Civil Aviation Development & Discussion

[nandakumar]

The man versus machine (manual piloting versus fly by wire approach to piloting) debate reminds me of a joke about journalism. It goes something like this.
If one authoritative source tells you that it is raining outside and another tells you it isn't, your job as reporter is not write a story quoting both but step out to the window and ****ing see outside, if it is raining.

[chetak]

How does moving engine up produce nose-up moment, pls? I assume the engine thrust line on a 737 is located below the c.g. Such increasing thrust increases nose-up moment, I can understand that. If they moved the engine upwards (did they?) it would have reduced the nose-up moment. Confusing. No wonder the software was also confused.
What I read was that it went into an extreme yo-yo, like "Phugoid". I thought that was some kind of feedback time lag problem that caused a divergence.
The decision on cutting training cost must have been made at pretty high level. Goes completely against Boeing historic culture: Maybe they hired Airboos managers.

Engines moved up and forward. So, the distance from CG increased. Also, the engines are wider and sitting forward, so they themselves are creating lift, which becomes worse at high AoA. The ****-oid was because the pilot was fighting the nose-down trim with the nose-up elevator input.

The root cause of the entire MCAS issue on the MAX is the present 737 undercarriage and everything on the MAX MCAS problem is traceable back to this one critical fact.

The redesign of the UC, essentially by making it longer and providing more ground clearance would have solved many a problem on the 737 series including the easy fitment of the new engines for the MAX.

It was the lack of ground clearance that dictated the peculiar positioning of the new engines and the sole reason for the very conception of the MCAS system itself and that was the progenitor of all the attendant problems as well as the coverup that followed.

But the redesign of the UC was always considered as economically unviable at boeing because it would have resulted in very major structural changes in the fuselage to accommodate the longer UC, essentially almost making it a new plane altogether and requiring the horrendously expensive and also the very long certification process all over again.

In the highly competitive short haul/medium haul market segment with national pride at stake and the enormous first mover advantage in a vital market segment as also the leadership stake in aviation circles, it looks like the boeing management made a bad judgment call.

Their prime motive seems like it was all done to reduce cost of ownership as well as the cost of operations thereby hoping for more sales and more profits, just like the robber barons of yore

That said, they may have had very little options left because of airbus breathing down their necks with the Neo.

The bean counters have had a major say in this aspect of the MAX design and the AOA issue was just another f(@k up in a long line of f(@k ups in this very sordid design saga.

[sudarshan]

OK, so based on following more of this thread and rereading on the saga online, below is a list of things which I got wrong in my earlier post. My post was based on my reading of some articles immediately after the two crashes, it seems I fell for some sensationalist press at the time.

* The decision to move the engines was made by Boeing for fuel savings reasons
(Seems not to be the case, apparently some journalist got confused by the fact that Airbus was offering a more fuel-efficient design and luring a key loyal customer of Boeing, and that Boeing panicked and had to do some fast work to catch up. So this journalist seems to have interpreted the above as - "Boeing tried to achieve fuel savings by moving the engines." The real reason for moving the engines seems to have been the low ground clearance.)

* The aircraft design was "inherently unstable"
(Maybe, but it seems other civilian aircraft have been designed that way before. Was the MAX significantly more unstable than the others? Maybe, why else would they need software compensation?)

* The instability was due to the shifted CG because of the engines being moved forward
(No, CG shifts can be corrected by redistributing weight, the real instability seems to have been the creation of additional thrust moment *in some situations,* which could push the nose up - thanks, Dileep)

* The software has to permanently fight the additional instability
(Still can't figure this one out, it seems the MCAS only has intermittent work to rectify the tendency of the aircraft to go nose-up)

* There was no way to disable the software compensation
(Some reports I read seem to indicate that there was a way to disable this, that the pilots on the previous LionAir flight used this to overcome the same issue, and also reported the issue to their superiors, but that it wasn't fixed, and that only the pilots on the doomed flight did not know how to disable the software)

* Sim-training is not going to help here
(Still conflicted on this, maybe it will - especially if there's a way to disable the software, maybe it won't)

Apologies for the misinformation, will lurk more and shoot off less.

But the lack of redundancy does surprise me, the aircraft industry seems to be moving towards quad-redundancy on critical components, especially when replacing hydraulic actuators with electrical ones - since electrical actuators have a tendency to get into "hard-jams," which would be disastrous for the corresponding flight-control surface (this is not based on reading now, this is based on some actual work I did in the past, so bound to be more accurate, I think).

[chetak]

OK, so based on following more of this thread and rereading on the saga online, below is a list of things which I got wrong in my earlier post. My post was based on my reading of some articles immediately after the two crashes, it seems I fell for some sensationalist press at the time.

* The decision to move the engines was made by Boeing for fuel savings reasons
(Seems not to be the case, apparently some journalist got confused by the fact that Airbus was offering a more fuel-efficient design and luring a key loyal customer of Boeing, and that Boeing panicked and had to do some fast work to catch up. So this journalist seems to have interpreted the above as - "Boeing tried to achieve fuel savings by moving the engines." The real reason for moving the engines seems to have been the low ground clearance.)

* The aircraft design was "inherently unstable"
(Maybe, but it seems other civilian aircraft have been designed that way before. Was the MAX significantly more unstable than the others? Maybe, why else would they need software compensation?)

* The instability was due to the shifted CG because of the engines being moved forward
(No, CG shifts can be corrected by redistributing weight, the real instability seems to have been the creation of additional thrust moment *in some situations,* which could push the nose up - thanks, Dileep)

* The software has to permanently fight the additional instability
(Still can't figure this one out, it seems the MCAS only has intermittent work to rectify the tendency of the aircraft to go nose-up)

* There was no way to disable the software compensation
(Some reports I read seem to indicate that there was a way to disable this, that the pilots on the previous LionAir flight used this to overcome the same issue, and also reported the issue to their superiors, but that it wasn't fixed, and that only the pilots on the doomed flight did not know how to disable the software)

* Sim-training is not going to help here
(Still conflicted on this, maybe it will - especially if there's a way to disable the software, maybe it won't)

Apologies for the misinformation, will lurk more and shoot off less.

