Dramatic Aussie propeller loss prompts industry changes

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October 10, 2018
Rex ATSB propeller loss
The Rex Saab after it had landed safely.

The dramatic loss of propeller from a Regional Express (Rex)  commuter plane near Sydney in 2017 prompted manufacturer General Electric to change its inspection procedures and the US regulator to issue an airworthiness directive.

The Rex Saab A340 was about 55nm (102km) southwest of the airport on a routine flight from the regional New South Wales center of Albury on March 17 when the crew noticed engine vibrations in the right engine.

As the crew started to shut down the right engine, the vibrations worsened and the propeller flew off the aircraft.

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The crew declared a PAN PAN, a step below declaring an emergency, calmly completed the engine shutdown and landed safely at Sydney Airport.

The propeller was recovered a few days later in the bush about 8nm south-west of the airport.

Investigators determined that the propeller separated after the propeller shaft connected to the propeller gearbox (PGB) fractured a result of a fatigue crack. The crack had started in a dowel hole in the propeller shaft flange.

A schematic showing the part that failed in red. Image: ATSB.

This was the first known critical failure of this type in this part of the GE Aviation CT7-9B engine.

An Australian Transport Safety Bureau report issued Wednesday found that the manufacturer’s maintenance documentation did not include specific inspection procedures to detect fatigue cracking of the propeller shaft.

“In addition, the operator’s inspection worksheets did not provide for the recording of inspection findings as defined within documented procedures,’’ the report said. “Consequently, this may not have provided for the best opportunity to ensure potential defects were identified, recorded and monitored.”

Engine manufacturer General Electric responded to the incident with a number of service bulletins requiring immediate inspections of the PGB propeller shaft.

Changes were also made to the engine mantiannance manuals to include more ongoing detailed inspections of the area.

The US Federal Aviation Administration added to this in February, 2018, by issuing an airworthiness directive requiring initial and repetitive visual inspection and fluorescent-penetrant inspection  of the main propeller shaft for affected engines

“This occurrence highlighted how non-life-limited components such as a propeller shaft may still develop defects and fail in-flight,’’ the ATSB said.

“Appropriate training, the use of checklists and effective crew interaction, provide the best opportunity for a positive outcome in the event of such a failure affecting flight safety.

“Additionally, operators are reminded of the importance of having worksheets that accurately reflect the requirements and intentions of associated maintenance documentation.”

Fatigue cracking is often difficult to detect and can be due to corrosion or defects in the part. The only other instance of a propeller flying off a Saab aircraft occurred in 1991 on a plane operated by US carrier Comair.

In that case, the aircraft also landed safely after experiencing similar problems to the Australian crew. The failure was eventually traced to a sub-surface flaw introduced when an ingot was melted to make the part.