Search teams are racing to find the flight recorders of the missing Malaysia Airlines plane before the exercise becomes a prolonged and potentially costly one resembling the search for Air France Flight 447, experts say.
An underwater locator beacon inside the black box that switches on automatically after a crash and sends out a sonar signal has not been detected.
"The battery life of the locator lasts 30 days. If they cannot find it within this window, it will become very hard to locate," said Professor Alan Lau Kin-tak, of Hong Kong Polytechnic University's engineering department.
No signal was received from the Malaysian plane's emergency locator transmitter, which is designed to emit distress signals from a plane after an accident. It has a lifespan of 24 hours.
David Newbery, a Hong Kong flight captain and accredited aircraft accident investigator, said search teams faced similar difficulties when investigating the disappearance of the Air France Flight 447 over the south Atlantic in June 2009. The black boxes were found two years later.
"If you still haven't found the wreckage by the time the pinger stops working, you really have a problem," said Newbery.
The two shoebox-sized devices, thought to be indestructible, are located towards the tail of most aircraft. One is a digital flight data recorder which documents parametric data such as airspeed, altitude, heading, pitch and instrumental readings such as cabin pressure and engine temperature. The other device records the dialogue and radio communication in the cockpit.
Downloading the data readings from the recorders would help investigators learn if Flight MH370 exploded - one of several theories raised- or suffered a sudden loss of cabin pressure through a hole in the fuselage, Lau said.
The two boxes, which are actually coloured bright vermillion, are built to withstand an impact of up to 3,400 times the force of gravity and temperatures up to 1,000 degrees Celsius for 30 minutes, he said.
The boxes are also watertight to 600 metres and can stay intact for 30 days.
In Hong Kong, commercial airliners are required to have one of each box installed. The voice recorder must record at least two hours of cockpit communication, while the flight data recorder must be able to record at least 25 hours of data.
Lau has urged airlines to invest in real-time data link communications through satellites to ensure that plane tracking signals were always available.
Black boxes equipped with satellite transmitters could also ensure a signal would be picked up after batteries drain, he added.
After the AF447 accident, some in the industry suggested aircraft could continuously live-stream flight data. But Lau said airlines had been reluctant to impose such changes because of the expense.
"More weight means more fuel which means higher costs. If no one proposes anything first, no one in the industry will have impetus to change," he said.
Malaysia Airlines confirmed earlier this week that the missing aircraft did not have a continuous satellite link, citing the cost.
Warren Chim Wing-nin, honorary secretary of the Hong Kong Institute of Engineers aircraft division, said the technology would be hard to implement because of the sheer amount of data from the flight recorders that would have to be managed and processed.
"This is very expensive and a lot of sensitive data will most likely have to go through a third-party processor," he said. "This will obviously raise issues of security, privacy and sovereignty."
A spokeswoman for the Hong Kong Civil Aviation Department said a plan to require real-time flight data from an aircraft to be transmitted to a ground receiver station for storage had been proposed after the Air France incident.
But the high volume of flight data needed to be transmitted through satellite on a continuous basis made it a challenge, the spokeswoman said.
"It is widely considered that such a proposal is not practical at today’s technology, let alone the high cost involved."
Cathay Pacific Airways did not respond as to whether the airline would incorporate real-time flight data transmission. But it said positions of their aircraft were regularly communicated throughout flight via aircraft communications addressing and reporting system (ACARS) messaging systems.
Hong Kong Airlines could not be reached for comment.