Issue 90 January–February 2013
web: www.casa.gov.au/fsa email: [email protected]
The rocky road to danger
A potentially catastrophic failure of a burner on a common commercial hot air balloon is a reminder that airworthiness vigilance is just as important for balloons as it is for any other aircraft.
It’s an industry sector that carries over 150,000 fare-‐paying passengers every year – a number that is growing fast. It uses type-‐certified aircraft, flown by operators that are certified and audited like airlines, and its fleet is maintained by qualified and authorised technicians.
And its aircraft are powered using BBQ gas LPG -‐ in aerospace grade containers, of course.
Balloons are considered aircraft, no matter how domestic their technology may first appear. This means that managing the airworthiness of balloons is a serious matter, and not merely ‘BBQ maintenance’.
Australia has the tragic distinction of having the worst ballooning accident in history: 13 people lost their lives in 1989 when two hot air balloons collided near Alice Springs. But, as in winged aviation, while operational factors have historically presented the greatest hazard, airworthiness-‐related hazards lurk just beneath the surface.
One such hazard is the potential for cracking in the load frames and burner assemblies. These structures, often made from stainless steel, connect the basket to the balloon envelope, and also hold the burner cans in place. As with any metal structure, they are susceptible to cracking.
CASA recently received a service difficulty report (SDR) where cracking caused a burner to become dislodged – thankfully, this happened when the balloon was on the ground. Had it been in the air, however, the story could have been tragic: burners are heavy (about 12kg) and emit flames extending for several metres. A burner held in place only by its lightweight handlebar, could have easily caused catastrophic damage to control cables, the balloon envelope, and attachment wires and fittings. In short, the balloon would have very likely been lost, and with some balloons carrying up to 20 passengers, a simple crack in a burner frame could have the potential for a tragedy.
After further investigation, it was found that the particular balloon with the broken burner frame had travelled many hundreds of kilometres – not in the air, but via road transport, including hundreds of kilometres over unsealed outback roads. A preliminary analysis by the manufacturer revealed that, in all likelihood, the extensive ground handling loads had eventually shaken the structure to the point of cracking. A major defect was now just a matter of time.
This was not, however, the first time such a failure had occurred. CASA received a report in 2007 of an almost identical failure which led to Airworthiness Bulletin 14-‐001, advising operators of Cameron Balloon Stratus double burner units to inspect the gimbal assembly on their balloons. Advice from the manufacturer indicated that ground transportation loads were placing stresses on the welds in these sections, and leading to cracks and complete failures.
Issue 90 January–February 2013
web: www.casa.gov.au/fsa email: [email protected]
And these few instances have not been the only reported cracking event on balloons, although they represent more serious occurrences. More than 20 instances of cracking of various kinds and severity have been reported to CASA since 2007. Many cases are picked up as part of regular maintenance inspections, but in some cases they are found in-‐service.
One cracked weld was found only after the pilot noticed the basket frame had a slight movement in a section beneath its padding. This happened after a flight.
Ground handling has been identified as the main culprit by several manufacturers as the leading cause of cracking. Such practices are mixed, and cause mixed results: some practices focus on gentle unloading at a launch site, others involve ‘dropping it off the side’ of a ute. Sometimes burners and frames are completely dismantled before transport (some manufacturers specify this in their flight manuals); but often they’re attached for the journey to and from a flight. Leaving burners attached, can lead to cracks – but alternatives, such as loading burners loose in the back of a ute can cause more damage.
CASA has recently released AWB 14-‐002, advising balloon owners and operators of the importance of following manufacturer’s advice concerning ground transportation. Operators should also ask manufacturers to clarify any instructions if required and, should a crack be found at any time, report it to both the manufacturer and as an SDR to CASA.
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