EASA has issued a new airworthiness directive (AD) instructing airlines to carefully check external air data probes before returning aircraft to service after pandemic storage.
This follows continuing instances of flightdeck instrument speed discrepancies, suggesting blocked sensors.
In August 2020, the European safety agency first issued a warning that aircraft that had been grounded during the pandemic should be carefully checked before being returned to service.
At that time EASA said it had noticed “an alarming trend in the number of reports of unreliable speed and altitude indications during the first flight(s) following the aircraft leaving storage, caused by contaminated air data systems. This has led to a number of Rejected Takeoff and Inflight Turn Back events.”
The accumulation of debris in aircraft sensors, such as insects or their nests, or simply a build-up of dirt, is a well-recognized danger in aircraft that have been on the ground for extended periods. Blocked pitot tubes, in particular, can lead to conflicting or erroneous airspeed readings for the pilots.
EASA has now issued a new airworthiness directive, effective June 28, specifically referring to the Airbus A320 family.
The safety agency noted that both Airbus and EASA had previously alerted operators to “apply appropriate protection measures when an aeroplane is parked or stored (even for short periods of time), and to follow recognized manufacturer’s procedures to check the Air Data Probes prior to return to service after such parking/storage.”
On June 21, EASA said that despite the previous alert, an increasing number of operational disruptions have been reported, due to airspeed discrepancies.
“Computational simulations identified that the occurrence of ‘consistent erroneous airspeed indications’ (which stands for 2 or 3 pitot probes delivering erroneous speed information within the same speed range) on A320neo family may affect the aeroplane’s response, in particular during the rotation phase,” EASA said.
The directive noted that the condition has not been encountered during operations. Nevertheless, EASA warned “this condition, if not corrected, could lead to an unstable flight path after takeoff, possibly resulting in reduced control of the aeroplane.”
EASA noted that “to address this potentially unsafe condition,” Airbus has issued an Air Flight Manual Temporary Revision (AFM TR)—“reinforcing the airspeed check during the take-off phase and providing instructions to abort take-off in case an unreliable airspeed situation is detected—and the MMEL TR [Master Minimum Equipment List Temporary Revision], requiring that the Integrated Standby Instrument System (ISIS) Airspeed Indication must be operative.”
The new AD requires the incorporation of the AFM TR and implementation of the MMEL TR. “This AD is considered to be an interim action and further AD action may follow,” EASA said.
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