747Whale wrote:

Amiga500 wrote:

Except the loading on the stick (and any displacement of the stick if held with iso-Force) would be the opposite to the actions of a conventional stick nudger.

MCAS trimming the stabilizer down would increase the load on a nose down elevator - which would increase the backward force on a forward pushed control column.

You have that precisely backward, actually.

For iso-deflection, stick load increases.

For iso-Cm, stick load decreases.


Yeah, I think I have it arse about face.

OldAeroGuy wrote:

If I understand you, you're saying that the pilot is holding enough elevator that the airplane is pitching up toward stall. Correct?

No - I'm saying the aircraft has pitched/is pitching up and the pilot is pushing forward to rotate the nose down - but is not at full forward column - not that that would really matter I suppose.

edit: Doesn't matter, see above. I've got my control forces wrong way round.

I should have been thinking about SLF trimming and not flap loading at increased AoA. The pilot will see reduced stick load to generate same pitching moment as the stabilizer trims its AoA positive.

OldAeroGuy wrote:

You're describing MCAS operation with a failed AoA indicator. Normal MCAS operation is helping the pilot get out of an edge of the envelope situation. In the Lion Air case, MCAS did not jump up suddenly. It was erroneously operating continually due the AoA vane failure.

Even in full operation, it only jumps in at X deg AoA. Hence not really a substitute for something that varies proportionally from -Y deg to + Z deg AoA to match the NG curves.

OldAeroGuy wrote:

Keeping MCAS from activating when it shouldn't means having better AoA vane reliability and/or shutting down AoA signals to MCAS in case of a disagree. Stick nudgers/stick push would have exactly the same issue.

I'm not even sure if its legal at that anyway. I think they can get past 25.203 with using MCAS.

25.672 is particularly thorny and I dunno how MCAS is treated for 25.255.

They definitely need to get demonstrable failure rates to 1E-9 before they can even consider either of the above two.

Amiga500 wrote:

OldAeroGuy wrote:

You're describing MCAS operation with a failed AoA indicator. Normal MCAS operation is helping the pilot get out of an edge of the envelope situation. In the Lion Air case, MCAS did not jump up suddenly. It was erroneously operating continually due the AoA vane failure.

Even in full operation, it only jumps in at X deg AoA. Hence not really a substitute for something that varies proportionally from -Y deg to + Z deg AoA to match the NG curves.

An approximate match of NG and MAX pitch characteristics is probably fine below X deg. There is no need for a one-to-one Cm vs Alpha match between the MAX and NG in the -Y deg to +Z deg alpha range. Operational CG location variation alone will cause significant differences in Cm vs Alpha and resulting trim settings and stick forces. As I said up thread, MCAS is probably needed to cure a "stick lightening" issue present on the MAX and not the NG. That's probably why MCAS only cuts in at X deg.

I have some ideas on the certification arguments that were likely made for the MCAS failure modes and effects analysis as to how and why the MAX was able to comply with 25.203, 25.255 and 25.672. Obviously, the crashes invalidate some of the assumptions but I'd prefer to hear the accident reports before discussing. As always, accidents are rarely caused by a single event. There are usually several contributing factors.

Amiga500 wrote:

747Whale wrote:

Amiga500 wrote:

Except the loading on the stick (and any displacement of the stick if held with iso-Force) would be the opposite to the actions of a conventional stick nudger.

MCAS trimming the stabilizer down would increase the load on a nose down elevator - which would increase the backward force on a forward pushed control column.

You have that precisely backward, actually.

For iso-deflection, stick load increases.

For iso-Cm, stick load decreases.

Yeah, I think I have it arse about face.

Actually, having slept on it - I'm not wrong.

A conventional stick nudger will push the stick forward and push the nose down.

MCAS will push the stick back and push the nose down.

MCAS moves horizontal stab trim position.

This is probably the right place to discuss this...

https://www.cnn.com/2019/03/24/politics ... index.html

Boeing, on Saturday, had pilots from 5 different airlines visit in Renton to test in simulators the current MCAS configuration and their new software fix.

At the gathering, pilots from the three American carriers, plus two smaller non-US airlines, ran simulated flights designed to mimic the situation that brought down the Lion Air flight in Indonesia last year, using the current and updated software, according to the person briefed on the session. Each pilot using the flight simulator landed the plane safely, the person said.

In the simulations with the current MCAS software, the test pilots used existing procedures to disable the system, while test flights using the new software required less intervention from the pilots, the person said.

The fix they're implementing will now use two AOA sensor inputs and MCAS will no longer be triggered repeatedly. How exactly they intend to prevent the system from repeatedly running is unknown to me, but at least in the simulator it appears the pilots were able to overcome the situation with significantly less effort.

Amiga500 wrote:

Amiga500 wrote:

747Whale wrote:

You have that precisely backward, actually.

For iso-deflection, stick load increases.

For iso-Cm, stick load decreases.

Yeah, I think I have it arse about face.

Actually, having slept on it - I'm not wrong.

A conventional stick nudger will push the stick forward and push the nose down.

MCAS will push the stick back and push the nose down.

MCAS has no connection with the stick.

How will MCAS push the stick back?

If you mean that MCAS will push the airplane nose down and that the pilot must pull the stick back to maintain AoA, that's correct but the pilot is taking action on the stick, not MCAS.

trpmb6 wrote:

This is probably the right place to discuss this...

https://www.cnn.com/2019/03/24/politics ... index.html

Boeing, on Saturday, had pilots from 5 different airlines visit in Renton to test in simulators the current MCAS configuration and their new software fix.

