Iced AoA sensors send A321 into deep dive
The autopilot was not on in the Max accidents. To have survived they needed to disable the trim system via the large red guarded trim disable switches and adjusted power to maintain an appropriate aiespeed. They did neither. Still with the auto trim interruption system via stick position and counter trim the Captains on both flights were able to maintain control until they handed the aircraft over to very inexperienced co pilots.
The autopilot was not on in the Max accidents. To have survived they needed to disable the trim system via the large red guarded trim disable switches and adjusted power to maintain an appropriate aiespeed. They did neither. Still with the auto trim interruption system via stick position and counter trim the Captains on both flights were able to maintain control until they handed the aircraft over to very inexperienced co pilots.
Can't believe that it would be hard for software to detect frozen AoA sensors. If you change the eleivator or thrust and there is no effect on AoA sensors at a certain point the data should he figured as unreliable. To only count on the pilots, that they push the right two buttons at the right time might not always work out.
The autopilot was not on in the Max accidents. To have survived they needed to disable the trim system via the large red guarded trim disable switches and adjusted power to maintain an appropriate aiespeed. They did neither. Still with the auto trim interruption system via stick position and counter trim the Captains on both flights were able to maintain controluntil they handed the aircraft over to very inexperienced co pilots.
Can't believe that it would be hard for software to detect frozen AoA sensors. If you change the eleivator or thrust and there is no effect on AoA sensors at a certain point the data should he figured as unreliable. To only count on the pilots, that they push the right two buttons at the right time might not always work out.
For the boeing case, they didn't even take care to have enough probes.
On airbus they have more probes, which make it far less likely, but they still have some occurences.
It's true that some pilots on some incident occurences mismanaged trim problems. For example, one never figured out that his trim switch was reverted.
I think trim is one of the most important flight control. Especially on jetliners where the THS has a larger pitching power than elevators. (Which isn't true on most light airplanes, it seems).
Because of that, even if it's very rare that this control should be closely monitored, there should still be a THS position indicator somewhere obvious in the cockpit. Above the PFD for example.
Also one can wonder about why the THS could go so far pitch down on the MAX. It's understandable it needs to go very high pitch up, for very low speeds and forward CG. But an airplane already at maximum speed and normal CG shouldn't have a large nose down THS margin, should it ? What's the use of that ?
It should also slightly reduce cost and complexity to have a smaller amplitude for the THS.
Join Date: Nov 2004
Location: Here, there, and everywhere
Posts: 1,122
Likes: 0
Received 12 Likes
on
7 Posts
Bottom line, keep the autopilot on during high altitude over speeds. You are more likely to just get yourself into trouble with inappropriate pitch inputs that were not necessary anyways. Just accept the overspeed, realize that it not dangerous, maybe use some speedbrake and then write it up as appropriate.
As for the faulty AoA concern, alpha prot strip increase is a slowly increasing value as Mach slowly increases because the AoA vanes are stuck in place instead of slowly moving toward what I will call the cruise altitude position. This particular event appears to be a sudden increase in the alpha prot strip likely due to some g-loading in turbulence causing vane movement. I suppose one wants to recognize the difference between g-induced alpha prot strip increase and stuck vane increase in alpha prot strip (recognize the circumstances likely to produce both).
As for the faulty AoA concern, alpha prot strip increase is a slowly increasing value as Mach slowly increases because the AoA vanes are stuck in place instead of slowly moving toward what I will call the cruise altitude position. This particular event appears to be a sudden increase in the alpha prot strip likely due to some g-loading in turbulence causing vane movement. I suppose one wants to recognize the difference between g-induced alpha prot strip increase and stuck vane increase in alpha prot strip (recognize the circumstances likely to produce both).
Bottom line, keep the autopilot on during high altitude over speeds. You are more likely to just get yourself into trouble with inappropriate pitch inputs that were not necessary anyways. Just accept the overspeed, realize that it not dangerous, maybe use some speedbrake and then write it up as appropriate.
However, it still doesn't make it acceptable that some pilots would be unable to properly control the aircraft in case they wanted to disengage it.
Forgetting the thrust while nose up and failing to push it down too when needed is not acceptable.
Join Date: May 2005
Location: uk
Posts: 573
Likes: 0
Received 0 Likes
on
0 Posts
The protections did not “fail”on the Iberia Bilbao accident. The aircraft behaved as designed at the time. The ELACs did not like the rate of pitch change and in anticipation of high nose event limited it. Airbus modified the ELAC standard after the incident and provided Iberia with a new A319. All details on the final report.
Meikleour
No one seems to have mentioned the fact that the THS can be moved manually to control the pitch at all times, even in flight.
