What happened
On 13 March 1999, a Piper PA18-150, registration EI-CIG, was conducting an aerial advertising mission over Dublin. The aircraft departed from Weston Airfield at approximately 11:30 hours, towing an advertising banner for a scheduled two-hour flight detail over the south Dublin city area.
Roughly 80 minutes into the flight, while flying at an altitude of approximately 1,700 feet over the Perrystown area, the banner became detached from the aircraft. The banner and its associated towing gear fell to the ground, coming to rest across electricity cables and a house. The incident resulted in no injuries and no damage to the aircraft, though the falling equipment caused live electrical cables to remain energized for several hours until emergency services could secure the scene.
The investigation
The investigation examined the mechanics of the tow release system, which consists of a fixed tow hook mounted to the aircraft's tail, a grapple line used for aerial pickups, and a 76-meter nylon towline connecting to the banner.
Following the event, a licensed aircraft inspector tested the release mechanism on 15 March 1999. The testing confirmed that the system was functional, though the inspector noted slight wear on the rubber block used in the mechanism and replaced the rotating bolt as a precaution. The investigation also reviewed manufacturer documentation, which noted that the release could be accidentally triggered if the latch arm was nudged forward by the cable assembly ring or by in-flight vibrations.
Findings
Several factors were identified that could have led to the accidental release of the banner:
- The latch arm of the release mechanism may have been nudged forward by the cable assembly ring prior to the banner pickup.
- The combination of in-flight vibration and a slightly worn rubber block may have eventually caused the release mechanism to activate.
- It remains possible that the pilot inadvertently operated the cockpit release control.
- The aircraft was not equipped with a recommended guard designed to prevent the accidental opening of the tow hitch.
Safety action
To prevent a recurrence, the following safety considerations were noted:
- The operator should consider installing a guard on the tow hitch to prevent accidental release, as suggested by the manufacturer.
- The release mechanism should undergo annual inspections, including the replacement of the rubber block, with all maintenance recorded in the aircraft logbook.
- The installation of a release mechanism featuring a more positive locking device should be considered.