Re: Near miss Australia

From: (TriStar500)
Organization: America Online, Inc. (1-800-827-6364)
Date:         15 Jun 95 14:25:24 
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>My question is, I know that this B747 had a collision avoidance radar and
>that the B737 did not. The first question is do all B747 have these
>radars or is it only the -400 ? The second question is, what is the range
>that the radar works at, that is how close does another plane have to get
>to a B747 before the warning is sounded and how long do the pilots have
>to react?
>And finally, why are more planes not fitted with this radar?

I think what you're talking about is Traffic and Collision Avoidance
System (TCAS). It's installed on all US airliners.

This system is not radar though. TCAS can only see other airplanes that
have a working transponder, any other aircraft are invisible to TCAS.

TCAS give it's warning based on altitude difference between the aicraft
and closing rate. This is from memory, but I think if the aircraft are 45
seconds apart a Traffic Alert (TA) is issued, then as the aircraft get
closer (25 seconds?) a Resolution Advisory (RA) is issued. During the TA,
the crew is supposed to look out the window, look for the other airplane
and then decide what to do. For a RA, the TCAS system will tell the crew
whether they should climb or descend to avoid the other aircraft.

Also, for a RA to be issued, both aircraft must be equipped with a Mode S
transponder, a special version of TPNDR designed to work with TCAS. If the
other aircraft only has a Mode C TPNDR then TCAS can only issure a TA.