Even as the Boeing company struggles with the fallout of the Boeing 737 MAX Lion Air and Ethiopian Airline crashes of 2018 and 2019, a result of inaccurate data being given by the ‘angle of attack’ sensors to the anti-stall computer to push the nose down, there is a further development in aviation circles. In both the crashes, the drop could not be over-ridden by the pilots and that is why the aircraft crashed.
To address what is called a potential unsafe condition, the European Union Air Safety Agency (EASA) sent out a caution on 31 July warning of a similar if remote possibility of it going similarly wrong on the Airbus 320neos. With 387 737max aircraft grounded and a loss of $3.4 billion and counting, this notification is not likely to disrupt the 320neos (new engine options) of which over 6500 have been ordered by 70 airlines and nearly 600 are in operation at present, with India’s Indigo and American Airlines its biggest buyers with the former in a $20 billion for 250 aircraft. In 2018 nine 320neos in India were grounded because of a shortage of Pratt and Whitney engine spares.
The reason why there is no dramatic flap over the EASA warning is predicated to new, more efficient engines, combined with airframe improvements and the addition of winglets, named Sharklets by Airbus. Airbus has engaged in due diligence by factoring in a scenario where the angle of attack sensors could fail and is swiftly moving to pre-empt such a possibility.
So, to negate any such event in the air in future the European air safety authorities quickly pushed out an Airworthiness Directive to change the flight manual to handle this scenario which never happened but they say could occur. While it hasn’t occurred in the same fashion even once there have been some glitches on carriers according to EASA and the report establishes grounds for pre-emptive caution. This Airworthiness Directive issued on the A320/321Neos may show that Boeing is not alone with this type of problem, in that the AOA (angle of attack) sensors and its associated computer has occasional malfunctioned or can potentially malfunction in a similar dangerous manner on Airbus A320/321neos.
The AOA sensor indirectly measures the amount of lift generated by the wings. The name refers to the angle between the wing and oncoming air. Its main purpose is to warn pilots/input to the computer when the plane could aerodynamically stall leading to loss of control.
In a sensible move to ensure 320neo pilots are made aware of such a possibility EASA has stated: This condition, although never encountered during operations, if not corrected, could lead to excessive pitch attitude, possibly resulting in increased flight crew workload.
To address this potential unsafe condition, Airbus issued the AFM TR (aeroplane flight manual, temporary revision) limiting the centre of gravity envelope, which prevents the aforementioned condition.
EASA has underscored its concern by placing on record certain observations. In brief, analysis and laboratory testing of the behaviour of the flight control laws of the A320neo identified a reduced efficiency of the angle of attack protection when the aeroplane is set in certain flight configurations and in combination with specific manoeuvres commanded by the flight crew. Airbus is alerting crews to this very outside possibility. The agency will revisit the issue after 30 August.
Updated Date: Aug 08, 2019 10:53:25 IST