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...and the tracking transponder was turned off. That is interesting. I would have guessed that it be impossible to turn off the transponder on a commercial gr

...and the tracking transponder was turned off. That is interesting. I would have guessed that it be impossible to turn off the transponder on a commercial grade aircraft.

mikeash 13y ago
What if it starts blasting out interference, or catches on fire? Everything needs a power switch.
- stcredzero 13y ago
  Not having a power switch contributed to an electrical fire on Swissair MDM-11 planes with an upgraded 1st class entertainment system. The entertainment system did not have an off switch, it had bad thermal engineering, and a form of wiring insulation turned out to not be self-extinguishing in real life.
phire 13y ago
Easy as, the pilots are required to turn the transponder off as soon as they land, so planes on the ground don't show up on radar.
- durandal1 13y ago
  Yes - even worse, having it on close to the runway will trigger TCAS alerts for aircraft on final approach.
  - kevin_nisbet 13y ago
    I also remember in one of the mayday episodes, that on one aircraft the transponder control was somehow near the foot rest. So it was very common for pilots on this model aircraft to accidentally disable or change transponder codes when they put their feet on the foot rest. Sorry I don't remember which aircraft model or episode this was.
    - cc439 13y ago
      Old cars used to have the high beam switch down there, a totally reasonable concept. A switch that instantly throws every pilot and controller in the area into panic mode? I want to meet the people who approved that and see what their Pro/Con list looked like.
      - jcrawfordor 13y ago
        I believe the transponder code can be changed to a special value to indicate a hijack condition. Perhaps they install a sort of "silent alarm" control to do this?
        cjrp 13y ago
        7500 - hence in light aircraft (with rotary dials to adjust each number) you have to switch the transponder to standby before changing squawk. Prevents briefly sending out a 75/76/7700 as you're rotating through them.
UVB-76 13y ago
Three of the four aircraft hijacked as part of the 9/11 attacks had their transponders turned off: > Controllers track airliners such as the four aircraft hijacked on 9/11 primarily by watching the data from a signal emitted by each aircraft's transponder equipment. Those four planes, like all aircraft traveling above 10,000 feet, were required to emit a unique transponder signal while in flight. > On 9/11, the terrorists turned off the transponders on three of the four hijacked aircraft. With its transponder off, it is possible, though more difficult, to track an aircraft by its primary radar returns. But unlike transponder data, primary radar returns do not show the aircraft's identity and altitude. Controllers at centers rely so heavily on transponder signals that they usually do not display primary radar returns on their radar scopes. But they can change the configuration of their scopes so they can see primary radar returns. They did this on 9/11 when the transponder signals for three of the aircraft disappeared. [1] http://www.9-11commission.gov/report/911Report_Ch1.htm http://www.9-11commission.gov/report/911Report_Ch1.htm
devindotcom 13y ago
It's still my guess that the Air Malaysia flight was hijacked - transponder off, flew away from radar range and landed somewhere - it had a lot of fuel when it disappeared. But yeah, transponder is just a piece of equipment. Jumbo jets can't really hide from radar, though, and if you're flying low enough to do so, somebody is going to notice.
- alexeisadeski3 13y ago
  If it were simply hijacked and flown "to the edge of radar range" (whatever that means, given the military vessels tracking it in the area independently of the civil air net), you'd expect to see it fly to the edge of radar range then disappear. But it didn't. The Malay flight disappeared within the radar range of at least two independent radar nets. That can happen if a plane were bombed or disintegrated mid air. Maybe.
  - snowwrestler 13y ago
    Can you provide some sources for this information? As far as I've been able to tell, the "radar" that news services keep citing is actually the transponder. I've not seen statements that military or other organizations were actually pinging the aircraft with a radar signal from a fixed or airborne antenna.
    - crazytony 13y ago
      I have to sadly agree that it seems like Malaysia had neither military nor civilian radar watching. Either that or they didn't have it recording. They have made vague statements about military radar but nothing conclusive.
      - dragonwriter 13y ago
        I thought the vague (or rather clear but soon contradicted) statements about military radar were from Vietnam, which was closer to where contact was lost.

