Wizz UK A321 at Doncaster on Jun 16th 2020, rejected takeoff due to unreliable airspeed

Last Update: November 12, 2020 / 18:23:35 GMT/Zulu time

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Photo of Wizz Air UK G-WUKJ, Airbus A321 — Wizz Air UK G-WUKJ, Airbus A321 (Photo credit: Anna Zvereva / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Jun 16, 2020

Classification
Incident

Cause
Rejected takeoff

Airline
Wizz Air UK

Flight number
W9-807

Departure
Doncaster Sheffield, United Kingdom

Destination
London Stansted, United Kingdom

Aircraft Registration
G-WUKJ

Aircraft Type
Airbus A321

ICAO Type Designator
A321

A Wizz Air UK Airbus A321-200, registration G-WUKJ performing flight W9-807 from Doncaster Sheffield,EN to London Stansted,EN (UK), was accelerating for takeoff from Doncaster's runway 20 when the crew rejected takeoff at high speed due to unreliable airspeed indications. The aircraft slowed safely and returned to the apron.

The AAIB reported the aircraft was to depart for its first flight after long term storage when the crew rejected takeoff at high speed due to unreliable airspeed indications. The occurrence was rated a serious incident, an investigation has been opened.

On Sep 13th 2020 the NTSB announced they have assigned an accredited representative, representing the state of design and manufacture of the flight data management unit, to join the investigation by the AAIB.

On Nov 12th 2020 the AAIB released their bulletin stating the aircraft had put into long term parking on Mar 25th 2020. On Jun 9th 2020 the air data system was flushed in accordance with the long term parking requirements. On Jun 15th 2020 works to return the aircraft to service began. The AAIB summarized the sequence of events:

On 16 June 2020, the aircraft was released to service for a non-revenue flight to Stansted. As the aircraft had been on the ground for an extended period, the commander and first officer decided to complete separate walkarounds as a precaution; they found no faults.

Shortly after 1030 hrs, the flight crew prepared the aircraft for flight, taxied to the holding point and were given clearance to takeoff on Runway 20. The commander reported that, during the initial acceleration, his Primary Flight Display (PFD) trend arrow indicated an increasing airspeed. As the aircraft continued to accelerate his attention was drawn to a number of birds that were in the takeoff path. When his instrument scan returned to the PFD he identified that the speed indication was reading zero. He immediately cross checked with the first officer and called to reject the takeoff. Maximum reverse thrust and automatic braking were applied and the aircraft stopped on the runway. The pilot reported that takeoff was rejected at 120 kt, which was also V1.

The AAIB reported with respect to the examination of the aircraft:

The post flight report produced a failure message '34-12-34 ADR1' associated with a flight control ECAM warning in the No 1 Air Data Reference (ADR1). Troubleshooting performed by the AMO transposed the No 1 and No 3 Air Data Inertial Reference Units (ADIRUs) and after a successful ground test, released the aircraft for the ferry flight.

During the subsequent takeoff, at approximately 1540 hrs, the aircraft performed a low speed rejected takeoff as the commander’s PFD was still not registering an air speed.

Further troubleshooting over the following two days finally found three small insect larvae, approximately the size of a grain of rice, within the No 1 pitot probe. These larvae were liberated whilst performing a pitot probe flush, which was advised by the aircraft manufacturer. The larvae were not retained to enable further identification of the insect species.

The operator concluded that the insect larvae may have been deposited in the pitot probe whilst it was parked with the pitot probe covers fitted. To prevent differential pressure measurement issues in the air data system, pitot probe covers supplied by the aircraft manufacturer do not completely seal the probes, it is therefore possible that an insect could enter the air data system during prolonged parking. It cannot be ruled out, however, that the larvae were deposited once the aircraft had been prepared to return to service on 15 June or an insect had been within the pitot probe covers before they were fitted.

Following safety actions were taken:

The operator has introduced a requirement to flush all total and static pressure lines before any aircraft is returned to operation after it has been parked for more than three days.

The operator is also looking to identify better pitot probe covers that may offer better protection than those currently used.

The aircraft manufacturer is looking to update the aircraft AMM Return to Operations task to require air data system flushing prior to the next fl ight after prolonged time on the ground.