corocks
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Transponder Question

Thu Jun 04, 2009 1:41 am

I was watching an documentary on 9/11 yesterday and they were talking about how the hijackers turned of the transponders which made it more difficult to track them. Dumb question: Why do pilots even have the option of turning this off? Why would there ever be a legitimate reason to turn it off? I would think you would always want to know where a commercial jet was.
 
N353SK
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RE: Transponder Question

Thu Jun 04, 2009 1:43 am

Transponders are turned off while on the ground (at most airports) and in the case of faulty equipment.
 
tinpusher007
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RE: Transponder Question

Thu Jun 04, 2009 1:44 am

On the ground, the transponder is turned off or put in standby mode. However, at most big airports, it is commonplace for aircraft to taxi with their transponders on.
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sccutler
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RE: Transponder Question

Thu Jun 04, 2009 1:45 am

In addition, of course, a transponder can provide faulty information such as in accurate altitude or improper "squawk code," or could fail in some other way. Like most every other functional device on the aircraft, the transponder can be switched on or off, and controlled, byth epilots.

Which, of course, is as it should be.
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Fly2HMO
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RE: Transponder Question

Thu Jun 04, 2009 1:49 am



Quoting COrocks (Thread starter):
I would think you would always want to know where a commercial jet was.

Controllers can still see primary (non-transponder) targets on their radar scopes.
 
futurepilot16
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RE: Transponder Question

Thu Jun 04, 2009 1:55 am



Quoting SCCutler (Reply 3):
In addition, of course, a transponder can provide faulty information such as in accurate altitude or improper "squawk code," or could fail in some other way. Like most every other functional device on the aircraft, the transponder can be switched on or off, and controlled, byth epilots.

Which, of course, is as it should be.

That's another thing I don't understand, why do they make it that everything can be turned on and off. I was watching a documentary about a fedex flight that was attacked by a pilot who was jumpseating. The documentary stated that the man turned off the CVR/FDR prior to starting the attack. Why should there even be an option to turn off something so vital?
"The brave don't live forever, but the cautious don't live at all."
 
Fly2HMO
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RE: Transponder Question

Thu Jun 04, 2009 2:05 am



Quoting FuturePilot16 (Reply 5):
Why should there even be an option to turn off something so vital?

Because sometimes what happens in the cockpit stays in the cockpit  Wink  duck 
 
ThePinnacleKid
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RE: Transponder Question

Thu Jun 04, 2009 4:38 am



Quoting FuturePilot16 (Reply 5):
That's another thing I don't understand, why do they make it that everything can be turned on and off. I was watching a documentary about a fedex flight that was attacked by a pilot who was jumpseating. The documentary stated that the man turned off the CVR/FDR prior to starting the attack. Why should there even be an option to turn off something so vital?

They're not with an On/Off switch... at least not in most aircraft... esp. not in the one I fly... but, you have the ability to turn it off thanks to the handy gadget called a Circuit Breaker... and you have to have them and they have to be accessible to the flight crew... so yeah, in a way it's required that we have the ability to turn them off...
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chrisjw
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RE: Transponder Question

Thu Jun 04, 2009 5:29 am



Quoting FLY2HMO (Reply 6):
The documentary stated that the man turned off the CVR/FDR prior to starting the attack. Why should there even be an option to turn off something so vital?

I know the exact documentary your talking about, it was a good one.

Problem is what happens if the CVR/FDR shorts out and theres no circuit breaker for it. You would have to shut down the entire electrical system for the plane to avoid a fire vs simply pulling the circuit breaker for it. As we all know, fire and aircraft don't get along to well.

Nobody except pilots and maybe an FA has access to the circuit breakers (the guy in the documentary was a pilot for Fedex).
 
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HAWK21M
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RE: Transponder Question

Thu Jun 04, 2009 6:52 am



Quoting Chrisjw (Reply 8):
Problem is what happens if the CVR/FDR shorts out and theres no circuit breaker for it. You would have to shut down the entire electrical system for the plane to avoid a fire vs simply pulling the circuit breaker for it.

You don't pull a CB in flight,The CB is supposed to trip.
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Mir
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RE: Transponder Question

Thu Jun 04, 2009 7:04 am



Quoting HAWK21M (Reply 9):
You don't pull a CB in flight,The CB is supposed to trip.

In an ideal world, yes. But if you've got a component that's producing an electrical fire and the CB isn't tripping, it's time to pull it.

-Mir
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PER744
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RE: Transponder Question

Thu Jun 04, 2009 7:06 am

I understand that on more modern aircraft, the CVR breaker works in conjunction with a fuse, so simply pulling the breaker won't disable the CVR unless the fuse also burns out, although I can't find a reference for this.

And a faulty transponder can definitely cause problems for ATC, better to use a flight plan track and procedural sep standards than an inaccurate radar track.
 
UAXDXer
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RE: Transponder Question

Thu Jun 04, 2009 8:04 am



Quoting PER744 (Reply 11):
I understand that on more modern aircraft, the CVR breaker works in conjunction with a fuse, so simply pulling the breaker won't disable the CVR unless the fuse also burns out, although I can't find a reference for this.

Simply pulling a circuit breaker will disable whatever system it is associated with on modern aircraft. Ever notice on the circuit breaker panels on a/c? The are all on a grid so they can easily be found incase the CB needs to be pulled.


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Quoting PER744 (Reply 11):
And a faulty transponder can definitely cause problems for ATC, better to use a flight plan track and procedural sep standards than an inaccurate radar track.

ATC Radar can still track an aircraft when the transponder is turned off. It just does not receive information specific to that target such as altitude and speed.
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PhilSquares
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RE: Transponder Question

Thu Jun 04, 2009 11:59 am



Quoting PER744 (Reply 11):
I understand that on more modern aircraft, the CVR breaker works in conjunction with a fuse, so simply pulling the breaker won't disable the CVR unless the fuse also burns out, although I can't find a reference for this.

What you're talking about is a RCCB, Remote Controlled Circuit Breaker. Those are generally used for high amp items. For the CVR and DFDR the CBs are in the cockpit and pulling a CB like that will cut the power from the unit.
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