Section 21 (2) of the Transport Safety Investigation Act 2003 (TSI Act) empowers the Australian Transport Safety Bureau (ATSB) to discontinue an investigation at any time. Section 21 (3) of the TSI Act requires the ATSB to publish a statement setting out the reasons for discontinuing an investigation.
On 10 April 2010, the ATSB commenced an investigation into a wirestrike that occurred at about 1737 Eastern Standard Time that day and involved a Cessna Aircraft Co. A188B/A1 Ag Truck aircraft, registered VH-JHR. The aircraft was being operated on an agricultural weed-spraying flight over a cane field that was located about 13km south-west of Ayr, Queensland. The aircraft was positioned to fly under powerlines that crossed the intended flight path at about 3.25 m above the top of the crop. The aircraft, which is about 3.6 m high, contacted the powerlines and severed the top of the aircraft's fin and rudder horn (Figure 1). Control of the aircraft was lost and it collided with terrain shortly afterwards in a steep, nose-down attitude. The pilot was fatally injured.
Figure 1: Power conductors and detached rudder horn
In the hours prior to the flight, witness, video and other information indicated that the pilot had consumed a quantity of alcohol. A postmortem examination subsequently indicated that the pilot had a high blood alcohol concentration.
The consumption of alcohol by pilots is regulated by Civil Aviation Regulation 256, which mandates that a person shall not:
- while in a state of intoxication, enter any aircraft
- act as, or perform any functions in preparation to act as a member of the operating crew of an aircraft within 8 hours of consuming alcohol
- operate an aircraft if, by reason of having consumed alcohol (or other prescribed substances), that person's ability to operate the aircraft is impaired.
The ATSB safety research report titled Alcohol and Human Performance from an Aviation Perspective: A review' found that alcohol use by pilots was a major potential risk to flight safety. Of particular relevance, alcohol:
- affects almost all forms of cognitive function, such as information processing, attention, vigilance, perception and reasoning
- impairs registration, recall and the organisation of information, which leads to increased reaction times and increased errors
- significantly impairs attention, especially in terms of tasks requiring sustained, selective or divided attention
- adversely affects psychomotor performance, particularly on tracking tasks. Performance was found to suffer most when an unexpected or unanticipated event occurred.
The ATSB's primary focus is on enhancing safety with respect to fare-paying passengers and, in particular, those transport safety matters that may present a significant threat to public safety and are the subject of widespread public interest. The ATSB therefore needs to direct significant attention to identifying systemic failures in aviation, marine and rail mass public transport systems.
Many accidents involve the repetition of past occurrences, where the contributing factors are similar and the safety issues are well known. The ATSB has investigated a number of accidents in which the operating crew were affected by alcohol and the cognitive impairment likely as a result of alcohol consumption, and its effects on tasks such as flying and driving, are well known. Given that existing knowledge, and the pilot's decision to carry out the flight after consuming alcohol, the ATSB considered there was limited potential to enhance transport safety by continuing this investigation.
On that basis, the ATSB has elected to discontinue the investigation. However, the data collected in the course of the investigation may be used by the ATSB for future statistical analysis and safety research purposes.