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Comment by downandout | Hacker News Reader

This begs the question: why on earth is it even possible to turn off a transponder mid-flight on a commercial plane carrying hundreds of human beings? I also don't understand why, if we can send bursts of engine data every 30 minutes from the middle of the ocean, we can't send a GPS location every couple of minutes. Maybe even throw some GPS data in with the engine data - at least we would know where it was within a 30 minute window. We're talking about a few extra bytes.

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Transponders have to be turned off while you're at the airport and while the plane's being serviced on ground. I think 777 has 2 transponders, so you also need the ability switch from one to the other. Lastly, I believe all electronics on the plane must be on a breaker circuit in case of electrical shorts so that pilots can isolate and turn off faulty circuits.

But you're right, ACARS (the system through which the engine information was routed - http://en.wikipedia.org/wiki/Aircraft_Communications_Address...) probably should be updated to add more information...

I get that, but what about just simple rules?

if(Plane.Altitude > 0 && Plane.FlightTime > 10 Minutes){ TransponderOn }

What if the altitude meter breaks? Does the transponder go off?

While this makes sense it may have to do what the poster above you said

Lastly, I believe all electronics on the plane must be on a breaker circuit in case of electrical shorts so that pilots :can isolate and turn off faulty circuits.

The altitude of the "ground" varies by thousands of meters:

https://www.google.com/search?q=highest+airport+altitude

Although, I guess you could just check if the landing gear is up. I'm sure there are corner cases I can't think of, but it seems like that would pretty much cover it.

Doesn't really solve the problem; a malicious actor could just lower the landing gear and then turn the transponder off.

Whatever, the point is, there should be a way to determine if a plane is in flight, and then disable the ability to turn off the transponder.

Many crucial functions rely on knowing if the aircraft is airborne or not. Weight-on-wheel sensors determine this.

The simple answer is you have dozens of planes on the ground at airports, which you don't want to appear on all the radars. Yes, a technological fix would be trivial, but those systems were designed decades ago, when being a pilot was quite prestigious and well paid. The thought of a rogue pilot never occurred, I guess.

Locaiton data is sent by the ACARS system, which was apparently turned off.

You don't need a transponder to show up on radar, it just makes it a lot easier.

Radar operators have a hard job telling a plane from clouds or echos. A transponder makes that job a lot, lot easier.

However, if you have a good radar system, you can happily track the contact without a transponder. In fact this happens all the time, I had a very nice chap at Farnbourgh West LARS (Low Altitude Radar Service) do this for me, when the shed I was flying had a little bit of a failure. For newewer systems such as those used by NATS automatically keeps the data assigned with the trace, using their proprietary algos to filter the noise.

If this happened over the UK, the transponder went off, ATC couldn't reach them, then a couple of Typhoons would be sent up to go have a look, and if need be escort.

With this background understanding of how modern Radar services are used piratically, taking into account a bit of background of the Malaysian authorities (short version: no terrorist attacks have ever happened even with our extremist religious views, honest.) Then this article will make some more sense: http://www.theguardian.com/world/2014/mar/13/mh370-satellite...

It is becoming clear they knew full well what was going on. They had the ACARS data. They had contacts on their radar, which they would have understood to be the plane, if not at the time, soon after. (But they really should have understood at the time!).

This stuff happens all the time in air safety investigations. See Egypt Air, or Air France!

This is my issue - an aeroplane disappearing from SSR and not making contact on the next frequency = sends up someone to have a look. Perhaps Malaysia's air force isn't as trigger-happy as here in England?

P.S. Never thought I'd see Farnborough West mentioned on HN! Hello fellow South Eastern pilot.

Why not have two types of transponders, one that is always on like lojack for planes and one that is only on for planes in the air. As long as there is some information being sent that determines what kind of signal it is, it should be trivial to have a radar system that filters out those only broadcasting their always on system.

It's probably less of an issue on larger/more modern planes where your squawk code is entered with a numeric pad - but on older/less complex planes you have to switch off the transponder when changing codes since it's a series of rotary dials and you don't want to accidentally broadcast an emergency code (7500/7600/7700) even for a second as it would trigger all sorts of alerts for the controller.

If it malfunctions you don't want it to overheat and burn the plane down. Thus the ability to cut power.

One might say the same about all of the electronic devices on planes. Cellphones and the like.

Hey man what are you doing! We can finally use our devices during take off and now you hint at keeping them off permanently! Eek! :P

I'm sure the first battery meltdown/fire on a plane is going to cause a riot in the news but the odds...

That did cross my mind when I posted it.

I should point out that I don't know what is true. It just seems to be a contradiction that every passenger can take on board and use whatever they want in-flight, yet transponders specially engineered to be safe on a plane must be able to be disabled.

I suspect the answer is that the transponder doesn't need to be under the control of anyone on the plane.

The answer is that when there's 100+ planes parked at an airport it's confusing to have 100's of transponders on as other planes are trying to land.

so just have a load cells on the undercarriage and a circuit that detects when a plane is landed so that you can only turn off the transponder when the plane is landed.

Maybe it has to do with the location on the transponder? A laptop in baggage or an electrical component buried deep in the bowels of the plane would be hard to get to in the event of a potential fire. A passenger's laptop would be fairly easy to put out with a fire extinguisher.

This device is a bigger piece of equipment using more power, with physical interconnects to other areas on a plan. Moreover it normally not located a place where you can lift it up and throw it in a bucket of water, or rip out its battery if something should go wrong.

And this is why Li-ion batteries are no longer allowed in checked bags.

they're not? I travelled with 2 laptops in my checked luggage in January.

https://xkcd.com/651/

If you can't trust the pilot then you can't trust the equipment either. Civil aviation requires a lot of trust, so there's no real reason to try to lock out the transponder.

Once the pilot is not trustworthy, you've entered the realm of military defense, and a lot of that is built around the ability to track targets that don't want to be tracked.

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