Four weeks into the hunt for MH370, pressure is building for better ways of tracking aircraft as regulators wrestle with the Malaysian jet’s disappearance armed with only minimal information on the fate of its 239 passengers.

As search efforts intensified on Saturday, four weeks after the Boeing 777 went missing, a U.S. pilots association called for existing satellite technology to be made mandatory so controllers can track jets.

Until recently, aircraft flying over oceans well outside the reach of air traffic control routinely gave their position through high-frquency radio links that are vulnerable to interference from the atmosphere.

Some airlines now use satellite-based voice and text communications, but these are not mandatory and may require a subscription that Malaysia Airlines had not signed up for, according to officials investigating the loss of Flight MH370.

Related: Beyond the Black Box: Fixing Aviation’s Broken Communications Systems

“Technology that exists today can pinpoint the location of aircraft in near real time and, in this day and age, it is unacceptable that the location of the aircraft is unknown,” the U.S.-based Air Line Pilots Association said.

“Implementation of technology such as ADS-B and use of satellite surveillance of aircraft during flight operations must become the standard across the industry,” it added in a statement received on Saturday.

ADS-B is a satellite navigation device capable of linking to the Global Positioning System or other space-based networks.

MH370 disappeared while en route from Kuala Lumpur to Beijing in the early hours of March 8.

Authorities have not ruled out mechanical problems but say evidence suggests it was deliberately diverted and crashed in the Indian Ocean, where an intensive search is trying to find the plane’s black box recorders before their batteries run out.

Black boxes come with locator beacons designed to work for 30 days. A Chinese ship detected a signal in the south Indian Ocean on Saturday, state news agency Xinhua reported, but it was not immediately clear whether it came from the missing jet.

Renewed Pressure

French authorities recommended extending the life of the batteries on the locating devices to 90 days after the crash of an Air France jet in the Atlantic in 2009, but the move will not become mandatory until 2018 or 2019.

France’s final report on the AF447 crash led to a rethink of how technology can help investigators track the wreckage, but aviation experts say changes can take years to negotiate.

Experts say the jet’s disappearance has renewed pressure for better use of tracking technology. Further recommendataions may, however, have to wait for the jet’s recorders to be found.

After the Air France crash, a United Nations agency began looking at three reforms, but not all would be required by law.

Under one of these, a jetliner would automatically beam back regular updates on its location throughout the flight. Under the second proposal, the jet would automatically send out useful tracking data when it senses it is about to crash.

A third idea calls for the black box to be ejected from the aircraft just before impact, avoiding the risk of destruction.

IFALPA, an association representing pilots globally, says better tracking would come about automatically through efforts already under way to overhaul air traffic by using satellites, but such schemes have been held up in part by budget problems.

One U.S. government official said the sheer scope of the international search effort, the frustration of not finding any sign of wreckage, and the lingering questions about whether there was a technical issue with the plane that caused the course change, could push the issue to a tipping point.

“I think it’s different this time,” said the official, asking not to be named. “People have been calling for this for years, but maybe now there’s enough momentum to make it happen.”

But some in the aviation industry remain sceptical, citing inertia over changes in regulations in the past and the astonishingly rare disappearance, albeit with many casualties.

The Flight Safety Foundation, a Washington-based non-governmental group campaigning on safety matters, has called for an international symposium to help improve flight tracking.

(Editing by David Holmes)

Photo Credit: Tiger75 launches from the Australian Navy ship HMAS Toowoomba as it continues the search in the southern Indian Ocean for flight MH370. Reuters