A320 -Stall

[alexban]

Having just flown for a few times the A320 on the sim , I have one question for an instructor/test pilot on the Bus:
In case of a failure that will invalidate the speed data , for ex the pitot system blocked, what would happen if the speed slows too much?
I was discusing the Air France accident with an instructor on the A320, from our company, and he said that you cannot stall an airbus.
But ,in my oppinion , if the plane knows a 'wrong' speed, then how will prevent it from stalling?
My friend said that the plane will start descending in a controlled fashion, and you can do 15 deg bank turns...like normal flight.
I've did some test flights on the 737,even stalls, and I think that whatever the plane is, it should follow the aerodynamics laws.
How will the computers help on an A320 if they don't have the speed info?
We had one event with unreliable speed, just prior landing , and the pilot flew pitch/power...all ok. What would've happened if he would've add no thrust?
Brgds
Alex

[IndAir967]

may be they use Gs calculations.
(was just a suggestion)

[Clandestino]

A320 can be stalled in alternate and direct control laws and alternate law is what one gets when: two or all ADRs (air data reference) fail, all three ADRs disagree or one fails and two others disagree (the list is not exhaustive).

Sadly, the XL crew has demonstrated that A320 can be stalled in normal law too, provided both AoA inputs are valid, in agreement and way below actual AoA.

[alexban]

Hy.
Clandestino, how will the plane stall? Lower the nose, or just some parachute like descent? How can we see that in the sim? Can we do a stall recovery in the sim? (Not just approach to stall)

[dhiraj singh]

well even i have heard that u cannot stall and airbus A320, every airspeed has a related AOA associated to it, +16 to -4 for most GA aircrafts, and no matter what the airplanes attitude or airspeed is if the the AOA is not in the range u can stall the airplane, coming to the a320 not stalling is , when the airplane is stalled u get the engines on full thrust in the TOGA and alpha 4 config and the plane can actually climb at 5000ft/min.,.it can also be rolled at 60 degrees bank which is outside the flight envelope.,.and the FD helps to get the plane in straight and level from any unusual attitude.,.:ok:it is strange that all the pitot probes are blocked at a time.,can though be done in the sim.,.

[Clandestino]

Sorry to disappoint you Alexban, I'm not instructor/test pilot on A320, I just wanted to make the point that Airbus is not above the laws of the aerodynamics. During my TR course I have practiced approach to stall recovery in direct and alternate laws and that was pretty uneventful. I never tried to push it to the simulated stall so I really have no idea what does the sim do at stall and know even less about real A320 behaviour when pushed to the edge of the envelope.

I'd love to see your questions answered by Airbus test pilot(s) too.

[wileydog3]

The -320 is not an exotic airplane and it does not have relaxed stability. It stalls just like any other airplane with all the magic off.

I had the chance to fly with the late Nick Warner and we visited the handling with all the magic off. As Nick said, "When everything goes down we are not going to fold our hands and say, 'thank you for a very nice life.' We still have options."

FWIW, I also had the opportunity to stall the 737-300 in clean and dirty configs. The first indication was a buzz which developed into a rumble and then a distinct and noticeable vibration as if the airplane was saying, "Do you really want to do this??" With the stall, the nose fell through; I released back pressure and added thrust to recover. Straight forward and simple.

[alexban]

Hy
The reason I've asked this question is that , after talking with some A320 pilots, I've got the impression that they think that whatever will happen, the plane won't stall. The last one told me that the plane will simply start descending, like in a normal flight, and that you will be able to fly it doing 15 deg bank turns, like nothing happened.
I am not a bus pilot, so I have no direct knowledge , but I think it can be potentially dangerous if their idea is wrong. If there is a fault that can result in a real stall ...and I'd like to do a sim demo for that.

[bad bear]

Of course an Airbus can stall.
It does require nature to provide energy loss in the form of wind shear or down draught alternatively a yawing gust while banked and near the stall will do the business. As the chap on star trek once said " ye canna suspend the laws of physics". If you are near the stall and nature takes some of your energy away it will happen.
Under normal circumstances it will not stall but in a dynamic situation like strong convection or turbulence it can stall. I don't think it has ever happened this way and doubt it ever will, but theoretically it could.
If one were to stall in this way the flight control laws will leave you in alternate law and normal law will not be available for the rest of the flight.
beam me up Scottie
b b

[safetypee]

Considering a demonstration ‘training’ stall what differences are there between an A320 etc, and a conventional aircraft?