The aerodynamic authority of the THS is way in excess of the elevator authority.
This fact was very obvious while conducting Upset Recovery Training in the sim when use of the THS greatly speeds up the recovery action.
Just because it isn't touched after setting the take-off trim after start doesn't mean that it can not be used in flight.
No Airbus manual will say this however.
No one seems to have mentioned the fact that the THS can be moved manually to control the pitch at all times, even in flight.
The aerodynamic authority of the THS is way in excess of the elevator authority.
This fact was very obvious while conducting Upset Recovery Training in the sim when use of the THS greatly speeds up the recovery action.
Just because it isn't touched after setting the take-off trim after start doesn't mean that it can not be used in flight.
No Airbus manual will say this however.
Sorry to chime in late on this thread...just noticed it.
@Meikleour said it all, "the THS can be moved manually to control the pitch at all times,"
The Airbus as with Boeing and all modern airliners uses lots of sensors to assist pilots and make the flying task easier. Sometimes failures make those helpful little angels turn into devils and cause problems.
But us old and experienced pilots should not be phased when something weird happens say in pitch. The first thing to do when the aircraft does something unexpected is, as Airbus recommends, disconnect the autopilot.
However, if you still have pitch control problems such as limited authority using the elevator control...well the only other primary control surface that is that gigantic all-flying-tail that we use for trim.
The elevators are small and so the pitch effect is for refined pitch adjustments. The all-flying tail is huge is is used to trim out the very large pitching moments associated with flap selection and the large CG and speed range of an airliner.
So if the elevators are insufficient to control pitch, then simply grasp the trim wheel and control the pitch using the all flying tail (trimmable horizontal stabiliser THS or whatever it's called on your jet).
If something else is automatically controlling the all flying tail (THS) and fighting you...turn it off!
In case of surprise...forget the yellow brick road, the magenta line, the magic of the autopilot, digital flight control stability and augmentation, or whatever and...
Fly the aircraft by manually controlling the surfaces that are needed for the situation.
In case of doubt or surprise, ignore the magic and you fly the aircraft...don't let it fly you!
We normally set the trim wheel for take-off and then we forget it all about it. Watch that little sucker from time t time next time you go flying...it will explain a lot as to what is going on.
(And in jet upset it may or will become the primary pitch control).
The protections did not “fail”on the Iberia Bilbao accident. The aircraft behaved as designed at the time. The ELACs did not like the rate of pitch change and in anticipation of high nose event limited it. Airbus modified the ELAC standard after the incident and provided Iberia with a new A319. All details on the final report.
The mere fact that they decided to change/improve the law, shows that they admit that it was not perfect.
In the end, and what matters, the bad design of the protection led to an accident.
The exact origin of this bad design, be it coding, mechanical failure, electrical failure, freezing, does not really matter. The protection unduly limited legitimate stick orders and led to an accident.
Hence they failed. They failed at doing their job properly.
Airbus talks about cases of "improper AoA protection activation".
If you think an activation leading to an accident was proper.. Good on you. Stop thinking that anything designed by the manufacturer is perfect.
A little bit of knowledge is a dangerous thing:
The Habsheim A320 protected the aircraft too. The system knew better than the pilots then.l So it (the system) landed the aircraft against the pilots wishes !!! Protections ??? Yeh sure.
The aircraft was below 100ft so the A-FLOOR protection was not active and the engines in any case would probably still have taken too long to spool-up and provide the thrust to avoid the trees. The pilot was flying at 30ft instead of the briefed 100ft
What about the A320 that crashed into the Mediterranean with 3 airbus test pilots on board?
They omitted an item on the Air Test Schedule, as I recall, and didn't want to climb back up to the recommended safe altitude to carry it out so they checked the low-speed protections at an unsafe altitude (3000ft) with tragic consequences when they AoA probes froze due to water ingress. Had they been at 14,000ft which is, I believe, the recommended altitude for the check they would probably have recovered from the stall.
The Habsheim A320 protected the aircraft too. The system knew better than the pilots then.l So it (the system) landed the aircraft against the pilots wishes !!! Protections ??? Yeh sure.
The aircraft was below 100ft so the A-FLOOR protection was not active and the engines in any case would probably still have taken too long to spool-up and provide the thrust to avoid the trees. The pilot was flying at 30ft instead of the briefed 100ft
What about the A320 that crashed into the Mediterranean with 3 airbus test pilots on board?
