Transponders have switches so they can turned on off before engine start or shutdown. They can malfunction, and ATC may ask you to turn it off do position reports verbally. They also draw a lot of current, in the event of an electrical failure and when running on batteries only the pilot has to shut down non-essential equipment. When flying in formation, only the lead aircraft has his transponder on, etc. Some of the reasons why they have switches. I have had instances where cycling the power on a transponder has fixed a problem with ATC picking me up on their scopes. Eventually the analog radar/transponder interraction as we know it now will go the way of the buggy whip. The FAA has been working on GPS-based digital transponders with data links. See http://www.alaska.faa.gov/capstone/faq.htm for details. Regards, Bob Richard Graziano wrote .. > The power switches were put on the transponders originally for test and > calibration but that was pre-crazy world. > > ----- Original Message ----- > From: "Robert B." > To: > Sent: Thursday, June 17, 2004 5:25 PM > Subject: Re: [OT:] Aircraft transponders > > > > I'd imagine they need to be able to be power cycled in the event of > failure, > > like pretty much every other electronic device. Also its undoubtedly > > protected through a fused circuit to prevent a fire in event of > malfunction, > > which makes a convenient way to "turn it off". > > > > > > ----- Original Message ----- > > From: "Mike Hord" > > To: > > Sent: Thursday, June 17, 2004 5:17 PM > > Subject: [OT:] Aircraft transponders > > > > > > > One of the things that I'm hearing in NPR coverage of the > > > 9/11 commision's findings is that the aircraft in question were > > > lost because the hijackers turned off the transponders. > > > > > > I'm now certain that any question I can ask can be answered > > > by someone on the PICLIST, so I'll ask this now: > > > > > > Why on Earth is there an off switch on the transponder? > > > What could EVER make turning the transponder off a good > > > idea? > > > > > > Side point: how difficult would it be to set up several > > > antennas to pick up aircraft transponders, triangulate their > > > position, and project that info onto a map? I think it would > > > be fun to monitor local air traffic. Is this even legal? I know > > > that's the kind of thing that may not go over well these days. > > > > > > Mike H. > > > > > > _________________________________________________________________ > > > Is your PC infected? Get a FREE online computer virus scan from McAfee. > > > Security. http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963 > > > > > > -- > > > http://www.piclist.com hint: The PICList is archived three different > > > ways. See http://www.piclist.com/#archives for details. > > > > -- > > http://www.piclist.com hint: The PICList is archived three different > > ways. See http://www.piclist.com/#archives for details. > > > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body