“ALL right, good night,” were the last words heard by air-traffic controllers from Malaysia Airlines flight MH370 on March 8th. That makes them a rarity in the baffling story of the disappearance of a Boeing 777 carrying 239 passengers and crew from Kuala Lumpur to Beijing: an undisputed fact. In the days following, the Malaysian government provided information only in dribs and drabs, much of it confusing, even contradictory.

As The Economist went to press, it seemed possible that the agonising wait for the passengers’ families might be nearing an end. On March 20th Australia’s prime minister, Tony Abbott, told parliament that satellite pictures showed debris in the southern Indian Ocean, some 2,500km southwest of Perth, in an area where the 777 might plausibly have crashed. At 20 metres or so, one object seemed the size of a wing or tail fin. Aircraft and ships were headed to the area to investigate further. If the plane’s wreckage is found, and especially if its “black box” flight recorder can be recovered, what happened to flight 370 should become clearer. What is already beyond doubt is that air-traffic communication protocols need to be updated to ensure that, however rare, such a disappearance cannot be repeated.

The distressed relatives of the mostly Chinese passengers are not alone in their bewilderment that, in a world of pervasive electronic surveillance, a 200-tonne passenger plane can vanish. With little concrete information, speculation has run wild. Commentators of varying degrees of authority have attempted to fill the blank canvas with theories ranging from an accident to suicidal tendencies on the flight deck, and conspiracies of a complexity that would seem farfetched in a disaster film.

Hijacking seems unlikely: flight-deck doors are locked and sturdy. And investigations into the backgrounds of the crew and passengers have so far turned up no plausible motive. The first credible theory was that the plane had suffered a catastrophic mechanical failure and crashed, probably at sea. But a search along its flight path failed to turn up any sign of wreckage.

Then news emerged that Malaysian military radar had tracked the plane apparently turning west off its route shortly after the final radio message. Malaysian authorities added that its ACARS, an on-board system which transmits intermittent data about the performance of engines and other parts, appeared to have stopped functioning just before that, and that the transponder, another device that communicates a plane’s position to air-traffic control radars, appeared to have been switched off around the time of the turn. The fact that the pilots had not reported the switch-off led the authorities to infer foul play. On March 15th the Malaysian prime minister blamed “deliberate action”, with suspicion falling on the pilot or co-pilot. That the plane vanished between signing off with Malaysian air-traffic controllers and establishing contact with Vietnamese ones, and apparently continued flying for several hours under the control of a skilled aviator, lent credence to the assertion.

But this version of events was later revised by the Malaysian authorities. The ACARS, which sends messages intermittently, might have ceased functioning at exactly the same time as the transponder, it turned out. This makes the notion of an emergency more likely, perhaps a fire that incapacitated crew and passengers, leaving the plane to fly on ungoverned. The risk of an electrical fire is one reason why pilots are able to switch off on-board equipment, including that responsible for communications. But many are now calling for an automatic alert to be sent in such circumstances, so that ground authorities know that they should start tracking the plane with conventional radar.

The ACARS has at least provided information about the jet’s continued path, albeit wildly imprecise. Though it stopped transmitting data it continued to “ping” (send out a signal with no information other than that it was still operating) for six hours. That is about how long the plane’s fuel tanks would have taken to empty. But the pings were only picked up by one satellite, making triangulation to establish the plane’s path during that time impossible.

Malaysian military radar apparently lost contact with the plane as it flew over the Indian Ocean. (According to reports on March 19th, Thai military radar may also have tracked it turning off course.) That suggests it is somewhere on an arc hundreds of miles wide running from Kazakhstan almost to Antarctica (see map). Planes and ships from 26 countries have now joined the hunt. The northern part seems less plausible: it approaches land and passes through several countries with military radar primed to look for unidentified aircraft. But to the south, where the search is now focused, there is little coverage.

The information age is taking to the skies only slowly. Planes far out at sea keep in touch using VHF radio, and the newer ones send ACARS data continuously via satellite. Many are also equipped with ADS-B, another system that uses satellites and GPS to pinpoint their location when they are out of radar range. But flight 370’s ADS-B seems to have stopped transmitting about the time its transponder went off.

Clearer skies

Aircraft-tracking websites use several of these newer sources of data. They will eventually replace radar when their safety and reliability are beyond dispute, a long process in the plodding world of aviation regulation. And the next generation of communications technology, due in around a decade, will relay all flight information at once, acting like a real-time version of the black box that all planes now carry. Adding internet connectivity, as many airlines are doing, will provide another way to get a message to the ground.

Until parts of the plane are examined, how it came to grief will remain unknown. In the meantime, for the grieving relatives, there is little comfort to be taken from the fact that such mysteries should soon be a thing of the past.