Piqued passengers who were denied seats or excess baggage, disgruntled employees, drunk travellers and business rivals of flyers formed a majority of the anonymous callers who disrupted 255 flights at Mumbai airport in 2012 with false bomb scares.

According to an analysis of such calls by the city airport operator, each of the 255 non-specific hoax calls resulted in flight delays of 30 minutes on an average. "The callers have been passengers who were late to reach the airport, passengers denied seat or excess baggage, a drunken passenger, a rival businessman, a mentally deranged individual, a disgruntled employee or just a prankster," said a Mumbai International Airport Limited (MIAL) spokesperson.

The airport also received three "specific" calls wherein the callers named a particular flight. According to the standard operating procedure specific threat calls result in longer delays because passengers are off loaded and the aircraft is taken to an isolated bay for through inspection.

The anti-sabotage check that follows is a cumbersome procedure taking up to 4 hours as the search is conducted using explosive sniffer dogs and explosive detectors, said airport official. Although the number of such calls dropped last year as compared to 2011 (362 non-specific calls), security officials said that there is no mechanism to stop the menace. "Most of these calls are made at the airlines' call centres. As a result the security agencies are unable to check their credibility," said a senior Central Industrial Security Force (CISF) official requesting anonymity.