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I am sure when getting their type rating for Airbus FBW aircraft, pilots learn how to fly in alternate and direct law. After that, how much opportunity do they get to practice this skill?

On Air France 447 and Indonesia AirAsia flight 8501, the A/P switched off unexpectedly and the control law degraded to alternate 2. It appears in both situations that the PF had trouble stabilizing the aircraft roll attitude. It's difficult to determine whether this contributed to the pitch up and eventual stall but the original pitch up command may have been inadvertent while struggling to level the wings.

Under normal law, which pilots are accustomed to flying, the FAC calculates the amount of aileron deflection required to turn the amount of lateral sidestick deflection into a rate of roll with a maximum of 15° per second. In alternate 2 law the computer cannot make these calculations so it becomes direct stick-to-aileron control.

This can mean that the aircraft responds very differently than what the pilot is used to. Sometimes the difference may be slight but at high speed and high altitude the same stick deflections can result in a significantly higher roll rate.

Additionally the stick does not provide tactile feedback as to how much force is required to move the control surfaces. With conventional flight controls "roll or pitch rate would more directly correlate with the force applied on the control wheel, and not the amount of deflection required."1

These things combined can result in the pilot over-controlling. The control inputs can get out of phase with aircraft movements resulting in pilot induced oscillation in the roll axis. This occurred in both of the above accidents.

It must be terribly disconcerting for a pilot when the A/P disconnects and they are handed control of an aircraft they fly every day, but doesn't respond the way they are used to. I'm wondering how much practice they get at flying in this configuration, either in a simulator or in the aircraft itself. Do most airlines flying FBW aircraft require this regularly? Does Airbus - or anyone else - recommend any amount of further training or practice? Have these recommendations changed in light of the accidents?


1Bill Palmer, Understanding Air France 447

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    $\begingroup$ The Roll wasn't the important part. The Pitch was. In both these accidents the problem wasn't an inability to control the aircraft, the problem was that one pilot in each case tried to pitch up (incorrectly) which cancelled out the other pilot trying to pitch down and prevented stall recovery. Without this, both flights would likely have recovered fine. $\endgroup$
    – Jon Story
    Jan 5, 2016 at 11:54
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    $\begingroup$ @Jon Story I disagree that the problem wasn't in part inability to control the aircraft. An a/p disconnect in cruise should be a non-issue. All that was required was to grab the stick and maintain level flight. Neither of these two pilots was able to do that. In the process of trying to right the plane with suddenly unfamiliar controls both pilots introduced the pitch up that cascaded through a series of other errors into tragedy. $\endgroup$
    – TomMcW
    Jan 5, 2016 at 20:13
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    $\begingroup$ @TomMcW "All that was required was to grab the stick and maintain level flight". It's easier to say, when you already know the pitot is obstructed intermittently, and you have to ignore the related indications. So I'd rephrase your statement as *a part of the solution was to understand the speed indicator was unreliable, but the artificial horizon was correct, and apply the procedure for unreliable speed indicator". $\endgroup$
    – mins
    Jan 7, 2016 at 7:05
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    $\begingroup$ @mins Of course it's easy to say in hindsight. I'm not pilot bashing, I'm saying the complexity of the aircraft worked against him. First order of business is to fly the plane but when he tried to do that he found it didn't fly like he was used to. He was giving full left and right stick movements to counter the roll oscillation even while the PNF was telling him to go light on it. They were in trouble before they even had time to do any troubleshooting. After the A/P disconnected it was only 5 seconds before he set off the stall warning and by 52 seconds they were in a full stall. cont... $\endgroup$
    – TomMcW
    Jan 7, 2016 at 9:18
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    $\begingroup$ ...There's no indication he doubted the artificial horizon, he was just trying to right the plane but was struggling with unfamiliar controls. After they got into the stall certainly there was confusion and bad decisions, but had he been familiar enough with flying in alt law there would probably have been no upset at all. $\endgroup$
    – TomMcW
    Jan 7, 2016 at 9:18

4 Answers 4

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It appears in both situations that the PF had trouble stabilizing the aircraft roll attitude.

Note that roll control is secondary when recovering from a stall.

