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-   -   MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures (https://www.pprune.org/rumours-news/621879-max-s-return-delayed-faa-reevaluation-737-safety-procedures.html)

OldnGrounded 24th May 2019 21:52

MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
 
Just published on WSJ site:

MAX’s Return to Flight Delayed by FAA’s Reevaluation of Safety Procedures for Older 737 Models

The agency is considering changes in how pilots are trained to respond when the flight-control computer or other systems erroneously push the plane’s nose down

FORT WORTH, Texas—A review of Boeing Co.’s 737 MAX jets has expanded to include emergency procedures used by pilots on earlier 737 models, further delaying the MAX’s return to service, according to U.S. government officials.

The Federal Aviation Administration hasn’t questioned the safety of older jets currently in service, these officials said, but the broadened review has become a significant factor in adding months to the time expected to get the grounded fleet of 737 MAX jets back in the air.

hans brinker 24th May 2019 22:04


Originally Posted by OldnGrounded (Post 10478950)
Just published on WSJ site:

MAX’s Return to Flight Delayed by FAA’s Reevaluation of Safety Procedures for Older 737 Models

The agency is considering changes in how pilots are trained to respond when the flight-control computer or other systems erroneously push the plane’s nose down

FORT WORTH, Texas—A review of Boeing Co.’s 737 MAX jets has expanded to include emergency procedures used by pilots on earlier 737 models, further delaying the MAX’s return to service, according to U.S. government officials.

The Federal Aviation Administration hasn’t questioned the safety of older jets currently in service, these officials said, but the broadened review has become a significant factor in adding months to the time expected to get the grounded fleet of 737 MAX jets back in the air.

It is about time. There is no difference between the NG and the MAX in manual trim, so if the pilots were unable to manually trim in the last crash, they wouldn't have been able to trim in any of the 6500 B737s flying.

Loose rivets 24th May 2019 22:11

I know it's too late now, but just why is the H-stabilizer not hinged at the front?

It would take a long lever arm to reach the jack-screw, but it is doable within existing confines.

b1lanc 24th May 2019 23:19


Originally Posted by hans brinker (Post 10478960)
It is about time. There is no difference between the NG and the MAX in manual trim, so if the pilots were unable to manually trim in the last crash, they wouldn't have been able to trim in any of the 6500 B737s flying.

So what you are saying is that all pre-Max versions of the 737 are unsafe? I don't think that is what the 'article' is implying. Has there ever been a non-Max 737 crash caused by inability of the crew to trim the horizontal stab?

kiwi grey 25th May 2019 01:33


Originally Posted by b1lanc (Post 10479002)
So what you are saying is that all pre-Max versions of the 737 are unsafe? I don't think that is what the 'article' is implying. Has there ever been a non-Max 737 crash caused by inability of the crew to trim the horizontal stab?

No, only the NGs.
As I understand it:
  1. the manual trim wheels were reduced in size from Classic to NG, making them harder to turn (less mechanical advantage)
  2. the trimmable horizontal stabiliser size was increased from Classic to NG, but the elevators were not proportionally increased, reducing the relative authority of the elevators; and
  3. the information about the 'bunt and wind the trim wheel' trim recovery technique disappeared from documentation and training syllabi for the NG
The Classics were properly certificated as safe, by the standards of the day

MemberBerry 25th May 2019 02:07

About "safe" vs "unsafe", many people like to divide things as "black" or "white", but usually reality consists of shades of gray.

Statistically previous versions are clearly safer. A stabilizer runaway that would bring the aircraft in a situation similar to that of the two crashed MAXes is much less likely in previous versions. That is enough to make them safer even with everything else being equal.

But there is no question that previous versions are susceptible to similar issues when electric trim is inoperable and the aircraft is severely out of trim. It was even documented in the manuals.

ProPax 25th May 2019 03:17


Originally Posted by MemberBerry (Post 10479048)
About "safe" vs "unsafe", many people like to divide things as "black" or "white", but usually reality consists of shades of gray.

In fact, ALL people divide safe and unsafe as black and white. Either the manufacturer guarantees that the plane will be safe and pilots in full control till the plane is disembarked at the gate, or it is unsafe. For the same reason the pregnancy test only has two indications. You cannot be "slightly pregnant".


hans brinker 25th May 2019 03:55


Originally Posted by b1lanc (Post 10479002)
So what you are saying is that all pre-Max versions of the 737 are unsafe? I don't think that is what the 'article' is implying. Has there ever been a non-Max 737 crash caused by inability of the crew to trim the horizontal stab?

