False Alarm

Airline crews can seldom prevent skyjackings, but they can usually alert ground stations to what is happening. Every commercial aircraft is equipped with a transponder, a small radio transmitter that sends out automatic signals on any chosen frequency. The secret signal for skyjackings in recent years was 3100 on the transponder. Any airliner "squawking" on that frequency had been skyjacked and could be expected to request a new destination.

That at least was what Australian ground stations assumed last week when the 3100 signal came from Olympic Airways Flight 472, which had just taken off from Sydney bound for Singapore. Australian military planes scrambled to shadow the Boeing 707 jet. Twice Australian stations radioed, "How are you going?" which according to prearranged codes meant, "Have you been hijacked?" "Normal," came the answer. In Singapore more than 100 policemen and soldiers mustered to meet the plane. Flight 472 was ordered to taxi to an isolated area of Singapore's airport, and passengers were held aboard. At the air terminal, meanwhile, an Olympic official arrived ready to pay whatever the skyjacker demanded to release the 42 people on the aircraft.

After half an hour in a grounded plane with no air conditioning, the irate captain finally convinced the airport controllers that there was no skyjacker. Only then did the cause of all the fuss come out. The flight engineer had dialed the emergency signal accidentally. On the assumption that it had not transmitted in the brief moment before he corrected it, he spun the radio dial and decided not to inform his captain.

The false alarm proved the effectiveness of the 3100 signal. But the publicity, along with other secrecy lapses in recent months, persuaded airline officials that the time had come to use a new frequency. It will of course be secret--for a while.

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