Restoring normal pitch and roll, he stresses, are "of secondary importance"

The situation required that the pilots heed the stall warnings, be aware of the stall and put the nose down to trade altitude for airspeed.

Have these recommendations changed in light of the accidents?

You can read the recommendations in the official accident reports. These usually explicitly state what such changes should be. I believe it is very rare (except when investigators disagree) for regulators, manufacturers and airlines to ignore any such recommendations.

From what I recall, the major problems in these two incidents were not that the pilots were simply unfamiliar with how control inputs affect flight in alternate law. major problems were that the pilots did not seem to be aware that they were in alternate law or even aware that the aircraft was stalled. In both cases the pilots were confused, failed to follow procedures and failed to coordinate their actions effectively (i.e. CRM failures)

Airbus Flight Crew Training Manuals do cover alternate law.


Recommendations included

5.3 Aircraft Manufacturer
1. The KNKT recommends that Airbus to consider in developing a means for flight crews to effectively manage multiple and repetitive Master Caution alarms to reduce distraction.
2. The KNKT recommends that Airbus to consider and review the FCTM concerning the Standard Call-Outs in all phases of flight.

The Indonesian report lists in some detail the actions taken by the airline and includes an Airbus article "What is a stall? How a pilot should react in front of a stall situation". It also includes some guidance issued by Airbus which includes recommendations concerning upset training in various control laws

enter image description here

After that how much opportunity do they get to practice this skill?

This depends on airline (and relevant regulators) more than on manufacturer. Upset recovery is probably something that all pilots should be trained in, and maintain familiarity with, regardless of who manufactured the aircraft.

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  • $\begingroup$ I understand that the roll was secondary to the accident but the roll was the first upset and it was during the process of controlling it that both pilots inadvertently induced the pitch up. Your last section answers my question, though. Was the paragraph in the image included in the Indonesian report or was it issued by Airbus separately? $\endgroup$
    – TomMcW
    Jan 5, 2016 at 19:53
  • $\begingroup$ @TomMcW: The image is from the Indonesian report. It is also part of a separate Airbus document. $\endgroup$ Jan 7, 2016 at 9:43
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    $\begingroup$ good answer and I feel adding that the problem of too much "autopilot" time (understandably, an A/P consumes way less fuel than a human pilot) is well known and discussed in the industry, to the point that a few airlines were discussing (idk how it ended up) about providing free/mandatory flying hours in gliders and GA planes to keep stick and rudders skill sharp. After all roll rates of a K13 aren`t that different from those of a 747 :p $\endgroup$ Sep 21, 2017 at 7:22
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Air France 477 was in a fully developed stall. In a normal flight attitude. All the way from 40,000 feet to the surface of the ocean. The aircraft was falling like a leaf from a tree, with an angle of attack of 90 degrees. No buffeting. Yes they rolled back and forth, again like a leaf in the wind.

Before AF 477, stall training focused on recognising the onset to stall, and how to prevent getting into one. The F/O who got the plane in a stall in the first place was partially guided there by the flight director: the BAE found in it accident report that Airbus avionics did not present vital flight information that the computers were aware of. Direct AoA indication to the pilots may have saved them, because they never realised they were in a fully developed stall. They were startled, alarms were going off, and they could not find a visual clue in their instruments what was happening.

Pitching the stick down would have initiated recovery. But the air data computer stops sounding the stall warning at AoA over 70 degrees because that can't make sense, right? at under 60 knots of forward speed. When they lowered the nose, the airflow came within the awareness region again and the alarm sounded. Pulling the stick back stopped the alarm sound. What would you have done, had you been the pilot?

They fell all the way into the ocean, not being aware that they were in a fully developed stall, because that was not incorporated in their flight training. Or in anyone elses - it has only recently been added to the training requirements. Alaska Airlines is one of the first to have added this facility to their simulator.

