Whats the logic here?

[F-16GUY]

Will repost my question here as there was no response in the accident and close calls section. My question relates to the multiple tail strike incident in italy in 2009.

With its high nose-up attitude of 15° the aircraft, having gained sufficient lift, became airborne at an airspeed of around 110kt. The pitch increased to 23° and, at 125kt, a stall warning sounded for 5s. The jet switched from direct to alternate flight-control law and a cabin altitude warning, indicating pressurisation problems from the damaged fuselage, sounded as it climbed through 9,750ft.

(source: FlightGlobal - http://www.flightglobal.com/news/art...ntinue-444260/)

Not an Airbus driver, but can anyone in the know explain to me why the Airbus degrades its flight controls to alternate and direct law in a situation like this where there obviusly is nothing physically wrong with the aircraft (all probes, vanes and FLCC's working as they should), and the only issue is an CG well aft of the approved?

Degrading the flight controls, removing the protections and changing the way the aircraft handels and feels in a situation like this is IMHO only going to stress the pilots more and reduce the chances of a safe recovery.

Whats the logic here?

[cinocav]

Full report available on ANSV website

It’s in Italian but g@#€*e translate might be of help. You find details of flight control logic at page 35

http://www.ansv.it/cgi-bin/ita/Relazione%20LZ-BHC.pdf

[RUMBEAR]

I am unable to read the report but assuming the aircraft did not encounter any faults ( aside from the tail strike), it’s possible that alternate law was triggered due to an abnormal attitude.

When an extreme attitude is encountered ( and the speed, pitch etc quoted is actually not extreme enough), alternate law is triggered to ensure the normal law protections don’t prevent a normal flight attitude being resumed.

That’s my best guess based on the limited info quoted.

[DaveReidUK]

Working link:

Tail-struck A320's crew originally chose to continue flight (https://www.flightglobal.com/news/articles/tail-struck-a320s-crew-originally-chose-to-continue-444260/)

[joe falchetto 64]

RUMBEAR

Wrong guess: the alternat law was triggered due to the stall warning activation at take off resulting in the FCS discarding at least two of the three AOA output through the ADIRS; then, due to the prolonged flight time with gear down, the direct law was triggered; when the gear was raised the alternate law was reinstated again and kept till the autopilot was on; with AP off (and gear down) the direct law was triggered again. Not let me get involved in this never ending talk about Airbus flight laws: as an Airbus pilot I like the aircraft and by the way it flies as a normal aircraft in direct law; controllability problems in direct law are related to other issues, like faults that leave the aircraft with partial flight control surfaces.

[vilas]

What's the logic here? What logic did you find in such a dangerously ignorant crew occupying pilot seats? If the nose pitches 15* at 50kts and after playing with thrust levers they continue the takeoff after multiple tail strikes they should be jailed and Airline's operating license should be cancelled. They manoeuvred the aircraft in such impossible manner that the computer was forced to reject the input as faulty and it went in alternate law and since gear was down direct law. There is no protection against ignorance and stupidity. Dangerous killers at large.

[F-16GUY]

vilas,

While it’s obvious to me what they should have done in that situation, I don’t believe that blaming the pilots is the answer. The logic behind the captain’s decision to continue the T/O after the first power reduction, was that he was more concerned with the damage that might be done to the aircraft if the nose was slammed onto the runway. Obviously he did not consider the dangers of flying with a CG well aft of the design limit.

There is protection against ignorance and stupidity. Its the regulators and airlines responsibility to ensure that only qualified and well trained crews are allowed into the cockpit. But since those protections are under pressure from economical interests, those protections are sometimes out of order….

Another question for joe and others in the know about the Airbus FCS.

Will the fact that the aircraft changes control laws give the pilots better or worse control response/control effectiveness in the pitch axis (in this situation), thereby increasing their chances of successfully avoiding a stall due to aft CG?

[Goldenrivett]

"The aircraft, with flaps at 10° and slats at 18°, began to lift its nose at just 30kt and both pilots pushed their side-sticks fully forward as the pitch reached 11°”

Originally Posted by F-16GUY
was that he was more concerned with the damage that might be done to the aircraft if the nose was slammed onto the runway

That’s amazing insight into stupidity.
Better not risk lowering the nose wheels during a low speed rejected take off - we are better off attempting to get airborne with this uncontrollable pitch up problem.

Words fail me.

[F-16GUY]

That’s amazing insight into stupidity.

That was not my insight though....

The ANSV analysed that obviously the captain intended to reject takeoff when the aircraft began to rotate unexpectedly at 50 knots, both pilots pushed the sticks forward, the thrust levers were moved aft, but then the captain decided otherwise and continued takeoff moving the thrust levers into the TOGA detent. The captain obviously realized following the decision to reject takeoff, that the thrust reduction would result in a rapid de-rotation resulting in a violent impact of the nose gear on the runway.

