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2.3.2 Analysis of the Stall Protection Logic
Stall protection is organized around three angle of attack thresholds, that for Alphafloor, that for Alpha-trim and that for triggering the stall warning (see 1.16.1.4).

Alpha-floor protection could not play its role as, when angle of attack of 14.5° was reached, the throttle levers were already on maximum thrust.

Alpha-trim protection was triggered at a value for angle of attack of slightly less than 15° in conditions where the flight dynamics were close to the extreme. It should be noted that it also functioned after coming out of the stall by giving the opposite order
to the THS.

The stall warning did not sound and the stick shaker did not operate in the flight phase prior to the stall. When questioned, the aircraft manufacturer indicated that the cause for non-operation of these two warnings was the disturbance of the angle of attack sensors due to the dynamics of the aircraft’s movements, with the speed having dropped below 60 kt before the angle of attack reached 17.5°. The flight crew had, however, been warned of the approach of a stall by buffeting.

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mm43
Back to AF447. Semantics can always be an issue. Neutralizing the elevator demand means just that, i.e. if continuous demand is made either NU/ND the THS will move in that direction until such time as the SS is placed in the neutral position. In Alt Law the Alpha protections are not available, and for this reason the elevator demand becomes a THS command as explained. At no time was the SS placed in the neutral position which would have enabled the autotrim function to maintain 1g, so effectively that function was over-ridden by the PF. Hence my reason for saying that 'autotrim' had nothing to do with it.

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GENERAL
The pitch control is achieved by the two elevators and the THS via the computers, and controlled by the pitch side sticks orders or autopilot commands.
Max elevator deflection :
30° Nose up
15° Nose down.
Max THS deflection:
14° nose up (THS)
2° nose down.

In AP mode, the Flight Management, Guidance and Envelope Computers
(FMGEC)
send the command orders to the FCPCs ; the FCPCs transmit them to the FCSCs

THS General
The aircraft has a Trimmable Horizontal Stabilizer (THS) , which has two elevators, for pitch trim control. The two elevators are attached to the trailing edge of the THS. The THS is attached to the rear fuselage and moves about an axis to permit pitch trim. The hydromechanical operation system of the THS (referredto as THS actuator) is controlled electrically by the Flight Control Primary Computers (FCPC) and mechanically.

Operation/Control and Indicating

There are three control modes for the THS:

autoflight (electrical control)

manual (electrical control)

standby (mechanical control)

In the autoflight mode the command signals fromthe autopilot are sent to the
FCPCs. The FCPCs transmit autotrim signals tothe electric motors which control the THS actuator.

In the manual mode the command signals from the side sticks are sent to the
FCPCs. The FCPCs transmit autotrim signals to the electric motors which control the THS actuator. The computers elaborate command orders to the servocontrols, depending on the different control laws.

In the standby mode the command signals are transmitted mechanically from
the control wheels to the override mechanism. The override mechanism cancels the autotrim signals from the FCPCs. It transmits the mechanical command signals directly to the hydraulic motors of the THS actuator.


ALTERNATE LAW WITHOUT PROTECTION
In this case, the pitch protections are lost except the load factor protection.
This alternate law without protection is activated in the FCPCs after a triple
ADR failure.

DIRECT LAW
In pitch Direct Law, all the pitch protections are lost.
The elevator deflection is proportional to stick deflection.
The autotrim function is lost and only the manual control of the THS is available.

Laws Reconfiguration - General
The reconfiguration of control laws is different in pitch axis and in lateral axis.
Control law reconfigurations are divided into two families :
- ALTERNATE
- DIRECT

In the event of loss of the normal control laws:
When the conditions required for keeping the normal control laws are no longer fulfilled, the control laws are reconfigured. The various degraded law states possible are (in flight or upon flare):

Roll and yaw:
- Yaw alternate law


Pitch:
- Nz law (with limited pitch rate and gains)
- Vc PROT law
- VMO2 law
- Pitch direct law

The laws called ”Alternate” are engaged when the protections related to the
normal laws (ALPHA 1, VM01) are lost.
The laws called ”Direct” are engaged when the Nz law is lost.

Pitch
The aircraft pitch control is achieved from the side sticks and in certain cases, from the pitch trim control wheels, which act on the elevators and on the THS, depending on the different laws.


Nz law
This law, elaborated in the FCPCs, is the normal pitch law engaged in the
flight phase.
Through a pitch action on the side stick, the pilot commands a load factor ;
the Nz law achieves this command, depending on the aircraft feedbacks, so
that:
- The short-term orders are achieved by the elevator servo controls.
- The long-term orders are achieved by the THS actuator (autotrim function).
The gains depend on the Vc, on the flap and slat position and on the CG
location.
In addition, the Nz law permits to achieve:
- A load factor limitation, depending on the flap and slat position.
- A bank angle compensation, for bank angles lower than 33°.
- A deflection limitation of the THS in the nose-up direction in the event of
the activation of the high angle-of-attackprotection, the excessive load
factor and the excessive bank angle exceeding.
The Nz law is such that the aircraft response is quasi independent of the
aircraft speed, weight, and CG location. If both ADIRUs are failed, the Nz
law is kept, but with limited pitch rate and gains. A consolidation of the vertical acceleration and pitch attitude rate is then performed via the two accelerometer units.