Your question is a valid one, but is based on only a small part of the chain of events that led to the crash:

  • Blocked pitot. Automation detects this, switches off, and sounds a tone. But where was the clear and immediate indication that the pitot data was invalid?
  • Confusing information on the Flight Director
  • Flying in alternate law, and therefore being able to actually enter a fully developed stall. The basis of your question.
  • Not recognising that they had entered a fully developed stall at cruise speed, cruise altitude. Stall prevention training had always focused on low airspeeds, not on Coffins Corner in the flight envelope.
  • Once they had entered the stall: no visual indication, only many sounds that there was something wrong. Pilot training 101: push the stick forward to recover from a stall. These guys had received those instructions during training in the little Cessnas! They knew that.

The captain was asleep when this happened, and locked out of the cockpit. He could have saved the situation, who knows? One of the blessings of middle age is less fight-or-flight and more of a clear head. Or just a fresh pair of eyes coming in and assessing the situation anew.

The Air Asia captain did realise they were in a fully developed stall, and immediately pitched the stick forward. He was an ex military pilot. The issue there was:

  • Language. An Indonesian national using English to instruct the French co-pilot to Push Back.
  • No direct force cue that the copilot was pitching back while the captain was correctly pitching forward. Airbus averages out conflicting stick inputs if no pilot has taken exclusive control by pressing the override button > 20 seconds.

Recommendations were made for Airbus to change flight information presentation. From Cockpit Standard 1.7 onwards, direct AoA information is presented when the automation switches off. See below under Update. Recovery from a fully developed stall will be part of the curriculum soon, and this is a challenge by itself. You've pointed the nose down, and you're diving straight down at mach 1. Please now gently pull the nose back up while keeping lower than N = 2.5 so that the wings don't snap off.

Update

Asked the question to an A380 pilot who upgraded from A330/A340 recently. According to him:

  • Training now includes flying in alternate law and basic law in multiple flight states, including cruise.
  • Proper procedure in the Air Asia crash would have been to command the F/O to not touch the stick.
  • The direct AoA I mentioned above is actually a backup speed tape which seems to work (is my understanding) on basis of AoA. Keep the needle in the green by providing pitch stick input.
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  • $\begingroup$ I saw the YouTube video. My understanding is they were in a rather severe pitchup. I would have gone to full throttle and levelled the nose. I think even in a full stall that will get the horizontal speed up to something the avionics could understand, and quite possibly that is enough to recover. $\endgroup$
    – Joshua
    Jan 16, 2019 at 1:58
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When I did my initial type rating on the Airbus it was rare to find the aircraft in normal law. The thing is most of the complex failures such as dual hydraulic failures, emergency electrical configuration, multiple ADR failures, dual radio altimeters etc always has an effect of downgrading aircraft control laws. The first time I flew in alternate law was in FFS (Full flight simulator) session 3. This is where the instructor forces the aircraft into alternate law to show you how it works. So, for 2 hours you fly in alternate law (no autopilot or flight director). It is pure raw data flying, doing ILS approaches and visual approaches. The whole point of the session is to get familiar with the reconfiguration control laws.

The sessions that followed also contained many scenarios where the aircraft went into alternate law. As I said complex failures always equal flying in alternate law and in the A320 the aircraft will always reconfigure to direct law when the gear is down (if in already in alternate law). That is the story of the one and a half month long conversion course. So, how about after that? As airline pilots we go back to simulator training once every 6 months so it is very frequent. My very first recurrent after the initial did include a complex failure. The dual radio altimeter failure. In this failure the aircraft goes into direct law once the gear is down and you have to fly a raw data approach in instrument conditions. So, do we fly alternate law every 6 months? The answer to that is no. We have so many failures that we need to practice so we cannot ram in failures that make the aircraft go into alternate law every time we come for recurrent. But the training is so frequent that it hardly poses a problem. There will always be alternate law here and there. And we do upset training which is now compulsory. It is always done in alternate law.

enter image description here

enter image description here

Here are Airbus approved A320 type program FFS 5 and FFS 6. I have marked in red those failures that put aircraft in a reconfiguration law.

I also want to comment on one of your statements.

This can mean that the aircraft responds very differently than what the pilot is used to. Sometimes the difference may be slight but at high speed and high altitude the same stick deflections can result in a significantly higher roll rate.

