The A320 and A321 aircraft have Angle-of-Attack issues
Found by AIRBUS in laboratory testing, but not in Type Certificate
Need for enhanced TC standards for software for FAA/Boeing and EASA/AIRBUS
For the last months, the front pages of The New York Times or The Washington Post ran, almost on a daily basis, articles on the Boeing 737 Max 8 tragic crashes, the problems of the MCAS computer, the foreign civil aviation authorities grounding of the troubled aircraft and the travails of the FAA.
Recently, EASA has issued Airworthiness Directives as to “excessive pitch problems” with the Airbus A320 and A321. Specifically, the Airbus’ angle-of-attack system was malfunctioning. The problem occurs under these conditions:
Firstly, the aircraft has aft biased center of gravity. Secondly, the aircraft is undergoing a sustained and continuous deceleration. Thirdly, the aircraft is in an approach or landing configuration. Lastly, the crew performs a dynamic pitch-up maneuver.
The EASA AD states that operators must comply with Airbus’ Flight Manual (AFM) Temporary Revision (TR). The AFM TR in question limits the A320neo’s center of gravity envelope, thus limiting the preconditions necessary for the angle of attack issue to arise.
Airbus found the aberration in its own testing, but like the MCAS difficulties, the AOA “weakness” was not found during the EASA Type Certification process. Yes, the European Aviation Safety Administration may have used DOAs to assess that software.
The common theme of some problem in computers responding to the AOA sensor data should cause all certificating authorities to focus more on the testing of software in the TC process.
Neither The New York Times nor The Washington Post has reported on the A320 or A321 issue; so here is a thorough article by the Aerotime News Hub:
“The Airbus A320neo has been found to be potentially subject to an angle-of-attack protection weakness, which, under certain circumstances, could lead to excessive pitch and higher flight crew workload conditions. The notification by the European Union Aviation Safety Agency (EASA) comes weeks after a similar excessive pitch anomaly was discovered on the A321neo.
According to the Airworthiness Directive (AD), issued by the EASA on July 31, 2019, a “reduced efficiency” of the A320neo angle-of-attack (AOA) protection under certain flight configurations, and in combination with specific commanded maneuvers from the flight crew, could lead to excessive pitch attitudes, possibly resulting in increased workload.
This “potentially unsafe” condition, although never encountered during operations, was discovered during analysis and laboratory testing of the A320neo flight control laws, the EASA says.
Airbus has issued temporary revisions to the A320neo flight manual (AFM TR) to address the situation, and the EASA has ordered operators of the type to revise their manuals accordingly. The revisions limit the center-of-gravity envelope for the plane. In addition, the manufacturer has provided loading recommendations.
The regulator’s instructions for the type come after a similar issue was found in another member of the Airbus A320 Family, the A321neo. In that case, Airbus’ temporary revisions to the A321neo flight manuals were necessitated after analysis of the elevator and aileron computer installed on the aircraft. A behavior anomaly in these computer units was also found to potentially lead to an excessive pitch scenario.
In the AD, issued by the EASA on July 17, 2019, operators of the A321neo were also urged to update their flight manuals according to temporary revisions developed by Airbus. The directive, considered as an “interim action”, has since been revised and published again on July 31, 2019. Operators must comply with a 30 day ‘window’ starting August 7, 2019.
As for the instructions regarding the A320neo, the AD comes into effect on August 14, 2019, already, with the commentary period postponed after its publication.”
An objective review of the Boeing and Airbus AOA problems should dictate that the FAA, EASA and other major CAAs must develop a more reliable testing regime for the software which controls flight in these critical stages.
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