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The Australian Transport Safety Bureau (ATSB) has recreated parts of an incident that caused a balloon to perform an emergency landing on a Melbourne residential street.
Investigators used the same balloon tethered to the ground to test its deflation system that failed, with the original pilot on hand to witness the unique test.
The balloon originally departed from Royal Park in the Victorian capital on the morning of 20 April 2022, for an intended destination of Moorabbin Airport. Thirteen passengers were onboard but only three suffered “minor injuries”.
The ATSB’s director of transport safety, Stuart Macleod, said, “Passenger photos showed the vent panel, designed to control the release of air from the top of the balloon was almost, or already, pushing through its opening at normal operating temperatures.”
About 10 minutes into the flight, the pilot noticed a gap between the panel and the edge of its vent aperture. The pilot was unable to seal it using the deflation system lines.
“As the flight progressed, the gap between the vent aperture and the vent panel expanded and altitude control became increasingly difficult,” Macleod said.
After an unsuccessful attempt to land in Fawkner Park, the pilot tracked the balloon, VH-RJR, to the south with the intent to land at Elwood Beach. Before reaching the beach, however, with the pilot unable to maintain altitude, the balloon would land outside the entrance of an apartment building in Elwood.
The interim report noted the accident flight was the balloon’s first since manufacture, and that prior to its manufacture in 2021, the balloon’s operator, Liberty Balloon Flights, requested a larger vent (both the vent aperture and panel) to increase the balloon’s descent performance.
As such, the incident balloon was the only one of its kind with the modified vent design produced by the manufacturer.
Following the incident, the ATSB arranged for the balloon’s deflation system to be tested. During that testing, the balloon was tethered to the ground, and its envelope inflated.
“During the test, at an internal envelope temperature of about 90 °C, which was below the maximum allowable temperature of 124 °C, edges of the vent panel between the vertical load tapes pushed up through the aperture creating many gaps for internal envelope air to vent out,” Macleod added.
“Attempts to seal the gaps using the parachute vent line and white line were unsuccessful, and at higher temperatures, the gaps became larger and more numerous.”
According to the pilot of the incident flight and analysis of passenger video, the vent gaps were very similar to those observed during the incident flight.
Macleod said that as the investigation continues, the ATSB will examine the balloon manufacturer’s processes and procedures for modifying the balloon’s design, and the balloon’s acceptance into service. A final report will be released at the conclusion of the investigation.
“However, should a critical safety issue be identified during the course of the investigation, the ATSB will immediately notify relevant parties so appropriate and timely safety action can be taken.”
