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.

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.

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.

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

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.

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".

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

So, that was very Cathy Newman

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.

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.

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:

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.

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.

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.

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.

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

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

Point of order Mr Chairman:

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

Not serious and I will now bow out again.

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.

From where I am sitting (1A, please) safety is not a continuum. It's not even a line. It's a dot where all those lines cross. What you're saying does make sense, but only as politics. Or, God forbid, policy. The law cannot scope all possible variables, of which aviation has a lot. But as long as safety is the priority for all parties involved, it's a very small dot in the universe.
If the engineer is absolutely sure he's done everything in his power and to his knowledge to make the plane safe, there is no continuum for him. He may have missed something that is impossible to check or even unknown (who knew you can't fly next to a volcano before BA9), and it very well may be the deciding factor in disembarking at the gate, but he should be sure he's done his part. The pilot must be sure he has full control of the aircraft and its systems. There should be no surprises for him, and he must have enough time to react to variables, be it a memory recall or an FCOM expedition. And for the passenger safety is an even smaller dot - will I be alive after the plane comes to a stop on the ground?

Everything else, the laws, the standards, the policies, is just politics, or worse, semantics. Bottom line that I hope everyone here agrees - if a plane is too expensive to be made safe, it mustn't fly.

Agreed. However in this particular case, you are walking on the edge of an icy precipice in a snowstorm while the weather forecast says sunshine and issues no warning about the precipice or it being icy. And you are pulling a sled with 200 people who rely on you to get them home safely. And the CEO of the weather forecast says it's absolutely safe because the Weather Supervisor allowed him to do that.

In you 43 years of safety investigations haven't you come to the conclusion that safety cannot exist if the people who are supposed to observe a system's safety don't understand the system or don't know it exists?

Despite the quirky website address the moonofalabama article is both interesting and well written. Hard to argue the 737 NG is not 'safe' given it's track record, but Boeing (and the FAA) will struggle to explain how they got to this place: 'We made the stabiliser bigger, which increased the loads it could generate, and made the trim wheel smaller, so it was harder to turn. And then deleted the procedure that told you how to use the trim wheel at high loads.'

Since I don't have any experience on other jetliners than the 737, can someone explain how trim runaways are sorted out on aircrafts that doesn't have a trim wheel at all. Personally I think that trim runaways happens so rarely, that once it's eliminated that MCAS can't trim full nose down anymore, I would not be to worried anymore to get on a MAX plane.

FBW planes like A320 and newer and B777 and newer have much more redundancy like several FCC with several channels each continuously comparing their output with each other, possibly more than one motor driving the jack screw, more than one signal path to the motors etc. In sum this makes it exceedingly unlikely that a runaway can happen. Think at how unlikely it is to loose both engines over water far from nearest airport on a two engine aircraft. It is not guaranteed it can never happen, but the likelyhood of it happening is so exceedingly small that the risk is deemed acceptable.

Edit: On FBW aircraft like the A320 there is no significant force required to hold say full aft stick, so less physically demanding compared to the B737 where a pilot might need to use all his force just to hold against a badly mistrimmed stabilizer. Further the elevator on say the A320 is much larger as a percentage of the stabilizer so the elevator has significantly more authority to hold against a badly mistrimmed stabilizer. In sum all these differences make the B737 much more demanding to controll when the stabilizer get significantly out of trim, and the likelyhood of it running away is probably also much larger.

FRogge, you then might find that the following runaway incident report is interesting.
It's a FBW airplane, of course.
Ultimately, the cause is linked to an incorrect safety risk assessment (again).

One of the manufacturer's responses was to put a button that disconnects the automation.

https://www.bea.aero/uploads/tx_elyd...0525.en_01.pdf

MCAS is not runaway stab. MCAS kicks in under certain conditions, MCAS was a solution for those conditions, and those conditions remain to be dealt with.

Currently, the ac has 2 sensors, one of which is used for STS and MCAS. The results a faulty or damaged AoA sensor initiated MCAS.
On the NG, the stab switches could cutoff AP and Elec stab control separately. Currently, the MAX stab switches cut off the electric stab control entirely, leaving the crew to manually trim the aircraft.
Given that it appears that in both cases, the AoA was damaged, it looks like the crew will be manually trimming the ac for the rest of the flight. That is not realistic.
Adding an AoA disagree light, so what? Changing the switches back to NG config...okay, then again, if one AoA is gone or damaged....
Adding a 3rd AoA vane, damn near impossible.
The underlying reasons and conditions MCAS was added in first place.

While it doesnt happen that often (until MCAS) when it did, it exposed the issues with the MAX AND the NG...
The "roller coaster" hasnt been in the manual since the -200 with a different stab/elev config.
Extending flying on manual trim with no AoA or limited, yet another lost art?

All adds up to a real big mess that a "software fix" is but a small part.