But the lack of redundancy does surprise me, the aircraft industry seems to be moving towards quad-redundancy on critical components, especially when replacing hydraulic actuators with electrical ones - since electrical actuators have a tendency to get into "hard-jams," which would be disastrous for the corresponding flight-control surface (this is not based on reading now, this is based on some actual work I did in the past, so bound to be more accurate, I think).

one way of inhibiting the MCAS was to extend the flaps. This may not have always been practical at all speeds.

The MCAS did not kick in so long as the flaps were not fully retracted. This was not known by many and was probably limited to the test pilot community and associated personnel at boeing and maybe the FAA too and possibly some very interested airline pilots.

[neerajb]

IMO, the huge engines were moved forward and upward to accommodate them under wing. MLG was also modified to increase ground clearance without impacting the wheel well size. This caused a pitchup tendency during high AOA and thrust situations ONLY due to engine nacelle generating extra lift which was absent in earlier models.

This pitchup tendency was not unsafe as such but would have needed more extensive certification and additional crew training which would have costed more time and money to Boeing and customers.

Boeing devised this MCAS, an additional software piece running on an existing box, which caters for this specific situation and MAKES the pilot FEEL as if he is flying an NG. Voila and you save on certification time and customers on simulator training for pilots. Only a short ipad based training was deemed sufficient.

MCAS can be turned off by trim cutoff switches which basically turns off the electric motors operating the horizontal stabilizer. There is a manual trim wheel available to both pilots to trim manually. Fortunately, just before lion air crash, another lion air max avoided crash because the pilots thought that it was trim runaway and cut off the auto trim and flew all the way trimming manually. Unfortunately the other crew didn't do this which led to the crash.

[SriKumar]

The designers and engineers won't be the ones making this decision. This is above their pay grade.

I would agree with you on this. Clearly it was a bean-counter decision to milk an extra few bucks to pull back on one sensor so airlines paid a little extra for it. Reminds of a similar story where the still missing MAlaysian airlines jet had a satellite link to locate its position continuously but it was not activated since the airlines had to pay extra for that 'feature' and MAA did not get that 'add-on'.

[Dileep]

* The decision to move the engines was made by Boeing for fuel savings reasons
(Seems not to be the case, apparently some journalist got confused by the fact that Airbus was offering a more fuel-efficient design and luring a key loyal customer of Boeing, and that Boeing panicked and had to do some fast work to catch up. So this journalist seems to have interpreted the above as - "Boeing tried to achieve fuel savings by moving the engines." The real reason for moving the engines seems to have been the low ground clearance.){and the bigger diameter engines to be introduced in MAX}

* The aircraft design was "inherently unstable"
(Maybe, but it seems other civilian aircraft have been designed that way before. Was the MAX significantly more unstable than the others? Maybe, why else would they need software compensation?){No. It was not unstable in most of the flight regimes. Only in extreme AoA cases it was unstable, for which a software compensation was built}

* The instability was due to the shifted CG because of the engines being moved forward
(No, CG shifts can be corrected by redistributing weight, the real instability seems to have been the creation of additional thrust moment *in some situations,* which could push the nose up - thanks, Dileep) {Updated as per UB Saar's sharp mind: It is the added lift because of the large engine nacelle that causes the problem.}

* The software has to permanently fight the additional instability
(Still can't figure this one out, it seems the MCAS only has intermittent work to rectify the tendency of the aircraft to go nose-up){No. It kicked in only when certain conditions met, like High AoA, high thrust or whatnot}

* There was no way to disable the software compensation
(Some reports I read seem to indicate that there was a way to disable this, that the pilots on the previous LionAir flight used this to overcome the same issue, and also reported the issue to their superiors, but that it wasn't fixed, and that only the pilots on the doomed flight did not know how to disable the software){There was no way to disable it. There was no way to indicate to the pilot that it is this darned software that push the nose down either. The only way to "disable" was the "cancer therapy". Cut power to the trim control (which MCAS uses to do the nose down action), which means pilot lost trim control as well. There is this manual "wheel" that is physically linked to the tail, which can theoretically move the trim, but it takes a lot of force to move it against the aerodynamic forces. Also, the wheel is in a position not suitable to excert a lot of force either. The Ethiopian pilots apparently did try this, but the airspeed was too high, so it didn't budge.}

* Sim-training is not going to help here
(Still conflicted on this, maybe it will - especially if there's a way to disable the software, maybe it won't)

Apologies for the misinformation, will lurk more and shoot off less.

But the lack of redundancy does surprise me, the aircraft industry seems to be moving towards quad-redundancy on critical components, especially when replacing hydraulic actuators with electrical ones - since electrical actuators have a tendency to get into "hard-jams," which would be disastrous for the corresponding flight-control surface (this is not based on reading now, this is based on some actual work I did in the past, so bound to be more accurate, I think).

[Dileep]

one way of inhibiting the MCAS was to extend the flaps. This may not have always been practical at all speeds.

Flaps will not extend if the speed is out of range. There is lot of logic that control the flaps with a number of conditions.

[chetak]

one way of inhibiting the MCAS was to extend the flaps. This may not have always been practical at all speeds.

Flaps will not extend if the speed is out of range. There is lot of logic that control the flaps with a number of conditions.

I know that and that is why I said:

"This may not have always been practical at all speeds. "

[UlanBatori]

The aspect of fuel efficiency may not have been entirely wrong: the larger diameter engine is I bet more fuel-efficient. When a plane takes off on a humid day and you look out seat 13A window, you see two vortices coming off the engine nacelle. These are roughly-speaking, "forebody vortices" and their presence shows that there is lift on the front of the nacelle, which causes pitching moment. Maybe some odd interactions with the wing as well. Long time ago, my Evil 6th coujin was told by someone v. see-near at an airplane company that shall not be named, that these days they have figured out how to make the Interference Effect of installing engines on their airliner wings, POSITIVE. i.e., more lift is added by presence of engine, than is lost because of the area of the wing where the engine is located. This is pretty crucial to getting that Lift/Drag ratio up. It is a proud achievement of airliner design. Unfortunate aspect of lift generation is that it also generates pitching moment.

