

Why Can Pilots Still Shut Off Transponders? - mhb
http://www.nytimes.com/2014/03/18/opinion/out-of-control.html?hp&rref=opinion&_r=0

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LoganCale
All systems on board an aircraft can be shut off for a number of reasons. In
case of a power failure, the pilot must choose what functions are the most
essential to the continued operation of the aircraft on the limited battery
power remaining. A transponder may then become nonessential. Similarly, if it
is faulty and is the cause of an electrical fire, power to the transponder
must be able to be shut off.

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cpncrunch
I can't read the article as it is behind a paywall. However as a pilot I can
tell you that you are generally meant to turn off your transponder while
taxiing on the ground. Also you shouldn't turn it on until you actually have a
transponder code, as you'll be transmitting an invalid code (possibly
conflicting with another flight).

Perhaps airliners should be made so that you can't turn off the transponder
while in the air.

Also, we don't know if they did actually turn off the transponder or not.

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tim333
The normal transponder system is not designed to be on all the time. In light
aircraft it's just a box on the dashboard like
[http://www.ebay.co.uk/itm/AIRCRAFT-B727-ATC-TRANSPONDER-
P-N-...](http://www.ebay.co.uk/itm/AIRCRAFT-B727-ATC-TRANSPONDER-P-
N-G1492-/290975920931?pt=Motors_Aviation_Parts_Gear&hash=item43bf843323)

that you can turn on if you are flying into controlled airspace.

What I think they should have is a new system that pings the location and
other data to satellites that can't be turned off and will work anywhere
unlike radar transponders.

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bulte-rs
One simple situation in which you would like to switch modes on the
transponder (ok, so this is not technically shutting the transponder down) is
when - for example - a loss of cabin pressure occurs. Since most (all?)
commercial arliners will have to perform an emergency decent to somewhere
around 10,000 feet it is dangerous for transponders to operate in TA/RA
(Traffic Advisory/Resolution Advisory) mode and give climb or descend
instructions to avoid other traffic. In this case pilots switch to a "squawk
only" setting.

