What happened
On 25 November 2004, at 21:05 UTC, a Learjet 35A, registration C-GRFO, was performing an ambulance flight from Lisbon Airport, Portugal, to Montreal, Canada, via the Azores and Newfoundland. The aircraft was carrying two pilots, three medical attendants, and one patient.
During the takeoff roll, once the aircraft reached approximately 125 knots, the captain heard an impact underneath the fuselage. Unbeknownst to the crew, the tread of the right-hand main gear tire had separated. The captain, believing the aircraft had struck foreign object debris (FOD), decided to abort the takeoff as the speed was below V1. During the subsequent braking, the second right-hand main gear tire also blew out. The aircraft skidded on its wheel rims for approximately 4,800 feet, eventually veering left and exiting the runway onto the grass, stopping about 6 meters from the runway edge. There were no injuries to the six occupants, and no fire occurred.
The investigation
The GPIAAF investigation examined the aircraft's landing gear, the tire remains, and the runway conditions. Investigators found that the first tire's tread separation occurred near the PAPA intersection. The aircraft's anti-skid system was found to be functioning normally, and no FOD was found on the runway during inspections.
Analysis of the tire remains by Goodyear Aviation suggested potential causes such as excessive sidewall flexing or heat generation from under-inflation, as well as possible impact damage. However, the investigation commission found the under-inflation hypothesis unlikely, as the crew had verified the tire pressures during the pre-flight inspection and found them to be correct.
Findings
- The initial failure was caused by the separation of the tread on the right-hand main gear tire.
- The second tire blowout occurred due to the supplementary loads and heat generated during the application of brakes during the rejected takeoff.
- The aircraft skidded on its wheel rims, causing substantial damage to the right-hand main landing gear, including destroyed tires, eroded rims, and damaged hydraulic lines.
- The use of the drag chute during the aborted takeoff could have assisted in deceleration and potentially minimized the damage to the landing gear.