Sudarshanji, NO civilian airliner will get certified in the foreseeable future if it is inherently unstable (I hope!!). But this software seems to have come close to making it that way..

The landing gear point makes sense. The whole thing was an exercise to make absolutely sure the nacelle did not hit when the landing gear shock absorber compressed during landing, I suppose. Hence the decision to not allow easy pilot override.

[hgupta]

* The aircraft design was "inherently unstable"
(Maybe, but it seems other civilian aircraft have been designed that way before. Was the MAX significantly more unstable than the others? Maybe, why else would they need software compensation?)

* The instability was due to the shifted CG because of the engines being moved forward
(No, CG shifts can be corrected by redistributing weight, the real instability seems to have been the creation of additional thrust moment *in some situations,* which could push the nose up - thanks, Dileep)

You can only do so much with redistributing weights with CG shifting. The fuel pump system could be use to redistribute weights but up to a certain extent. Otherwise, it calls for a redesign of the undercarriage. In this instance, it was a case of a bridge too far when the MAX engines were placed forward and upward and created bouts of instability that needed to be compensated with other than redistribution of the weights.

In civilian aircraft, redistribution of weights through the use of fuel pump systems is only permissible when you have different loads being placed. Of course it has limits. Do recall that horrific 747 cargo freighter crash in Afghanistan back in the 2000s when a cargo pallet broke loose and went all the way to the end of the tail and no amount of weight redistribution could account for that sudden shift of CG which led to the crash.

[nachiket]

MCAS can be turned off by trim cutoff switches which basically turns off the electric motors operating the horizontal stabilizer. There is a manual trim wheel available to both pilots to trim manually. Fortunately, just before lion air crash, another lion air max avoided crash because the pilots thought that it was trim runaway and cut off the auto trim and flew all the way trimming manually. Unfortunately the other crew didn't do this which led to the crash.

In the Ethiopian crash there were additional factors involved. I had linked a video explaining them long back on this thread.

Essentially the aircraft was flying faster than it normally would have been at that altitude for unrelated reasons. When the MCAS went haywire and started pushing the nose down, the pilots initially reacted by pulling the control column back, which was not going to work. But then they realized what was happening (probably remembered the Lion Air crash) and followed the right procedure - Using the trim cutoff switches to cut electrical power to the stabilizer trim system. This deactivates MCAS as well (or rather the MCAS inputs have no effect).

However, the stabilizer is still in nose down trim and has to be moved up manually now using the wheel in the cockpit. The pilots found that at their speed it was humanly impossible to move the stabilizer manually. The forces on it were too much to overcome using muscle power. So in desperation they turned the electrical power back on for the trim system and tried to use the switches on the control column to trim the aircraft.

But this meant that the MCAS also had control again! And it overrode their inputs and pushed the nose back down. It was too late to even try anything else at this point. They were too close to the ground.

There was no OFF switch for the MCAS itself in the cockpit. How could there be? Boeing hadn't told the pilots what the MCAS was and why it was there. Because if they had, the pilots would have required sim training to understand it.

[UlanBatori]

Moody's has downgraded Boeing stock. Kind-of late to the party (stock has lost 1/3 from its peak), or do they know something we don't?

[UlanBatori]

I have not understood why MCAS was so keen to push nose DOWN. How does that protect against nacelle striking ground? Avoiding stall as pilots try desperately to hold nose up during landing? Lost track of that line of argument.
So let's see: Larger engine on a low-slung plane (built for stylish self-deploying interior stairs in door?) with low wings. So at landing, as L/G strut compresses, nacelle bottom might strike runway.
Solution: move engine forward, maybe clear the entire fan section above the wing leading edge? If nacelle is moved forward the pitched-up attitude during touchdown prevents nacelle striking. I follow so far.
I can sense that such a thing might also cause pitch-up due to lift on nacelle at higher angle of attack. But that would be a simple simulator exercise to tell pilots that the 737MAX would have a higher dCL/d(alpha) slope at higher angles of attack, watch out as you pitch the nose up. No big deal.

Planes shake when approaching stall and pilots are auto-conditioned to push the nose down if they sense that.

Can someone pls tell why MCAS software was needed then? I lost it. Thx.

[nandakumar]

I have not understood why MCAS was so keen to push nose DOWN. How does that protect against nacelle striking ground? Avoiding stall as pilots try desperately to hold nose up during landing? Lost track of that line of argument.
So let's see: Larger engine on a low-slung plane (built for stylish self-deploying interior stairs in door?) with low wings. So at landing, as L/G strut compresses, nacelle bottom might strike runway.
Solution: move engine forward, maybe clear the entire fan section above the wing leading edge? If nacelle is moved forward the pitched-up attitude during touchdown prevents nacelle striking. I follow so far.
I can sense that such a thing might also cause pitch-up due to lift on nacelle at higher angle of attack. But that would be a simple simulator exercise to tell pilots that the 737MAX would have a higher dCL/d(alpha) slope at higher angles of attack, watch out as you pitch the nose up. No big deal.

Planes shake when approaching stall and pilots are auto-conditioned to push the nose down if they sense that.

Can someone pls tell why MCAS software was needed then? I lost it. Thx.

I am no aviation expert. But let me venture a theory. Both Boeing and Airbus have bought into this theory that computers should be able to do everything and that the pilot is a mere adornment. All aspects of aircraft design has been woven around this philosophy. So if design wise you encounter a problem the answer is to tweak the software some more. That is how you have MCAS.

[neerajb]

IMO MCAS is all about money and not safely or stall avoidance. Mcas doesn't work with flaps extended so any use cases involving landing and takeoff are ruled out.

