What happened
On 26 October 2015, a Comair Boeing 73/400, registration ZS-OAA, was performing a scheduled domestic flight from Port Elizabeth to Johannesburg. During the landing phase on runway 03R at O.R. Tambo International Aerodrome, the aircraft experienced a sudden vibration shortly after touchdown. As the crew applied brakes and reverse thrust, the aircraft began rolling toward the left. The left main landing gear eventually detached from the airframe, causing the aircraft to skid on its number one engine cowling. The aircraft came to a halt slightly left of the runway centerline with the nose gear elevated. There were no injuries to the 94 passengers, 4 crew members, or the two animals on board.
The investigation
SACAA AIID investigators examined the aircraft's mechanical state and the flight parameters leading up to the event. The investigation focused on the structural integrity of the landing gear and the stability of the approach. Technical analysis of the left main gear revealed that the shimmy damper had failed a laboratory test and contained fluid in the thermal relief valve. Additionally, significant wear was identified on the upper torsion link bushing and flange. The investigation also reviewed flight data to determine if the approach met stabilized criteria, noting the aircraft's ground speed and sink rate at the moment of impact.
Findings
- The primary cause of the gear failure was excessive shimmy oscillations on the left landing gear, which led to its structural failure.
- The approach was determined to be unstable, characterized by an early flare initiation at approximately 65 feet.
- The aircraft experienced a high ground speed of 167 knots at touchdown combined with a low sink rate of 1.8 feet per second.
- The separation of the left main gear caused the engine to scrape the runway surface, resulting in substantial damage to the engine, landing gear mounting points, and wing fairings.
- The aircraft sustained damage to the runway surface, including fuel and hydraulic fluid spillage.