[vilas]

F-16GUY
Now come on! Right from the time the load sheet was brought till the time they landed you will be hard put to find any decision by the crew that was not only wrong but insane. At 30kts with full stick forward 11 degrees nose up? screw the nose wheel! Just stop the aircraft would you? Then you reduce thrust and go TOGA then multiple tail strikes are better than nose wheel damage? I hope they tested the crew for drugs.I don’t believe that blaming the pilots is the answer So who else is at fault? Surely the passengers who travel by such a stupid airline or Unless you are preparing the grounds for some thing equally silly in future .

[Uplinker]

With due respect to F16 guy and vilas, I think the control issue is a red herring, and I don’t 100% blame the pilots either, (nor am I excusing them).

We all know that every accident is a combination of more than one factor.

I have not read the full report but in this case we probably had:
A quick turnaround.
A possible language problem or a misunderstanding.
Loading instructions not carried out.
Incorrect CG of aircraft.
Incorrect THS setting entered in FMGS and set for take-off.
Incorrect operation of flight controls on take-off (half pitch-down should be applied until 80 kts).
Incorrect decision to continue take-off following recovery of nose pitching up.
Incorrect decision not to immediately return to airfield.

In an ideal world, the pilots would not have been under time pressure and would have checked the load sheet properly. They would also have insisted that a double check be made of the passenger distribution in the cabin. But it is not an ideal world and turnarounds, slots and general pressure to stick to schedules are causing a potentially dangerous atmosphere these days.

I have never in any SIM been given, or seen a badly out of limits CG, leading to a mis-set THS, leading to a premature pitch-up. These guys/gals probably never had either. By the time they had recovered from the pitch-up situation it might have appeared to them that there was insufficient runway left to stop on - hence the initial power off followed by power back on and decision to continue the take-off.

Some might respond that we are pilots and should be able to handle any eventuallity, but again, we all know that is not how the world is, and unusual things like this should be demonstrated to us in the SIM*

You would not expect a concert violinist to be able to play a piece of music they had never seen before to performance standard first time - they practice, practice, practice - and a similar thing applies to pilots of large complex jet transports.



*without pre-warning, as this will have a much stronger learning value than if the situation is pre-briefed.

[vilas]

Uplinker
I read the full report. You are trying to defend undefendable stupidity. Report says there was no time pressure aircraft was ready before time, rather crew wanted to leave early. They were told that passengers need to be relocated the captain didn't do anything. The decision to not abort at 30 kts with nose pointing in the sky was insane and so was everything else. The whole decision making and logic behind it I cannot believe is from a pilot. May be they should stop inquiries into accident. Because no matter what anyone does they are not responsible. Once in a while just clap some Sullenberger's act and move on till another one happens.

[F-16GUY]

vilas,

I dont disagree that the decisions made in the cockpit where wrong. My point is only that behind those two pilots there is an organisation (airline/regulators) that has failed big time in allowing those two pilots to end up in a cockpit.

[SomebodyFromFarAway]

Welcome to Eastern Europe, especially Bulgaria. People don't get selected/promoted based on ability, but those decisions are based rather on social/policital connections, going back to the era couple of decades ago.

In this part of the world, if you get fired from an airline for whatever reason, you become the prime candidate for the head of CAA. What oversight?

[tdracer]

The captain obviously realized following the decision to reject takeoff, that the thrust reduction would result in a rapid de-rotation resulting in a violent impact of the nose gear on the runway. Sorry, but that is just stupid. First off, whatever was causing the nose to already in the air at 30 knots wouldn't magically go away with a thrust reduction - the only way the nose might come down hard would be if he stood on the brakes. An RTO at less than 50 knots doesn't even NEED the brakes.:ugh:

[Fursty Ferret]

First off, whatever was causing the nose to already in the air at 30 knots wouldn't magically go away with a thrust reduction

Pitch-power couple?

[tdracer]

But reducing the pitch-power couple isn't going to 'slam' the nose into the ground, any more than it causes an uncontrollable pitch-up (and if it is causing an uncontrollable pitch up, all the more reason to low speed abort because you'll have no chance once in the air).
This pilot basically chose a smoking hole over the potential for a slightly bent airplane - that it didn't end up in a smoking hole was little more than dumb luck.

[vilas]

Uplinker, F16 I wonder if your family was on board this flight would you still say the same things? Actually the stick half forward on A320 is for standardization with other airbuses(wide bodies).It is not critical on A320. The badly out of range CG was the cause. Stick forward wouldn't have prevented the pitch up. Pilots are trained to reject takeoff for anything unusual during low speed phase and that is enough. No one can be trained for RTO with hundred different reasons.