At the gathering, pilots from the three American carriers, plus two smaller non-US airlines, ran simulated flights designed to mimic the situation that brought down the Lion Air flight in Indonesia last year, using the current and updated software, according to the person briefed on the session. Each pilot using the flight simulator landed the plane safely, the person said.

In the simulations with the current MCAS software, the test pilots used existing procedures to disable the system, while test flights using the new software required less intervention from the pilots, the person said.

The fix they're implementing will now use two AOA sensor inputs and MCAS will no longer be triggered repeatedly. How exactly they intend to prevent the system from repeatedly running is unknown to me, but at least in the simulator it appears the pilots were able to overcome the situation with significantly less effort.

I suspect that an AoA sensor disagree will disable MCAS.

OldAeroGuy wrote:

MCAS has no connection with the stick.

How will MCAS push the stick back?

As the stabiliser increases its AoA, then the loading on the elevator increases accordingly (for a constant elevator deflection). This will manifest in the cockpit as an increase in stick loading.

While MCAS has no direct connection with the stick - the aerodynamic load changes induced by MCAS most definitely will be connected with the stick.


[Of course, as stabiliser increases AoA, H-stab lift increases, so the pilot may be able to slack off their push on the control column - but that obviously is not replicating the actions of a stick pusher.]

OldAeroGuy wrote:

trpmb6 wrote:

The fix they're implementing will now use two AOA sensor inputs and MCAS will no longer be triggered repeatedly. How exactly they intend to prevent the system from repeatedly running is unknown to me, but at least in the simulator it appears the pilots were able to overcome the situation with significantly less effort.

I suspect that an AoA sensor disagree will disable MCAS.

I feel as if we are running in circles - or maybe it's just me.
At the very moment you most need additional help with an anti-stall device (MCAS), it is taken away from you.

In the "good old days" proper aircraft design gave you help without any drama because benign stall behaviour was built in from scratch. Some aircraft would pretty much sort themselves out without the pilot doing anything.

Wikipedia wrote:

Piston-engined and early jet transports had very good stall behaviour with pre-stall buffet warning and, if ignored, a straight nose-drop for a natural recovery.

Wing developments that came with the introduction of turbo-prop engines introduced unacceptable stall behaviour. Leading-edge developments on high-lift wings and the introduction of rear-mounted engines and high-set tailplanes on the next generation of jet transports also introduced unacceptable stall behaviour.

I accept Wikipedia has somewhat simplified matters, but if we accept that the 737NG already has "unacceptable stall behaviour", then the MAX without MCAS can only be worse. And Boeing are now showcasing pilot training to expect the real possibility of flying the MAX without a functioning MCAS.

This is not making a safe plane safer.

It's not even maintaining par with the NG.

Yes, the MAX with new improved full-disclosure MCAS v2.0™ will most of the time be safer than the aircraft our grandfathers risked their lives in, but is that enough?

SheikhDjibouti wrote:

This is not making a safe plane safer.

It's not even maintaining par with the NG.

Yes, the MAX with new improved full-disclosure MCAS v2.0™ will most of the time be safer than the aircraft our grandfathers risked their lives in, but is that enough?

OK, so, please first provide a definition of "safe enough" ( in quantifiable terms).

Who says the 737NG has "unacceptable stall behavior" ? The demonstrated accident rate over several decades of service ?

Amiga500 wrote:

OldAeroGuy wrote:

MCAS has no connection with the stick.

How will MCAS push the stick back?

As the stabiliser increases its AoA, then the loading on the elevator increases accordingly (for a constant elevator deflection). This will manifest in the cockpit as an increase in stick loading.

While MCAS has no direct connection with the stick - the aerodynamic load changes induced by MCAS most definitely will be connected with the stick.


[Of course, as stabiliser increases AoA, H-stab lift increases, so the pilot may be able to slack off their push on the control column - but that obviously is not replicating the actions of a stick pusher.]

I think you need to re-think your whole premise.

The reason the MCAS is on the airplane is to increase stick pull force to maintain or increase AoA.

If MCAS were to decrease stick pull force to maintain or increase AoA, it would amplify the problem its incorporation is meant to solve.

You should drop this line of thinking, it's totally offbase.

stephanwintner wrote:

SheikhDjibouti wrote:

This is not making a safe plane safer.

It's not even maintaining par with the NG.

Yes, the MAX with new improved full-disclosure MCAS v2.0™ will most of the time be safer than the aircraft our grandfathers risked their lives in, but is that enough?

OK, so, please first provide a definition of "safe enough" ( in quantifiable terms).

Who says the 737NG has "unacceptable stall behavior" ? The demonstrated accident rate over several decades of service ?

To answer your two questions;
1) Certainly not; I was the one asking if that was enough; it is up to respondents to answer that in the context of their own definition.
2) Who says? - read the quote box in my post above - it gives the necessary attribution.

BTW I wrote behaviour (with a "u") to mimic the original article. If you are going to quote me, do try to be accurate.

Here is another quote from the same source;

For example, first generation jet transports have been described as having an immaculate nose drop at the stall.

Loss of lift on one wing is acceptable as long as the roll, including during stall recovery, doesn't exceed about 20 degrees, or in turning flight the roll shall not exceed 90 degrees bank. If pre-stall warning followed by nose drop and limited wing drop are naturally not present or are deemed to be unacceptably marginal by an Airworthiness authority the stalling behaviour has to be made good enough with airframe modifications or devices such as a stick shaker and pusher. These are described in "Warning and safety devices".

