PROTECTIONS


OBJECTIVES

One of the PF's primary tasks is to maintain the aircraft
within the limits of the normal flight envelope.
However, some circumstances, due to extreme situations
or aircraft mishandling, may provoke the violation of these limits.

Despite system protections, the PF must
not deliberately exceed the normal flight envelope.

In addition, these protections are not designed to be structural
limit protections (e.g. opposite rudder pedal inputs).
Rather, they are designed to assist the PF in
emergency and stressful situations, where only instinctive
and rapid reactions will be effective.

Protections are intended to:

• Provide full authority to the PF to consistently achieve
the best possible aircraft performance in extreme conditions

• Reduce the risks of overcontrolling, or overstressing the aircraft

• Provide PF with an instinctive and immediate procedure
to ensure that the PF achieves the best possible result.

BANK ANGLE PROTECTION

Bank angle protection prevents that any major upset,
or PF mishandling, causes the aircraft to be in a high-bank situation
(wherein aircraft recovery is complex, due to the difficulty to properly
assess such a situation and readily react).

Bank angle protection provides the PF with full authority
to efficiently achieve any required roll maneuver.

The maximum achievable bank angle is plus or minus:

• 67 °, within the Normal Flight envelope (2.5 g level flight)
• 40 °, in high Speed protection (to prevent spiral dive)
• 45 °, in high Angle-Of-Attack protection

HIGH SPEED PROTECTION

When flying beyond maximum design speeds VD/MD (which are greater that VMO/MMO),
there is an increased potential for aircraft control difficulties
and structural concerns, due to high air loads.

Therefore, the margin between VMO/MMO and VD/MD must
be such that any possible overshoot of the normal flight envelope
should not cause any major difficulty.

High speed protection adds a positive nose-up G demand to a sidestick order,
in order to protect the aircraft, in the event of a dive or vertical upset.
As a result, this enables a reduction in the margin betwen VMO/MMO and VD/MD.

Therefore, in a dive situation:

• If there is no sidestick input on the sidestick, the aircraft
will slightly overshoot VMO/MMO and fly back towards the envelope.

• If the sidestick is maintained full forward, the aircraft will
significantly overshoot VMO/MMO without reaching VD/MD.

At approximately VMO +16 / MMO +0.04, the pitch nose-down
authority smoothly reduces to zero (which does not mean that
the aircraft stabilizes at that speed).

airbus HIGH SPEED PROTECTION

The PF, therefore, has full authority to perform a high speed/steep
dive escape maneuver, when required, via a reflex action on the sidestick.

Note:

1. An OVERSPEED warning is provided.

2. At high altitude, this may result in activation of
the angle of attack protection.

Depending on the ELAC standard, the crew may have to
push on the stick to get out of this protection law.