Just because it hasn’t caused a crash doesn’t mean it’s okay. After the A330/QF72, the Iberia Bilbao crash, the DLH Bilbao incident Airbus changed the programming/procedures to prevent these things from happening again. None of these had any fatalities, but it was enough to change things. Two B737s have crashed, in both the runaway trim part was caused by something new, but it seems likely at least one crew was unable to manually trim the aircraft before they left the envelope. There have been several videos of sim sessions showing just how hard it is to manually trim once you get very AND and high speed. These were in NG sims, and Boeing has just admitted the sims underscore the severity. I think Boeing should at least reconsider the procedure where you always switch both trim switches off, and rewire the max back to the NG way, so pilots have the electric manual trim option without the automatic electric trim.

yarpos 25th May 2019 04:06

" So what you are saying is that all pre-Max versions of the 737 are unsafe? "

So, that was very Cathy Newman

fdr 25th May 2019 04:36


Originally Posted by yarpos (Post 10479073)
" So what you are saying is that all pre-Max versions of the 737 are unsafe? "

The Max8 MCAS debacle has exposed inadequacies in the certification standards. The NG is different to the Classics, however the MCAS shows that if the aircraft encounters conditions that place it out of trim substantially, then handling that is not being trained, and airspace etc is needed in order to recover. The NG/Max has a greater potential problem due the the design change from the Classic, but none of these aircraft, and likely many other Part 25 aircraft can enter conditions that unloading of the stab could be required, the certification standard does not give protection from all possible conditions, just the level as specified.


SMT Member 25th May 2019 07:56

And yet, Boeing are still telling us the aim is to have the aircraft back in the air by end June, or roughly a month from now. They might twist the arm of the FAA sufficiently to achieve that in the US, but I have serious doubt the grounding will be lifted anywhere else by that time.

MemberBerry 25th May 2019 12:08


Originally Posted by ProPax (Post 10479061)
In fact, ALL people divide safe and unsafe as black and white. Either the manufacturer guarantees that the plane will be safe and pilots in full control till the plane is disembarked at the gate, or it is unsafe. For the same reason the pregnancy test only has two indications. You cannot be "slightly pregnant".

I disagree. Safe/safer/safest. You can clearly compare safety levels, so safety is a continuum. I could even argue that this continuum is multidimensional, but for simplicity let's assume it's unidimensional.

In any case, you can't guarantee with 100% certainty that "the plane will be safe and pilots in full control till the plane is disembarked at the gate". At most you could guarantee that, statistically, 99.9999999% of the time it will happen.

But, indeed, while subjective, as demonstrated by the FAA being the last to ground the MAX, there are two distinct conditions: either the aircraft should be allowed to fly, or it should not. Meaning that it's either "safe enough to fly", or "not safe enough to fly". From a legal point of view that would be called "airworthy" vs "not airworthy".

According to Wikipedia:


Airworthiness is defined in JSP553 Military Airworthiness Regulations (2006) Edition 1 Change 5 as:

The ability of an aircraft or other airborne equipment or system to operate without significant hazard to aircrew, ground crew, passengers (where relevant) or to the general public over which such airborne systems are flown

This definition applies equally to civil and military aircraft. However, military aviation despite being governed by regulations, this is performed in a less standardized and more fragmented way as compared to civil aviation.

An example of a method used to delineate "significant hazard" is a risk reduction technique used by the military and used widely throughout engineering known as ALARP (As Low As Reasonably Practicable). This is defined as:

‘The principle, used in the application of the Health and Safety at Work Act, that safety should be improved beyond the baseline criteria so far as is reasonably practicable. A risk is ALARP when it has been demonstrated that the cost of any further Risk reduction, where cost includes the loss of capability as well as financial or other resource costs, is grossly disproportionate to the benefit obtained from that Risk reduction.’
The key point is "without significant hazard". You can't completely eliminate risks. The only question is if the risks are acceptable or unacceptable, in relation to the cost of reducing them further.

Anyway, that's enough semantics for me. And no, I don't even want to open the pregnancy can of worms.

b1lanc 25th May 2019 13:09


Originally Posted by hans brinker (Post 10479071)

There have been several videos of sim sessions showing just how hard it is to manually trim once you get very AND and high speed. These were in NG sims, and Boeing has just admitted the sims underscore the severity. I think Boeing should at least reconsider the procedure where you always switch both trim switches off, and rewire the max back to the NG way, so pilots have the electric manual trim option without the automatic electric trim.

I've seen the videos and manual trim on the NG is just about impossible at higher speeds. But there is a subsequent procedure to unload the force on the stab to allow pilots to regain the ability to manually trim and allow some elevator authority (assuming sufficient altitude and trim isn't jammed). I agree with the last sentence, however. That change was not well thought out.

b1lanc 25th May 2019 13:14


Originally Posted by SMT Member (Post 10479150)
And yet, Boeing are still telling us the aim is to have the aircraft back in the air by end June, or roughly a month from now. They might twist the arm of the FAA sufficiently to achieve that in the US, but I have serious doubt the grounding will be lifted anywhere else by that time.

