Rockwell Shrike Commander 500

The ATSB found that the aircraft had not broken up in flight and that it impacted the water at a relatively low speed and a near wings-level attitude, consistent with it being under control at impact. It is likely that the pilot encountered rain and reduced visibility when manoeuvring to commence a visual approach. However, there was insufficient evidence available to determine why the aircraft impacted the water.
Several aspects of the flight increased risk. The pilot had less than 4 hours sleep during the night before the flight and the operator did not have any procedures or guidance in place to minimize the fatigue risk associated with early starts. In addition, the pilot, who was also the operator’s chief pilot, had either not met the recency requirements or did not have an endorsement to conduct the types of instrument approaches available at Horn Island and several other locations frequently used by the operator.

Findings as to Causes and Contributing Factors:
1. At the fuel compound, the 45-gallon drum containing slops was located near the stock of sealed 45-gallon drums of 100LL AVGAS, contributing to the fuel handler selecting the drum of slops in error.
2. The 45-gallon drum of slops had similar markings to the stock of sealed 45-gallon drums of 100LL AVGAS, preventing ready identification of the contaminated drum.
3. The fuel handler did not notice that the large bung plug was not sealed on the second 45-gallon drum and, as a result, delivered the drum of slops to the aircraft.
4. The pilots did not notice that the large bung plug was not sealed on the second 45-gallon drum and, as a result, fuelled the aircraft with contaminated fuel.
5. The pilots were inexperienced with refuelling from 45-gallon drums and did not take steps to ascertain the proper fuel grade in the second 45-gallon drum. As a result, slops, rather than 100LL AVGAS, was pumped into the aircraft’s fuel system.
6. The fuel system design was such that the fuel from both wing fuel cells combined in the centre fuel cell and, as a result, contaminated fuel was fed to both engines.
7. The contaminated fuel resulted in engine power loss in both engines and the aircraft was unable to maintain altitude after takeoff.
Finding as to Risk:
1. The impact force angles were substantially different from that of the ELT’s G-switch orientation. As a result, the ELT did not activate during the impact. This could have delayed search and rescue (SAR) notification.

A total loss of engine power due to fuel exhaustion as a result of the pilot’s inadequate preflight inspection.

Loss of control in altitude for undetermined reasons.

The pilot-in-training inadvertently shutting off both engine fuel control valves causing a loss of power in both engines, and the pilot's failure to maintain control of the airplane resulting in a stall. Contributing to the accident was the chief pilot's inadequate supervision of the pilot-in-training.

Structural failure and damage:
From the detailed examination and study of the aircraft wreckage undertaken by ATSB investigation staff, it was evident that all principal structural failures had occurred under gross overstress conditions i.e. stresses significantly in excess of the physical strength of the respective structures. The examination found no evidence of pre-existing cracking, damage or material degradation that could have appreciably reduced the strength of the failed sections, nor was there any indication that the original manufacture, maintenance or repair processes carried out on the aircraft were in any way contributory to the failures sustained.

Breakup sequence:
From the localised deformation associated with the spar failures, it was evident that the aircraft had sustained a large negative (downward) loading on the wing structure. That downward load resulted in the localised bending failure of the wing around the station 145 position (145” outboard of the aircraft centreline). The symmetry of both wing failures and the absence of axial twisting within the fuselage section suggested that the load encountered was sudden and well in excess of the ultimate strength of the wing structure. Based upon the witness marks on both wing under-surfaces and the crushing and paint transfer along the leading edges of the horizontal stabilisers, it was concluded that after separating from the inboard structure, both wings had moved aft in an axial twisting and rotating fashion; simultaneously impacting the leading edges of both horizontal tailplanes. Forces imparted into the empennage structure from that impact subsequently produced the rearward separation of the complete empennage from the fuselage. The loss of the left engine nacelle fairing was likely brought about through an impact with a section of wing leading edge as it rotated under and to the rear. The damage sustained by all of the aircraft‟s control surfaces was consistent with failure and separation from their respective primary structure under overstress conditions associated with the breakup of the aircraft. There was no evidence of cyclic or oscillatory movement of the surfaces before separation that might have suggested the contribution of an aerodynamic flutter effects.

Findings
The following statements are a summary of the verified findings made during the progress of the aircraft wreckage structural examination and analysis:
- All principal failures within the aircraft wings, tailplanes and empennage had occurred as a result of exposure to gross overstress conditions.
- The damage sustained by the aircraft wreckage was consistent with the aircraft having sustained multiple in-flight structural failures.
- The damage sustained by the aircraft wreckage was consistent with the structural failure sequence being initiated by the symmetric, downward bending failure of both wing sections, outboard of the engine nacelles.
- Breakup and separation of the empennage was consistent with having been initiated by impact of the separated outboard wings with the leading edges of the horizontal stabilisers.
- There was no evidence of material or manufacturing abnormalities within the aircraft structure that could be implicated in the failures and breakup sustained.
- There was no evidence of service-related degradation mechanisms (such as corrosion, fatigue cracking or environmental cracking) having affected the aircraft structure in the areas of failure.

Engine failure in flight following a fuel exhaustion. It was determined that the crew failed to prepare the flight properly and did not calculate the fuel consumption correctly. Investigations determined that the crew calculated a fuel consumption of 100 liters per hour while the true consumption was 120 liters per hour. The following contributing factors were identified:
- Overconfidence on part of the crew,
- Poor organisational culture that affected flight safety,
- Poor flight planning,
- The crew failed to feather the propeller following the engine failure, causing drag and contributing to the loss of control at low height.

Due to the absence of evidences, the cause of the accident could not be determined.

Double engine failure on approach caused by a fuel exhaustion. The following findings were identified:
- Poor flight preparation on part of the pilot,
- Miscalculation of fuel consumption for the flying distance (about an hour),
- The day prior to the accident, tanks were filled with a quantity of 130 liters of fuel, barely 13 liters more than the quantity theoretically necessary for the flight in the conditions existing at the time of the accident,
- No technical anomalies were found on the airplane and its equipment,
- Poor organizational culture within the operator regarding fuel policy,
- Qualitative deficiency in the instruction given to the pilot who had not acquired the basic knowledge for fuel management,
- Failure to observe the actual quantity of fuel in the tanks prior to departure,
- Shortcomings in the operator's organizational processes,
- Inadequate supervision of flight planning activities by the operator who failed to identify any flaws in the fuel management procedures by the pilots.