A passenger said the plane was taxiing to the runway before it was turned around. "... The engineers were then having a look at what may have been a problem within the air-conditioning," passenger Matthew Smith told ABC Radio. The incident was the latest in a recent run of scares for Australia's national airline. The spate of problems started last month when an explosion ripped a hole in the fuselage of a Qantas jet en route from Hong Kong to Melbourne, forcing an emergency landing at Manila. Last week, a domestic flight was forced to return to Adelaide after a wheel bay door failed to close. A Qantas Boeing 767 flight turned back to make an emergency landing at Sydney airport on August 2 after a hydraulic fluid leak was discovered. On Monday, a jet was grounded for almost three hours after a technical fault was discovered in a pre-flight inspection at Sydney airport.