The disappearance of Malaysia Airlines flight MH370 a year ago has led to one of the largest search exercises in history. The 140-tonne aircraft and all its 239 passengers and crew remain missing, and the search continues across 17,000km² of ocean up to 5km deep. For comparison, we knew within 20km where the 50,000 tonne Titanic sank in 1912, in water 4km deep – and even then it took 73 years to find it.

A steel ship is much easier to find than an aluminium aircraft because it has a far larger effect on the earth’s magnetic field and so is easier to detect. More obviously, locating something as big as a cruise liner based on a fairly good knowledge of the location is much easier than finding a much smaller aircraft in a large area of the Indian Ocean.

Why don’t we know where MH370 went, wasn’t it being tracked? Near to major cities and population centres, state air traffic control uses primary radar – which locates objects using reflected radio waves. But radar’s range is only a few hundred miles, and while airliners carry their own radar this is calibrated for detecting storms and mountains, not other aircraft.

Radar only takes you so far

Beyond radar range we use secondary surveillance radar or SSR, this is built upon a World War II technology called “IFF” or “Identify Friend or Foe” and receives a coded signal from a ground station or another aircraft, then transmits back another coded signal which can include identity, position, altitude and speed. MH370 was equipped with ADS-B (Automatic Dependent Surveillance – Broadcast): a state-of-the-art secondary radar technology, detectable by ground stations and other aircraft.

Most accidents will cause power to the transponder to fail, but there are two more systems in the event of an emergency. Underwater, the Flight Data Recorder (the “black box”) emits an audible beacon for about 30 days. When on the surface Emergency Locator Transmitters transmit location for 1-2 days by radio. Throughout the flight, there’s also an automatic maintenance messaging system called ACARS which works through a satellite communications antenna.

In the case of MH370, while the transponder and ACARS had been shut down, the satellite antenna continued to respond to hourly handshake signals. This suggests that the disappearance of MH370 was caused by unlawful interference – but probably not by the captain. Why? If you asked a commercial pilot to commandeer an unfamiliar aircraft and fly it somewhere undetected, they would disable the ACARS, transponder, and radios – but without more detailed type knowledge probably wouldn’t disable the more obscure satellite communications antenna.

The search so far. Andrew Heneen

As the person on board with the greatest systems knowledge was the captain, this makes him an unlikely candidate for a hijacker. Also, with more than 18,000 flying hours (the minimum to command an airliner is 1,500) and an examiner’s qualification on the Boeing 777, he was capable of flying anywhere in Asia and landing safely without assistance.

This suggests that if anyone was flying the aircraft, it probably wasn’t him. That said, this is only my opinion: Captain Zaharie Shah was in the right place after all, and had allegedly made no social plans after March 8, 2014. That could be taken as suspicious.

The fact we have any idea where the aircraft was headed at all is due to brilliant mathematics by engineers at Inmarsat. They analysed the satellite handshake signals – not normally used for navigational purposes – and came up with an approximate flightpath, ending about the same time the aircraft fuel would have been expected to give out. That narrowed the search area to “only” 17,000km². They didn’t find the needle, but they offered a clue as to in which haystack it could be found.

To track or not to track

There have been calls from many quarters for tracking systems to be fitted to commercial aircraft that cannot be turned off, or for detachable, floating location beacons as fitted onto some military aircraft. It’s important that these don’t endanger the aircraft – I’ve had to turn off a transponder in-flight following a systems failure, so this isn’t a hypothetical concern. But creating transponders unable to threaten the aircraft is a solvable problem.

This will be expensive, but airlines won’t complain so long as it is mandatory: regulations that affect all competitors equally will just add a little to the cost of all airline tickets. Unions worry that some options – for example transmitting flight data by satellite link – could grow into a “spy in the cockpit” for management to monitor them, but the same concern was resolved with Flight Data Recorders and Cockpit Voice Recorders by making use of the data without the crew’s permission illegal for any purpose other than safety.

Ultimately, we must keep looking. It’s not acceptable that an aircraft with 239 people on board can simply vanish. We must find out why – not to allocate blame, as that doesn’t really matter: indeed if it’s known that blame will be allocated people are less likely to co-operate with any inquiry. What matters is learning how to avoid similar accidents in the future.

For this reason, if no other, it remains vital that we find MH370, and when found, the evidence retrieved and analysed.

This article was originally published on The Conversation.