The aircraft was operating a night freight operation from Brisbane to Sydney. While cruising at flight level (FL) 130 in visual conditions, the crew reported a loud bang and the right engine suddenly ran down. When the crew were about to feather the propeller, the blades were found to be already in the feathered position, and one of the blades was missing. As the aircraft handling was normal, and after considering a diversion to Bankstown, the pilot in command elected to continue to Sydney due to the availability of emergency services, which were placed on standby. The aircraft subsequently made a safe approach and landing on runway 34L.
A post-flight inspection revealed substantial damage to the engine and its mountings. The rear turbine bearing oil supply line had failed and the subsequent loss of oil pressure had resulted in the propeller auto-feathering. The right wingtip fuel tank attachments were loose and the fuel tank could be moved by hand.
The propeller blade had failed about 96 mm from the blade butt. An analysis of the failure surface determined that the failure was the result of fatigue. Fatigue cracking had initiated at the end of the blade pilot tube bore in the region of smallest section thickness on the thrust side of the blade. The cracking did not appear to be associated with any discrete mechanical or corrosion damage.
The propeller is overhauled every 3,000 hours. The last overhaul was in November 1994, 790 hours prior to the accident. During the overhaul the blade pilot tube bore was inspected using the dye penetrant inspection process as required by Airworthiness Directive AD/PHZL/48. Examination of the fracture surface features and an assessment of the rate of crack growth indicated that a region of fatigue cracking, approximately 12 mm in length and 6 mm in depth, was present at the time of the overhaul. However, compounds containing calcium had contaminated this region, reducing the ability of the dye to penetrate the cracks.
As a result of this occurrence, the Bureau of Air Safety Investigation is investigating a perceived safety deficiency. The deficiency identified relates to inspection periods and processes used to inspect Hartzell propeller pilot tube bores.
Any recommendation issued as a result of this deficiency analysis will be published in the Bureau's Quarterly Safety Deficiency report.
|Date:||20 June 1997||Investigation status:||Completed|
|Time:||0430 hours EST|
|Location:||222 km N Sydney, Aero.|
|State:||New South Wales||Occurrence type:||Propeller/rotor malfunction|
|Release date:||01 February 1999||Occurrence category:||Accident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||Mitsubishi Aircraft Int|
|Type of operation||Charter|
|Damage to aircraft||Substantial|
|Departure point||Brisbane, Qld|
|Role||Class of licence||Hours on type||Hours total|