If you want more, ask D.P.Davies (GalaxyFlyer's hero) and Brian Trubshaw (if I need to explain who he is, it's not worth it)

SheikhDjibouti wrote:

OldAeroGuy wrote:

I suspect that an AoA sensor disagree will disable MCAS.

I feel as if we are running in circles - or maybe it's just me.
At the very moment you most need additional help with an anti-stall device (MCAS), it is taken away from you.

In the "good old days" proper aircraft design gave you help without any drama because benign stall behaviour was built in from scratch. Some aircraft would pretty much sort themselves out without the pilot doing anything.

....but if we accept that the 737NG already has "unacceptable stall behaviour", then the MAX without MCAS can only be worse. And Boeing are now showcasing pilot training to expect the real possibility of flying the MAX without a functioning MCAS.

This is not making a safe plane safer.

It's not even maintaining par with the NG.

Yes, the MAX with new improved full-disclosure MCAS v2.0™ will most of the time be safer than the aircraft our grandfathers risked their lives in, but is that enough?

The problem is that we haven't been in the "good old days" for quite some time. As I discussed up thread, swept wing airplane stall characteristics are often "unacceptable" from a handling characteristics standpoint. Systems are often added to improve stall characteristics.

The 757 with the leading edge slat in the takeoff position has unpleasant stall characteristics that are uncertifiable from both a stick lightening and roll off characteristics. The solution was to develop an "auto slat" for the airplane. For an AoA near stick shaker operation, the slat will move from the takeoff position to the landing position. With the slat in the landing position, stalls are benign.

The system is single threaded as a failure of the slat system actuator will keep the slat form moving. So why was this acceptable to both FAA and the JAA (EASA's ancestor)? It was a combination of these factors:

1) While stalls in the takeoff position were unpleasant and uncertifiable, they were safe. In fact, operational stall speeds were developed with takeoff slat positions even though landing slats would have lower takeoff speeds. The single thread nature of the "auto slat" prevented use of the lower stall speeds.

2) The "auto slat" failure rate is low.

3) In service stall encounters are rare.

4) The joint failure rate of the "auto slat" and stalling is in the "improbable" range and if the "improbable" event occurs, the airplane is safe.

The reason I think disabling MCAS for an AoA vane disagree would be acceptable is based on similar reasoning.

1) Unaugmented Flaps Up 737 MAX stall handling behavior is uncertifiable but safe.

2) AoA vane failure rate should be low.

3) In service stall encounters are rare.

4) The joint failure rate of an AoA vane and stalling should be in the "improbable" range and if the "improbable" event occurs, the airplane is safe. In other words, if there is an AoA vane disagree and MCAS shuts down and the airplane stalls, airplane handling during stall approach will not meet the certification standard but the airplane is stable (ie safe). Realistically, if the failed vane sets off the stick shaker when the airplane is not near stall, the pilots will be very reluctant to get the airplane in a stalling situation. This situation will be reinforced if the pilots are notified of the vane disagree.

In summary, a solution that shuts down MCAS for a vane disagree should be acceptable for normal operation if vane failures are acceptably low.

Vane failure rates are for the 737 MAX are a huge part of the ongoing mystery. I suspect that the current implied vane failure rates have blown holes in a number of failure mode and effects analysis.

For a historic note on "auto slats", they were used to improve maneuver capability on both the Bf109 and the F-86.

trpmb6 wrote:

https://www.cnn.com/2019/03/24/politics/boeing-software-737-max/index.html

Boeing, on Saturday, had pilots from 5 different airlines visit in Renton to test in simulators the current MCAS configuration and their new software fix.
...

The fix they're implementing will now use two AOA sensor inputs and MCAS will no longer be triggered repeatedly. How exactly they intend to prevent the system from repeatedly running is unknown to me, but at least in the simulator it appears the pilots were able to overcome the situation with significantly less effort.

A small step for Boeing, but not a giant leap for certification in EASA, CAAC, CAA, etc., even if the FAA re-certifies. I predict the MAX is given a new type certification by authorities outside the US, if it can be certified at all outside the US. "New type" reasoning: deactive MCAS and the MAX does not handle like an NG, therefore a different type. "No re-certification" reasoning: "huge fan hung forward" has inherent instability issues that MCAS attempts to reduce, but does not solve. Does Boeing lower the nacelles and lengthen the LG, or spend the money on NSA?

Making MCAS single instance, vs. repetitive, is a trivial task: gear-up, count one instance, disarm until next gear up. The danger zone is during take-off, based on the two crashes.

WPvsMW wrote:

"No re-certification" reasoning: "huge fan hung forward" has inherent instability issues that MCAS attempts to reduce, but does not solve.

Do you have any data to support this statement?

Remember the engine doesn't change position when the flaps are down. If the engine position is "inherently unstable", why isn't MCAS used when the flaps are down?

HaulSudson wrote:

strfyr51 wrote:

HaulSudson wrote:

Wonder how much people like 747whale get paid by Boeing to spam and derail conversations.

747 Whale is exactly RIGHT! if the system had cut out? The Pilot might have recovered the airplane. NO system should override the Pilot's input! And if that was the case?
Then WHY have a pilot at ALL?

My math skills are insufficient to calculate the number of times you are contradicting yourself - in merely six sentences with randomly dropped exclamation and question marks.

But perhaps that's exactly the idea behind derailing conversations. Keep up the good work.

Give it a Break will you? What are you? An English teacher? You don't like the Narrative? Attack the Poster?
Do you or do you NOT have any technical "chops"?? I happen to KNOW the Airplane and airplane systems in particular!! No I wasn't an English major.
But I took many classes in technical writing in my Aviation maintenance Management Undergrad degree. We had to..

