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Cessnaflyer

Dual transponders

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Some high end GA aircraft are equipped with dual transponders. Why? Simply redundancy?

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Exactly. Sometimes they stop working in mid flight and that way you can simply switch to the second xpndr.

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I've heard many 'low end' GA aircraft refused takeoff permission at KADS and sent back to the hanger/ FBO because of a transponder not working. They won't let a C-152 takeoff without a working transponder in that airspace.Two means the difference between being able to takeoff and not sometimes.

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Are those dual transponder equipped GA aircraft also equipped with a second set of flight instruments for the right seat?Usually the second transponder is tied to the right seat altimeter, so that while the guy in the right seat is flying that second transponder is reporting his altitude, which may not be the same as what the altimeter is reporting in the left seat.

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Many of those GA airplane have no pilot in the right seat - there is only one pilot.Whether the second transponder is tied to the second altimeter is really immaterial. The second transponder is just for redundancy in case the first one fails. If your are in some higher end GA aircraft, usually flying in class A airspace and transponder fails ATC would ask you to get below FL180. The second transponder is to prevent such eventuality - going below FL180 would often be a fuel-expensive proposition and major inconvenience.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg

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On the other hand I took off from Pueblo, Co. and went right thru the Denver class B airspace with a non working transponder and they were fine about it (it was intermittent and finally came back in Wyoming-I think sitting in the hot sun in Pueblo did it-haven't had a problem since).GeofaMy blog:http://geofageofa.spaces.live.com/

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If you're already in the air and in contact with ATC, you can continue to your destination with an intermittent/inoperative transponder. It increases the controller's workload to be sure, but you still show up on their scopes. The only exception would be in an area that has secondary only radar, in which case they'd just handle you as a non-radar target. So you'd have to give position reports periodically until radar contact is re-established. It amazes me how much trouble these things cause though. I'm not sure if it is the ground equipment or the equipment in the aircraft, but I hear controllers asking pilots on a daily basis to check the operation of their transponders.

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>It amazes me how much trouble these things cause though. I'm>not sure if it is the ground equipment or the equipment in the>aircraft, but I hear controllers asking pilots on a daily>basis to check the operation of their transponders. Usually, it's the pilot forgetting to change it from standby, to on & alt (mode C).L.Adamson

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It isn't "immaterial". Ever wonder how they determine who was flying the airplane in the instance that the CVR is destroyed in a crash? Also, you aren't asked to stay clear of Class A airspace if your transponder goes to the morgue in flight. I was recently flying out of SLC and my co-pilot neglected to turn on the transponder before takeoff. ATC never said a word for the first 20 minutes of the flight, and one of the subsequent controllers finally said something as we were climbing through FL250 or so.

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WrongIt doesn't matter all transponders use only 29.92" of Hg to transmit altitude so an errant altitude setting doesn't throw off the radar.

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>Wrong>>It doesn't matter all transponders use only 29.92" of Hg to>transmit altitude so an errant altitude setting doesn't throw>off the radar.It will most certainly show an altitude error on radar. Atc radar is adjusted for local altimeter. If you use the wrong setting then you will be off altitude and your pressure altitude being transmitted will show the deviation.

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>>Wrong>>>>It doesn't matter all transponders use only 29.92" of Hg to>>transmit altitude so an errant altitude setting doesn't>throw>>off the radar.>>It will most certainly show an altitude error on radar. Atc>radar is adjusted for local altimeter. If you use the wrong>setting then you will be off altitude and your pressure>altitude being transmitted will show the deviation.My GA transponder is connected to my altitude incoder, which is pre-set; and has no connections to my altimeter. Whatever the incoder say's, is what ATC gets.L.Adamson

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>>>Wrong>>>>>>It doesn't matter all transponders use only 29.92" of Hg to>>>transmit altitude so an errant altitude setting doesn't>>throw>>>off the radar.>>>>It will most certainly show an altitude error on radar. >Atc>>radar is adjusted for local altimeter. If you use the wrong>>setting then you will be off altitude and your pressure>>altitude being transmitted will show the deviation.>>My GA transponder is connected to my altitude incoder, which>is pre-set; and has no connections to my altimeter. Whatever>the incoder say's, is what ATC gets.>>L.Adamson>Local altimeter 30.42"Assigned altitude 5000'You accidentally left 29.92" in the altimeter. You are fat dumb and happy at 5000. Your xpdr transmits 5000 as well because it is set permanently at 29.92. However on the ground the controller sees 5500 as your altitude since he has set 30.42 into his display. The radar adds 500' to your reply to compensate for the local altimeter. He says to you "Check altimeter 3042 I show you 500 feet high." You look at your altimeter and say "oh crap" and dial in 3042 and see that you are actually at 5500 feet. When you land you file an ASRS report for your altitude deviation.

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>Local altimeter 30.42">Assigned altitude 5000'>>You accidentally left 29.92" in the altimeter. You are fat>dumb and happy at 5000. Your xpdr transmits 5000 as well>because it is set permanently at 29.92. However on the ground>the controller sees 5500 as your altitude since he has set>30.42 into his display. The radar adds 500' to your reply to>compensate for the local altimeter. He says to you "Check>altimeter 3042 I show you 500 feet high." You look at your>altimeter and say "oh crap" and dial in 3042 and see that you>are actually at 5500 feet. When you land you file an ASRS>report for your altitude deviation.I agree. The ground controller is compensating for the difference.............but I would have "screwed up'!L.Adamson

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