TURBULENCE DAMPING FUNCTION
General
The purpose of the Turbulence Damping Function implemented in the Electrical
Flight Control System is to damp the structural modes induced by atmospheric
turbulence.
Architecture
The Turbulence Damping Function consists of two lanes:

Longitudinal lane
The longitudinal Turbulence Damping command is computed by the FCPC1
(FCPC2 as a redundancy) as a function of the Nz accelerometer information.
It is added to the normal law command and transmitted to the associated elevator servo-controls.

Rear lateral lane
The rear lateral Turbulence Damping command is computed by the FCPC1
(FCPC3 as a redundancy) as a function of the informationof a specific Ny
accelerometer located at the rear bulkhead level.
It is added to the normal law command and transmitted to the associated yaw damper.
Specific equipment
The equipment specific to the Turbulence Damping Function are:
- the TURB. DAMP pushbutton switch
- the Ny front accelerometer
- the Ny rear accelerometer.

In the standby mode the command signals are transmitted mechanically from
the control wheels to the override mechanism. The override mechanism cancels the autotrim signals from the FCPCs. It transmits the mechanical command signals directly to the hydraulic motors of the THS actuator.

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mm43
As an example, go back and have a look at the the initial zoom climb. The initial elevator NU commands were not aided by the THS moving because the allowable 'g' in Alt Law was exceeded ([+1.25/-0.75] where did I get that? Don't know - must have read it somewhere). During the climb the THS moved to maintain the pitch attitude when the SS movements were nominally around the neutral position, but when the 'g' went negative it moved back to 3°NU and only started tracking toward maximum with continued SS NU as the aircraft proceeded to leave the flight envelope.

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GerardC :after the, so far unexplained, FBW malfunction

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A33Zab : Nothing to explain here, there wasn't a FBW malfunction.

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GerardC : and smarter design are solutions for a better flight safety

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A33Zab : but what if a smart design is not understood and not properly used by the user? like AF477.

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why is such a smart AP/FD system unable to maintain for a few seconds the average pitch of, say, the past 5 or 10", until the proper ECAM alert message is displayed ?

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Automatic pitch trim is frozen in the following cases:
- manual trim order
- radio altitude below 100ft for flare
- load factor lower than 0.5 g
- in high speed protection
When angle of attack protection is active, THS is limited between setting at entry in protection and 2° nose down (i.e. further nose up trim cannot be applied).
Similarly, when the load factor is higher than 1.3 g, or when the bank angle gets outside +/- 33°, the THS is limited between the actual setting and 2° nose down.

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JD-EE

RetiredF4 & airtren, if I wish to be provocative I can argue that AF447 suggests we have gone as far as we can go on transport aircraft which are not fully automated with no humans involved on the flight deck except as special deluxe SLF seats with all its controls disabled, permanently under computer control. That is an "improvement" in the current direction FBW is moving. {o.o}

At least with AF447, data available on the plane, and some improved computers and algorithms the pilots didn't even need to know there was a loss of airspeed indication from all three pitot tubes. There probably are other sorts of incidents that would benefit from a human pilot or two in the cockpit. But, if a rule can be evolved for the humans to follow, wouldn't a computer follow that rule better?

Humans are for when the rule based flying vanishes. But, the sense I get from descriptions of flight training as have floated through this discussion is that it is very very rule based with a lot of if-then-else-endif involved. That is a computer's playground. And on a computer's playground humans do very badly. While you add a three digit number in your head the computer has added millions or billions of them (depending on whether you are autistic or not.)

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Instrument rated pilots tend to fly according to instruments, not according to their senses.

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Definition of "properly trained IR pilot" includes, but is not limited to: proper initial IR training, proper type rating training and proper recurrent training.

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Also if the turbulance dampening mode was activated and if that one would influence the response to inputs.

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BEA in its report mentiones the ALT2B law as present, but does not describe in detail, what kind of protections had been lost and which ones still had been active. In my references i couldn´t find what the letter "B" in Alt2B stands for.

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At no time was the SS placed in the neutral position which would have enabled the autotrim function to maintain 1g, so effectively that function was over-ridden by the PF. Hence my reason for saying that 'autotrim' had nothing to do with it.

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VGCM66
Please,

if you are new to this thread and want to contribute something useful out of your expierience as an engineer or any other profession you are familiar with, it would be appropriate to read the nearly 1.000 pages filled about this flight.
That would tune you in the loop of the discussion.

There had been failures, there had been mistakes, and there are things which can be improved to reduce the probability of similar accidents.
The big question to all these matters is "why"?

Your ranting does not contribute to this task.