[joe falchetto 64]

What's the logic here? What logic did you find in such a dangerously ignorant crew occupying pilot seats? If the nose pitches 15* at 50kts and after playing with thrust levers they continue the takeoff after multiple tail strikes they should be jailed and Airline's operating license should be cancelled. They manoeuvred the aircraft in such impossible manner that the computer was forced to reject the input as faulty and it went in alternate law and since gear was down direct law. There is no protection against ignorance and stupidity. Dangerous killers at large.

Very well said

[Uplinker]

Uplinker
I read the full report. You are trying to defend undefendable stupidity. Report says there was no time pressure aircraft was ready before time, rather crew wanted to leave early. They were told that passengers need to be relocated the captain didn't do anything. The decision to not abort at 30 kts with nose pointing in the sky was insane and so was everything else. The whole decision making and logic behind it I cannot believe is from a pilot. May be they should stop inquiries into accident. Because no matter what anyone does they are not responsible. Once in a while just clap some Sullenberger's act and move on till another one happens.


Fair enough. That does indeed sound shocking.
I was not trying to defend anything, I was trying to understand how this could have happened.

[Uplinker]

As an aside, I once landed an A320 or 321 which had a reverser locked out. Our SOP in this situation was to put both thrust levers into reverse rather than just the one that was working.

However, something went wrong and when I applied full reverse to both engines, the good one went into full reverse but the faulty one went into FORWARD thrust at whatever N1 full reverse is. As a result the aircraft suddenly pitched up, lifting the nosewheel off the ground and yawed. This was completely unexpected, but I instinctively controlled the aircraft with rudder and elevator, and cancelled reverse thrust and brought it to a safe stop.

[Officer Kite]

was there any write up on this? I imagine it was classed as an incident at least? I'd be interested to read something on it if it was deemed report worthy

[Fursty Ferret]

Would be interested to read this too.

[Uplinker]

If you both mean my reverser incident, no but am happy to explain more by pm.

[FCeng84]

Please excuse my lack of pilot training experience as I am a career flight controls engineer, but not a pilot. It seems to me that having thrust reverse inoperative on one engine of a twin would be good reason to avoid thrust reverse usage all together due the the known yaw asymmetry that will cause.

It is my understanding that landing field length considerations do not count on the availability of thrust reverse and thus planning not to use it would not impact the performance decision as to whether a particular field is long enough given airplane type and weight. Am I wrong here? Is credit taken for availability of thrust reverse when calculating required landing field length?

Always looking to learn more.

[Goldenrivett]

Hi
FCeng84,
It seems to me that having thrust reverse inoperative on one engine of a twin would be good reason to avoid thrust reverse usage all together due the the known yaw asymmetry that will cause.

Have a quick look at:
https://aviation-safety.net/database/record.php?id=20070717-0

[FCeng84]

Goldenrivett - thanks for posting that link, I found it to be an interesting read about a sad event that should have been preventable.

It seems to me that any procedure that calls for asymmetric control of the throttle levers during landing introduces a safety risk. In the event referenced, one lever was left commanding significant forward thrust while the other was moved to idle and then to reverse. Would it not be better to have a procedure that calls for both throttle levers being retarded to idle with reverse thrust being commanded on both throttle levers at pilot discretion provided there is not a known reverser fault?

There is mention in the report of a 55 meter landing distance penalty related to how the throttles are used during landing, but it is not clear if that would mean that longer runway is required for landing with no usage of reverse vs. landing with one of the reversers known to be inop but planning to use the other.

Having a system where moving the throttle lever to command reverser can result in increased forward thrust if the reverser fails to deploy seems to me to be a major design error. There should be interlocks such that engine spool up for increased reverser action will not happen unless the reverser has properly deployed.

I am still left with the question as to whether or not landing field length requirement determination takes credit for availability and usage of reverse thrust.

[Check Airman]

Stopping distance does not take credit for reverse thrust. If I'm not mistaken, the only time reverse thrust is accounted for is a rejected takeoff an a wet runway [25.109(f)], with the good engine at idle reverse. Standing by to be corrected if I'm wrong.

That said, if I'm landing with an inoperative reverser, I'll select idle reverse on the god side. The asymmetrical force isn't that significant at idle.

[A320ECAM]

Guys, the reason the Bus downgrades protection during abnormal situations is because it is giving you more control.

Logical and simple if you ask me.

[vilas]

In A320 recommend procedure is to select both reversers. It doesn't cause any control difficulties. However if due to strong gusty crosswind causes a problem it is supposed to be brought to idle reverse, control the direction and reapply as necessary. There is no point making one's own procedures.

[vilas]

A320ECAM
It is not called degraded protection but Abnormal attitude law. If the aircraft gets into unusual attitude(which is defined) due to environmental factors full application of controls to recover is enabled in this law.

[Fursty Ferret]

Would it not be better to have a procedure that calls for both throttle levers being retarded to idle with reverse thrust being commanded on both throttle levers at pilot discretion provided there is not a known reverser fault?