Mcas was created to allow max to grandfather the certification from 737 NG. Boeing told regulators that max is an iteration over the earlier model, so certification was less extensive. It helped in time to market and beat the competition from a 321 neo family. Max was different from NG but not unstable or unsafe. So Boeing came up with a bandaid half baked software solution aka mcas or maneuvering characteristics augmentation system to make it fly like old one.

It had one more benefit, customer airlines would save money on pilot sim training. Mcas allowed computer based training to be sufficient for pilot conversion. Boeing played it down and didn't highlight it to even the pilots resulting in the two crashes.

Cheers....

[nachiket]

I have not understood why MCAS was so keen to push nose DOWN. How does that protect against nacelle striking ground? Avoiding stall as pilots try desperately to hold nose up during landing? Lost track of that line of argument.
.....

Can someone pls tell why MCAS software was needed then? I lost it. Thx.

UB saar, Boeing had promised that the MAX would handle exactly like the previous 737-NG. This is so that no additional simulator training was necessary and certification was faster like neeraj has said above.

The problem is that the aircraft does not handle like an NG and its stall characteristics are different because of the new engines. Boeing's answer was to build a automated system that would change the aircraft's behavior to mimic the older NG without anyone knowing about it.

[nachiket]

I am 400% sure that during the development of this system some engineers must have brought up the question "How can we let this system take input from a single AoA sensor? What happens if the sensor fails and provides incorrect data?".

But their arguments must have been brushed aside just like when the Thiokol engineers tried in vain to get the Challenger space shuttle launch postponed because the weather conditions were outside the safety limits of the seals made by Thiokol. Their arguments were brushed aside too and the shuttle blew up.

[UlanBatori]

^ Thx nachiketji. So in a nutshell, from UBCN's famed Start2Finish Inside Explanation Department (S2F - IED):
1. Boeing needed to do an end-run around Airboos and keep 1965-vintge 737 line going, so they put a bigger, more efficient engine on the 737 and called it 737MAX.
2. Bigger engine, but plane still had to operate from small airports w/o big wheeled AeroBridge or staff wheeling tall ladders etc. So ground clearance became marginal.
3. Boeing moved engine forward so that (a) it could be raised a bit with the the fan cowling part (fattest) clearing the wing and (b) being further forward, it would not hit ground at landing conditions (plane held nose up until landing gear has hit, compressed and recovered to full extension.
4. Noticed that at landing or higher AOA, the engine cowling would produce lift at its front end, and a nose-up pitching moment. Coming in for landing, that COULD cause a bit more pitchup and cause stall before the pilot was ready to stall (most planes touch down, ideally, with wheels touching JUST as plane reaches stall, but then hold the nose up a bit longer b4 nose-wheel touchdown and max reverse thrust).
5. This would require re-training pilots in simulators so they wouldn't go hop-hop at landing like I have done many times.
6. Boeing Mgrs said: "Dont b coming 2 me with complications. Just set the software so it compensates automatically and the changes are all user-transparent. NO new simulator/training time, no new manuals! Our profit margin is 6% at best of times... r u engineers With Us or Against Us, hain?
7. So!
a) they programmed it to do additional nose-down **IF** AoA was high.
b) No one cared until one din the AOA sensor went kaput and started showing 15 degrees.
c) MCAS said: HIGH AOA! ABOUT 2 STALL! DIVE!!!
d) Pilots said WTH! Pull up! and increased thrust too.
e) Smart MCAS said: U IDIOT SOOSAI PILOTS! Trying to INCREASE AOA when it says already 15 degrees!!! DIVE! DIVE!.
f) And so it went. With the response lag of a heavy airliner turning it into a steepening vertical yo-yo until it was too late. Plane was actually going at 2 deg. AOA at the start, so each nose-down made it lose altitude - and increase speed. Pilots probably increased thrust because that is also the automatic response to falling nose: increase lift. Losing battle.

So my pooch is: Why did they allow the MCAS to operate in cruise? **THAT** is the weird - and fatal - part. Should have confined its operation to landing approach after full flap deflection and l/g extension. But that is 20-20 hindsight because hey, who would imagine that an AOA sensor with no backup would actually fail, and the pilot-overriding MCAS would believe only that one sensor?

Something went wrong in their Nightmares Division deliberations. Hurry? Insuffficient testing? No Red Team Review by experienced pilots because those have all been driven out of the company? I have always wondered how they come up with the Nightmares and put in the fixes for those - for instance, the original motivator for MCAS was the high-AOA pitching moment and what might cause pilots to do. Maybe THAT part came out in their own simulator tests, but the AOA sensor failure did not occur there.

It's not very criminal, guys, Such things happen. The stupidity was allowing the "No need to tell pilots about the mod" part to become part of company policy.

******************************

Now for UBCN soosai dive:

Look: they will probably figure out brilliantly that the MCAS software was outsourced to u-no-hu, as the all-purpose "explanation". And if u look at the quality of software systems in such items of prime visibility as say, the Income Tax Preparation Tools sold to the GOI by so-called Six-Sigma experts (see my posts in the IT/ Banking threads from real experience), there is no way to point fingers at anyone else for biss-boor software standards. Bhavitavyam Bhavedeva. Can anyone convince me that the mofo "Managers" who approved those products (and keep repeating the nonsense every year) on these Prestigious Contracts of National Importance to Be Used By Hundreds of Millions of Compatriots, are any better than the ones who handle outsourced stuff from phoren?

(Ducking now as the Bredators with MCAS dive at me..)

[neerajb]

What amazes me is why MCAS was designed to operate out of one aoa sensor. Max already has two sensors, all they needed was to use data from both.

Secondly mcas had no min max values for stab movement. That is another blunder. Every time it triggered, it used aoa value to calculate stab movement irrespective of current position.

[SriKumar]

I am 400% sure that during the development of this system some engineers must have brought up the question "How can we let this system take input from a single AoA sensor? What happens if the sensor fails and provides incorrect data?". .

This is the part that is unbelievable. How can any one expect any instrument (especially one sitting outside of the aircraft, exposed to the elements) to work 100% all the time? Do they expect it to never malfunction, or malfunction only when on ground. To hook a nose-pitch down control to a single sensor is madness.