Hard to believe that will happen given that United for one just cancelled their Max flights into August. Also, 150 hour per Max for a fix seems like more than a software upgrade.

LowObservable 25th May 2019 13:42

Safety, for the passenger, is always relative and a matter of perception. I have been regular SLF since 1974, in which year there were 11 major losses including the THY Paris crash, the first 747 loss, two Pan Am 707s and a TWA bombing. To take a SWAG, with today's traffic and aircraft sizes, such a mishap rate would see a crash every week with an average of ~200 fatalities.

That's been the result of both improved engineering, better training in sims, and better understanding of flying practices (CRM), among other things.

As for perception: I believe the passenger expects the flight to be safe. I'm estimating that most people in the flying public have never lost a family member or an acquaintance in a public-transport aviation mishap. They may not be consciously aware of how much safety has improved (perhaps because of the prominence given to protection against terrorist attack), but it would be unwise at this point to underestimate the impact of the MAX accidents: two closely related accidents, with large loss of life, hitting the same aircraft type within months of its introduction.

Chas2019 25th May 2019 13:56


Originally Posted by OldnGrounded (Post 10478950)
Just published on WSJ site:

MAX’s Return to Flight Delayed by FAA’s Reevaluation of Safety Procedures for Older 737 Models

The agency is considering changes in how pilots are trained to respond when the flight-control computer or other systems erroneously push the plane’s nose down

FORT WORTH, Texas—A review of Boeing Co.’s 737 MAX jets has expanded to include emergency procedures used by pilots on earlier 737 models, further delaying the MAX’s return to service, according to U.S. government officials.

The Federal Aviation Administration hasn’t questioned the safety of older jets currently in service, these officials said, but the broadened review has become a significant factor in adding months to the time expected to get the grounded fleet of 737 MAX jets back in the air.

if that is what it takes to prevent future crashes then it is justified.

capngrog 25th May 2019 14:12


Originally Posted by ProPax (Post 10479061)
In fact, ALL people divide safe and unsafe as black and white. Either the manufacturer guarantees that the plane will be safe and pilots in full control till the plane is disembarked at the gate, or it is unsafe. For the same reason the pregnancy test only has two indications. You cannot be "slightly pregnant".

I agree that most people use the terms "safe" and "unsafe"; however, there is no such thing as "safe". "Safety" is a concept of relativity. There will always be risk in every human endeavor, ranging from "slight risk" to "severe risk", and the real world deals with risk management, not attempts to achieve absolute safety ... whatever that is. For example, walking is a relatively safe activity given normal circumstances; yet, walking on the edge of an icy precipice in a snowstorm involves more risk, requiring more caution ... hence "risk management". I could go on and on about this, but I won't.

This is just my opinion; but that opinion is based on 43 years of safety related work and accident investigation.

Cheers,
Grog

GlobalNav 25th May 2019 15:51


Originally Posted by fdr (Post 10479077)
The Max8 MCAS debacle has exposed inadequacies in the certification standards. The NG is different to the Classics, however the MCAS shows that if the aircraft encounters conditions that place it out of trim substantially, then handling that is not being trained, and airspace etc is needed in order to recover. The NG/Max has a greater potential problem due the the design change from the Classic, but none of these aircraft, and likely many other Part 25 aircraft can enter conditions that unloading of the stab could be required, the certification standard does not give protection from all possible conditions, just the level as specified.

How can you be sure the standards are inadequate? I think it’s more likely the process of delegation and signing off on compliance. If exiting standards had been complied with, this would not have happened.

yellowtriumph 25th May 2019 16:15


Originally Posted by ProPax (Post 10479061)
In fact, ALL people divide safe and unsafe as black and white. Either the manufacturer guarantees that the plane will be safe and pilots in full control till the plane is disembarked at the gate, or it is unsafe. For the same reason the pregnancy test only has two indications. You cannot be "slightly pregnant".


Point of order Mr Chairman:

https://www.rottentomatoes.com/m/a_s...y_pregnant_man

Not serious and I will now bow out again.

OldnGrounded 25th May 2019 18:57


Originally Posted by b1lanc (Post 10479311)
I've seen the videos and manual trim on the NG is just about impossible at higher speeds. But there is a subsequent procedure to unload the force on the stab to allow pilots to regain the ability to manually trim and allow some elevator authority (assuming sufficient altitude and trim isn't jammed).

Emphasis added.

Right, and the videos and reports from the sim episodes suggest that "sufficient altitude" may well be 8K feet in addition to whatever else you may need. The porpoising maneuver seems very much like a Hail Mary play, at least in many of the circumstances in which it might be seen as necessary.



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