By rights, the mobile phone should not have rung. Had BA flight 179 from Heathrow to New York JFK not taken off a couple of hours late last Sunday, the errant item would have been in mid-Atlantic and way out of range of the transmitters. And what turned out to be possibly the most expensive phone call in aviation history would simply not have got through.
Of the five cabin-baggage regimes that British Airways passengers and staff have had to come to terms with in the past 20 days, the one that prevailed on Sunday was the toughest. Your passport, boarding pass, wallet and keys were allowed through the checkpoint, plus (delete where inapplicable) baby milk, medicines, tampons and nappies. So sneaking a phone on board was, in a sense, very clever. But leaving it switched on proved very silly - and very expensive.
Ring tones on mobile phones are often irritating; on this occasion, the sound of an incoming call must have been terrifying. Three days earlier, news had broken about an alleged plot to blow up airliners en route to America. The 217 passengers on board BA179 had endured two searches from security staff, together with a tough interrogation.
Officials were particularly sensitive about electronic gear, because the alleged terror plot is said to have involved detonators disguised as MP3 players or mobile phones. So when that familiar trill rang out as the plane passed through 30,000 feet, you and I would probably have drawn the same conclusion: that something awful was about to happen.
The crew immediately, and courageously, investigated. They found the phone and removed the battery. A public-address announcement asked the owner to own up, but no one did - even though I imagine matching the phone to the passenger list once on the ground will not prove to be too taxing. Intensive discussions ensued between the captain and security officials at Heathrow about the best course of action. The conclusion: that the flight to JFK was safe to continue. So the commander of the aircraft was confident about continuing the flight.
End of story? Regrettably, no. A number of understandably upset passengers said they were worried by the incident, and wanted to get off. Did the captain, who is in sole charge of the aircraft, overrule their representations and carry on so that everyone could get to their destination? No, the man who is paid handsomely to exercise his judgement in the light of years of experience agreed to land.
The fuel tanks were emptied: cost to British Airways £10,000, to the environment rather more. At the time the decision was taken to abort the flight, the Boeing 747 was over Shannon, which has often been used as a diversion airport. Yet the pilot did not land at the Irish airport - he flew back to Heathrow. The sequence of events raises some serious issues: the airline to which the passengers had entrusted their safety concluded the discovery of a mobile phone does not represent a threat. Nonetheless BA agreed to bow to passenger pressure and land - but not just yet.
There are plenty of logistical reasons why the captain would want to prolong the flight in order to get back to the airline's main base at Heathrow. But either the aircraft is in imminent danger, whereupon it should land as soon as possible, or it is not - in which case it should have continued to New York. When finally BA179 took off again at 2am all but 65 of the original passengers were on board.
"We always err on the side of caution," says a BA spokeswoman. In that case, the airline must surely ground its entire operation. BA's aircraft are extremely safe in the air, but logic dictates they must be even safer on the ground. And presumably, anxious passengers will be able to cite the BA179 affair as a precedent for overruling a captain's judgement. Stand by for many more flights to nowhere, via Wales and Ireland.
The eventual cost to BA was around £100,000, which even by the standards of some mobile-phone operators is an expensive phone call - especially since the caller didn't even get through.