They omitted an item on the Air Test Schedule, as I recall, and didn't want to climb back up to the recommended safe altitude to carry it out so they checked the low-speed protections at an unsafe altitude (3000ft) with tragic consequences when they AoA probes froze due to water ingress. Had they been at 14,000ft which is, I believe, the recommended altitude for the check they would probably have recovered from the stall.
The Habsheim A320 protected the aircraft too. The system knew better than the pilots then.l So it (the system) landed the aircraft against the pilots wishes !!! Protections ??? Yeh sure.
The aircraft was below 100ft so the A-FLOOR protection was not active and the engines in any case would probably still have taken too long to spool-up and provide the thrust to avoid the trees. The pilot was flying at 30ft instead of the briefed 100ft
The aircraft was below 100ft so the A-FLOOR protection was not active and the engines in any case would probably still have taken too long to spool-up and provide the thrust to avoid the trees. The pilot was flying at 30ft instead of the briefed 100ft
So why did the flight control law refuse to go up to this ?
The small margin between their actual alpha and alpha max could have allowed to fly over. Could have, I didn't run any simulation.
If the software observes that AoA remains completely constant on two sensors despite the significant flight control inputs produced by alpha protection, meanwhile the third sensor shows changes in its readings consistent with the commanded manoeuvre, isn’t that a pretty good indicator that those 2 sensors are frozen?
There needs to be an indication that the mechanism of each AoA sensor is reliable, independent of any other sensor reading.
For example, one could use electromagnetic coils to modulate a small variation of torque on the AoA vane to see if it moves as expected. If + and - torque yields no + and - change in the AoA sensor reading then the sensor is flagged as unreliable. Subsystem testing could continue to be used on the off chance the sensor frees up, and then return it to the voting pool. This could also be used on the ground before departure and runs less risk than using the entire plane as a roller coaster to check the sensors or hoping for a situation that would change the AoA a meaningful amount over digitization noise.
It does raise the question - since all three sensors aren't identical in reading, what does the flight control software do with the readings? Does it average them, take the two that are closest and average them, take the middle one? What is the fallback if one is eliminated? Average or flip a coin and pick one? They are within some margin of each other, but then what if one more is eliminated? It cannot be disagreement on reading, right?
For example, one could use electromagnetic coils to modulate a small variation of torque on the AoA vane to see if it moves as expected. If + and - torque yields no + and - change in the AoA sensor reading then the sensor is flagged as unreliable. Subsystem testing could continue to be used on the off chance the sensor frees up, and then return it to the voting pool. This could also be used on the ground before departure and runs less risk than using the entire plane as a roller coaster to check the sensors or hoping for a situation that would change the AoA a meaningful amount over digitization noise.
It does raise the question - since all three sensors aren't identical in reading, what does the flight control software do with the readings? Does it average them, take the two that are closest and average them, take the middle one? What is the fallback if one is eliminated? Average or flip a coin and pick one? They are within some margin of each other, but then what if one more is eliminated? It cannot be disagreement on reading, right?
The majority of pilots these days survive because the aircraft don’t fail 99.999% of the time and they just follow the SOPs designed for the weakest pilot in the weakest operation with the autopilot doing the flying for 99.999% of the time.
This isn’t the fault of the pilots; it’s the fault of training departments filling the training syllabus with inane rubbish like watching an RNAV approach with the AP on for twenty minutes or ten minute briefings in a full motion simulator doing laps of the hold with again the AP on.
Remember the Children of the Magenta? Well they grew up and became today’s training department managers and chief pilots. It ain’t the fault of the line pilots for the last 10-15 years. They only do what they are told/trained to do.
Attitude is a reflection of leadership and leadership in training is non-existent in the majority of airlines these days.
With regard to the specifics of this thread; the problem can be solved by doing two easy things 1) turn off the affected system 2) fly the aircraft manually.
1) Most crew wouldn’t know what hit them if this kind of failure occurred - see all above examples 2) most pilots can’t fly the aircraft manually.
This isn’t the fault of the pilots; it’s the fault of training departments filling the training syllabus with inane rubbish like watching an RNAV approach with the AP on for twenty minutes or ten minute briefings in a full motion simulator doing laps of the hold with again the AP on.
Remember the Children of the Magenta? Well they grew up and became today’s training department managers and chief pilots. It ain’t the fault of the line pilots for the last 10-15 years. They only do what they are told/trained to do.
Attitude is a reflection of leadership and leadership in training is non-existent in the majority of airlines these days.
With regard to the specifics of this thread; the problem can be solved by doing two easy things 1) turn off the affected system 2) fly the aircraft manually.
1) Most crew wouldn’t know what hit them if this kind of failure occurred - see all above examples 2) most pilots can’t fly the aircraft manually.