OldAeroGuy wrote:

WPvsMW wrote:

"No re-certification" reasoning: "huge fan hung forward" has inherent instability issues that MCAS attempts to reduce, but does not solve.

Do you have any data to support this statement?

Remember the engine doesn't change position when the flaps are down. If the engine position is "inherently unstable", why isn't MCAS used when the flaps are down?

For a discussion of the aerodynamics, see viewtopic.php?f=5&t=1418079
No published data TMK. The issue of "inherent instability" in is the context of approaching the critical AOA... and in recovery from stalls. Both crashes involved stalls and failure to recover from those stalls. Adding AOA sensors doesn't change the aerodynamics of the upper nacelle putting the wing in the shadow of the upper nacelle at the critical AOA, inducing a stall (the basic difference in critical AOA in the MAX vs. the NG... MAX nacelle's disrupting wing lift nose up, and the nacelle itself providing lift approaching the critical AOA, for which MCAS ver. 1 was a kludge). My point is that certification authorities outside the US will scrutinize whether MCAS ver. 2 solves the problem, or there is a supervening aerodynamics problem approaching, at, and above the critical AOA.

SheikhDjibouti wrote:

stephanwintner wrote:

SheikhDjibouti wrote:

This is not making a safe plane safer.

It's not even maintaining par with the NG.

Yes, the MAX with new improved full-disclosure MCAS v2.0™ will most of the time be safer than the aircraft our grandfathers risked their lives in, but is that enough?

OK, so, please first provide a definition of "safe enough" ( in quantifiable terms).

Who says the 737NG has "unacceptable stall behavior" ? The demonstrated accident rate over several decades of service ?

To answer your two questions;
1) Certainly not; I was the one asking if that was enough; it is up to respondents to answer that in the context of their own definition.
2) Who says? - read the quote box in my post above - it gives the necessary attribution.

BTW I wrote behaviour (with a "u") to mimic the original article. If you are going to quote me, do try to be accurate.

Here is another quote from the same source;

For example, first generation jet transports have been described as having an immaculate nose drop at the stall.

Loss of lift on one wing is acceptable as long as the roll, including during stall recovery, doesn't exceed about 20 degrees, or in turning flight the roll shall not exceed 90 degrees bank. If pre-stall warning followed by nose drop and limited wing drop are naturally not present or are deemed to be unacceptably marginal by an Airworthiness authority the stalling behaviour has to be made good enough with airframe modifications or devices such as a stick shaker and pusher. These are described in "Warning and safety devices".

If you want more, ask D.P.Davies (GalaxyFlyer's hero) and Brian Trubshaw (if I need to explain who he is, it's not worth it)

You seem to have missed the point. I'll try again. The demonstrated accident rate over several decades of service says that at the end of the day, the 737NG has fairly reasonable stall characteristics.

stephanwintner wrote:

You seem to have missed the point. I'll try again. The demonstrated accident rate over several decades of service says that at the end of the day, the 737NG has fairly reasonable stall characteristics.

No it doesn't.

(I am so tempted to leave it there...)

But I'm feeling overly generous today, so you're in luck.

Ask yourself how many times has the average airline pilot stalled his (or her) 737?
Either with, or without passengers on board?
Or even whilst safely on the ground in a simulator?

In all it's 50 years of service, basically there are only two kinds of pilots that have ever actually stalled a 737 in flight.
a) Boeing test pilots
b) Airline pilots who left a big hole in the ground

There might possibly be a very small group of others who survived such a rare encounter, easily identified by their ash-white complexion, grey hairs, and tell-tale nervous twitch.

The excellent safety record of the 737 is made up of all those pilots who reacted quickly enough to prevent a stall from happening in the first place.

But... it is easier to put a MAX in the coffin corner than an NG... thus MCAS ver. 1.

WPvsMW wrote:

trpmb6 wrote:

https://www.cnn.com/2019/03/24/politics/boeing-software-737-max/index.html

Boeing, on Saturday, had pilots from 5 different airlines visit in Renton to test in simulators the current MCAS configuration and their new software fix.
...

The fix they're implementing will now use two AOA sensor inputs and MCAS will no longer be triggered repeatedly. How exactly they intend to prevent the system from repeatedly running is unknown to me, but at least in the simulator it appears the pilots were able to overcome the situation with significantly less effort.

A small step for Boeing, but not a giant leap for certification in EASA, CAAC, CAA, etc., even if the FAA re-certifies. I predict the MAX is given a new type certification by authorities outside the US, if it can be certified at all outside the US. "New type" reasoning: deactive MCAS and the MAX does not handle like an NG, therefore a different type. "No re-certification" reasoning: "huge fan hung forward" has inherent instability issues that MCAS attempts to reduce, but does not solve. Does Boeing lower the nacelles and lengthen the LG, or spend the money on NSA?

Making MCAS single instance, vs. repetitive, is a trivial task: gear-up, count one instance, disarm until next gear up. The danger zone is during take-off, based on the two crashes.

they're going to reprogram the Flight control computers. and use inputs from BOTH angle of attack sensors. ( a no brainer as no single sensor should ever take sway over pilot input) The AOA is advisory at best and may be disabled if the Heating system should fail. I've changed many of them during my career for the heater failing although I've never seen a double failure on the same airplane.

All good, but maybe not enough to avoid being a new type. Compared to the NG, the critical AOA is probably different, and shift in C/L around the critical AOA likewise. Boeing's numbers and arguments face an uphill battle outside the US. We wait and see.

