What happened
On September 26, 2013, a Twin Commander 690 (registration PR-ORB), operated by Orbisat Indústria e Aerolevantamento S.A., was performing a takeoff roll from runway 20 at Senador Petrônio Portela Airport (SBTE) in Teresina, Brazil. The aircraft was engaged in an aerial survey mission with two crew members and one passenger on board.
As the aircraft reached approximately 80 knots, the crew heard a noise originating from the nose landing gear tire, followed by intense vibrations. This was immediately followed by the inadvertent retraction of the nose gear. The aircraft continued down the runway for approximately 300 meters before coming to a complete stop. All occupants escaped the incident without injury.
The investigation
CENIPA investigators examined the aircraft and the runway conditions at SBTE. Post-incident inspections revealed that the nose gear's down-and-locked mechanism was functioning correctly under normal operating conditions. However, the investigation found that the force generated by the rolling friction of the deflated tire was high enough to overcome the stability of the gear's locking mechanism. This excessive force caused the gear to partially retract, bending control rods and joints and breaking locks.
Regarding the tire, investigators noted that the reference marks between the tire and the wheel hub were offset by approximately 120 degrees. This misalignment suggested that the valve stem had been sheared by the relative movement between the inner tube and the wheel hub during the roll. While the tire and tube had been recently replaced, the specific cause of the initial deflation during the takeoff roll could not be determined.
Additionally, the investigation noted that the asphalt surface of the runway at SBTE was deteriorating, with visible cracks and loose fragments, which may have contributed to the irregular rolling of the deflated tire.
Findings
- The nose gear retraction was caused by an excessive force acting on the locking mechanism, triggered by the high rolling resistance of a deflated nose tire.
- The pilot failed to perform a thorough check of the tire pressure and the alignment of the reference marks during the pre-flight turnaround inspection.
- The deteriorating condition of the runway pavement, characterized by cracks and loose debris, likely contributed to the instability of the deflated tire during the takeoff roll.
- The aircraft sustained substantial damage to the nose gear articulation and locking mechanism, as well as damage to the ventral fuselage skin and stringers due to friction with the runway.