Charter/Taxi (Non Scheduled Revenue Flight)

Engine failure for unknown reasons.

The reported loss of engine power from the left engine, and the failure of the left propeller to feather for undetermined reasons, resulting in the inability to maintain altitude, and subsequent ditching.

The accident under examination, as most aviation accidents, has been determined by a series of events linked one another, which caused the final ditching. The ditching was primarily due to the both engines flame out because of fuel exhaustion. The incorrect replacement of the fuel quantity indicator (FQI) was one of the contributing factors which led irremediably to the accident. The accident’s cause is therefore traceable firstly to the incorrect procedure used for replacing the FQI, by means of the operator’s maintenance personnel. This shall be considered the disruptive element, which caused the final ditching of the aircraft due to the lack of fuel that caused the shutdown of both engines. As said before the accident was determined by a series of events (contributing factors) linked one another. Hereafter are listed some considered of major importance.
- Errors committed by ground mechanics when searching for and correctly identifying the fuel indicator.
- Errors committed by the flight crew: non-respect of various operational procedures.
- Inadequate checks by the competent office of the operator that flight crew were respecting operational procedures.
- Inaccuracy of the information entered in the aircraft management and spares information system and the absence of an effective control of the system itself.
- Inadequate training for aircraft management and spares information system use and absence of a responsible person appointed for managing the system itself.
- Maintenance and organization standards of the operator unsatisfactory for an adequate aircraft management.
- Lack of an adequate quality assurance system;
- Inadequate surveillance of the operator by the competent Tunisian authority.
- Installation characteristics of fuel quantity indicators (FQI) for ATR 42 and ATR 72 which made it possible to install an ATR 42 type FQI in an ATR 72, and vice versa.
The analysis of various factors that contributed to the event has been carried out according to the so called Reason’s "Organizational accident" model. Active failures, which had triggered the accident, are those committed both by ground mechanics/technicians the day before the event while searching for and replacing the fuel quantity indicator, and by the crew who did not verify and fully and accurately complete the aircraft’s documentation, through which it would have been possible to perceive an anomalous situation regarding the quantity of fuel onboard. Latent failures, however, remained concealed, latent in the operator’s organizational system until, some active errors (by mechanics and pilots) were made, overcoming the system’s defence barriers, causing the accident. Analysing latent and active failures (errors) traceable to various parties, involved in the event in several respects, it clearly emerges that they were operating in a potentially deceptive organizational system. When latent failures remain within a system without being identified and eliminated, the possibility of mutual interaction increases, making the system susceptible for active failures, or not allowing the system to prevent them, in case of errors. Active failures were inserted in a context characterised by organizational and maintenance deficiencies. The error that led to the accident was committed by mechanics who searched for and replaced the FQI, but this error occurred in an organizational setting in which, if everybody were operating correctly, probably the accident would not have occurred. Inaccuracy of information entered in the aircraft management and spares information system, particularly regarding the interchangeability of items and the absence of an effective control of the system itself, has been considered in fact one of the latent failures that contributed to the event. The maintenance and organization standards of the operator, at the time of event, were not considered satisfactory for an adequate management of the aircraft. The flight crew and maintenance mechanics/technicians involved in the event, when they made incorrect choices and took actions not complying with standard procedures, did not receive sufficiently effective aid from the system in order to avoid the error.

Findings:
• There were no indications prior to, or during the flight, of problems with any aircraft systems that may have contributed to the circumstances of the occurrence.
• The pilot continued flight into forecast and known icing conditions in an aircraft not approved for flight in icing conditions.
• The global navigation satellite constellation was operating normally.
• The pilot did not comply with the requirements of the published instrument approach procedure.
• The pilot was known, by his Chief Pilot and others, to adopt non-standard approach procedures to establish his aircraft clear of cloud when adverse weather conditions existed at Mount Hotham.
• The pilot may have been experiencing self-imposed and external pressures to attempt a landing at Mount Hotham.
• Terrain features would have been difficult to identify due to a heavy layer of snow, poor visibility, low cloud, continuing heavy snowfall, drizzle, sleet and approaching end of daylight.
• The pilot’s attitude, operational and compliance practices had been of concern to some Airservices’ staff.
• The operator’s operational and compliance history was recorded by CASA as being of concern, and as a result CASA staff continued to monitor the operator. However, formal surveillance of the operator in the preceding two years had not identified any significant operational issues.
Significant factors:
• The weather conditions at the time of the occurrence were extreme.
• The extreme weather conditions were conducive to visual illusions associated with a flat light phenomenon.
• The pilot did not comply with the requirements of flight under either the instrument flight rules (IFR) or the visual flight rules (VFR).
• The pilot did not comply with the requirements of the published instrument approach procedure and flew the aircraft at an altitude that did not ensure terrain clearance.
• The aircraft accident was consistent with controlled flight into terrain.

Findings as to Causes and Contributing Factors:
1. The aircraft was loaded in such a manner that the C of G was beyond the rearward limit. This resulted in the aircraft’s aerodynamic pitch control limitation being exceeded.
2. A weight and balance report was not completed by the pilot prior to departure and, as a consequence, he was unaware of the severity of the aft C of G position.
Finding as to Risk:
1. The weight of the passengers was underestimated due to the use of standard weights. This increased the potential of inadvertently loading the aircraft in excess of its maximum certified take-off weight.

The pilot's failure to obtain minimum controllable airspeed during the takeoff climb, which resulted in a loss of aircraft control when the left engine lost partial power. A fatigue failure to an oil tube, which resulted in the partial power loss to the left engine, procedures/directives not followed by the pilot, and the pilot's lack of recent experience and no recurrent training in the type of aircraft were factors.

It is believed that the engine lost power on approach because of the poor fuel quality.