What happened
On 5 June 2010, a Cessna 172Q, registration G-CSFM, was performing aerial work near Woodingdean, East Sussex. While the pilot was returning from a banner towing mission, the cable used to tow the banner experienced a structural failure. The banner became positioned at a right angle to the cable axis, causing it to detach from the aircraft. The banner subsequently fell onto a residential property at Cowley Drive, resulting in damage to the house's roof tiles. There were no injuries to the two crew members on board, and the aircraft sustained no damage during the incident.
The investigation
An AAIB field investigation focused on the integrity of the tow cable, which consisted of stranded steel encased in a plastic sheath. Engineers examined the fracture surfaces of the two broken cable segments. The analysis showed that the plastic sheathing had been damaged within the same plane as the cable failure. The investigation revealed that most of the steel strands had failed due to an overload, and these failures occurred near the site of the sheath damage. The pattern of the break was consistent with a sequential failure of the strands following an initial compromise of the cable's outer layer. The operator noted that the cable had been sourced from a specialist American firm that is no longer in business.
Findings
- The banner cable had been in service for a period of time prior to the final failure.
- The cable's plastic sheath had sustained damage, though the specific cause of this sheath damage could not be identified.
- The primary cause of the cable separation was sequential strand failure following initial damage to the sheath.