Threats & Errors – Case Study
ATSB AO-2012-143 28 October 2012
Airship 10m Balloon and Gondola (7.6kg)
Flight Test of a new X tail configuration
On the 28th of October 2012, an Unmanned Aircraft System was being flight tested with a new tail configuration. The intention was to remain below 200ft AGL and within 200m of the launch area to avoid Moorabbin Airport Control area. Moorabbin Airport is a general aviation training airport and has a control boundary is 3NM. Prior to the flight, the pilot visited Moorabbin Tower to advise them of their intentions, but as the flight was to remain clear of the control zone, the controllers were not concerned. The crew intended to comply with CASA regulations requiring the aircraft to remain below 400ft AGL, Outside Controlled Airspace, not over a populous area and not within 3NM of an airport.
Shortly after take-off the crew noticed the untethered airship had a nose up attitude, due to a rearward centre of gravity. This was corrected with Elevator trim.
When the airship was 130ft the pilot realised he could only turn the ship right. He therefore decided to land the airship. However, due to the rearward centre of gravity, the airship continued climbing, even after power was reduced to idle. When the airship did not respond to elevator or power, it was determined that control had been lost, although the data link was still operating. Meanwhile the airship continued to climb and track towards Moorabbin control area. When contact with the tower via radio failed, both the pilot and engineer followed the airship in a vehicle, while the observer remained to contact the tower and emergency services via telephone.
The airship reached a height of 1930ft and came within 2.7NM of Moorabbin airport before landing with minor damage on the roof of a commercial building.
The following investigation, identified that a mechanical tail-fin control rod had been incorrectly installed and a quality assurance check had not been conducted.
Additionally, there was a lack of training and documentation for centre of gravity calculations, checklists and flight operations.
Case Study Analysis
Using the Threat and Error Management Model:
- identify the threats, errors and Undesired Aircraft States of this incident;
- Identify strategies and countermeasures that the crew could have avoided, prevented and managed the threats and errors of this incident.
Threats:
- Controlled airspace close to flight testing area
- Untested aircraft
- Lack of organisational training and procedures (including use of testing procedures in a simulator, checklists)
- Lack of procedural risk assessment
Errors:
- Decision to fly an untested aircraft without tethering
- Flight testing near a control zone and populous area
- Flight testing with unknown flight characteristics near high-risk areas
Undesired Aircraft States:
- Crew lost control of Airship
- Airship entered controlled airspace, vertically and laterally