Cameron Balloons Ltd V-77 , VH-LPO

The balloon pilot and his two passengers were conducting a private flight as part of the Canberra balloon festival. The balloon's equipment included three aluminium liquefied petroleum gas (LPG) fuel cylinders, dual burners, three radios, a motorcycle-type lead-acid battery, an altimeter and a variometer. After completing a normal flight, the pilot prepared to land the balloon on an area of parkland. This area was relatively small, with large trees on the approach and a street and houses in the direction of flight. Following the touchdown, as the balloon envelope continued to travel, the basket gradually tipped over and the pilot pulled the ripline to deflate the envelope. At about that time, the occupants of the basket noticed a fireball in the basket and immediately evacuated. Witnesses described the flames as yellow. The pilot stated that he let go of the ripline and allowed the balloon to ascend, deciding that it was safer for the fuel cylinders to be in the air than on the ground surrounded by bystanders. Witnesses heard an explosion and saw an object fall from the remains of the basket. The fire continued to burn, and subsequently consumed the wicker basket and damaged the lower panels and skirt of the envelope. Debris from the balloon fell across three suburbs and damaged several houses. The remains of the balloon were subsequently found 1.6 km from the initial landing point.

The pilot of the balloon was wearing a hat, a short-sleeved cotton shirt, trousers, gloves and shoes. He sustained serious burns to his forearms, face and neck. The male passenger was wearing a woollen lumberjack-style long-sleeved shirt, jeans, gloves, boots, sunglasses and a hat. He sustained minor burns to his face and wrists and was the only occupant not admitted to hospital. The female passenger was wearing running shoes, three-quarter length pants, gloves and a long-sleeved top which did not tuck into the waistband of her pants. She sustained serious burns to her shins and stomach.

The intensity, size and rapid onset of the fire after the balloon landed suggested that a rapid, uncontrolled leak of LPG had occurred. The most likely source of the LPG leak was the fractured liquid offtake valve. It is also likely that the fracture occurred during the landing. The yellow flames reported by witnesses and the sooting of the ruptured cylinder suggest that the fire was fuel-rich, consistent with a high-volume gas or liquid fuel supply.

The position of the pilot light valves indicated that the pilot lights were on during the landing. Each of the radios or the battery could have provided an ignition source, but it is most likely that the pilot lights ignited the leaking LPG. Had the pilot lights been turned off prior to the landing, in accordance with the flight manual and standard ballooning practice, it is unlikely the leaking gas would have ignited.

The condition of the ruptured fuel cylinder indicated that it had failed as a result of flame impingement and subsequent softening of the aluminium shell. The explosion of the cylinder was therefore a consequence of the fire, rather than contributing to its development.

The length of the broken fitting provided significant leverage that would have required only a relatively small force to be applied before the fitting broke. There was also limited protection for the fitting because it extended significantly beyond the fuel cylinder guard ring. While the Rego 8101P5/7141M combination liquid offtake valve may have been appropriate for some applications, it was not appropriate for aviation. A firm or tip over landing could have resulted in the fitting being bumped or otherwise subjected to stress by occupants or equipment moving around.

The occupants of the balloon generally sustained burns to exposed areas of skin. Had they been wearing natural fibre clothing that more effectively covered these exposed areas, the extent of their burns would almost certainly have been reduced.

The investigation revealed that fuel cylinder fittings similar to the fitting that failed are relatively common in the ballooning industry in Australia. This suggests that the ballooning industry as a whole is not sufficiently aware of the safety implications of fittings extending significantly beyond the fuel cylinder guard ring.

The selection of suitable fittings for fuel cylinders in balloons requires the expertise of both the gas supply industry and the aviation industry. Both industries have specific requirements related to fuel cylinder fitting selection and configuration that may not be completely understood by the other.

Sequence of events

The balloon pilot and his two passengers were conducting a private flight as part of the Canberra balloon festival. The balloon's equipment included three aluminium liquefied petroleum gas (LPG) fuel cylinders, dual burners, three radios, a motorcycle-type lead-acid battery, an altimeter and a variometer. After completing a normal flight, the pilot prepared to land the balloon on an area of parkland. This area was relatively small, with large trees on the approach and a street and houses in the direction of flight. Following the touchdown, as the balloon envelope continued to travel, the basket gradually tipped over and the pilot pulled the ripline to deflate the envelope. At about that time, the occupants of the basket noticed a fireball in the basket and immediately evacuated. Witnesses described the flames as yellow. The pilot stated that he let go of the ripline and allowed the balloon to ascend, deciding that it was safer for the fuel cylinders to be in the air than on the ground surrounded by bystanders. Witnesses heard an explosion and saw an object fall from the remains of the basket. The fire continued to burn, and subsequently consumed the wicker basket and damaged the lower panels and skirt of the envelope. Debris from the balloon fell across three suburbs and damaged several houses. The remains of the balloon were subsequently found 1.6 km from the initial landing point.

