LOAD FACTOR PROTECTION

On commercial aircraft, high load factors can be
encountered during evasive maneuvers due to potential collisions,
or CFIT …

Pulling "g" is efficient, if the resulting maneuver
is really flown with this "g" number.
If the aircraft is not able to fly this trajectory,
or to perform this maneuver, pulling "g" will be detrimental.

On commercial aircraft, the maximum load that is structurally allowed is:

• 2.5 g in clean configuration,
• 2.0 g with the flaps extended.

AIRBUS LOAD FACTOR PROTECTION and safety

On most commercial aircraft, the potential
for an efficient 2.5 g maneuver is very remote.

Furthermore, as G Load information is not continuously
provided in the cockpit, airline pilots are
not used to controlling this parameter.

This is further evidenced by inflight experience, which
reveals that: In emergency situations, initial PF reaction
on a yoke or sidestick is hesitant, then aggressive.

With load factor protection, the PF may immediately and
instinctively pull the sidestick full aft:
The aircraft will initially fly a 2.5 g maneuver without losing time.

Then, if the PF still needs to maintain the sidestick full aft stick,
because the danger still exists, then the high AOA protection will take over.

Load factor protection enhances this high AOA protection.

Load factor protection enables immediate PF reaction,
without any risk of overstressing the aircraft.

Flight experience has also revealed that an immediate 2.5 g reaction
provides larger obstacle clearance, than a hesitant
and delayed high G Load maneuver (two-second delay).

HIGH PITCH ATTITUDE PROTECTION

Excessive pitch attitudes, caused by upsets or
inappropriate maneuvers, lead to hazardous situations:

• Too high a nose-up ▸ Very rapid energy loss

• Too low a nose-down ▸ Very rapid energy gain

Furthermore, there is no emergency situation that
requires flying at excessive attitudes.
For these reasons, pitch attitude protection
limits pitch attitude to plus 30 °/minus 15 °.

Pitch attitude protection enhances high speed protection,
high load factor protection, and high AOA protection.

HIGH ANGLE-OF-ATTACK (AOA) PROTECTION

High AOA protection enables the PF to pull the sidestick full aft
in dangerous situations, and thus consistently achieve
the best possible aircraft lift.

This action on the sidestick is instinctive, and the
high AOA protection minimizes the risk of stalls or control loss.

High AOA protection is an aerodynamic protection:

• The PF will notice if the normal flight envelope is exceeded
for any reason, because the autopitch trim will stop,
the aircraft will sink to maintain its current AOA (alpha PROT, strong
static stability), and a significant change
in aircraft behavior will occur.

• If the PF then pulls the sidestick full aft,
a maximum AOA (approximately corresponding to CL Max) is commanded.
In addition, the speedbrakes will automatically retract, if extended.

airbus AOA PROTECTION

In addition to this aerodynamic protection, there are
three more energy features:

• If ATHR is in SPEED mode, the speed cannot drop below VLS,
even if the target speed is below VLS

• If the angle-of-attack still increases and reaches
ALPHA Floor threshold, the A/THR triggers TOGA thrust and
engages (unless in some cases of one engine-out).

In case of an emergency situation, such as Windshear or CFIT,
the PF is assisted in order to optimize aircraft performance via the:

• A/THR: Adds thrust to maintain the speed above VLS

• ALPHA FLOOR: Provides TOGA thrust

• HIGH AOA protection: Provides maximum aerodynamic lift

• Automatic speedbrake retraction: Minimizes drag.

OPERATIONAL RECOMMENDATIONS:

When flying at alpha max, the PF can make gentle turns, if necessary.

The PF must not deliberately fly the aircraft in alpha protection,
except for brief periods, when maximum maneuvering speed is required.

If alpha protection is inadvertently entered, the PF must exit
it as quickly as possible, by easing the sidestick forward
to reduce the angle-of-attack, while simultaneously adding power
(if alpha floor has not yet been activated, or has been cancelled).
If alpha floor has been triggered, it must be cancelled with
the instinctive disconnect pushbutton (on either thrust lever),
as soon as a safe speed is resumed.

In case of GPWS/SHEAR:

• Set the thrust levers to TOGA

• Pull the sidestick to full aft
(For shear, fly the SRS, until full aft sidestick).

• Initially maintain the wings level

This immediately provides maximum lift/maximum thrust/minimum drag.

Therefore, CFIT escape maneuvers will be much more efficient.

PROTECTED A/C VERSUS NON PROTECTED A/C GO-AROUND TRAJECTORY

The above-illustrated are typical trajectories flown
by all protected or not protected aircraft, when the PF applies
the escape procedure after an aural “ GPWS PULL UP” alert.

The graph demonstrates the efficiency of the protection,
to ensure a duck-under that is 50 % lower, a bucket-distance
that is 50 % shorter, a safety margin that more than doubles
(due to a quicker reaction time),
and a significant altitude gain (± 250 ft).

These characteristics are common to all protected aircraft,
because the escape procedure is easy to achieve, and enables
the PF to fly the aircraft at a constant AOA, close to the max AOA.

It is much more difficult to fly
the stick shaker AOA on an aircraft that is not protected.