Missed this when it first appeared:
Interesting info on the runaway procedure change, hard to see what advantage it would have other than keeping things simple at the cost of eliminating the possibility of using manual electrical trim.

And from a later post:

While relays can get stuck (welded) it is much more likely to happen as it closes due to arcing while the contacts are bouncing. The length of time in the closed position is very unlikely to be a factor.
Toggle switches are very unlikely to get stuck, especially when infrequently operated, the contacts are positively driven, not relying on a spring to open as in the case of a relay or momentary contact switches such as thumb switches on the yoke.

The previous (NG) switches had multiple paths to disable trim with the left disconnecting the main power to the motor via a (single) relay, while the right (autopilot) disabled inputs from the autopilot. The max has 2 switches in series, either of which kills the main power via the same single relay.

now that makes sense !
there's just so much mud flying around
it seems, a little clarity is very welcome 👍

Single relay!? That would seem to obviate the safety factor that the series switch modification gives. Well, at least in part. I would be horrified to learn there was truly only one point of cut off to that vital flying surface motor.

It wouldn't surprise me to learn it stayed on with a delayed opening, to avoid stop-starts as different inputs to the HStab came in quick succession.


The last relay I had fail was on a Mercedes. It left the secondary air fan on, which wrecked it as it was not continuously rated. When I finally found the darn thing the welded points took a lot of parting. In the car case the fan runs at start-up and shut down. So regular use. On the Boeing, I don't know what current that isolation relay would have to switch during (I presume) pre-flight checks. There was talk in this thread of the motor running - and the clutches choosing the driving logic. I have never found out just how long the H-Stab motor runs for during normal ops.

There is one main (3 phase) power relay to the the trim motor block, on the MAX at least it is shown feeding a AC/DC/ converter so not an inductive load.
The NG diagram has less detail in the motor block.
This relay is controlled by the cutout switches but is normally on (energized).
There are also a number of 'enable' as well as direction input shown connected to the motor block, on the NG the autopilot signals are interrupted by the right hand switch. The left switch kills power to the power relay. On MAX either switch kills power (and control inputs)..

Note both of these are labelled "functional description" so don't include all details.

Just a curious observation. The focus has been on DEP and AoA. this is understandable, as the ac in the climb.
In the first instance, the MCAS issues were first noted on ARR, (and corrected) not DEP.
From what has been reported, all pilot reports were issues on DEP....

Good questions.

I’m seeing quite a few posts of “should have done this”, “should have done that” and "I would have immediately xyz”.

When you get a stick shake during/after rotation or early in the climb out, which may or may not be associated with UAS symptoms, what are you going to do? Well, before you do anything, you need to have some idea if it is genuine or not.

How do you ascertain that? The traditional answer is performance attitudes (which we see a lot of in postings) but an aeroplane can be approaching a stall in a normal takeoff/climb attitude for many reasons, such as: strong adverse wind gradient, temperature inversion (often combined with the item before), incorrect loading, wrong flap setting, incorrect performance data and/or incorrect FMC weight/speed entries. If you leap straight into the UAS checklist at that moment, what will happen if you really *are* on the stick shake? I never tried this in the 737 sim but my gut feeling is that isn't a good place to be: on the back of the drag curve, keeping the nose high and likely take a bit of power off... Hmmm.

Remember, this is at 7,600’ASL, density altitude of nearly 9,500’ at the airport with MSAs of 14-16,000’, so close to the edge of the envelope in many respects. Some thought required before rushing into actions that may make the situation worse and that’s before MCAS rears its ugly head. Will flying the UAS pitch and power give enough of a climb gradient for terrain separation here? I can quite understand any reluctance to reduce power in this scenario, although it’s quite possible the workload was such that it didn’t get actively examined.

TL;DR If you have multiple scenarios with different required actions but similar symptoms, if you don’t do a bit of analysis first you are relying on luck...

Good question. How indeed?
For a moment or two after rotation when the stickshaker and stall warning burst out you are doubtless momentarily and firmly in the land of half-crown, threepenny bit, dustbin lid. But within a very short period of time you see TOGA thrust confirmed, airspeed/groundspeed confirmed, attitude correct and your sphincter begins to relax the dustbin lid to manageable proportions; then you see the usual huge Boeing ROC and realise the thing is flying as normal and thus the warnings must be false and the laundry-threatening event is all but over. The mere fact you're not mushing along the runway at thirty feet and 20' pitch in ground effect should tell you this. IMMEDIATELY.
Then you know the next thing to do is AIRSPEED UNRELIABLE chex. - What else fer chrissakes? WHAT tf ELSE???
If you don't - in the sim - you've just failed that check. Bombed it.
That's why we train these events in the sim, so we learn to recognise them and know better than to repeat them on the line.
I know I won't be thanked for it but it appears to me that these crews hadn't left this lesson behind in the sim.

Why?
Well, that's quite another matter...and one I suspect will become the crux of investigation in the months to come.

There can be little doubt that merely carrying out AIRSPEED UNRELIABLE chex would have pevented these accidents altogether.
(as would a number of other fundamental vital/airmanship actions too)

The more I think about this the more I see this as a training/culture/airmanship/professionalism/HF failure than anything else.
That's not to exonerate Boeing by any means, but when all else is said and done all 4 pilots had it entirely within their power and ostensibly within their training (tbc) to avoid both these accidents regardless of what the airplane seems to have done. In neither case did the airplane begin the event in anything approaching an unflyable condition, but just as in AF 447 the pilots very quickly and unnecessarily managed to put it in one through gross mishandling.