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Halfway serious question.... :
Could you have recited that list without your notes (AND clearly visualised or 'conceptualised' each particular case) in a car going down-hill with the power steering having given up, and a broken brake line - while pumping the brakes ?

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If you set and hold 5° and set climb power, the aeroplane will climb, after a while power available goes down with altitude, EAS goes slowly down, AoA goes gently up and aeroplane levels off when AoA reaches five degrees minus wing incidence angle.

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what is the relationship between elevator and THS in this trajectory?

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There are issues associated with differences between simulator training and aircraft recoveries. A simulator can provide the basic fundamentals for upset recovery, but some realities such as positive or negative g’s, startle factor, and environmental conditions are difficult or impossible to replicate. These limitations in simulation add a degree of complexity to recovery from an actual aircraft upset because the encounter can be significantly different from that experienced during simulator training. Therefore memory checklists or procedural responses performed in training may not be repeatable during an actual upset situation. The limitations of simulators at the edges of the flight envelope can also cause fidelity issues because the simulator recovery may or may not have the same response characteristics as the aircraft being flown. However, provided the alpha and beta limits are not exceeded, the initial otion responses and instrument indications of the simulator should replicate airplane responses.

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It has already been stated that airplane upsets do not occur very often and that there are multiple causes for these unpredictable events. Therefore, pilots are usually surprised or startled when an upset occurs. There can be a tendency for pilots to react before analyzing what is happening or to fixate on one indication and fail to properly diagnose the situation. Proper and sufficient training is the best solution for overcoming the startle factor. The pilot must overcome the surprise and quickly shift into analysis of what the airplane is doing and then implement the proper recovery. Gain control of the airplane and then determine and eliminate the cause of the upset.

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Airline pilots are normally uncomfortable with aggressively unloading the g forces on a large passenger airplane. They habitually work hard at being very smooth with the controls and keeping a positive 1-g force to ensure flight attendant and passenger comfort and safety. Therefore, they must overcome this inhibition when faced with having to quickly and sometimes aggressively unload the airplane to less than 1 g by pushing down elevator.

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Pilots must anticipate a significantly different cockpit environment during less-than-1-g situations. They may be floating up against the seat belts and shoulder harnesses. It may be difficult to reach or use rudder pedals if they are not properly adjusted. Unsecured items such as flight kits, approach plates, or lunch trays may be flying around the cockpit. These are things that the pilot must be prepared for when recovering from an upset that involves forces less than 1-g flight.

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Utilizing full flight control authority is not a part of routine airline flying. Pilots must be prepared to use full flight control authority if the situation warrants it. In normal conditions, flight control inputs become more effective with increased speed/ reduced angle of attack. Conversely, at speeds approaching the critical angle of attack, larger control inputs are needed for given aircraft reactions. Moreover, during certain abnormal situations (partial high lift devices, thrust reverser in flight) large or full-scale control inputs may be required. Attitude and flight path changes can be very rapid during an upset and in responding to these sorts of upset conditions, large control inputs may be necessary. It is important to guard against control reversals. There is no situation that will require rapid full-scale control deflections from one side to the other.

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Pilots are routinely trained to recover from approach to stalls. The recovery usually requires an increase in thrust and a relatively small reduction in pitch attitude. Therefore, it may be counterintuitive to use greater unloading control forces or to reduce thrust when recovering from a high angle of attack, especially at lower altitudes. If the airplane is stalled while already in a nosedown attitude, the pilot must still push the nose down in order to reduce the angle of attack. Altitude cannot be maintained and should be of secondary importance.

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A stall is an out-of-control condition, but it is recoverable. To recover from the stall, angle of attack must be reduced below the stalling angle—apply nosedown pitch control and maintain it until stall recovery. Under certain conditions, on airplanes with underwing-mounted engines, it may be necessary to reduce thrust to prevent the angle of attack from continuing to increase. If the airplane is stalled, it is necessary to first recover from the stalled condition before initiating upset recovery techniques.

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Situation: Pitch attitude unintentionally more than
25 deg, nose high, and increasing.
Airspeed decreasing rapidly.
Ability to maneuver decreasing.

Nose-high, wings-level recovery:
◆ Recognize and confirm the situation.
◆ Disengage autopilot and autothrottle.
◆ Apply as much as full nosedown elevator.
◆ Use appropriate techniques:
• Roll to obtain a nosedown pitch rate.
• Reduce thrust (underwing-mounted engines).
◆ Complete the recovery:
• Approaching horizon, roll to wings level.
• Check airspeed, adjust thrust.
• Establish pitch attitude.

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Pitch may be controlled by rolling the airplane to a bank angle that starts the nose down. The angle of bank should not normally exceed approximately 60 deg. Continuous nosedown elevator pressure will keep the wing angle of attack as low as possible, which will make the normal roll controls effective. With airspeed as low as the onset of the stick shaker, or lower, up to full deflection of the ailerons and spoilers can be used. The rolling maneuver changes the pitch rate into a turning maneuver, allowing the pitch to decrease.

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