What happened
On April 29, 2011, an Airbus A319, registration G-EZBO, operated by EasyJet, was performing a scheduled passenger flight from Rome Fiumicino Airport to Venice. During the takeoff roll on Runway 25, the flight crew heard an unusual noise and notified Air Traffic Control. Although all onboard indications appeared normal and the landing gear was subsequently retracted, the crew was later notified by controllers that a piece of tire tread had been found on the runway.
The flight continued to its destination without further incident. However, during the approach and landing phase in Venice, the activation of the landing gear triggered an ECAM alternate brake warning. Upon inspection after landing, the crew discovered that the left parking brake was non-functional and that the left semi-wing had sustained damage. Specifically, the separation of the tread from the number 4 main landing gear tire had caused the breakage of a brake pipe mounting flange. Debris from the tread and the flange struck the lower surface of the left semi-wing, resulting in a deformed flap and a small puncture in the fuselage paneling.
The investigation
The ANSV investigation focused on the condition of the affected Michelin tire, which had been retreaded at a facility in Bourges, France. The investigation examined the retreading process, which includes receiving, scraping, applying a liquid rubber layer, applying new tread, and vulcanization, followed by various quality controls.
Technical analysis of the tire and a subsequent report from the manufacturer revealed that the separation was not caused by foreign object damage, cuts, or incorrect inflation pressure. Instead, the investigation identified a manufacturing defect related to the retreading process itself.
Findings
- The primary cause of the event was a technical defect originating from the tire retreading process.
- The separation was attributed to the formation of an adhesion failure channel between the regenerated layers during the retreading process.
- This specific defect was not detectable through visual inspections.
- While shearographic testing (a non-destructive method) is used during the initial stages of retreading, it is not required by current standards to be performed at the end of the process.
- The defect grew in size during the aircraft's service life, eventually leading to the tread separation during takeoff.
Safety action
Following the investigation, the ANSV issued safety recommendation ANSV-4/636-11/1/I/25 to EASA. The agency recommended that EASA develop or identify specific requirements for the retreading of aviation tires, specifically mandating the use of non-destructive testing at the conclusion of the retreading process to prevent similar tread decohesion issues in service.