FW: Analysis from a JHU CS Prof

Thu Sep 13 22:06:53 UTC 2001

On Thu, Sep 13, 2001 at 03:31:37PM -0500, Borger, Ben wrote:
> Somehow the people who did this managed to turn off the transponders on
> these planes.  Normally a plane flying in controlled airspace squawks a
> unique id and altitude which is decoded by their radar and associated with
> each blip.  Sometimes low cost homebuilts/ultralights fly with no
> transponder, but Boeings <sarcasm>usually</sarcasm> do.  If you set a
> transponder to 7500, it means you're being hijacked.

	Some obvious things to do:

	1) Turn off altitude reporting -- most of the transponders I've
	used have 3 settings (off, on, and on with altitude reporting)
	2) Then sqwak VFR.
	3) Turn the transponder off 
	4) Pull the breaker.  (All flight avionics are on resettable
	breakers, accessible to the flight crew.  There is good 
	reason for this.)

	I wouldn't find it exactly surprising that any of the transponders
had been switched off.  It only takes a moment.

	--msa