What happened
On 17 November 2013, a Condor Airlines Boeing 767-300, registration D-ABUK, was completing a scheduled commercial flight from Frankfurt, Germany, to Cape Town International Airport. The flight proceeded without any reported malfunctions or difficulties for the duration of the 11-hour journey.
During the approach to runway 01 at Cape Town, a component detached from the aircraft's landing gear assembly. At approximately 0645Z, a resident in the Welgelegen suburb, located roughly 14 km from the airport, heard a loud noise and discovered a large metal spring embedded in his garden soil. The resident, a commercial pilot, alerted Air Traffic Control and the Airports Company South and South Africa (ACSA) regarding the object found directly beneath the aircraft's flight path.
The investigation
Following the report, the SACAA AIID initiated an investigation. Upon inspection of the aircraft, engineers confirmed that the spring from the left-hand main landing gear drag brace jury strut was missing. The investigation established that the component likely broke away while the landing gear was being extended for landing.
Metallurgical analysis performed by CrashLAB on the recovered spring revealed that the failure was a result of a fatigue-mode fracture. The analysis noted that the fracture originated on the surface of the spring and spread through approximately 30% of its diameter. The presence of surface stress-raisers was identified as a critical factor in the failure. It was noted that these indentations might have been introduced during previous maintenance or installation processes.
Findings
- The primary cause of the incident was the shearing of the left main landing gear drag brace jury strut spring.
- Metal fatigue was the contributing factor to the component's failure.
- The crew was unaware of the component's separation because the spring is a mechanical part and is not monitored by any cockpit warning or electrical system.
- The loss of the spring did not compromise the operational functionality of the landing gear, allowing the aircraft to land safely.
- The spring had been in service since the aircraft's last overhaul in June 2009.