Why Wizz Air A321 aborted take-off at V1

An AAIB report finds that pitot probes had become blocked by something the size of a grain of rice…

The crew of a Wizz Air Airbus A321 were forced to reject a take-off at high-speed back in June after they noticed one of the jet’s airspeed indicators (ASI) was reading zero. 

The aircraft, G-WUKJ (c/n 8879) – which had been parked for nearly 12 weeks at Doncaster Airport prior to the flight – was being repositioned on a non-revenue service to London/Stansted. 

WUKJ
G-WUKJ (c/n 8879) was delivered to Wizz Air UK on June 21 last year. Wikimedia Commons/Anna Zvereva

A report by the Air Accidents Investigation Branch (AAIB) found that after applying take-off power, the commander said his primary flight display (PFD) trend arrow indicated increasing airspeed, but as the aircraft continued to accelerate his attention was drawn to a number of birds in the take-off path. When he returned his view to the instruments the ASI was reading zero.  

The AAIB says the captain immediately cross-checked with the first officer and called to reject the take-off. Maximum reverse thrust and automatic braking were applied, and the aircraft came to a stop on the runway.

wizz air a321
The incident occurred on June 16 earlier this year. Wizz Air

The pilot reported that the take-off was rejected at 120kts, which also happened to be V1. Data from the aircraft’s flight recorder showed that the jet reached a peak airspeed of approximately 128kts, occurring one second after the crew initiated the stopping action. 

According to the report, the aircraft was left in long-term parking in a ‘flight-ready’ condition in accordance with regulations. In the days leading up to its departure on June 16, maintenance personnel at the facility carried out a work package to return it to service.  

The post-flight report produced a failure message associated with a flight control ECAM warning in the number 1 air data reference (ADR1) computer. During troubleshooting over the following days, three small insect larvae, approximately the size of a grain of rice, were found within the number 1 pitot probe. These larvae were liberated whilst performing a pitot probe flush but were not retained to enable further identification of species. 

a321
Wizz Air Holdings - which owns the UK subsidiary - holds a all-Airbus fleet comprising 135 examples. Aviation Image Network/Bailey

The operator concluded that the insect larvae may have found their way into the pitot probe while it was parked, despite the covers being fitted. The covers supplied by the manufacturer do not seal to prevent differential pressure measurement issues in the air data system.  

The AAIB’s report said Wizz Air has introduced a requirement to flush all total and static pressure lines before any aircraft is returned to operation after being parked for more than three days. The airline is also looking to acquire better pitot covers that may offer increased protection compared to those currently in use.  

For Airbus’ part, the manufacturer is looking to update the ‘return to operation’ section in the aircraft maintenance manual to require air data system flushing prior to the resumption of operations after a prolonged period on the ground.