The Indonesian carrier Garuda has become the first airline to scrap its order for the Boeing 737 Max, saying it was cancelling a multibillion-dollar deal due to lack of public trust in a jet which has crashed twice in five months.

The move came as the manufacturer Boeing attempted to tackle fears about the safety of the 737 Max, which has crashed in both Ethiopia and Indonesia with the loss of 346 lives, by building enhanced warning devices as standard into every plane.

Garuda had so far taken just one of 50 737 Max planes it has on an order worth up to $6bn on listed prices. A spokesman said: “We have sent a letter to Boeing requesting that the order be cancelled.

“Garuda passengers in Indonesia have lost trust and no longer have the confidence.”

After two deadly disasters in five months, can Boeing survive? Read more

All but two of the 189 people who perished in the crash of a Lion Air-operated 737 Max near Jakarta in October were Indonesian nationals.

The investigation into the crash has highlighted problems with the flight controls on the 737 Max, which had only been in service for a few months.

The current global fleet of 387 Boeing 737 Max planes remains grounded, as investigations continue into the Lion Air crash and the Ethiopian Airlines disaster earlier this month, where regulators have noted clear similarities.

The Garuda spokesman said the carrier was awaiting a response from Boeing. The airline is the first to publicly break ranks and cancel out of dozens who have placed orders totalling a notional $560bn for the 737 Max.

Lion Air has also said it could cancel its 737 Max orders.

Boeing is set to make a cockpit warning light compulsory in all 737 Max models sold. The safety feature had been installed in many planes – including the American Airlines fleet – but was not purchased by Lion Air or Ethiopian.

The light would warn pilots if the readings from critical sensors do not match and are therefore faulty.

In a preliminary report, investigators in Indonesia found one of the “angle of attack” sensors provided false readings that triggered the Lion Air plane’s new anti-stall software, the manoeuvring characteristics augmentation system or MCAS, and forced the plane’s nose down, against the pilots’ commands.

The cockpit voice recorder, recovered from the wreckage, has shown that the Lion Air pilots were consulting a handbook to understand why the 737 Max continued to lurch downwards in the final minutes before it crashed into the sea.

The black box recorders from Ethiopian Airlines flight 302 are being analysed in Paris, at the facilities of the French air accident authority, BEA. It has also said there are “clear similarities” with the Lion Air crash.

Ethiopian Airlines issued a further statement on Friday emphasising the modernity of its safety and training systems, which include its own dedicated simulator for the 737 Max. Its chief executive said that its pilots had been made aware of Lion Air’s problems with the MCAS, but that there was no simulator training to deal with such an emergency.

Boeing has said it was making software upgrades that it expected to be approved by the US Federal Aviation Administration (FAA) in coming weeks. Officials told Reuters that the manufacturer would also retrofit 737 Max models it has already delivered with the cockpit warning light.

The 737 Max is still expected to be out of the skies for several months, while regulators review and approve the changes. Europe’s safety agency EASA has said it will conduct an independent review of any new system. The US regulator, the FAA, was one of the last to act in the wake of the Ethiopian crash, as regulators noted similarities in the flight data, and reports that the captain had again said he was having trouble controlling the plane soon after take-off.

Boeing shares have fallen by 12%, wiping $28bn off its market value since the Ethiopian crash on 10 March. The manufacturer faces a criminal investigation by the US Department of Justice, which now involves the FBI, according to the Seattle Times.

The department also plans to audit the FAA’s approval of the 737 Max. Questions have been raised over the licence the regulator has given to Boeing to self-certify aspects of aircraft production.