Sadly reminiscent of the rudder design flaw in the B732 and B733. Thousands of uneventful operations, then fatal crashes for UA, US, and other operators.

WPvsMW wrote:

OldAeroGuy wrote:

WPvsMW wrote:

"No re-certification" reasoning: "huge fan hung forward" has inherent instability issues that MCAS attempts to reduce, but does not solve.

Do you have any data to support this statement?

Remember the engine doesn't change position when the flaps are down. If the engine position is "inherently unstable", why isn't MCAS used when the flaps are down?

For a discussion of the aerodynamics, see viewtopic.php?f=5&t=1418079
No published data TMK. The issue of "inherent instability" in is the context of approaching the critical AOA... and in recovery from stalls. Both crashes involved stalls and failure to recover from those stalls. Adding AOA sensors doesn't change the aerodynamics of the upper nacelle putting the wing in the shadow of the upper nacelle at the critical AOA, inducing a stall (the basic difference in critical AOA in the MAX vs. the NG... MAX nacelle's disrupting wing lift nose up, and the nacelle itself providing lift approaching the critical AOA, for which MCAS ver. 1 was a kludge). My point is that certification authorities outside the US will scrutinize whether MCAS ver. 2 solves the problem, or there is a supervening aerodynamics problem approaching, at, and above the critical AOA.

There is absolutely no evidence that either of these accidents involved a stall. Stall recovery was not a factor in the Lion Air accident and I suspect that it wasn't in Ethiopian either. Unwanted MCAS inputs due to a spurious AoA vane output appears to be a primary cause for the Lion Air crash but the airplane did not stall. Please review the known facts before going down erroneous paths.

There is also no data that shows that the MAX is unstable. A region of reduced stability and "stick lightening" for Flaps Up is certainly possible but I sincerely doubt that Boeing test pilots would have accepted or the FAA would have certified an airplane that was unstable during a stall with a low gain augmentation system like MCAS. And I'm sure that EASA would not have done so. EASA typically sends an evaluation pilot for a 737 MAX type certification and that pilot would have wanted to see stalls with MCAS on and off.

The reports should clarify whether there were or were not stalls, and whether MCAS, an anti-stall system, was active and detected a non-existent stall in ET 302.

We know MCAS detected a stall in JT610, erroneously. After the first of 26 interventions of MCAS in JT610,
https://www.seattletimes.com/business/b ... ol-system/
was there one or more stalls? The report may clarify that, but from the flight path....

Ditto on ET302. Boeing would not like the French agency to report Flaps 1 (or whatever) and MCAS not active during takeoff and climb, which is entirely possible.
https://aviation.stackexchange.com/ques ... -on-a-b737

SheikhDjibouti wrote:

In all it's 50 years of service, basically there are only two kinds of pilots that have ever actually stalled a 737 in flight.
a) Boeing test pilots
b) Airline pilots who left a big hole in the ground

There might possibly be a very small group of others who survived such a rare encounter, easily identified by their ash-white complexion, grey hairs, and tell-tale nervous twitch.

The excellent safety record of the 737 is made up of all those pilots who reacted quickly enough to prevent a stall from happening in the first place.

I realize you're being facetious but many other pilots have stalled 737's over the years. They include:

- FAA test pilots

- UK-CAA test pilots including the aforementioned Capt. Davies. As a newly minted engineer, I sat in a post flight test and listened to his ideas about 737-200 stall handling. The takeoff configurations were modified satisfactorily and he allowed certification to proceed.

- JAA test pilots

- EASA test pilots

- Airline line pilots who didn't leave a smoking hole after stalling.

The 737 has probably been stalled (intentional and unintentional) more than any other commercial airplane since there are so many of them.

With regard to safety, if we compare the 737NG with the A320 family, we find:

Hull Losses
737NG: 0.17 per million departures
A320 Family: 0.21 per million departures

Hull Losses with Fatalities
737NG: 0.08 per million departures
A320 Family: 0.10 per million departures

Source: http://www.boeing.com/resources/boeingd ... tatsum.pdf

The 737NG stall characteristics you're maligning don't seem to have put it at a significant disadvantage compared to an airplane that can't be stalled in normal operation.

WPvsMW wrote:

The reports should clarify whether there were or were not stalls, and whether MCAS, an anti-stall system, was active and detected a non-existent stall in ET 302.

We know MCAS detected a stall in JT610, erroneously. After the first of 26 interventions of MCAS in JT610,
https://www.seattletimes.com/business/b ... ol-system/
was there one or more stalls? The report may clarify that, but from the flight path....

Ditto on ET302. Boeing would not like the French agency to report Flaps 1 (or whatever) and MCAS not active during takeoff and climb, which is entirely possible.
https://aviation.stackexchange.com/ques ... -on-a-b737

The DFDR trace for JT610 is shown in this link. Please point out where the airplane stalled. If the airplane had actually stalled, one would think both stick shakers would have been triggered.

https://leehamnews.com/wp-content/uploa ... otated.png

As you say, we'll have to wait for the ET302 traces.

and for both reports.

I appreciate your posts, OldAeroGuy.

OldAeroGuy wrote:

I think you need to re-think your whole premise.

The reason the MCAS is on the airplane is to increase stick pull force to maintain or increase AoA.

If MCAS were to decrease stick pull force to maintain or increase AoA, it would amplify the problem its incorporation is meant to solve.

You should drop this line of thinking, it's totally offbase.

I'm not talking about pulling on the stick though (I agree with you - it would increase pull forced required to maintain/increase AoA - but note it would decrease pull force for consistent elevator deflection)

When pushing on the stick, MCAS activation would feedback as a centering reaction on the stick.

