|Source: Grahame Hutchison|
Fatigue caused the in-flight separation of the propeller of a Regional Express Saab 340B turboprop passenger aircraft flying a routine flight to Sydney on 17 March 2017 , Australian Transport Safety Board says in the preliminary investigation report.
An inspection of the aircraft by the ATSB at Sydney airport identified that the propeller shaft had fractured, leading to the separation of the propeller attached to the propeller gearbox (PGB) of the GE CT7-9B turboprop engine.
This is the first known critical failure of this type initiating within the propeller hub flange of a GE Aviation CT7-9B engine.
The crack was found to be a fatigue fracture that had initiated within the propeller mounting flange, and then transitioned into the shaft section. The crack originated at the bore of a dowel pin near the forward face of the propeller hub flange.
The dowel pin bore was corroded in parts, and corrosion pitting was found near the fracture.
About 55 nautical miles south-west of Sydney airport, the crew noticed uncommanded engine indications and began the necessary checklists. While undertaking the checklist items, the crew experienced minor vibrations from the right engine.
These vibrations worsened as the checklist progressed and became visually evident to the First Officer. As a result the crew commenced the engine shutdown procedure.
During the engine shutdown procedure, the propeller separated from the aircraft. The crew made a Pan-Pan call to air traffic control, and completed the engine shutdown procedure. The aircraft landed without incident at Sydney airport.
The same propeller gearbox (PGB) is fitted to multiple variants of the CT7 engine (5A2, 7A1, 9B, 9C, and 9C3) and powers the SAAB 340 and the Airbus CN-235 transport aircraft.
The report says currently no maintenance procedures are available to detect such fatigues and advises all operators of this type PGB equipped aircraft to take note of the investigation report.
Following the incident, Regional Express has quarantined all propeller gearboxes with propeller shafts of the same series as that installed in VH-NRX.