After TAM3054 at Sao Paulo, that's exactly the procedure. If at least one thrust reverser works, both thrust levers are moved to the reverse detent. Although this is really to ensure ground spoiler deployment, any reverse thrust helps with stopping distance on a wet runway.

[Uplinker]

Hi
FCeng84,


Have a quick look at:
https://aviation-safety.net/database/record.php?id=20070717-0


Oh man, what a disaster. No matter what the reverser situation was, both thrust levers should have been reduced to idle in the first instance, while flaring, and then reverse selected.

My situation was that the reverser that should have been locked out wasn’t, so when I selected reverse on both, the engine with the faulty reverser spooled up but the reverser did not deploy, so I got forward thrust on that engine and reverse thrust on the other.

As long as one is careful, and is landing on a runway with normal grip: using reverse on just one engine of a twin does not present any significant yaw control problems.

[tdracer]

My situation was that the reverser that should have been locked out wasn’t, so when I selected reverse on both, the engine with the faulty reverser spooled up but the reverser did not deploy, so I got forward thrust on that engine and reverse thrust on the other.
Uplinker, I don't know much about the Airbus implementation, but if this happened as you described - i.e. you selected reverse but got above idle forward thrust, it violates the FAR/CS regulation 25.933:
(3) Each system must have means to prevent the engine from producing more than idle thrust when the reversing system malfunctions, except that it may produce any greater forward thrust that is shown to allow directional control to be maintained, with aerodynamic means alone, under the most critical reversing condition expected in operation.
I can't help but think there is more to what happened to you. Making sure an engine stays at idle if the T/R is not in the commanded position is one of the most basic design requirements.

[Vessbot]

I suppose that the "means" to prevent the system from developing more than idle power could malfunction. So you'd need a means to prevent the means from malfunctioning. And a means to prevent the means to prevent the means...

[tdracer]

Vessbot, it's not that simple. 25.1309 requires a safety assessment - I can't speak for Airbus, but Boeing (at the FAA's insistence) treats above idle thrust in an uncommanded direction to be potentially catastrophic. That in turn means the probability of the failure needs to be less than 1/billion flight hours (among other things - that also means it can't happen due to a single failure - it needs to require multiple failures).
Somehow I don't think Uplinker is that unlucky...

[galaxy flyer]

Is any of this related to the A320 accident at São Paulo Congnhas accident? That was attributed to a reverser malfunction or crew’s response to one.

[vilas]

Gf
Off cours it is. Golden rivet has given the link you can read it.

[galaxy flyer]

Vilas,

Sorry ‘bout that, thanks.

[Nubboy]

Going back to the opening post.
On my bus conversion course ground school, it was hammered into us that a 320 tends towards being tail heavy and to avoid passenger splits with front cabin empty and rear cabin full like the plague. This was already a well known problem in 2004.
Later in my career I had exactly this happen on a triangular charter where check in staff allocated passengers to the first destination to the front cabin and second destination the rear cabin despite company loading instructions being to divide destinations by left aisle and right aisles instead.
During disembarking at first destination I had the FO monitor the nose wheel strut extension. Sure enough the aircraft was going to go very nose wheel light. There then followed a period of musical chairs as transiting passengers were moved forward to reload the nose wheel. Nightmare as we had to do the same on boarding as the new passengers had been allocated seats in the front cabin based on the seating plan sent from our original departure point. All compounded by the baggage being loaded as per the passengers. First landing in the forward holds. Second in the rear. Would you believe that 3 weeks later, despite the air safety report I filed as well as complaining directly to tech management the same airport repeated the same offence. My comments were completely unprintable. The reason they gave was it was driven by making the baggage handling easy and keeping families together.
My awareness of the potential for loading issues goes back to flying freight in Shorts 360 where the rear hold being bigger than the forward hold was an obvious target for incorrect loading. In fact we had the habit of feeling the weight on the nose leg during the take off roll to check all was well . This probably saved the life of some friends when it was seriously out of balance and wanted to rotate of its own accord at about 30 kts.

To go back to the Verona incident if the passenger split was brought to the captains attention, then this elevates the incident gross professional negligence.

[Uplinker]

Sorry for the thread creep; just to answer tdracer:

Uplinker, I don't know much about the Airbus implementation, but if this happened as you described - i.e. you selected reverse but got above idle forward thrust, it violates the FAR/CS regulation 25.933:

I can't help but think there is more to what happened to you. Making sure an engine stays at idle if the T/R is not in the commanded position is one of the most basic design requirements.

I agree with you entirely, and I thought I had screwed up in some way, but I have landed on that runway in A320/321 about a thousand times. It could have been more slippery than usual, but that does not explain the pitch up.

Anyway, back to the thread.