Before I came to Airbus I flew in my airline's regional operations. I flew Dash 8s into small airports with short runways with little to know approach guidance facilities. So, we did a lot of visual approaches and a lot of hand flying. For me, personally, flying the Airbus is the same. I have never felt anything that different. And flying in alternate law is a non event. I have not found the response of the aircraft any difficult to handle. You should not make a statement based on what is written. You have to have first hand experience before you say something like that. One of the most important skills of a pilot is his ability to adapt. I mean in the Dash 8s, sometimes the control cable rigging makes aircraft controls heavy and sometimes weird which makes each air frame unique. But as a pilot you handle the situation and fly the aircraft. Flying in alternate law should not be a problem for a trained pilot. And we cannot really use one accident or actions of one set of pilots and use it to define the whole piloting community.

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    $\begingroup$ Thanks for your response. I'm glad you hear that you get upset training. I think that might have been made compulsory in response to the two accidents I mentioned in my question. There are many questions that are probably unanswerable in the AF447 crash. But the one I keep coming back to is this: why could a trained pilot not seem to be able to fly his aircraft straight and level for 30' seconds in cruise flight without stalling it. From the data and CVR he appeared to be struggling with pitch oscillations, which I simply wouldn't expect from a trained pilot. $\endgroup$
    – TomMcW
    Dec 13, 2020 at 23:37
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    $\begingroup$ I'm conjecturing, really that the change in control laws without any force feedback threw him off enough that he struggled to contain the oscillations. I'm sure that roll inputs feel very different in the coffin corner than they do low and slow and usually the computer accounts for that. With the Dash 8, for example, you can immediately feel the difference between stiff or sloppy controls. With a sidestick there's no such feedback. The good thing is that the industry learns from these things and today you will hopefully be prepared in these situations better than the AF447 was. $\endgroup$
    – TomMcW
    Dec 13, 2020 at 23:43
  • $\begingroup$ This actually answers the question asked: "Do Airbus pilots train for flying in Alternate Law?". All the other answers address specifics of the two crashes mentioned in the question, but not the question asked. Surprised it doesn't have the check mark it deserves. $\endgroup$
    – FreeMan
    Mar 30, 2023 at 16:54
  • $\begingroup$ My first sentence in my answer also answered his question. "Airbus pilots do practice in alternate law when in training. As far as I know, it's a requirement". Also another person's comment stated " Training now includes flying in alternate law and basic law in multiple flight states, including cruise". I don't see how those statements were not answering the question. Of course nowhere near as detailed as Anas Maaz own in regards to practicing to fly in alternate law since I'm not a pilot and he's a real A320/A321 pilot. His answer should have the check mark tho. $\endgroup$
    – Clayson A
    Mar 31, 2023 at 10:32
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Airbus pilots do practice in alternate law when in training. As far as I know, it's a requirement. As you note, in alternate law (A320 family) and alternate law 2 for the other FBW widebody Airbuses, direct proportional commands is given to the ailerons and spoilers where roll sensitivity depends on the airspeed. Combine that with the lack of artificial force feedback to stiffen the sidestick at such high speeds with a startled pilot who's taken by surprise and is required to make an input right away to keep wings level after the aircraft starts banking (or yawing like in AZ8501 thanks to the slight rudder deflection), it's no wonder why both co pilots of AF447 and AZ8501 were overcontrolling in the roll axis. Normal law with it's roll rate, pitch rate/g-load and the flight envelope and speed protections provide mitigation for the lack of force feedback and changing speeds but it can be real problematic when you ain't in normal law and a pilot gets startled at high altitudes and is overcontrolling. A non startled Airbus pilot might be able to control the roll axis in alternate or direct law just fine but with a startled one, that mode change might cause an issue.