...and the tracking transponder was turned off. That is interesting. I would have guessed that it be impossible to turn off the transponder on a commercial grade aircraft.

mikeash 13y ago

What if it starts blasting out interference, or catches on fire? Everything needs a power switch.

stcredzero 13y ago
Not having a power switch contributed to an electrical fire on Swissair MDM-11 planes with an upgraded 1st class entertainment system. The entertainment system did not have an off switch, it had bad thermal engineering, and a form of wiring insulation turned out to not be self-extinguishing in real life.

phire 13y ago

Easy as, the pilots are required to turn the transponder off as soon as they land, so planes on the ground don't show up on radar.

durandal1 13y ago
Yes - even worse, having it on close to the runway will trigger TCAS alerts for aircraft on final approach.
- kevin_nisbet 13y ago
  I also remember in one of the mayday episodes, that on one aircraft the transponder control was somehow near the foot rest. So it was very common for pilots on this model aircraft to accidentally disable or change transponder codes when they put their feet on the foot rest. Sorry I don't remember which aircraft model or episode this was.
  - cc439 13y ago
    Old cars used to have the high beam switch down there, a totally reasonable concept. A switch that instantly throws every pilot and controller in the area into panic mode? I want to meet the people who approved that and see what their Pro/Con list looked like.
    - jcrawfordor 13y ago
      I believe the transponder code can be changed to a special value to indicate a hijack condition. Perhaps they install a sort of "silent alarm" control to do this?
      - cjrp 13y ago
        7500 - hence in light aircraft (with rotary dials to adjust each number) you have to switch the transponder to standby before changing squawk. Prevents briefly sending out a 75/76/7700 as you're rotating through them.

UVB-76 13y ago

Three of the four aircraft hijacked as part of the 9/11 attacks had their transponders turned off: > Controllers track airliners such as the four aircraft hijacked on 9/11 primarily by watching the data from a signal emitted by each aircraft's transponder equipment. Those four planes, like all aircraft traveling above 10,000 feet, were required to emit a unique transponder signal while in flight. > On 9/11, the terrorists turned off the transponders on three of the four hijacked aircraft. With its transponder off, it is possible, though more difficult, to track an aircraft by its primary radar returns. But unlike transponder data, primary radar returns do not show the aircraft's identity and altitude. Controllers at centers rely so heavily on transponder signals that they usually do not display primary radar returns on their radar scopes. But they can change the configuration of their scopes so they can see primary radar returns. They did this on 9/11 when the transponder signals for three of the aircraft disappeared. [1] http://www.9-11commission.gov/report/911Report_Ch1.htm http://www.9-11commission.gov/report/911Report_Ch1.htm

devindotcom 13y ago

It's still my guess that the Air Malaysia flight was hijacked - transponder off, flew away from radar range and landed somewhere - it had a lot of fuel when it disappeared. But yeah, transponder is just a piece of equipment. Jumbo jets can't really hide from radar, though, and if you're flying low enough to do so, somebody is going to notice.

alexeisadeski3 13y ago
If it were simply hijacked and flown "to the edge of radar range" (whatever that means, given the military vessels tracking it in the area independently of the civil air net), you'd expect to see it fly to the edge of radar range then disappear. But it didn't. The Malay flight disappeared within the radar range of at least two independent radar nets. That can happen if a plane were bombed or disintegrated mid air. Maybe.
- snowwrestler 13y ago
  Can you provide some sources for this information? As far as I've been able to tell, the "radar" that news services keep citing is actually the transponder. I've not seen statements that military or other organizations were actually pinging the aircraft with a radar signal from a fixed or airborne antenna.
  - crazytony 13y ago
    I have to sadly agree that it seems like Malaysia had neither military nor civilian radar watching. Either that or they didn't have it recording. They have made vague statements about military radar but nothing conclusive.
    - dragonwriter 13y ago
      I thought the vague (or rather clear but soon contradicted) statements about military radar were from Vietnam, which was closer to where contact was lost.