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Re: Analysis from a JHU CS Prof
From: Owen DeLong <owen () delong sj ca us>
Date: Thu, 13 Sep 2001 16:28:03 -0700

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: owner-nanog () merit edu [mailto:owner-nanog () merit edu]On Behalf Of
Hire, Ejay
Sent: Thursday, September 13, 2001 2:35 PM
To: 'Borger, Ben'; 'nanog () 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 () merit edu [mailto:owner-nanog () merit edu]On Behalf Of
Borger, Ben
Sent: Thursday, September 13, 2001 2:32 PM
To: 'nanog () 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
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
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.


"Every time you turn on your new car, you're turning on 20
 microprocessors.  Every time you use an ATM, you're using a computer.
 Every time I use a settop box or game machine, I'm using a computer.
 The only computer you don't know how to work is your Microsoft
 computer, right?"
        - Scott McNealy, CEO of Sun Microsystems, Inc.,
          from an April 1997 interview in Upside Magazine

"One World, One Web, One Program." - Microsoft Promotional Ad
"Ein Volk, Ein Reich, Ein F├╝hrer" - Adolf Hitler

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