A few days ago Virgin Airlines flight 45 was diverted to Halifax from its original destination of New York, because it was inadvertantly transmitting a hijack distress code. Apparently Halifax has more highly trained counterterrorism personnel, or no one at NORAD cares if Halifax gets blown up. It's not a high-profile place like New York. Apparently Canada is now the standard place to divert possibly hijacked aircraft.
How it happened is easy. Every pilot has probably experienced the phenomenon of the transponder transmitting a different code than the one we've set on the face of the little box. We're briefly amused by the fact that our radar signal shows up on ATC radar screens as a B747 or a Sikorsky 76, and then we try to fix the problem. Usually turning the little digits away and then back to the assigned number does the trick, or recycling the transponder (turning it off and then on again). If it doesn't, it becomes maintenance's problem. It's usually stuck on 0000 or the last code we were assigned, and is only a nuisance. In this case, the crew was unlucky enough that out of 4096 possible combinations, their box fixated on the one that is means the pilot has a gun pointed at his head.
So despite repeated assurances that it was only a transponder problem, that the aircraft was under no threat, they were escorted to Halifax by a couple of CF-18s. I'd hate to be the one making the cabin PA to explain that one to the passengers.
I think ATC took the correct action. I might not even have remarked on the story except that the media has done something unexpected. Ordinarily such stories pussyfoot around the issue of the distress code used, and even the equipment used, to indicate that a hijacking has taken place. You notice I haven't even stated it, so trained am I to make at least a pretence that this is inside information. It's hardly a big secret. It's published in textbooks. It's required knowledge to get any kind of pilot licence. But it's not traditionally shouted from the rooftops. Yet the media stories this time around all give out the code. This one initially had a sidebar listing ALL the reserved codes, but I notice now that they have reduced it to a description of the transponder with a mention that certain codes are never assigned.
Now we pilots will have to come up with an even BETTER secret decoder ring.