On a different note, both the crashes occurred after take-off and probably during climb, certainly the Ethiopean airlines crash that occured within 7 minutes of take-off (Lion Air within 13 minutes of TO). THe Lion Air plane had a similar event in a prior flight but somehow got out of it. The EO crash is particularly sad because the pilots knew what to do, but Boeing Co did not know or forgot that the power-assist to move the stabilizers (?) was also connected to the MCAS off switch!!

[chetak]

I am 400% sure that during the development of this system some engineers must have brought up the question "How can we let this system take input from a single AoA sensor? What happens if the sensor fails and provides incorrect data?".

But their arguments must have been brushed aside just like when the Thiokol engineers tried in vain to get the Challenger space shuttle launch postponed because the weather conditions were outside the safety limits of the seals made by Thiokol. Their arguments were brushed aside too and the shuttle blew up.

The MAX aircraft all have 2 AOA sensors each.

One AOA sensor is connected separately to the one flight control computer while the other AOA sensor is separately connected to the second FCC, and only one of the FCC is operational during any given flight.

These two flight control computers alternate every flight meaning FCC1 connected to AOA1 is on during the first flight, and for the next flight, FCC2 connected to AOA2 comes on thus each FCC sees only the one AOA connected to it and by foolish design is disconnected from the other already existing AOA making the flight critical AOA sensor a single point of failure item.

Boeing, however, offered a paid modification in which the existing second AOA sensor was connected to both the FCCs and in case of failure or malfunction, when the two AOA sensor data differed from each other, a warning light called "AOA disagree" would come on in the cockpit thus alerting the pilot to the fact that the AOA sensor data was unreliable.

Thereafter, a set of actions to deal with such a situation was prescribed by boeing and it involved switching off the electric trim system thus completely disabling the MCAS.

But none of this critical information was either described in the vital FCOM/POH or otherwise made known to the flight and engineering crews in a bid to maintain the myth that there was no difference between the 737 Max and the previous version, the 737NG thus obviating the need for additional SIM training for the pilots or recertification for the MAX

There is a manual trim wheel in the cockpit that can be used to change the trim setting in flight but this will not work after a certain speed because this wheel will not be able to overcome the aerodynamic forces, no matter how much force the pilots use to try and move this trim wheel.

If the airplane is not trimmed correctly, the stick forces become extremely heavy making the aircraft very very difficult to fly.

So to retrim the aircraft, the pilots would have to revert back to the electric trim which in turn turned the MCAS back on again and the MCAS went back to doing its work (if the AOA sensor data indicated an unacceptably high AOA (meaning a stall condition) because of some sensor fault/malfunction) which was to push the nose down.

Traditionally, the design of flight critical systems has always and mandatorily included an alternate backup system in case the first one failed or malfunctioned. This golden design principle was violated in the case of the MCAS design and its implementation and wantonly introduced the fatal single point of failure condition into the loop.

while the physics used may have been logical, the designers were criminally negligent when they introduced the fatal single point of failure condition as were indeed the boeing test pilots and test engineers who allegedly did not fully investigate this failure mode during the flight tests and signed off on it.

the FAA baboo(n)s like all bleddy baboo(n)s the world over have neatly absolved themselves and squarely blamed boeing for the fatal mishaps and also accused boeing of misleading the FAA by suppressing certain critical facts.

If we ever ran short of baboo(n)s in India, we could simply import a whole lot of them from the FAA, all well trained and accomplished in the arcane baboo(n) arts of obfuscation, blame deflection and total self absolution. These guys all know how to emerge unsullied and smelling of roses especially after finding themselves deep inside the septic tank.

It looks like the MCAS work was done by honeywell but that still makes boeing solely responsible for the safe functioning of the MCAS system and all errors of commission and omission have to be laid squarely at boeing's door.

Now, the two FCCs will both come on during every flight, thus bringing the two AOA sensors back into the loop with a comparator to sense the failure or malfunction of any one (or both) of the two AOAs. This combined with the AOA disagree warning light to warn the pilot of potentially unreliable AOA data will allow him/her to take corrective action without endangering the safety of the aircraft.

This, boys and girls, is what is known as blood flight safety, meaning that unless considerable blood has not been spilled to propitiate the aviation gods, flight safety will not receive the attention it deserves.

[UlanBatori]

Unfortunately this is the sort of gyan that makes jet engine MTBF much longer for Advanced Manufacturers than it is for poor GTRE. The infinite combinations of human thoughtlessless/greed/haste/drowsiness/drunkenness plus the laws of nature, weather, material properties.... The Excellent Systems become that way on the blood of 100s of 1000s.

Perhaps this is the challenge for ArjunPanditji and his AI troops: automatically generate nightmares for use with simulators.

[SriKumar]

I am 400% sure that during the development of this system some engineers must have brought up the question "How can we let this system take input from a single AoA sensor? What happens if the sensor fails and provides incorrect data?".

But their arguments must have been brushed aside just like when the Thiokol engineers tried in vain to get the Challenger space shuttle launch postponed because the weather conditions were outside the safety limits of the seals made by Thiokol. Their arguments were brushed aside too and the shuttle blew up.

The MAX aircraft all have 2 AOA sensors each.

One AOA sensor is connected separately to the one flight control computer while the other AOA sensor is separately connected to the second FCC, and only one of the FCC is operational during any given flight.

the FAA baboo(n)s like all bleddy baboo(n)s the world over have neatly absolved themselves and squarely blamed boeing for the fatal mishaps and also accused boeing of misleading the FAA by suppressing certain critical facts.