That is not the action of a stick pusher.


MCAS is on the aeroplane because control authority is marginal at high AoA.

The trimming reason is largely a red herring. If Boeing were seeking to equalise stick load for MAX vs. NG, the appropriate solution would be a continuously intervening system - not something activating at a threshold AoA that then needs manual retrim by the pilot when out of the high AoA zone.

OldAeroGuy wrote:

There is absolutely no evidence that either of these accidents involved a stall. Stall recovery was not a factor in the Lion Air accident and I suspect that it wasn't in Ethiopian either.

Indeed. The problem is more likely to be at the other end of the spectrum - overspeed and blowback.

OldAeroGuy wrote:

A region of reduced stability and "stick lightening" for Flaps Up is certainly possible but I sincerely doubt that Boeing test pilots would have accepted or the FAA would have certified an airplane that was unstable during a stall with a low gain augmentation system like MCAS. And I'm sure that EASA would not have done so. EASA typically sends an evaluation pilot for a 737 MAX type certification and that pilot would have wanted to see stalls with MCAS on and off.

Hopefully that is the case.

Amiga500 wrote:

I'm not talking about pulling on the stick though (I agree with you - it would increase pull forced required to maintain/increase AoA - but note it would decrease pull force for consistent elevator deflection)

When pushing on the stick, MCAS activation would feedback as a centering reaction on the stick.

That is not the action of a stick pusher.

No, it's more like a stick nudger that gently increases stick force required to hold or increase AoA. A pusher would apply enough force to make it very difficult for the pilot to hold the stick in an aft position.

Amiga500 wrote:

MCAS is on the aeroplane because control authority is marginal at high AoA.

No, there seems to be plenty of control at high AoA Flaps Up. The problem is that the MAX appears to have reduced stability at high AoA. The terms "stability" and "control" are not interchangeable. MCAS makes the airplane seem more stable at high AoA by increasing stick forces to increase AoA.

Amiga500 wrote:

If Boeing were seeking to equalise stick load for MAX vs. NG, the appropriate solution would be a continuously intervening system - not something activating at a threshold AoA that then needs manual retrim by the pilot when out of the high AoA zone.

As the MAX vs NG stick force mis-match only occurs at high AoA, MCAS is only needed at high AoA.

OldAeroGuy wrote:

SheikhDjibouti wrote:

In all it's 50 years of service, basically there are only two kinds of pilots that have ever actually stalled a 737 in flight.
a) Boeing test pilots
b) Airline pilots who left a big hole in the ground

There might possibly be a very small group of others who survived such a rare encounter, easily identified by their ash-white complexion, grey hairs, and tell-tale nervous twitch.

The excellent safety record of the 737 is made up of all those pilots who reacted quickly enough to prevent a stall from happening in the first place.

I realize you're being facetious but many other pilots have stalled 737's over the years.

Yes, I most certainly exaggerated the point in order to emphasize the last sentence about prevention. I'm grateful that you took it in good humor, and also for providing much appreciated additional clarification.

The 737NG stall characteristics you're maligning don't seem to have put it at a significant disadvantage compared to an airplane that can't be stalled in normal operation.

True, but that isn't how the FAA see it. For them, stall characteristics are a key element, and hence MCAS!

In normal operations, stalls are avoided. Of the safety records you referred to, how many incidents involved a stall at any point?

Hull Losses
737NG: 0.17 per million departures
A320 Family: 0.21 per million departures

And behind that data? Statistics are wonderful things but....
In the case of the A320, the data you show equates to 35 documented hull-losses.
I was able to positively identify 27 of these in order to attribute a cause. With more time I could probably identify the remaining eight too.

One was at an airshow, 3 were incidents that happened on the ground, 3 were terrorism, 1 was pilot suicide

There were 5 CFIT (one due to a pilot ignoring pull up 21 times, another due to no GPWS fitted, two were TOGA/pilot error)

There were five runway over-runs, and six runway undershoots (often due to windshear)

I don't see stalling as being a factor in any of the above.

And finally we come to potential stall situations - just two. TWO !
AirAsia QZ8501 - non-critical rudder malfunction, pilot error, STALL, splashdown.
And I've saved the best until last;
GXL888T, a test flight with 3 pilots, 3 engineers, and a member of NZ CAA.
During flight testing (with frozen / damaged AoA sensors), they STALLED the a/c whilst exploring low speed handling.
They were too low, too slow, and too late.

So ¼ of the stats are barely relevant to aircraft type.
Nearly half occurred on or near the runway.
And just two referenced an actual stall condition.

Unless you want to include "stalling" after a windshear incident on final approach, stalling just doesn't feature significantly in the numbers you or the previous poster quoted. From that, one could argue that stalling characteristics are not relevant for airline operations; but as I said earlier, that is something you can argue with the FAA.

Oh, and I nearly forgot Sully landing in the Hudson River.

But adding him in with all the other dubious incidents gives 0.21 incidents per million and makes it "worse" than the 0.17 for the 737NG(¹)

Don't you just love statistics?
I think they're great, but they do require sensible interpretation.

(¹) Do I need to add that the "0.17" for the NG also includes plenty of dubious occurrences? Hopefully not, but this is a.net....

Here's part of the FAA's side of the story.

https://aviationweek.com/commercial-avi ... 8db64f6e8c

SheikhDjibouti wrote:

In all it's 50 years of service, basically there are only two kinds of pilots that have ever actually stalled a 737 in flight.
a) Boeing test pilots
b) Airline pilots who left a big hole in the ground

Bullshit.

