To explain the Airbus A320 Habsheim (A320 into the woods) accident, again:
The accident airplane was in NORMAL flight control law. NORMAl law is "normal;" there's no flight control law
"better" than NORMAL - no super-normal, no mega-normal, etc. In NORMAL law, you have three (3) axis control
and the following flight envelope protections: - load factor limitation; - pitch attitude protection; - high angle of
attack protection; - high speed protection, and - bank angle protection.
NORMAL law has both a Ground and a Flight mode. I'll skip the Ground mode discussion, but the Flight mode
is active from lift-off until Flare mode engages during landing at 50 feet RA.
NORMAL law - Pitch: The Normal flight mode is load factor demand law with automatic (pitch) trim and full
flight envelope protection that maintains a 1g load with the sidestick at neutral and the wings level. When using
the sidestick, the elevator and stabilizer trim achieve a load factor proportional to sidestick deflection. Pitch trim
is automatic with or without the autopilot engaged. (And the elevator trim wheel DOES move as the stab trims - my
comment!)
Automatic pitch trim is inhibited under the following conditions:
- Radio altitude (RA) is below 50 ft (100 ft with autopilot engaged)
- Load factor less than 0.5g
- High speed/Mach protection is active
- 33 deg bank exceeded
- Load factor greater than +1.25g (nose up trim inhibited)
- During manual trim (obviously!)
Load Factor Limitation:
- Flaps Retracted: +2.5g to -1.0g
-Flaps Extended: +2.0g to 0.0g
Pitch Attitude Protection:
The airplane's pitch attitude is protected, as follows:
- 30 deg nose up with Flaps (position) 0 to (position) 3,
**********progeressively reduced to 25 deg at low speed;
- 25 deg nose up with Flaps Full (progessively reduced to
**********20 deg at low speed;
- 15 deg nose down
The flight director bars are removed when pitch exceeds 25 deg up
or 13 deg down.
High Angle of Attack Protection: (In this discussion, I will substitute the symbol "@"
in place of the Greek letter for "alpha," which my keyboard doesn't have - or I can't find.
The alpha protection provided by Normal Law comprises three (3) angle of attack
functions. They are: (1) alpha protection (@ prot) alpha floor (@ floor) and alpha maximum
(@ max). The associated V speeds, V@ prot. V@ floor and V@ max vary with airplane weight
and configuration.
In pitch normal law, the elevator control changes from normal mode to a protection mode when the
angle of attack is greater than @ prot. When this occurs, the autopilot disconnects, the speed brakes
retract and the angle of attack is proportional to sidestick deflection. In the @ prot range, from @ prot*****
to @ max, the side stick demands an angle of attack directly; however, @ max cannot be exceeded even
if the sidestick is pulled and held fully back against the mechanical stop. If the sidestick is released,
the angle of attack returns to and maintains @ prot. This function, which provides protection against
stall and windshear has priority overcall other protections. On take-off, @ prot is equal to @ max for
5 seconds. If angle of attack protection is active, the sidestick must be pushed forward to return to the
normal mode.
The @ floor protection, which occurs at a predetermined angle of attack between @ prot and @ max, engages
the autothrottle system. TO/GA thrust is provided regardless of throttle position. The @ floor function *****is NOT
available in the landing configuration below 100 ft RA! (Any guesses why??????????)
NOTE: Alpha Floor is ONLY available in NORMAL (flight control) Law.
I provide the above explanations/descriptions so that you can't accuse me of editing out important information
about the Airbus' Normal flight control laws. *****
)
CAUTION: Alpha Floor protection is only available in NORMAL Law.
A Low Energy Warnibg is triggered during deceleration before Alpha Floor ir reached. (The delays between Low
Energy Warning and Alpha Floor activation depends on deceleration rate.) "SPEED, SPEED, SPEED"
is repeated every 5 seconds to indicate airplane energy is lower than a threshold under which to recover a positive
flight path angle though pitch control; THRUST must be INCREASED! The low energy warning is computed by the
FACs (Flight Augmentation Computers), based on airplane configuration Flaps [position] (2, 3 or Full), airspeed
deceleration rate and flight path angle.
The Low Energy Warning is inhibited:
- When TO/GA is selected
- Below 100 ft RA and above 2,000 ft RA
- When Alpha Floor or a GPWS alert is triggered
- In ALTERNATE or DIRECT law
- If both RAs are failed
- At Flaps 1 or UP
- - -*****
The Captain of the Habsheim accident airplane: 1) did not receive Company or (French) FAA approval
to conduct the maneuver; 2) did not brief the F/O; 3) it was a revenue flight; passengers were on board;
4) had the airplane in the landing configuration; 5) was below 100 ft RA, thus Alpha Floor was disabled),
6) Low Energy Warning was also disabled.
I'm assuming that either the autothrottles were not engaged or the Mode Control Panel speed had been
manually dialed down to a normal Vapp speed. In any event, the engines were at relatively low thrust and
I'm sure the Captain was thinking, during*****the approach/low altitude fly-by, that "any second now the throttles
will go to TO/GA," I'll just pull gently back on the sidestick and the airplane will perform a nice go-around
maneuver. That did not happen as both Alpha Floor and the Low Energy Warning had been (inadvertently/
unknowingly) disabled. I think the Captain pushed the throttles up; but it was too late. The flight path angle
never became positive.
:bawling: :angryfire
