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.
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.
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.
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?
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.
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.
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.
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.
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.
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.
"What we have done is actually look into the recording on the radar that we have and we realised there is a possibility the aircraft did make a turnback," Rodzali Daud, the Royal Malaysian Air Force chief, told reporters at a news conference.
The problem I have with the above statement is that radar is unambiguous. Either the aircraft turned back, continued on, descended rapidly below radar coverage or broke in to bits. They all have different returns so you can't say "it may have possibly..."
> The problem I have with the above statement is that radar is unambiguous. Either the aircraft turned back, continued on, descended rapidly below radar coverage or broke in to bits. They all have different returns so you can't say "it may have possibly..."
Thanks for the specific statement.
I rather have the impression that, especially under less-than-ideal conditions (range, terrain between radar site and target, weather, etc.) radar is not unambiguous.
Also, even if it had disintegrated... Yud expect a radar (were there coverage) to pickup some of the larger bits right? Isn't a portion of 777 fuselage larger than other entire aircraft?
None of that applies here. Range at 35,000 feet for primary radar systems is over 100NM (~190km). It was a clear night over open ocean using a country's primary early warning and defense mechanism situated along the coast.
The US located the cargo door that departed from UA 811 in 1983 using radar analysis to find the part. They could see a 6meter piece of metal fall from the aircraft at 25,000 feet. 100km off shore.
The term "radar" is ambiguous, as authorities and the press use it to refer to both active sweeping radar and the passive transponder system. What they are saying above is that they were recording the transponder trace, and a change in bearing appeared to be in progress when the transponder signal ceased. But no one knows why it ceased.
That is interesting. I would have guessed that it be impossible to turn off the transponder on a commercial grade aircraft.