Analysis from a JHU CS Prof

Thu Sep 13 21:15:22 UTC 2001

Most ATC towers do not have true radar.  I.e. the ability to detect flying
objects above altitude x by bouncing radio waves off of the object and
computing the time vs. Doppler shift vs. inclination to determine
altitude/heading/speed.

In modern (non-military) atc systems, this info is relayed by the
transponder to atc.

Source:  "How to become a Pilot" Bantnam Press.

-----Original Message-----
From: Leigh Anne Chisholm [mailto:lachisho at tnc.com]
Sent: Thursday, September 13, 2001 5:11 PM
To: Borger, Ben; nanog at merit.edu; Hire, Ejay
Subject: RE: Analysis from a JHU CS Prof

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.

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...

  -- Leigh Anne

> -----Original Message-----
> From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu]On Behalf Of
> Hire, Ejay
> Sent: Thursday, September 13, 2001 2:35 PM
> To: 'Borger, Ben'; 'nanog at merit.edu'
> Subject: RE: Analysis from a JHU CS Prof
>
>
>
> The transponders, like most avionics, has a handy-dandy off switch.
>
> -----Original Message-----
> From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu]On Behalf Of
> Borger, Ben
> Sent: Thursday, September 13, 2001 2:32 PM
> To: 'nanog at merit.edu'
> 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