Not so fast. FAA lost credibility here and that is actually BOeing's bigger problem. FAA grounded the MAX well after other airlines started to ground them. In fact, I recall it was Trump who grounded them, and not FAA.
I recall China Air, Lion Air and one more airlines grounding it before the FAA woke up and said 'me too' . And this is not the first time. When 787 was introduced many years ago, the Lithium batteries were smoking and burning..... FAA held the party line (Boeing's line) that the aircraft need not be grounded....until JAL or All Nippon Airways (forget which) grounded it. THEN...FAA grounded it. This is the second time around. And this time the Airlines grounded it first, not waiting for FAA. They are not going to look to the FAA for an endorsement anymore. FAA lost credibility. In fact, FAA Is taking heat from NTSB on another crash (that killed Kobe Bryant). The NSTB usually would not publicly chide another govt organization but this time around (maybe a couple of years ago?) made some statement criticising FAA's decision not to mandate terrain warning devices on helicopters (which could potentiallly have prevented the Kobe Bryant crash).

I dont undertstand the logic of using one AoA sensor with one FCC and switching to the other AoA sensor in the next flight. EAch one is a single-point of failure for that flight. If true, then every flight is a test of the AoA instrumentation- both are 'tested' in a macabre sort of way. And one has to pay extra to get simultaneous usage to get the 'disagree' light? Very weird.

[chetak]

The MAX aircraft all have 2 AOA sensors each.

One AOA sensor is connected separately to the one flight control computer while the other AOA sensor is separately connected to the second FCC, and only one of the FCC is operational during any given flight.

the FAA baboo(n)s like all bleddy baboo(n)s the world over have neatly absolved themselves and squarely blamed boeing for the fatal mishaps and also accused boeing of misleading the FAA by suppressing certain critical facts.

Not so fast. FAA lost credibility here and that is actually BOeing's bigger problem. FAA grounded the MAX well after other airlines started to ground them. In fact, I recall it was Trump who grounded them, and not FAA.
I recall China Air, Lion Air and one more airlines grounding it before the FAA woke up and said 'me too' . And this is not the first time. When 787 was introduced many years ago, the Lithium batteries were smoking and burning..... FAA held the party line (Boeing's line) that the aircraft need not be grounded....until JAL or All Nippon Airways (forget which) grounded it. THEN...FAA grounded it. This is the second time around. And this time the Airlines grounded it first, not waiting for FAA. They are not going to look to the FAA for an endorsement anymore. FAA lost credibility. In fact, FAA Is taking heat from NTSB on another crash (that killed Kobe Bryant). The NSTB usually would not publicly chide another govt organization but this time around (maybe a couple of years ago?) made some statement criticising FAA's decision not to mandate terrain warning devices on helicopters (which could potentiallly have prevented the Kobe Bryant crash).

I dont undertstand the logic of using one AoA sensor with one FCC and switching to the other AoA sensor in the next flight. EAch one is a single-point of failure for that flight. If true, then every flight is a test of the AoA instrumentation- both are 'tested' in a macabre sort of way. And one has to pay extra to get simultaneous usage to get the 'disagree' light? Very weird.

It matters not a whit who grounded the aircraft or what logic was used in the design.

The ultimate responsibility was/is that of the FAA, whether they acted or not. It was their LEGAL responsibility.

Trusting boeing or delegating work to boeing does not take away the primary responsibility of the FAA for the clearance of the MAX.

They were and are, as they will continue to be, the only agency in the world that is legally able to tell boeing to bugger off and to go back to the drawing board and do it all over, again and again, until a safe and workable and verifiable system was delivered.

This they did not do.

in kobe bryants case, who stopped uncle from installing a terrain warning system. Was such an installation forbidden by the FAA, they merely said that it was optional, not mandatory.

Were plush leather seats mandated by the FAA, did he ask their approval to install them.

In the same way he should have got the terrain warning system installed for his own safety.

Why did he not have a moving map display system, after all that costs only a few hundred bucks per year in subscription to operate.

or why did they not have an Ipad or samsung tab sort of device to show the route map like every ordinary uber driver does, after all they were following well used motorways to navigate to their destination exactly as uber does.

does FAA need to tell uncle that too.

why were they flying so low in bad weather and why did they simply not set down somewhere safe and wait to the fog to clear.

why, why, why and a hundred more whys.

IMHO, and also very simply stated, his time was up and this was the way that was chosen for him to depart. He departed.

karma onlee

[SriKumar]

I think you missed the import of what I wrote, so I'll put it in plain terms. It was FAA's responsibility, and/but they have a history of not being true to their responsibility (787 and 737-Max). Hence they have lost credibility to a point where even if they certify a plane (MAX for example) as fit to fly, they will be second-guessed/not believed by airlines and pilots.Their blaming Boeing will not change this.

[chetak]

I think you missed the import of what I wrote, so I'll put it in plain terms. It was FAA's responsibility, and/but they have a history of not being true to their responsibility (787 and 737-Max). Hence they have lost credibility to a point where even if they certify a plane (MAX for example) as fit to fly, they will be second-guessed/not believed by airlines and pilots.Their blaming Boeing will not change this.

EASA and CAA, just to name two also kept quiet.

As far as boeing and FAA are concerned, try telling that to the families of the unfortunates who lost their lives. i am guessing that it wouldn't make the least bit of difference to them.

a much touted ameriki certification agency has not done its job, a famous aircraft manufacturer has messed up in a way that would have been inexcusable in a middle school kid

and neither one is actually going to pay in terms of jail time for the guys who messed up.

Both of them have been criminally negligent and both are responsible jointly and severally.

in fact, this should be seen and prosecuted as premeditated murder.

[SriKumar]

As far as boeing and FAA are concerned, try telling that to the families of the unfortunates who lost their lives. i am guessing that it wouldn't make the least bit of difference to them.

I dont know why this was necessary here or why you suggest I do so. It is a needless instrument of rhetoric for this discussion. If you are genuinely concerned about such things, you please try telling them whatever your impressions are that is worth their time and attention.

Calling it pre-meditated murder seems a bit much but I would definitely classify the second crash as requiring criminal charges and prosecution; when the Lion Air crash clearly showed the vulnerabilities of their design and Boeing CEO continued to insist that the craft was safe to fly (continued to do so after the EA crash as well). He was allowed to continue for a year and kicked out only after 737-MAxes piled in parking lots and they were not selling i.e. he was removed for financial reasons. Shows the priorities of the Board of Directors.

