mirrodie
Posts: 6789
Joined: Wed Apr 19, 2000 3:33 am

Transponders And Black Boxes

Wed Sep 19, 2001 9:20 am

My apologies if this is a repeat question, but I have one glaring question indirectly related to the WTC incident.

My naive understanding is that a black box tells you info about what's going on in the cockpit and the transponder tells you where you are. Right?

Then why in the world would you want to turn either off??? Why should it even be an option to disconnect these?
Forum moderator 2001-2010; He's a pedantic, pontificating, pretentious bastard, a belligerent old fart, a worthless st
 
Staffan
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RE: Transponders And Black Boxes

Wed Sep 19, 2001 9:28 am

If you have a powerdown in an aircraft, the batteries can't power everything, therefore the pilot must be able to turn non vital systems off in order to power the important stuff.

Staffan
 
Guest

RE: Transponders And Black Boxes

Wed Sep 19, 2001 10:30 am

Uhmm...If I'm not mistaken, both of these devices are considered essential and aren't powered down in emergencies. I think the only times these are turned off would be if they were shorted and on fire/creating smoke.

 
nbirger
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Joined: Tue Mar 13, 2001 4:03 pm

RE: Transponders And Black Boxes

Wed Sep 19, 2001 10:38 am

Hello,

From what I have heard, (and so has probably everyone else) the transponders were turned off by the terrorists. This would make the plane a little less visible to ATC radar because it would remove some information about the status of the flight from the controller's screen.

One thing is for certain though the transponder is very important, especially during an emergency because it shows vital information to ATC.

My thoughts and prayers are with the victims and their families.

-Nick
 
cdfmxtech
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RE: Transponders And Black Boxes

Wed Sep 19, 2001 10:44 am

OK - we're getting 2 different things confused here:
1. (Black Boxes) Flight Data Recorders and Cockpit Voice Recorders (CVRs) - and - 2. ATC Transponders.

Flight Data recorders contain vital aircraft parameters (speed, acceleration, etc) gathered from a Data Aquisition Unit.
Voice Recorders are recording everything going on in the cockpit.
These devices cannot be turned off physically turned off by some kind of button or switch. They are energized by air mode or engines running (flt rec) or at all times (CVR)

Now the transponder tells the tower through interrogation where the aircraft is, alt, going up or down...that kind of stuff. This can be turned of via a control panel in the flightdeck. The aircraft will still show up as a blip on teh radar screens, but info such as alt won't be avail.

All above mentioned components run off essential power (or standby power) on the B757/767 aircraft.
 
delta-flyer
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RE: Transponders And Black Boxes

Wed Sep 19, 2001 10:58 am

I think Mirrodie's question is not what the transponders and black boxes are, but why do they even have the option of being turned off?

Saving power is a good reason, but if these devices contained rechargeable batteries those could take over when a power shortage/failure occurs. That's when you would most need these devices -the transponeder to help track the a/c and the black boxes to shed light on the events leading to the incident.

Pete
"In God we trust, everyone else bring data"
 
avt007
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

RE: Transponders And Black Boxes

Wed Sep 19, 2001 12:34 pm

Airliners have more than one transponder(txp). There has to be a way to turn one off and the other one on in the event of one failing. I have seen lots of them fail outright, or transmit incorrect information, or, for that matter, go up in smoke. The ability to turn off avionics is important. As for FDRs and CVRs, they can turned off by pulling the associated circuit breakers.
 
airplay
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RE: Transponders And Black Boxes

Wed Sep 19, 2001 1:05 pm

Flight Data Recorders and Cockpit Voice Recorders (Black Boxes) have a limited amount of storage space available. In most aircraft the CVR has about 30 minutes and the FDR has about 30 hours. If they were left to record after a crash the vital data would be over-written.

The certification standards for these flight recorders require a means to remove power from them following a crash. This can be done in many different ways such as monitoring engine oil pressure etc.

Flight Recorders are not vital to flight. Don't confuse "required" equipment with "essential" equipment or "vital services". An aircraft will not crash if the flight recorders do not work. Electrical systems must all have a means to be disabled by the flightcrew in the event of a fault which can threaten continued safe flight. Even battery operated devices can pose a threat.

Transponders are also not vital to flight. As stated before the aircraft will still normally produce a "primary" return based soley on the ground radar reflection. Almost all airliners in US airspace use mode A/C/S transponders. If the transponder is disabled, only the identification code assigned by ATC, the aircraft pressure altitude, the unique mode s address (which identifies exactly which aircraft it is) and TCAS inter-aircraft data will be missing.

There are special codes flightcrew use to signal hijacking to ATC and additional inflight emergencies. These codes unfortunaely are not secret. Anyone with access to pretty much any civil airworthiness athority flight operations information can learn them.

 
delta-flyer
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RE: Transponders And Black Boxes

Thu Sep 20, 2001 1:05 pm

OK, we see what these devices do and how they work. Still, it would be useful if they could not be disabled from the cockpit. Pulling a breaker does not have to shut the black boxes off. They can be designed to continue on battery power, and turn themselves off when a the end of a flight is detected. Airplay mentions a couple of ways that can be done, I am sure we could find dozens more.

Similarly, transponders can switch automatically in case of failures.

While these are not essential for safety of flight, they are useful for finding out what went wrong (black boxes) or what is about to go wrong (transponders). So what's wrong with this idea?

Cheers,
Pete
"In God we trust, everyone else bring data"
 
242
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RE: Transponders And Black Boxes

Thu Sep 20, 2001 1:15 pm

OK, we see what these devices do and how they work. Still, it would be useful if they could not be disabled from the cockpit. Pulling a breaker does not have to shut the black boxes off. They can be designed to continue on battery power, and turn themselves off when a the end of a flight is detected. Airplay mentions a couple of ways that can be done, I am sure we could find dozens more.

Similarly, transponders can switch automatically in case of failures.

While these are not essential for safety of flight, they are useful for finding out what went wrong (black boxes) or what is about to go wrong (transponders). So what's wrong with this idea?



I'm not so sure about the idea of a battery backup, but I'd be willing to bet that the location of the circuit breakers for the CVR/DFDR will be relocated to somewhere other than the flight deck.



 
avt007
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

RE: Transponders And Black Boxes

Fri Sep 21, 2001 3:20 am

Once again, my point is, if one of these units fails, and produces large quantities of smoke (which they can) the crew has to be able to shut them off from the flight deck. Let's not create more problems in our attempts to
prevent future hijackings.
 
Seseal
Posts: 19
Joined: Mon Jul 31, 2000 2:52 am

RE: Transponders And Black Boxes

Fri Sep 21, 2001 11:09 pm

CVR AC and FDR AC and DC C/Bs are on P11 panel in the cockpit. Pull them and you disable both.

There is no internal/external battery backup neither for CVR no FDR.

These a/c were equipped with mode S xponders which give you a/c identification as well. Shut them and ATC have no idea of what is flying out there.

Seseal

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