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The Boeing 737-800 was transmitting a unique transponder identification code. If the equipment on the SA-15 that picks that up, called an IFF interrogator, was malfunctioning, battery operators would typically look at the schedule of airline traffic through their area and see if the target matched with a scheduled flight, Deptula says. Flight PS 752 was delayed by almost an hour from its scheduled departure, taking off at 6:12 a.m.
The SA-15 operators also would have considered the path and speed of the plane on radar. “Is it operating at low altitude, at high speed, headed toward a sensitive area”? Deptula asks. Flight PS 752 was rising toward 8,000 feet at a relatively sedate speed of 275 knots when flight tracking data from its transponder cut out, a normal profile for an airliner, he says. “It is departing the area, climbing through medium altitude, not trying to hide its signature, looking like a routine operation.”
Complicating decision-making for the soldiers operating the battery would have been the high state of alert.