[chetak]

As far as boeing and FAA are concerned, try telling that to the families of the unfortunates who lost their lives. i am guessing that it wouldn't make the least bit of difference to them.

I dont know why this was necessary here or why you suggest I do so. It is a needless instrument of rhetoric for this discussion. If you are genuinely concerned about such things, you please try telling them whatever your impressions are that is worth their time and attention.

Calling it pre-meditated murder seems a bit much but I would definitely classify the second crash as requiring criminal charges and prosecution; when the Lion Air crash clearly showed the vulnerabilities of their design and Boeing CEO continued to insist that the craft was safe to fly (continued to do so after the EA crash as well). He was allowed to continue for a year and kicked out only after 737-MAxes piled in parking lots and they were not selling i.e. he was removed for financial reasons. Shows the priorities of the Board of Directors.

It was a general statement and not meant in the way that you have chosen to take it.

Of course, you would not go anywhere near the affected families so why would you interpret in that way.

FAA is the first guilty party here (51/49 %).

To suggest that they have no credibility or no control over boeing is to say that the FAA has no need to exist.

Why don't we find another topic to discuss.

[chetak]

twitter


This is a story of pride

A chronology of events on how Indian aviation regulator DGCA's improbable deadlines & super client IndiGo's threats forced a US aerospace major to its knees

Pratt & Whitney is now hiring charters to ferry engines to IndiGo & set up an MRO in India.

[UlanBatori]

IMO IndiGo is Going. The Kingfisher way. 230 brand-new airliners on order? A one-size-fits-all fleet, so that every grounding grounds the entire fleet.
chetakji, please provide links. All I know is that IndiGo announced a decision to go with SNECMA/ CFM injins dissing Pee & Dubya. But that's another disaster story: any glitch in CFM injins will also ground airline fleet. Strange business strategies adopted by India-based airlines. Death wish I suppose.

[nachiket]

UB saar, Southwest has a much much bigger "one-size fits all" fleet and they seem to make it work.

[Deans]

IMO IndiGo is Going. The Kingfisher way. 230 brand-new airliners on order? A one-size-fits-all fleet, so that every grounding grounds the entire fleet.
chetakji, please provide links. All I know is that IndiGo announced a decision to go with SNECMA/ CFM injins dissing Pee & Dubya. But that's another disaster story: any glitch in CFM injins will also ground airline fleet. Strange business strategies adopted by India-based airlines. Death wish I suppose.

Indigo leases aircraft for 6 years, so their projected fleet size cannot be calculated by adding all purchases. The Airbus aircraft are a mix of A320 & 321, which makes sense at it significantly reduces complexity. However, they actually deviated from one size fits all when they inducted the ATR-72

[chetak]

IMO IndiGo is Going. The Kingfisher way. 230 brand-new airliners on order? A one-size-fits-all fleet, so that every grounding grounds the entire fleet.
chetakji, please provide links. All I know is that IndiGo announced a decision to go with SNECMA/ CFM injins dissing Pee & Dubya. But that's another disaster story: any glitch in CFM injins will also ground airline fleet. Strange business strategies adopted by India-based airlines. Death wish I suppose.

Indigo leases aircraft for 6 years, so their projected fleet size cannot be calculated by adding all purchases. The Airbus aircraft are a mix of A320 & 321, which makes sense at it significantly reduces complexity. However, they actually deviated from one size fits all when they inducted the ATR-72

as far as sourcing, training and support go, the three aircraft are from the airbus family.

These guys run the tightest ship among all the airlines in India.

too bad about the Pratt and Whitney engines though. It's a black swan event for indigo as well as goair

Just goes to show how complicated the entire business of aircraft engines really is and why they form the core part of a nation's technological assets.

With DGCA ordering IndiGo to replace all A320neo aircraft with unmodified Pratt and Whitney (PW) engines by January 31, the airline on Wednesday designated this matter as one of the "revenue headwinds" of 2019-20, and said it is "likely to have an impact on future capacity". On November 1, aviation regulator Directorate General of Civil Aviation (DGCA) had asked IndiGo to replace all unmodified PW engines on its 97 A320neo family aircraft or face grounding of planes.

Later, unsatisfied with IndiGo's speed in replacing the unmodified PW engines, the regulator on November 25 instructed it to ground an old A320neo family aircraft with an unmodified PW engine for every new A320neo plane added to its fleet to prevent large-scale cancellation of flights from January 31 onwards.

On Wednesday, in its presentation to investors and analysts, the airline said that PW engine issues is "likely to have an impact on future capacity".

It said it is expecting a capacity increase of 15-20 per cent in fourth quarter of 2019-20.

The airline added that the overall capacity increase would be 22-23 per cent in 2019-20.

The PW engine-powered A320 neo planes in the fleets of IndiGo and GoAir have been facing glitches both mid-air and on-ground since their induction way back in 2016.

The airline, in its presentation that was posted on BSE's website, said that adverse movement in fuel prices "and/or foreign currency" from the current levels are "major risks".

The budget carrier stated that pilot shortage, uncertainty on Jet Airways' slots and bilateral rights, risk of losing other bilateral rights and PW engine issues are the major "revenue headwinds" of 2019-20.

[chetak]

IndiGo Takeoff Procedure Could Be Behind A320neo Engine Issues

IndiGo Takeoff Procedure Could Be Behind A320neo Engine Issues


by Henry Bewicke
November 30, 2019

The Indian Directorate General of Civil Aviation has reportedly informed IndiGo that its pilots have been revving the engines too hard on the airline’s Airbus A320neos. This practice is believed to have been responsible for the large number of Pratt & Whitney engine failures on IndiGo’s Airbus A320neos.




An IndiGo Airbus A320neo


IndiGo has had problems with the engines on a number of its Airbus A320neos.

Reports by Bloomberg yesterday have shed some light on the potential cause of the recurring engine failures which have plagued IndiGo’s Airbus A320neos.

