All A318,A319,A320,A321 Operators ATA 34 – ABNORMAL V ALPHA PROT
**** Hidden Message ***** CUSTOMER SERVICES DIRECTORATE1 ROND POINT MAURICE BELLONTE
31707 BLAGNAC CEDEX FRANCE
TELEPHONE + 33 (0)5 61 93 33 33
FLIGHT OPERATIONS TRANSMISSION - FOT
FOT ref: 999.0147/14 Rev 00 Page 1 of 3 Date: 08-DEC-2014
© AIRBUS S.A.S. 2014. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT
TO: All A318,A319,A320,A321 Operators
SUBJECT: ATA 34 – ABNORMAL V ALPHA PROT
OUR REF.: 999.0147/14 Rev 00 dated 08-DEC-2014.
CLASSIFICATION: Airworthiness
APPLICABLE AIRCRAFT: This FOT is applicable to all A318,A319,A320,A321 aircraft.
1. PURPOSE
The purpose of this document is to inform operators about:
- Possible activation of high Angle-Of-Attack (AOA) protection (Alpha Prot) in normal law
following blockage of AOA probes
- The operational procedure to apply in order to prevent the above-mentioned effect
- The publication of a new Operational Engineering Bulletin(OEB) n°48, associated with AFM
Temporary Revision (TR) n°502.
2. EVENT DESCRIPTION
An Airbus aircraft equipped with AOA flat cover plates recently experienced an in-service event.
During climb, two AOA probes remained blocked at a constant value. Further in the climb and
during a turn, as the Alpha Prot strip increased quickly, the flight crew disconnected the AutoPilot
(AP). The Alpha Prot activated, resulting in a nose down pitch order. The flight crew stabilized
the aircraft altitude by applying pitch-up orders on the sidestick. Reversion to alternate law
stopped the Alpha Prot activation, and restored control of the pitch orders with the sidestick.
3. INVESTIGATION STATUS
3.1 Cause
The blockage of two or three AOA probes at the same angle may cause the Alpha Prot of the
normal law to activate, depending on Mach number.
3.2 Consequences
In normal law, if two or three AOA probes are blocked at the same angle, an increase of the
Mach number may activate the high angle-of-attack protection (Alpha Prot). This is due to the
fact that the AOA value of the Alpha Prot decreases as the Mach number increases. When the
AOA value of the Alpha Prot decreases, the Alpha Prot strip on the PFD moves upward.
Notice: This FOT provides information about a significant operational issue that is
related to airworthiness or safety. It is each Operator’s responsibility to distribute this
FOT or to distribute the information contained in this FOT, to all of their applicable
flight crews without delay. Failure to apply this FOT may have a significant impact on
safe aircraft operations.
FLIGHT OPERATIONS TRANSMISSION - FOT
FOT ref: 999.0147/14 Rev 00 Page 2 of 3 Date: 08-DEC-2014
© AIRBUS S.A.S. 2014. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT
In the case of Alpha Prot undue activation due to blocked AOA probes, the flight control laws
order a continuous nose down pitch rate that may not be stopped with backward sidestick inputs,
even in the full backward position. If the Mach number increases during a nose down order, the
AOA value of the Alpha Prot will continue to decrease. As a result, the flight controls laws will
continue to order a nose down pitch rate, even if the speed is above VLS.
Two or three blocked AOA probes may induce the following visible effects in the cockpit:
‐ The Alpha Max strip (red) on the speed scale of the PFD may completely hide the
Alpha Prot strip (black and amber) in a stabilized wings-level flight path (without an increase in
load factor), or
‐ The Alpha Prot strip (black and amber) may rapidly move by more than 30 kt during
flight maneuvers (with an increase in load factor, for example turns or pitch variations), with the
Auto Pilot (AP) engaged and the speed brakes in the retracted position.
Blocked AOA probes does not affect the current speed indication on the PFD.
In addition, in OP CLB or CLB with blocked AOA probes, the pitch order of the flight guidance
may be affected by the value of the blocked AOA probes. Therefore, the aircraft may not be able
to accelerate in order to reach the target speed.
4. OPERATIONAL RECOMMENDATIONS
· AT ANY TIME, with a speed above VLS, if the aircraft goes to a CONTINUOUS NOSE DOWN
PITCH RATE that cannot be stopped with backward sidestick inputs, IMMEDIATELY APPLY:
ONE ADR...............................................................................................KEEP ON
TWO ADRs.............................................................................................OFF
If the flight crew sees the cockpit effects described below, they must apply the following
procedure to revert to the alternate law. This prevents activation of the Alpha Prot in normal law:
· If the Alpha Max strip (red) hides completely the Alpha Prot strip (black and amber) in a stabilized
wings-level flight path (without an increase in load factor):
ONE ADR...............................................................................................KEEP ON
TWO ADRs.............................................................................................OFF
The AP, FDs and ATHR are lost for the remainder of the flight.
Switch two ADRs to OFF for the remainder of the flight in order to revert to alternate law to
prevent undue Alpha Prot activation.
In case of dispatch with one ADR inoperative, switch only one ADR to OFF.
CAUTION: RISK OF ERRONEOUS DISPLAY OF THE VSW STRIP (RED AND BLACK)
FPV USE................................................................................................CONSIDER
· If the Alpha Prot strip (black and amber) rapidly moves by more than 30 kt during flight
maneuvers (with an increase in load factor), with AP ON and speed brakes retracted:
ONE ADR...............................................................................................KEEP ON
TWO ADRs.............................................................................................OFF
The AP, FDs and ATHR are lost for the remainder of the flight.
Switch two ADRs to OFF for the remainder of the flight in order to revert to alternate law to
prevent undue Alpha Prot activation.
In case of dispatch with one ADR inoperative, switch only one ADR to OFF.
CAUTION: RISK OF ERRONEOUS DISPLAY OF THE VSW STRIP (RED AND BLACK)
FPV USE................................................................................................CONSIDER
FLIGHT OPERATIONS TRANSMISSION - FOT
FOT ref: 999.0147/14 Rev 00 Page 3 of 3 Date: 08-DEC-2014
© AIRBUS S.A.S. 2014. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT
5. OPERATIONAL DOCUMENTATION
Airbus will publish OEB N°48, named ABNORMAL V ALPH A PROT, to provide the flight crew
with the procedure applicable in the case of two or three blocked AOA probes.
Airbus will also publish AFM Temporary Revision n°5 02 to introduce the operational
recommendations in the AFM.
In addition, FCOM-DSC-27-20, FCOM-PRO-SUP-27-40 and FCTM-OP-020 sections provide a
detailed description of the high angle-of-attack protection in Normal Law.
6. FOLLOW-UP PLAN
OEB n°48 is issued as a precautionary measure until Airbus completes investigations and
provides a final fix to the issue described in this FOT.
Please submit questions about the operational content of this FOT to:
A320/A330/A340 Flight Operations & Training Support - STLL
mailto: fltops.fbwstd@airbus.com
Best regards,
Capt Dominique DESCHAMPS
Vice President Flight Operations & Training Support
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