In this regard I am interested in the behaviour of the trim system.
With a conventional aircraft, it is normally trimmed for slow flight at a speed above the stall, e.g. 1.3Vs, so that during recovery there is a known ‘standard’ of pitch-feel, a pull force up to the stall, etc.
With Airbus, conventional feel differs due to the side stick. In the higher order control laws, trim appears to have a follow-up action, which might be hazardous at the lower speeds if an inadvertent dynamic situation is encountered.

Thus, are training stalls limited to the basic pitch control laws, and if so, do these laws require manual trim input and crew awareness of the trim position due to the lack of speed/trim feel feedback through the side stick?

[Mad (Flt) Scientist]

Thus, are training stalls limited to the basic pitch control laws, and if so, do these laws require manual trim input and crew awareness of the trim position due to the lack of speed/trim feel feedback through the side stick?

I believe the main reason for only demonstrating stalls in the more degraded control modes is that without degradation, you don't get much of anything happening - the aircraft just sits at the envelope limited alpha and waits for you to get bored.

And other types can also end up stalling with trim settings in unfortunate positions - the recent B737 incident in the UK being one relatively recent example.

[WeekendFlyer]

You have to remember that all aircraft can stall if the aerodynamic conditions required for doing so are met. All wings have a CLmax and associated AOA that, if they are exceeded, will result in a stall. The A320 and other FBW airliners are protected in that the flight management computers won't let you actually stall the aircraft because they have an AOA limit which they will not permit the pilots to exceed. However, in the event of a system failure, freak windshear or erroneous data from the air data system, you can lose that protection and a stall can then occur.

The key with FBW aircraft is knowing exactly how the flight control laws work in normal, degraded and failure modes, and understanding which modes,failures or combinations of such will degrade or negate the AOA limit protection.

[safetypee]

Thanks MFS.
If we consider two situations, first the conventional a/c with manual control, and second the technologically enhanced a/c - FBW manual or auto, or conventional with autos, then there are differences in the trimmed state approaching the stall.

With ‘conventional manual’ the crew command trim and are aware of the trimmed state via stick force.
With the ‘enhanced’ situation, an auto/conventional aircraft will probably revert to manual at Vss, except, as you indicate, that the trim may be in an unfortunate position. The significance of this is that crews probably have never seen the situation before because of the method of demonstrating training stalls – no trim below 1.3Vs. This is not to say that training is inadequate, more that the systems are ‘remiss’ in not handing over the aircraft in a suitable trimmed condition;- hence the push force during the recovery in the AMS 737 accident, the UK incident, and perhaps a component of the Q400 accident.

Where training (demonstration/simulation) stalls are flown in FBW aircraft they are made in the basic control law; do these aircraft suffer inappropriate trim conditions?
If ‘follow up’ auto trim is disabled in the basic law, then thereafter how are the crew aware of the trimmed condition? All the crew might do is to refer to the trim wheel or ECAM display, but this might be of little value without knowledge of the required trim setting ‘during a stall’ (the 1.3VS equivalent). I assume that there is no force feedback, and that manual trim is still enabled. Is this electric or only mechanical?
Perhaps this problem was a contributor to the recent A320 flt test accident.

[TyroPicard]

I will try to answer alexban's "one question"...
In case of a failure that will invalidate the speed data , for ex the pitot system blocked, what would happen if the speed slows too much?In Normal Law there are two protections designed to prevent a stall - high AoA protection in which the FBW limits the a/c to αmax, and ALPHA FLOOR in which the A/THR provides TOGA thrust. With invalid speed data tha A320 switches to Alternate Law and these protections are no longer available. So if the a/c slows too much it will stall.
On a type rating course recovery is practised from the approach to the stall in clean config (alternate law) and landing config (direct law). The stall is completely conventional.
TP (A320 SFI)

[Radhaz]

Whilst thinking about the 'simulation' aspects, the old 'rubbish in, rubbish out' adage still applies. There is no guarantee that the flight model in the sim is accurate (especially if it is an area where the aircraft 'cannot' go). The edges of simulator models are notoriously poorly defined and should not be relied upon to provide realistic training / the truth!

[WeekendFlyer]

I can give you a prime example of that! A very experienced and greatly respected colleague of mine recently asserted that he thought a certain aircraft type's air data system was excellent because in the sim the numbers were "all good" even in the transonic region of the envelope. However, subsequent discussion with another colleague who was working on the real aircraft's air data system revealed that it was actually quite poor, particularly the static pressure errors which were "somewhat unpredictable".

The lesson I learnt? Never assume the sim represents the real aircraft unless you know the system or flight envelope behaviour you are seeing has been validated by data from the real thing!

[izzyshore]

Don't get too wrapped up in sims. Like every simulation, they are designed for specific reasons - tools in boxes. Like every tool, it's not how much it cost, it's knowing how to use it that counts.