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Re: Analysis from a JHU CS Prof

  • From: Owen DeLong
  • Date: Thu Sep 13 19:37:51 2001

Leigh Anne Chisholm wrote:
> I despise posting off-topic, but I want to say two things...
> 1.  If a transponder is turned off, it doesn't mean that you don't show up
> on radar--a blip appears on the radar screen as long as you're high enough
> to be detected.  If however you fly low enough, you can fly below the
> radar's detection capability.  I don't offhand recall what height that
> is--it's been years since I was active as a pilot and prospective Air
> Traffic Controller.
That depends.  The FAA has begun removing "Primary Target" service from
of it's control center, citing cost-savings, etc. Some ARTCC and TRACON
facilities (Air Route Traffic Control Center and Terminal Radar Approach
have primary-target capabilities on their scopes, some do not.  Some of
recording systems record the primary targets, some do not.

As to the height at which you are undetectable, there are so many
factors, that it's on a location by location basis. Factors include
of the antenna, terrain, distance from the antenna, number of radar
covering the area (yes, there is an overlap in most of the US these
etc.  For example, I know bay can see me on the ground at PAO if I leave
my transponder on.  However, Oakland Center can't see me in some parts
of Northern CA if I drop below 12,000 feet MSL (~4000 AGL in some of
those areas).

> 2.  What's the point of having transponder codes for hijacking if they're so
> well published everyone is aware of them?  The purpose of the codes was so
> that the pilot could communicate this information without the hijacker
> becoming aware of what was happening.  I have always REALLY DISLIKED the now
> common practice of advertising this information.  You're taking away one of
> the pilot's best tools...
Yes and no. There was a time when this was so poorly publicized that
many of
my fellow pilots didn't know that there was a hijack code. The fact is,
has always been published in the AIM, so anyone who cared could easily
up a copy of the AIM (Airmans Information Manual) at their local pilot
and find out. I don't think the knowledge of the code necessarily
the pilot from using it.  Any hijacker that's going to know about the
from any publicity it may have will already know enough to turn the
transponder off anyway for other reasons.

>   -- Leigh Anne
Owen DeLong
PP ASEL, Instrument Airplane

> > -----Original Message-----
> > From: [email protected] [mailto:[email protected]]On Behalf Of
> > Hire, Ejay
> > Sent: Thursday, September 13, 2001 2:35 PM
> > To: 'Borger, Ben'; '[email protected]'
> > Subject: RE: Analysis from a JHU CS Prof
> >
> >
> >
> > The transponders, like most avionics, has a handy-dandy off switch.
> >
> > -----Original Message-----
> > From: [email protected] [mailto:[email protected]]On Behalf Of
> > Borger, Ben
> > Sent: Thursday, September 13, 2001 2:32 PM
> > To: '[email protected]'
> > Subject: FW: Analysis from a JHU CS Prof
> >
> >
> >
> > >>At 06:05 PM 9/12/2001, you wrote:
> > >>
> > >>
> > >>Quite more interesting is why nobody noticed that 4 airliners where
> > hijacked
> > >>almost the same time.
> > >
> > >Not surprising.  Aircraft are "flight followed" by a series of control
> > >centers across the nation, each responsible for a given chunk of
> > >airspace.  Something happening in an area controlled by Center "A", for
> > >example, wouldn't be passed on to Center "B" (which has it's own
> > problems
> > >to work) unless it impacted Center "B".  Furthermore, unless
> > someone TELLS
> > >Center they're being hijacked, there's no way for a controller -
> > looking at
> >
> > >a blip - to know what's up.  And any controller can tell you
> > that pilots do
> >
> >
> > 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 XXXXX, it means you're being hijacked.
> >
> > BTW if you see your friend Jack at the airport, be sure to say,
> > "What's up,
> > Jack!" instead of "Hi Jack!"
> >
> > So how do you deal with this?  Blowing up a whole country?  I
> > wonder if the
> > US should adopt a 'fire w/ fire' approach and invest in
> > intelligence, covert
> > ops and assassinations.  It would seem that it is open season on terrorism
> > by every democratic nation, I expect to see very conspicuous
> > Samuel Jackson
> > style ass whoopins on whiny extremist groups to satiate America's anger.
> > Terrorize the terrorists.
> >
> > Oh yeah, obviously Echelon should probably have MacOS loaded on it.
> >
> > -b

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