There have been numerous stalls in Boeing aircraft, in all boeing aircraft; I'm aware of a number of them. You speak as though the aircraft will fall out of the sky, or that a stall or high angle of attack condition is certain death.

Rubbish.

SheikhDjibouti wrote:

In all it's 50 years of service, basically there are only two kinds of pilots that have ever actually stalled a 737 in flight.
a) Boeing test pilots
b) Airline pilots who left a big hole in the ground

747Whale wrote:

Bullshit.

There have been numerous stalls in Boeing aircraft, in all boeing aircraft; I'm aware of a number of them. You speak as though the aircraft will fall out of the sky, or that a stall or high angle of attack condition is certain death.

Rubbish.

I'm so grateful that you took it in good humor, and also for providing much appreciated additional clarification.
Oh wait, that reply was for somebody else.....

Within the past hour I posted a comment about an A320 that was stalled during a handover test flight, killing three pilots, three engineers, and a CAA inspector, so yes, I am aware that stalling occurs. I am also aware that some years ago full stall training was omitted from normal training in transport category aircraft because it was deemed too dangerous.

Wally Moran, in 2011 wrote:

Full stalls are required training by the FAR’s for pre solo students but are never mentioned again unless one trains to be a CFI.

Airline pilots don’t get the benefit of doing full stalls either. Air line pilots are taught to recover at the activation of the stall warning. So it is possible for an airline pilot to fly their entire career without ever actually stalling the plane.

And here is APS commenting on revised FAA rules for stall training (in simulators)
https://apstraining.com/faa-improvement ... he-future/

APS, 2013 wrote:

Regulations are being changed to require simulators to accurately represent aircraft behavior all the way to a full aerodynamic stall in the future (to be introduced circa 2018?)

In order to transition from the present policy of recovering only from initial indications or warnings of a stall to teaching pilots recovery from fully stalled flight, simulator enhancements are required.

Regarding actual in-flight training;

Because the proper technique of stall recovery is rarely aircraft-specific, it is possible to train for full stall recovery in an aircraft that may be different from a Transport Category airline aircraft which is certainly not designed for safety in the stall training regime.

So if regular airline pilots only ever practice stall training in a Cessna 172, when exactly do they meet it in a 737?

It can only be whilst in service with passengers on board, and as such I would have expected to hear more about these instances if they occur as often as your expletives suggest.

Feel free to come up with more than your "I'm aware of a number of them". And what exactly does that mean anyway - I've read books by test pilots too. You don't specify where or when this happened, and maybe you rub shoulders with pilots who do this almost daily. If so, that's great, but I want to know about Joe Average.

Have a nice day.

OldAeroGuy wrote:

No, there seems to be plenty of control at high AoA Flaps Up. The problem is that the MAX appears to have reduced stability at high AoA. The terms "stability" and "control" are not interchangeable. MCAS makes the airplane seem more stable at high AoA by increasing stick forces to increase AoA.

Yeah, wasn't really caring for being a stickler on definitions.
MCAS will improve gust stability and pitch down control authority - but the latter *may* not be required (and I remain to be convinced on that).


But of course, that leaves the question - what would happen a 737 if the trim function has broke and it got into a high alpha state? Might not end well.

OldAeroGuy wrote:

As the MAX vs NG stick force mis-match only occurs at high AoA, MCAS is only needed at high AoA.

I should have drawn attention to *a* threshold AoA.

It doesn't blend in (beyond the ~0.3deg/sec implementation time), it just happens at X AoA - rather than introducing itself proportionally from Y to Z deg alpha.

SheikhDjibouti wrote:

SheikhDjibouti wrote:

I am also aware that some years ago full stall training was omitted from normal training in transport category aircraft because it was deemed too dangerous.

As stall training is done in a simulator, then you're probably aware that simulator training isn't dangerous.

You're also doubtless aware that current standards for stall training include full aerodynamic stalls.

Amiga500 wrote:

But of course, that leaves the question - what would happen a 737 if the trim function has broke and it got into a high alpha state? Might not end well.

That's what pilots are for.

OldAeroGuy wrote:

SheikhDjibouti wrote:

In all it's 50 years of service, basically there are only two kinds of pilots that have ever actually stalled a 737 in flight.
a) Boeing test pilots
b) Airline pilots who left a big hole in the ground

There might possibly be a very small group of others who survived such a rare encounter, easily identified by their ash-white complexion, grey hairs, and tell-tale nervous twitch.

The excellent safety record of the 737 is made up of all those pilots who reacted quickly enough to prevent a stall from happening in the first place.

I realize you're being facetious but many other pilots have stalled 737's over the years. They include:

- FAA test pilots

- UK-CAA test pilots including the aforementioned Capt. Davies. As a newly minted engineer, I sat in a post flight test and listened to his ideas about 737-200 stall handling. The takeoff configurations were modified satisfactorily and he allowed certification to proceed.

- JAA test pilots

- EASA test pilots

- Airline line pilots who didn't leave a smoking hole after stalling.

The 737 has probably been stalled (intentional and unintentional) more than any other commercial airplane since there are so many of them.

With regard to safety, if we compare the 737NG with the A320 family, we find:

Hull Losses
737NG: 0.17 per million departures
A320 Family: 0.21 per million departures

Hull Losses with Fatalities
737NG: 0.08 per million departures
A320 Family: 0.10 per million departures

Source: http://www.boeing.com/resources/boeingd ... tatsum.pdf

The 737NG stall characteristics you're maligning don't seem to have put it at a significant disadvantage compared to an airplane that can't be stalled in normal operation.