That is true. But the roller coaster method of regaining partial manual stabilizer control certainly is effective in the Boeing 737 Classic simulators despite nothing in the FCTM that specifically states how it is done. It is alluded to by the FCTM statement "In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming" The roller coaster method is designed to do just that.

Accident investigators must understand all factors involved in an accident, and reaching that understanding is the point of the investigation. Accident investigators begin the process from a point of relative ignorance and, must maintain a rather steep learning curve, hopefully resulting in an understanding of the circumstances/factors of the accident. These circumstances/factors range primarily from hardware, to software, to the human element and many others; however, nobody is expert or even conversant in the intricacies of all aspects of modern technology, hence such procedures as the "Party to the Investigation" system utilized by the NTSB (USA) and others. The "Party" system employed by the NTSB, for example, relies heavily upon outside expertise, and the NTSB Investigators themselves have their specialties such as "Power Plant", Weather", "Structures", "ATC" etc. As you suggested in your above statement, to reach an understanding of complex factors in an investigation, requires the input of many competent individuals.

Cheers,
Grog

I'm sure I read in an initial report of the Ethiopian accident, the crew left/forgot to reduce power after takeoff. Whatever any MCAS problems, leaving full power on until you make a hole in the ground is not good practice?

One must remember that the 737 was a "certified" aircraft, and so was supposed to be trimmable at any speed within the flight envelope.
So there is nothing wrong with leaving full thrust with a stickshaker alarm at takeoff.

Duly warned and briefed pilots experienced great difficulties in the sim when confronted with the same scenario.
Even though nothing was at stakes, they say they had their hands full with dealing with the recovery and fighting tunnel vision.

What with a real unexpected alarm in a real aiplane with no previous briefing ?
And remember, the "certified" 737 was supposed to be hand trimmable at the time.

Only now do we know Boeing "autocertified" their airplanes, and there are suspicions of trim difficulties on the MAX as well as the NG.

Totally aggree with above, while leaveing power up was not ideal it was not a cause of inability to trim, snip from a post in other thread:

Known facts from, report.
Airspeed at start of first MCAS input 250 kts.
MCAS applied 9 seconds ND trim the ET pilot applied 3 seconds NU trim 6 seconds later.
MCAS acitvated 5 seconds after that but was interrupted at 6 seconds by 9 seconds NU trim. (possibly interrupted by trim cutout)

Total MCAS 15 seconds ND total pilot NU 12 seconds left the aircraft severely out of trim and just under VMO in under 40 seconds and likely unrecoverable using manual/mechanical trim.

Remember the trim works at two speeds too. The pilots can command a slow speed trim with flaps up and fast with flaps not up. MCAS works at fast speed I believe? 9 seconds at full speed and 3 seconds back at half speed wouldn't end well....

This was exactly the argument used for the Nimrod MR2 until 14 aircrew were killed by a latent airworthiness problem that had not manifested to the point where it had been recognised in the previous 25 years. (Yes, the number of aircraft and hours flown were a couple of orders of magnitude different but it's the same logic.) As ever, it's the combination of unforeseen circumstances that are the killer but if the manufacturer had foreseen and ignored, you have a very different equation.

there's still the issue if MCAS is disabled under certain circumstances. how can the MAX meet the certification requirement about consistently increasing forces on the Yoke as the aircraft approaches a stall, which seems a very desirable attribute!

And the liability/fraud issue about the Boeing paperwork that stated MCAS authority would be limited to 0.4 units, thus justifying much less scrutiny and code that wasn't level 1, then actually allowing it 2.5 units of authority? It would be even worse if it was found that B deliberately wrote in 0.4 to get it passed under the radar whilst knowing/having a good guess it would need much much more in actual use. That counts as gaming the regulator.

G

Of course, in the classic.

The NG has a larger stab, and a smaller elevator....

What is the procedure for this configuration?

It appears the FAA has finally caught up, and well,

the lazy B has been caught.

In reality, I am far over this ****. The aircraft industry is held back by all of the bull**** regulations, that when you read them, are so old, dont relate, or are so vague to be unusable.
New designs and technology are hampered by attempts to fit into 1950s capabilities, (or abused by compliance)

If you want to let the aviation business really soar, fix the regulatory process to allow technology to expand as a NEW FN system, rather than a legacy bull**** system. FK the " its the same and no new training is required or type" It is not....

I would much rather be trained on a new fightdeck capabilities, and the intricacies of the AP, than they tell me it is the same as a -700 or -800, FK an iPAD and I am cert'd, and expect me to react when the FN nose points down......

I WANT to know the differences, I WANT to know when the **** hits the fan, what I need to do about it. This bull**** about hand flying the aircraft, is becoming just that, bull****.
The MTOW and thrust alone between these variants should tell someone with "experience' that it just doesnt work that way anymore...

They also put a damper in there as well because there was also a new trim motor.

International Skeptics Forum - View Single Post - [Ed] 737 Max Crashes (was Shutdown caused Boeing crash.)

The elevator has stayed the same size on every 737 variant as the size of the stab gradually grew.