i.e. If the stab motor is still operating) Figure 2 of the FAA AD#2018-23-51 says "If runaway continues, hold the stabilizer trim wheel against rotation and trim the airplane manually" What this means is that the force (torque) stab motor can exert on the jackscrew must be less than that a pilot using the trim wheel is expected to be able to apply. The troubling conclusion of this might be that:- IF stab air loads are very high and, as reported, trim wheel forces so high that it is not possible for the pilot to move the stabiliser THEN the stab motor will also not be able to move the stabiliser if column switch electric trim is applied. I'm happy to be corrected but this would be a very bad place to be and might be relevant to understanding the final moments of ET302. |
Let's assume that Boeing satisfies the several certifying bodies with the modifications made to MCAS by limiting the software's authority, providing clearer warnings, preventing repetitive activations, and reliance on multiple inputs etc.
Can the MAX be recertified without solving the issues related to the manual trim system? And how is the manual trim system handled on older versions? |
Originally Posted by Lake1952
(Post 10581515)
Can the MAX be recertified without solving the issues related to the manual trim system? And how is the manual trim system handled on older versions? |
Originally Posted by Speed of Sound
(Post 10581354)
So presumably the system has been reviewed every time there has been a change in size, shape and geometry of the HS as well as the speed at which it operates. |
Originally Posted by Busbert
(Post 10581488)
Generally there is a mechanical clutch on the input that will disengage the trim motor if there is a restriction on the mechanical input, either due to the trim wheel being held or manually operated. |
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