You have to be able to “turn off” the transponders for a lot of sensible reasons:

1) When the plane is on the ground, say at the terminal, or in a hanger, you need to be able to turn the transponder off

2) In the case of an electrical fault with the system, you need to be able to isolate the system to prevent fires etc

3) During maintenance etc, you need to be able to remove power from the transponder to allow that maintenance.

4) ATC might want the pilots to disable or change their transponder settings during a flight etc

The thing is, if you can’t “trust” the pilots, then what use are any “safety” systems on the plane? I mean, they can still fly the thing into a mountain quite easily. The entire system revolves around trusting the pilots, and if you can’t do that, well, what’s the point?

tying stuff the crash investigator talked about and some other theories doing the rounds there’s a train of events that might explain it

1. an emergency (a fire say that knocks out the systems)
2. pilot makes a turn for what he thinks is his best bet, Penang International airport.
3. fumes or an air issue knocks out the flight crew.
4. flight attendant with a better oxygen supply attempts to steer the plane on auto pilot sending it on it’s final course into the indian ocean.

Unfortunately, for the passengers and their families, even if they managed to limit the search area to a few square miles then if there is no signal coming from the plane now it’s never going to be found due to the depth of the ocean. I really hope they do find it but it looks very unlikely.

Fair points maxtorque.

Because very occasionally they return incorrect or garbled data – since the same info is used for TCAS it makes sense to be able to switch them off if necessary.

You have to be able to “turn off” the transponders for a lot of sensible reasons:

thanks, shame I had to get this answered on a mountain bike forum as they didnt explain that in the documentary, which was my point.

The thing is, if you can’t “trust” the pilots, then what use are any “safety” systems on the plane?

that was my issue with the 20 minutes of new wonder tech, if it can be turned off from the cabin/cockpit it wont change the game as much as they suggested.

At most it’s not a huge amount deeper than where the AF447 black boxes were recovered, and certainly within the range of what was used in that operation. The search area for AF447 was also similarly large to the current search area for MH370, so it’s far from impossible.

Latest today was that they now ‘know’ the place was on autopilot and that the ships were looking ion the wrong area.

Presumably there is no new data, and this is more theorising?…it does seem that they make definitive announcements without proof….For the relatives it must seem they are making it up as they go along

Also today the 8 minute ping was associated with the plane running out of fuel and the auxillary power kicking in and booting up the satellite system.

I don’t know if the APU kicks in automatically, or requires a manual intervention, or if it is simply a battery, or a fuel-powered generator, which I’m sure is the case on some planes.

The APU is in effect a small jet engine, used to supply air or generate electricity.
It will auto start in flight under some circumstances – but since it uses the same fuel tanks as the main engines it won’t run for long if they’ve stopped.

http://www.theage.com.au/national/missing-mh370-plane-flying-on-autopilot-before-crashing-as-new-search-zone-announced-20140626-3awfu.html

Aus’ newspaper coverage

60,000sqkm search area 1200km from land – could take a year to search but will take 3 ships 3months to map seabed before the search actually begins

http://en.wikipedia.org/wiki/Ram_air_turbine

Article in The Times today says that the investigators now reckon the hypoxia/loss of consciousness theory is the most likely with some sort of incident/accident triggering a loss of cabin oxygen and the pilots trying to turn the plane back towards Malaysia but failing to complete the action and the plane ending up on autopilot until it ran out of fuel.

I guess there’d have to be something pretty dramatic to knock out all communication systems though…

I guess there’d have to be something pretty dramatic to knock out all communication systems though…

That’s the problem with all these theories. That such an odly specific fault knocks out the transpoder but not a load of other critical systems.

The Helios flight gives an example of how the hypoxia scenario could go down but in that scenario ATC know where the plane was and fighters were scambled.