The technology to find a downed aircraft exists -

Technology which means that planes cannot just "drop off the radar" like Malaysia Airlines Flight 370, exists, but airlines felt it was too expensive to bother with.

Medium reports how technology needed to stream crucial flight data to the ground is already on the market - only airlines balked at the $100,000 price tag.

Commercial airliners do transmit some information: radio transponders identify them when scanned by radar, and many are fitted with an Aircraft Communications Addressing and Reporting System, or ACARS, which periodically relays text-message like snippets of information about the aircraft's status.

In the case of Flight MH370, the transponders seem to have stopped transmitting, and the airline has reportedly declined to comment about ACARS signals while the incident is being investigated.

Computer scientist Krishna Kavi, now at the University of North Texas, proposed streaming this data to cloud storage, in a system he dubbed the "glass box".

The only problem is that transmitting data through satellites isn't cheap, and if such a system were operating continuously, the cost would be prohibitive. Wired claimed it would cost "billions of dollars" to implement flight data streaming across the airline industry.

But most of the data is based on the maker of the existing black box technology L-3 which spun a false premise that all flight data would need to be streamed, all of the time.

Paul Hayes, safety and insurance director with Ascend, an aviation consultancy based said that systems could be designed to be triggered by unusual flight events, and only then start streaming flight data.

Such devices are already on the market, fitted to around 350 planes run by about 40 operators and they transmit data that help airlines plan maintenance, or work out how to minimise fuel consumption.

Richard Hayden, a director of FLYHT, the company that makes the system said that it transmits data via Iridium satellitesand can be programmed to start streaming flight data when a plane deviates from its flight plan, or instruments suggest something is going wrong.

If a plane is blown out of the sky by a bomb, or suffers a sudden catastrophic structural failure at cruising altitude it will not be much help but in those rare cases, conventional black boxes are really the only viable technology.

After the Air France disaster, the International Civil Aviation Organisation did consider installing the technology but the industry has concluded that the likely savings were too small.