The pilot of the balloon was wearing a hat, a short-sleeved cotton shirt, trousers, gloves and shoes. He sustained serious burns to his forearms, face and neck. The male passenger was wearing a woollen lumberjack-style long-sleeved shirt, jeans, gloves, boots, sunglasses and a hat. He sustained minor burns to his face and wrists and was the only occupant not admitted to hospital. The female passenger was wearing running shoes, three-quarter length pants, gloves and a long-sleeved top which did not tuck into the waistband of her pants. She sustained serious burns to her shins and stomach.

Wreckage examination

An examination of the wreckage of the balloon established that two aluminium fuel cylinders were each connected to one of the two burners. One tank was connected by both the vapour feed line and the liquid feed line, while the other was only connected by the vapour feed line. Both pilot-light valves were on, the cross-feed valve was off and both the liquid and vapour offtake valves on both fuel cylinders were on. It was also noted that a male connector fitting had broken off flush with the top of the threaded portion of the body of the corresponding fuel cylinder liquid offtake valve.

Further examination of the broken fitting showed that it had been partially fractured when the fire developed. The fracture was sufficiently large to allow the uncontrolled escape of LPG into the balloon's basket. The fracture surfaces indicated that the fire was no longer burning near the fracture at the time the fitting broke away completely. The fitting had fractured in a downward direction, and there was no evidence of fatigue or pre-existing defects.

One aluminium fuel cylinder was found along the debris trail between the initial landing site and the final location of the remains of the balloon. This cylinder had failed because of a single ductile rupture of the upper shell section, characterised by a large bulged area, outwardly turned fracture lips and extensive blackening and sooting around the rupture.

Pilot light usage

The balloon manufacturer's Flight Manual section 4.6 'Landing', stated that the pilot light should be turned off before touchdown. Some balloon pilots indicated that they sometimes left the pilot lights on for landing if they were certain that the balloon basket would not tip over, allowing them to conduct a go around if required. Once the pilot lights were turned off, if insufficient height was available to relight the pilot lights, a pilot would normally be prevented from conducting a go around before the balloon touched down.

Fuel cylinder fitting selection

The broken fitting consisted of a Rego 8101P5 service valve coupled to a 7141M check connector. With this configuration, the assembly extended outside the fuel cylinder guard ring.

A comparison of the Rego 8101P5/7141M combination liquid offtake valve (left), and the Rego 8180 valve (right), and their relationship to the fuel cylinder guard ring

The balloon manufacturer's maintenance manual stated that "only factory supplied parts and materials are permitted to be used for repair or maintenance actions". The manufacturer advised that they previously supplied the Rego 8180 valve, but now supplied the BMV 344 handwheel-type liquid offtake valve in place of the Rego 8180 valve. The BMV valve was similar to the Rego 8180 valve. Balloon industry personnel suggested that while the Rego 8180 valve was the most widely used fitting, the Rego 8101P5/7141M combination was also relatively widely used in ballooning applications.

While the balloon manufacturer's documentation provided guidance regarding selection of fuel cylinder fittings, general practice among balloonists was for gas supply companies to replace, if required, fuel cylinder fittings during the mandatory 10-yearly cylinder inspection. Gas supply company personnel generally have extensive experience and knowledge regarding fuel cylinder maintenance, but they do not normally have much involvement in the aviation industry. They are not provided with detailed guidance regarding the appropriate selection and configuration for fuel cylinder fittings for aviation applications.

The investigation did not establish who had installed the Rego 8101P5/7141M combination liquid offtake valve.

As a result of this investigation, the Australian Transport Safety Bureau issues the following recommendations.

R20010133

The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority, in conjunction with appropriate specialist organisations, develop and promulgate requirements that specify which fuel cylinder fittings are suitable for use in balloons, and suitable configurations for those fittings.

R20010134

The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority ensure that balloon owners and operators identify and remove gas tank fittings that are not suitable for balloon operations.