Teams searching for the black box flight recorders of a missing EgyptAir jet that crashed with 66 people aboard face technical constraints that aviation experts increasingly blame on a slow regulatory response to earlier disasters.

As a three-year deep-sea search for Malaysia Airlines Flight MH370 draws towards a close in the Indian Ocean without finding the airplane, another is starting in the Mediterranean Sea where the lessons of previous crashes have yet to be applied.

Rescuers have barely 30 days until the batteries die on two underwater beacons designed to guide them to the black box flight recorders as they scour 17,000 sq km of sea north of the Egyptian port city of Alexandria.

After previous crashes at sea, regulators agreed to increase the transmission time and range of such beacons to increase the chances of finding evidence and preventing future accidents.

The changes, trebling the life of the 'pingers' to 90 days, were first recommended by French investigators in late 2009, six months after the crash of an Air France plane in the Atlantic.

But they were only adopted in response to the disappearance over four years later of Malaysia's missing MH370 and do not come into effect until 2018: too late to help find EgyptAir 804.

French investigators say the Egyptian jet sent warnings indicating that smoke was detected on board. The signals did not indicate what caused the smoke, and aviation experts have not ruled out deliberate sabotage or a technical fault. Egypt has sent a robot submarine to join the hunt.

It is the second time in little more than a year that sea search operations have been forced to rely on decades-old black-box technology after an AirAsia plane crashed into the Java Sea.

Delays in implementing the changes to the beacons to extend their battery life and improve the chances of finding the black boxes have been criticised by a number of experts including the former head of the French BEA agency, which is helping the search for Egyptair.

"PRETTY SCANDALOUS"

"The battery situation is pretty scandalous," Jean-Paul Troadec, who headed the French government BEA air accident investigative agency during much of the Air France probe, told Reuters.

"It hardly costs anything to install new batteries. There was no reason to wait until 2018."

In the first days after a crash at sea, the priority is to use passive devices capable of listening for the pinger's clicking pulse. Once these die, searchers must use sonar devices and robots, which are costly and time-consuming. It took two years to find Air France 447 in the Atlantic this way.

"You can imagine the pressure this 30-day deadline creates," Troadec said.

Manufacturers say that implementing the recommendations to extend the life of a beacon is not just a simple switch.

"Industry does not develop technology overnight and for the aircraft manufacturers to be ready, two years seems reasonable," a spokesman for the European Aviation Safety Agency said.

The search for EgyptAir's Airbus A320 is especially challenging because its wreckage lies in one of the deepest parts of the Mediterranean, at a depth of 2,000-3,000 metres which is on the edge of the range for hearing pinger signals.

That may mean towing hydrophones more than a mile below the surface, using specialist devices that are in short supply.

This task could have been made easier by other still-pending safety proposals. In 2009, the BEA suggested black-box makers add a new, lower frequency that carries further and is easier for military vessels - typically first on the scene - to spot.

European regulator EASA has ordered airlines to fit the longer-range devices from the start of 2019, almost a decade after the crash that first inspired the change.

To many, such slow progress highlights the regulatory problems facing the aviation industry which is struggling to adapt to a series of accidents including the loss of MH370 with 239 people on board, the shooting down of another Malaysian aircraft over Ukraine in 2014 and last year's crash by a Germanwings pilot who flew his plane into the French Alps.

Despite the high-profile plane crashes, regulators say flying remains exceptionally safe, thanks in part to a unique system of standardised rules overseen by the United Nations.

LENGTHY APPROVALS

But the task of maintaining global standards by consensus requires lengthy approvals.

And critics say reforms have been held up before by bureaucracy and a lack of resources at the United Nations' aviation agency, where a special panel on black boxes did not meet between 1998 and 2006 because it had no secretary.

A spokesman for the United Nations' International Civil Aviation Organization declined further comment beyond a statement in March announcing improvements to flight recorders and better ways of tracking jetliners over remote areas.

Experts say the delays also reflect a tussle between regulators, airlines and manufacturers over how safety dollars should be spent. Planemakers, airlines and pilot unions are represented at ICAO because of the industry's complexity.

"The people who pay for searches are governments and the people who pay for the equipment are companies," Troadec said, asked to explain the time it takes to apply BEA recommendations.

The French recommendations on black boxes and proposals for tracking were discussed at ICAO after the crash of Air France's AF447 but were only fully embraced after the loss of MH370 made it a global issue, according to people involved in the talks.

"After MH370 there was momentum," the head of ICAO's special panel, Philippe Plantin de Hugues, said in a recent interview.

Still, some airlines, including Air France, have installed the longer batteries without waiting for the 2018 changeover.

"Airlines are not pushing back. They are as eager as anybody to quickly have access to the black box data after an accident," said a spokesman for the International Air Transport Association, which represents most airlines.

"But we need to be sure that any change is fully thought through ... and capable of being supported by reliable technology."  - Reuters