The Weekly Reflektion 12/2022

The quality of a Quality Assurance system is only as good as the people responsible for it. When a company loses focus on the quality of processes in place and work carried out then an accident is just waiting to happen.

Aircraft ZS-OEZ, type Boeing B737-200, with starboard engine missing

How do you ensure your Quality Assurance system is working satisfactorily?

In week 9/2022 we used the engine failure on Southwest Airlines Flight 1380 to emphasise the importance of imagination in risk assessments. The initiating event for this failure was fatigue in a fan blade in the engine. This week we continue to focus on fatigue and again it is an engine failure in a commercial aircraft. Thank you to Krassimire Entchev in WintershallDea for bringing this incident to our attention.

South African Airways (SAA) flight left Cape Town airport on 7th November 2007 on a scheduled flight to Johannesburg. The aircraft was a Boeing B737-200. During the take-off, just as the aircraft lifted into the air, the starboard engine became detached from the wing. The crew noticed erratic readings from the starboard engine gauges, followed by drastic attitude changes. The aircraft started behaving erratically and rolled to the right. The crew managed to recover control of the aircraft,climbed to 3000 ft, and established a normal flight attitude at 3000 feet. An emergency was declared and the crew informed air traffic control (ATC) of their intention to return to Cape Town airport. Rescue and Firefighting Services were requested to clear the runway of debris from the damaged engine. The crew prepared for an engine failure landing as described in the emergency checklist. The aircraft was then safely landed, and the passengers were evacuated using the normal exits. 

The aircraft engine is held in place by two engine mount support fittings that attach the engine to the wing, one forward and one aft. Each fitting is secured by two bolts. The investigation revealed that a bolt holding the forward fitting had fractured and this caused the forward fitting to fail. The resulting load on the rear fitting was such that it also failed, and the engine detached from the wing. The engine mounting fittings are designed to fail in a way that prevents structural damage to the wing so that the aircraft can still fly.

The investigation found that the cause of the fracture of the bolt was fatigue most likely by incorrect fitting of the bolt. Either the bolt was under-torqued or over-torqued. The resulting loss in bolt tension led to the fatigue that in turn initiated a crack that propagated to failure.

The aircraft had old type engine mounting fittings, and these required a mandatory crack inspection every 700 cycles. However, the aircraft operator failed to comply with these requirements. Further investigations indicated irregularities with the Aircraft Maintenance Organisation system (AMO), and failure to close out major findings from audits by the Regulator over the previous four years. 

Personnel in key management positions in the operating company, in particular the Quality Manager, had been frequently changed out over the years. The main reason for the change out of personnel were resignations related to failures to manage quality control, carry out mandatory inspections and follow up audits. How do you ensure that your quality control system is working properly?

Reflekt AS