Although imo the autotrim in combination with the lack of artificial force feedback in the longitudinal axis were bigger problems imo. Basically it's easier to stall a FBW Airbus in alternate law (if the other pilot don't take priority with his sidestick push button) than pretty much any conventional airliner or C * U FBW equipped airliner flying right now since there's no increased artificial feel pressure at those higher speeds other than a basic centering spring that don't change force based on airspeed and with alternate law, the autotrim will trim the trimmable horizontal stabilizer (THS) automatically to maintain nose up attitude and you don't have any out of trim force to have to trim for. The A320 family in alternate law has low speed stability where it will introduce a nose down input if the AOA is too high and the speed is getting to low but even that can be overridden by just keep pulling back on the stick with little to no challenge. With alternate law 2 in the widebodies, low speed stability is lost. All these is why I prefer C * U FBW in aircraft like the A220, 777, 787 etc over the C * FBW used in FBW Airbus and the Dassault Falcon 5x-10x aircraft. Every C * U aircraft I know of has artificial force feedback regardless of the FBW mode it's in to decrease the chance of over control at higher speeds in roll and pitch and requires manual trim to trim out the forces where the THS moves automatically afterwards, even though in normal mode at least you're trimming a reference speed and C * U is speed stable, allowing for speed cues. Airbus had to get special conditions approved from the FAA and if it wasn't for normal law with all it's protections and the use of rates in the roll and pitch axis along with g-load, FBW Airbus aircraft would not have been certified according to some pilots from a few aviation websites and an A350 captain who told me this in a YouTube comment.

All those cues and tactile feedback from C * U FBW aid in situational awareness and is not a guarantee to make a disoriented pilot not persist with nose up inputs to stall the airplane, but certainly would not have been as easy to do at higher speeds and high altitude. It's better to have those cues cause it may help the pilot get back to his senses and return the plane back to normal level flight. These could really make a difference when a pilot is confused and disoriented and has to manually hand fly, especially if there's a FBW mode change. 2 Boeing 777 captains I came across said it's very difficult to keep a continuous nose up attitude at high altitudes and airspeed to stall the plane as the artificial feel forces extremely strong and you have to consciously trim for the horizontal stabilizer to move. It won't move on it's own to help make it easy to keep a nose high attitude to stall it. Even an Airbus Captain in YouTube comments who flew the A330/340 previously (who questioned how the FBW Airbus's got certified in the first place), told me AZ8501 and AF447 might not have even stalled had the C * U FBW system been in place as it might have made Bonin thing twice about persisting with nose up commands and might have made them cease doing that, prevented the stall and thus preventing the 2 accidents entirely. I like FBW Airbus aircraft and they have a great safety record, but I definitely prefer C * U FBW it's competitor Boeing uses, especially the advanced one on the 787. Has more benefits.

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    $\begingroup$ Fully agree. Active force feedback is a necessity in an emergency. $\endgroup$
    – Koyovis
    Mar 30, 2023 at 1:17
  • $\begingroup$ ...What are "C * " and "C * U"? $\endgroup$
    – Vikki
    Apr 2, 2023 at 17:22
  • $\begingroup$ From how I understand it, C* is the FBW version where in regards to pitch inputs there's a gradual change from pitch rate (low speed) to g-load factor (high speed). C* FBW maintains neutral stability for the aircraft that uses it and requires an autotrim system for the horizontal stabilizer to maintain the pitch attitude the pilot sets when the stick is released. It will keep the attitude regardless of airspeed loss which is a consequence of C* FBW. This design eliminates speed cues as a result and artificial feedback isn't provided. Airbus FBW and the Dassault Falcon 5x-10 don't provide that. $\endgroup$
    – Clayson A
    Apr 3, 2023 at 1:42
  • $\begingroup$ C*U is the speed stability version where you're provided feedback on if the aircraft is trimmed for speed or not. The pilot trims for speed changes and the aircraft has longitudinal static stability, where the aircraft will change pitch depending on if the airspeed is getting slower or higher from it's current trimmed airspeed. The pilot trims for a certain airspeed and then the horizontal stabilizer will move to allow for it. artificial feedback is provided. These provides a cue if you're low on airspeed or flying fast. Aircraft with this FBW version fly more like a conventional aircraft. $\endgroup$
    – Clayson A
    Apr 3, 2023 at 2:12
  • $\begingroup$ With C*U artificial feedback is provided for not only the pitch axis, but the roll axis also on all the aircraft that has it that I know of. $\endgroup$
    – Clayson A
    Apr 3, 2023 at 2:14

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