I would suggest that if a stick shaker is genuine at rotation, you wouldn't be getting airborne, you would be tail scraping your a*** down the runway. If the take-off has been normal (ie normal acceleration, rotation and lift-off at the expected distance to run, airspeed and pitch attitude) and you get a stick-shaker, it's the stick-shaker that is not normal. In which case the Airspeed Unreliable checklist is the correct procedure to follow.

Interestingly in Airbus world, they have a memory checklist procedure for Stall Warning at Lift-Off. It says to set TOGA thrust, 15° nose up and wings level, which unsurprisingly are essentially the same initial actions as their Unreliable Speed checklist. No wasting time in a time critical situation - go straight to the Power + Attitude settings that will give you the fly away from the ground Performance that you want.

If Bleve appears to have mimiced my post above it is only fair to say they were posted simultaneously.

Thanks meleagertoo. Yes simultaneous postings. Thankfully with the same message. As they say out in my part of the world: 'Happy Landings'.

Do the engines in the MAX have a time limit at TOGA?

So. Imagine for some reason you’ve cocked up the performance calculation and/or entered the wrong weights in the FMC, like EK407, maybe even not as grossly. What are you going to see? Thrust - what you intended, airspeed - as bugged, attitude - somewhere in the takeoff range. Nothing *obviously* wrong? Given differing density altitudes, runway parameters, terrain constraints, variable flap settings, ATM & fixed derates, etc. there is no “one size fits all” measure of performance these days. In a FBW aircraft, any “feel” in the controls will be based on false data.
If the crew on the BA56 had dismissed the stall warning as false, things would most likely not have gone well from then on. They had no indication that anything was amiss but they respected the stick shaker.

JK5022 is what can happen when you ignore a stall warning at low-level.

You could also say that you are training a single response to something that is much more nuanced in reality. Yes, you can pass the sim but fail dramatically in real life...

Yes possibly but that single response is a bloody starting point.

Fullwings are you a pilot?

George Glass

All good but...what you're saying is that in the case of the Birgenair crash,The Captain should have set 80% N1 and 10 degrees instead of......simply handing control to the FO whose ASI was totally functional?
IAS DISAGREE is not UAS.
We dont wish to criticize dead men.We all now know MCAS design was erroneous but that doesnt excuse a pilot from flying the plane does it now?
Some have said that establishing that the stick shaker activation was spurious was not possible and that the crew should have flown the UAS procedure.
This is not correct.
Flaps were set,takeoff power was confirmed,pitch attitude consistent with takeoff(a stable flight regime),no windshear warning,stick shaker active on Captains side only,disagree warnings are seen,FO's ASI agrees with ISFD....all point to a faulty sensor and not a real stall warning.
Its not wrong or dangerous for the Captain to retain control,set 80% N1 and fly 10 degrees but why?Why would you do that ?
In reflection,these 2 accidents are more about airmanship and crew composition than MCAS.
MCAS is stealing the headlines but actually an experienced FO would immediately say "I have control",just as the Birgenair FO should have done 23 years ago.
Rananim sends....for the last time

Yes. But it might be an ending point as well, if you are doing it for the wrong reasons. Try the UAS drill from *actually* being close to stalled and see how that goes. In the 747 incident I linked above, had they done the UAS drill instead of reducing pitch because of the stick shake, I doubt they’d be around now to talk about it.

Are you?

All I’m doing is pointing out that in a scenario which may have multiple causes and multiple recovery (or not) options, a hasty reflex action may not always work as expected. A situation with warnings, some possibly true, some possibly false is difficult to evaluate when the data you are using to make that evaluation may itself be compromised. This is just to balance the assertions that it was an “easy” recovery for the two lost 737s.

Fly the Aircraft....
 

I think what some of us are trying to say is that if you are in tune with your aircraft, it becomes apparent very quickly what kind of situation you are dealing with. Initial rotation is approximately 10 degrees. No matter what alarms are going off, if the aircraft rises into the air as it normally does then it is almost certain that you are not approaching a stall. Maintain takeoff power setting, continue rotation to 15 degrees and get some space between you and the ground. At some point later, according to preference, execute the Airspeed Unreliable procedures.

On the other hand, if the aircraft acts mushy and hovers in ground effect, then respect the stick shaker. Gingerly apply full power, carefully manage the pitch, accelerate and climb.

If a pilot puts the aircraft into the proper rotation attitude and the PIC can't tell the difference between these two situations within seconds, then, quite frankly, they are not qualified to be in that seat. People's lives are literally hanging in the balance as to whether the Captain can make this distinction.

Let me stress, however, the crew's actions in either of the MAX accidents are not necessarily because they were "bad" pilots. I do not have any personal experience with the training and operational cultures at either Ethiopian or Lion Air. If these crews were simply responding according to their training, then the scrutiny should be placed there.

I strongly suspect that there is a mismatch between the proficiency standard implicit in the aircraft design and the actual training and experience level in the field. Sadly, I think Boeing, the airlines and the certificate authorities are all aware of this mismatch, but fail to either 1) insist the aircraft design be sufficiently fault tolerant, or 2) emphasize the need for better training and deeper experience.

Icarus
"Fullwings are you a pilot?"
I have to observe, having trawled these forums for over 20 years (and knowing 'FullWings' for most of those ), that your response is typical of those who flee into a batcave when people do not seem to agree with them/worship their utterances/genuflect before them. They find, scrawled on the wall of the cave, in ancient hieroglyphics, the words 'Is u a pilut' which they then copy and paste (with spellchecker, of course) into their next post.

I can assure you that
a) 'Fullwings' is indeed a pilot
b) 'Fullwings' is very experienced in jet transport operation
c) 'Fullwings' is indeed capable of measured and logical thought processes.


Which, if any of the above, do you fit?