India’s Directorate General of Civil Aviation has been looking into IndiGo’s Airbus A320neo issues. So far this year, IndiGo has suffered 13 shutdowns of the Pratt & Whitney geared turbofan engines fitted to its Airbus A320neos.

Back at the start of November, the DGCA ordered IndiGo to replace the engines on its entire Airbus A320neo fleet, consisting of 98 aircraft in total. IndiGo was given just 13 weeks to complete the engine replacements for all of its Airbus A320neos. So far it has replaced just 86 engines, leaving 110 to complete by 31 January 2020.

What did the DGCA find?
IndiGo’s Airbus A320neo troubles have seemed slightly odd to many observers since the beginning. Indigo may well have the largest fleet of Airbus A320neos in India, but it isn’t the only Indian carrier operating the type.

GoAir also operates a sizeable fleet of 38 Airbus A320neos. GoAir’s A320neos also have the same Pratt & Whitney engines as IndiGo’s aircraft. However, unlike IndiGo, GoAir has not suffered any turbofan engine shutdowns.


GoAir’s Airbus A320neos have not suffered the same issues.

The fact that the engine failures were limited to IndiGo’s aircraft was a pretty strong indication that they were the result of some sort of mishandling. The DGCA compared the operating practices of the two airlines to determine the root of the issue.

Although unconfirmed as of yet, Bloomberg’s sources appear to suggest that the DGCA has concluded that IndiGo’s throttle practices during takeoff are responsible for the engine failures.

Different practices at IndiGo and GoAir
Supposedly, IndiGo pilots usually take off using full throttle, as it can end up burning less fuel. In the highly competitive Asian low-cost airline industry, every little cost-saving counts. By comparison, GoAir pilots use what is known as the ‘alt-climb’ method, which does not involve applying maximum thrust during the initial ascent.

IndiGo’s full-throttle approach to takeoffs in its Airbus A320neos appears to have had a detrimental effect on their Pratt & Whitney engines. The additional stress placed on the engine components likely caused them to fail.

GoAir and IndiGo A320neo grounding
IndiGo is the world’s biggest operator of the A320neo family.

Now that the airline has been made aware of the issue, it will most likely alter its takeoff approach to reflect that of GoAir.

Although the cause of the issue may now have been identified, most of IndiGo’s Airbus A320neos have probably been affected by the full-throttle takeoff procedure already. It remains to be seen whether the DGCA will extend the deadline for IndiGo’s engine refit program.

[nachiket]

This is the Airline industry version of Steve Jobs' infamous "you're holding it wrong" statement when confronted with the iPhone's antenna issues.

Unless there were specific instructions from PW to avoid using full throttle during takeoff, Indigo pilots were not flying it beyond the limits. It just means that PW had not done enough testing to validate effects of throttle settings during takeoff on their new engines and advised operators of the proper limits.

[UlanBatori]

UB saar, Southwest has a much much bigger "one-size fits all" fleet and they seem to make it work.

True. I heard they were really walking the tightrope on the 737MAX issue & Boeing was making special efforts for them. Otherwise they may also be into "headwinds".

But my fear is about the huge investment in new planes by IndiGO. Leased may be OK... but someone is paying capital costs on a large number of new planes, and that is basically what Kingfisher did a few years back, as they turned a good, functioning airline into bankruptcy.

[UlanBatori]

How do you save fuel by using full throttle at takeoff? Violates 2nd law of thermo. Unless they were trying to use the rocket launch equation and use up all the fuel in one big impulse on the ground..

[chetak]

This is the Airline industry version of Steve Jobs' infamous "you're holding it wrong" statement when confronted with the iPhone's antenna issues.

Unless there were specific instructions from PW to avoid using full throttle during takeoff, Indigo pilots were not flying it beyond the limits. It just means that PW had not done enough testing to validate effects of throttle settings during takeoff on their new engines and advised operators of the proper limits.

looks like the ameriki aviation industry is currently beset with bad news and both the primary engine as well as the primary airframe manufacturer is desperately trying to shift the blame elsewhere.

their commercial testimonials are in a bind.

It's all echandee onlee.

[Indranil]

I used to always think that HAL was reinventing the wheel with the civilian Dornier project. Everything looked so similar to the 228 NG. Now I get it.

Lucknow/Bengaluru, February 6, 2020: Hindustan Aeronautics Limited (HAL) received the modification document of HAL Do-228 (Upgraded) civil aircraft for 5700 All Up Weight (AUW) from DGCA during the ongoing DefExpo-2020 today.

The document was handed over by Mr. G. Rajsekhar, JDG, DGCA to Mr. Apurba Roy, General Manager at HAL’s Transport Aircraft Division, Kanpur in the presence of Mr R Madhavan, CMD, HAL and senior executives from HAL and DGCA.

Two Civil Do-228 produced by HAL for launch under UDAN scheme having state-of-the-art configuration certifications from DGCA for MTOW at 6200 kgs. But in order to meet the prospective operator’s requirement of a transport aircraft flyable under Commercial Pilot License (CPL) category, HAL undertook efforts to reduce the aircraft weight below 5700 Kgs.

Apart from weight criterion, HAL Do-228-201(Upgraded) civil aircraft will also be equipped with digital cockpit which will ensure more accurate readings, precise information and ergonomic data displays with feedback loops and capability for self-check to alert pilot in emergencies. The Glass Cockpit architecture enabled aircraft will be most sought after new age aviation technology.

Also, the incorporation of civil certified turbo-prop minus 10 (TPE331-10?) Engine ensures more reliable torque sensing system, higher component life, lighter in weight and higher time between overhaul (TBO) as compared to previous minus 5 engine (TPE331-5?).

It is also assured that the integration of the five blade propeller to HAL Do-228-201(Upgraded) aircraft will augment in significant reduction in noise levels, faster engine start, less lubrication and better damping characteristics.

First of all whose job is it in HAL to proof read press releases before issue? Second, how is the TPE331-10 lighter than the TPE331-5?