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The pilot did not maintain minimum controllable airspeed while on final approach with a partial loss of power in the right engine, which resulted in a loss of control. Contributing to the accident was the partial loss of engine power in the right engine due to the improperly installed o-rings in the engine’s throttle and control assembly.

Conclusions
Findings as to Causes and Contributing Factors:
1. The right engine lost power when the intermediate spur gear on the torque sensor shaft failed. This resulted in loss of drive to the high-pressure engine-driven pump, fuel starvation, and immediate engine stoppage.
2. The ability of the left-hand No. 2 ejector pump to deliver fuel to the collector tank was compromised by foreign object debris (FOD) in the ejector pump nozzle.
3. When the fuel level in the left collector tank decreased, the left fuel level warning light likely illuminated but was not noticed by the crew.
4. The pilots did not execute the fuel level warning checklist because they did not perceive the illumination of the fuel level left tank warning light. Consequently, the fuel crossfeed valve remained closed and fuel from only the left wing was being supplied to the left engine.
5. The left engine flamed out as a result of depletion of the collector tank and fuel starvation, and the crew had to make a forced landing resulting in an impact with a concrete noise abatement wall.
Findings as to Risk:
1. Depending on the combination of fuel level and bank angle in single-engine uncoordinated flight, the ejector pump system may not have the delivery capacity, when the No. 1 ejector inlet is exposed, to prevent eventual depletion of the collector tank when the engine is operated at full power. Depletion of the collector tank will result in engine power loss.
2. The master caution annunciator does not flash; this leads to a risk that the the crew may not notice the illumination of an annunciator panel segment, in turn increasing the risk of them not taking action to correct the condition which activated the master caution.
3. When cockpit voice and flight data recordings are not available to an investigation, this may preclude the identification and communication of safety deficiencies to advance transportation safety.
4. Because the inlets of the ejector pumps are unscreened, there is a risk that FOD in the fuel tank may become lodged in an ejector nozzle and result in a decrease in the fuel delivery rate to the collector tank.
Other Findings:
1. The crew’s decision not to recover or jettison the birds immediately resulted in operation for an extended period with minimal climb performance.
2. The composition and origin of the FOD, as well as how or when it had been introduced into the fuel tank, could not be determined.
3. The SkyTrac system provided timely position information that would have assisted search and rescue personnel if position data had been required.
4. Saskatoon police, firefighters, and paramedics responded rapidly to the accident and provided effective assistance to the survivors.

It is believed that the loss of control on final approach was the consequence of the failure of both right engines n°3 and 4.

The cause of the occurrence was uncontained failure of the 2nd stage disk of LP compressor of Engine # 4 due to fatigue fracture which resulted in in-flight fire and damage to adjacent areas of right wing / flaps to an extent that flight could not be sustained.
The use of mishap engine beyond its manufacturer’s assigned life without assessment and life enhancement by the manufacturer was the cause of its uncontained fatigue failure.

Contributing safety factors:
• While the aircraft was climbing to 9,000 feet the right engine sustained a power problem and the pilot subsequently shut down that engine.
• Following the shutdown of the right engine, the aircraft's descent profile was not optimized for one engine inoperative flight.
• The pilot conducted a descent towards Bankstown Airport that was consistent with a normal arrival profile without first verifying that the aircraft was capable of achieving adequate performance with one engine inoperative.
• Following the engine problem, the aircraft's flightpath and the pilot’s communication with air traffic control indicated that the pilot's situation awareness was less than optimal.
• The aircraft collided with a powerline support pole on the eastern side of the intersection of Sackville Street and Canley Vale Road, Canley Vale, about 6 km north-west of Bankstown Airport.
Other safety factors:
• The pilot did not broadcast a PAN following the engine shutdown and did not provide air traffic control with further information about the nature of the problem in order for the controller to positively establish the severity of the situation.
• Section 4 of Civil Aviation Advisory Publication (CAAP) 5.23-2(0), Multi-engine Aeroplane Operations and Training of July 2007 did not contain sufficient guidance material to support the flight standard in Appendix A subsection 1.2 of the CAAP relating to Engine Failure in the Cruise. [Minor safety issue]
Other key finding:
• Given the pilot’s extensive experience and testing in the PA-31 aircraft type, and subsequent endorsement training on a high performance turboprop multi-engine aircraft since the issue by CASA in 2008 of a safety alert in respect of the pilot’s PA-31 endorsement, it was unlikely that any deficiencies in that endorsement training contributed to the accident.

Loss of control following the failure of the attitude indicator while climbing in IMC conditions.

The overweight condition of the airplane due to the pilot's inadequate preflight planning, resulting in the airplane's degraded climb performance. Contributing to the accident was the pilot's retraction of the flaps prior to reaching the manufacturer's recommended flap retraction speed.

The pilot's failure to maintain aircraft control and secure the right engine during a loss of engine power after takeoff. Contributing to the accident was the loss of engine power on the right engine for undetermined reasons.

The pilot's spatial disorientation and subsequent failure to maintain airplane control.