Agreed, my point exactly.

I'd also argue that handling characteristics as an aircraft nears stall, thus allowing skilled pilots to sense and avoid one, are just as significant as post-stall characteristics. That includes the various control systems, stick shakers, and so forth. If, as alleged, very few pilots have actually stalled the aircraft unintentionally - well that's precisely the point, actually. Whether stalls were successfully recovered from, or avoided in the first place, or perhaps never even closely approached, are all indicative of "fairly reasonable stall characteristics".

747Whale wrote:

That's what pilots are for.

Aye, thats an idea.... sure weren't the control systems of the Fokker Eindecker and B.E.2 perfectly adequate.


What have we been doing this past century trying to make flying safer?

Quite a lot, in case you. missed it. Including pilot training which has become better, more accurate, and more technologically advanced.

Systems such as MCAS are there in the event the pilot does not do his or her job, but the pilot is there to prevent the high alpha condition in the first place.

When all else is said and done, it comes down to the pilot.

stratclub wrote:

Something I was curious about is that I thought read that MCAS only becomes operational at flaps full up. So if the MCAS autotrim issue didn't become obvious until flaps Zero, wouldn't have been prudent to return to flaps one airspeed permitting? I could see after the single AOA input issues is redesigned, training and airlines oversight by each countries version of the FAA would be a big part of the fix.

You have to make the connection ( and have speed low enough to .. )
With zero knowledge about MCAS this is not a shallow solution.

stratclub wrote:

WIederling wrote:

stratclub wrote:

Something I was curious about is that I thought read that MCAS only becomes operational at flaps full up. So if the MCAS autotrim issue didn't become obvious until flaps Zero, wouldn't have been prudent to return to flaps one airspeed permitting? I could see after the single AOA input issues is redesigned, training and airlines oversight by each countries version of the FAA would be a big part of the fix.

You have to make the connection ( and have speed low enough to .. )
With zero knowledge about MCAS this is not a shallow solution.

Could you explain your reply? If you don't know anything about MCAS why did you respond? What do you mean by shallow solution??? The solution I eluded to is probably exactly what the FAA, Boeing and the airlines will do. I would imagine after analysis some software changes will be Made to MCAS as well. Boeing designed the thing even though there is a lot of work to be done they certainly are very capable to come up with a solution that is proven to be safe. The FAA will certainly be all over this with a high power microscope.

I would still like to know if what I read about the flaps being in position 1 or greater does inhibit MCAS and if it would have been prudent to go back to flaps 1 from flaps zero, airspeed permitting, to take MCAS out of the picture and still have electric trim still available.

When something goes wrong you go back to the last thing you did and if the aircraft started auto down trimming immediately after going to flaps zero,wouldn't you go back to flaps 1 because it was the last flight config that wasn't trying kill them? If they had known about MCAS my guess would have been they probably would have.

Also, where does the PFD synoptic get it's data from? An AOA or some other data source(s)?

should make a stronger effort when replying to posters.

we were talking about the crew in the relevant situation.
( But you knew that, ? )

WIederling wrote:

With zero knowledge about MCAS this is not a shallow solution.

I think Wlederling was trying to say, "If a pilot has zero knowledge about MCAS this is not an obvious solution."

For NNES (non-native English speakers), "literal translation" from a mother tongue create gotchas like this.

stratclub wrote:

I would still like to know if what I read about the flaps being in position 1 or greater does inhibit MCAS and if it would have been prudent to go back to flaps 1 from flaps zero, airspeed permitting, to take MCAS out of the picture and still have electric trim still available.

According to Boeing, yes. FCOM excerpts at
https://aviation.stackexchange.com/ques ... -and-max-9
and
http://www.b737.org.uk/mcas.htm
"MCAS was therefore introduced to give an automatic nose down stabilizer input during steep turns with elevated load factors (high AoA) and during flaps up flight at airspeeds approaching stall."

and layman's summary at
https://theaircurrent.com/aviation-safe ... cas-jt610/

stratclub wrote:

Something I was curious about is that I thought read that MCAS only becomes operational at flaps full up. So if the MCAS autotrim issue didn't become obvious until flaps Zero, wouldn't have been prudent to return to flaps one airspeed permitting? I could see after the single AOA input issues is redesigned, training and airlines oversight by each countries version of the FAA would be a big part of the fix.

If a problem occurs immediately with a configuration change, then yes, go back to the previous configuration. In the case of MCAS, however, the change occurs at a slow rate, and does not manifest until some time later, especially in the case of mis management with multiple runs of MCAS stab trim action. Accordingly, associating the out of trim condition with the flap retraction might be more difficult.

What is very apparent, however, is stab trim movement. When stab trim motion occurs during autoflight, excess motion is met with a trim in motion clacker, as well as a visual indication of the trim wheels. Any trim motion that's not pilot commanded when the autopilot is not engaged should be cause for immediate notice, and the solution to stop that is the same regardless of the cause; the cutoff switches.

In the case of MCAS movement, the stab trim can still be set by the pilot to a desired position, which has the dual effect of retrimming and stopping MCAS operation. A period of inactivity follows before the next MCAS activation, providing time to reassess, and cutoff, or if an actual high angle of attack condition exists, take corrective action .

We know that ET had the latest sims, and the ET pilots had been trained on MCAS. The CA, if not the very junior FO, should have made an immediate decision to cut off stab trim, if in fact MCAS had activated... which is still unknown. MCAS had to be a front and center in the mind of every MAX pilot after the LT 610 crash.