Investigators are preparing to study the pilots’ last words for clues as to the cause of last week’s Air India plane crash after recovering the cockpit voice recorder from the wreckage.

The voice recorder was in the Boeing 787 aircraft’s second black box, which the Indian authorities said they had found on Sunday. The first, containing the flight data recorder, was located within 28 hours of Thursday’s disaster in Ahmedabad, in which at least 279 people died.

Most of the victims were onboard flight AI171 bound for London Gatwick, all but one of whom died after the plane crashed into buildings moments after failing to properly take off from Ahmedabad airport.

Air India captain sent mayday less than minute before crash, say authorities

Read more

The captain, Sumeet Sabharwal, sent a mayday call seconds after the plane left the runway.

No evidence or explanation has yet been shared from the investigation, led by Indian officials with assistance from the UK and US. They were reported to be initially focusing on engine failure and issues with the wing flaps and landing gear to trace the causes of one of the world’s worst ever plane crashes.

Most relatives of the 279 known victims, 38 of whom were killed on the ground, were still waiting on Monday for results of DNA testing before health officials could return the bodies of their ones.

About 80 of the deceased had been identified by late on Sunday, according to a doctor at Ahmedabad’s civil hospital, Rajnish Patel. “This is a meticulous and slow process, so it has to be done meticulously only,” Patel said.

While some mourners have held funerals, most are facing an anguished wait.

Rinal Christian, 23, the younger brother of a passenger, told the AFP news agency: “They said it would take 48 hours. But it’s been four days and we haven’t received any response. My brother was the sole breadwinner of the family. So what happens next?”

One of the latest victims identified was a former chief minister of Gujarat state and senior member of India’s ruling party, whose flag-draped coffin was carried in Ahmedabad by soldiers.

One victim’s relatives who did not want to be named told AFP they had been instructed not to open the coffin when they receive it.

Air India said there were 169 Indian passengers, 53 British, seven Portuguese and a Canadian onboard the flight, as well as 12 crew members.

In London, members of the UK’s Indian community took part in a multi-faith vigil outside the Indian high commission on Sunday. Only one passenger survived the crash, a British man, Vishwash Kumar Ramesh.

1:08

‘I saw people dying in front of my eyes’: British survivor describes Air India crash – video

It was the first crash involving a Boeing 787 Dreamliner. Air India was ordered to carry out additional maintenance and checks on the 33 remaining planes in its fleet but big airlines around the world continue to operate the model as normal. More than 1,000 are in regular service.

Investigators will also have to consider the possibility of human error and aspects such as aircraft maintenance at the airline, which is owned by Tata Group. The company has been trying to revamp its ageing fleet.

Air India’s chair, N Chandrasekaran, told staff on Monday that the crash should be a catalyst to improve safety, urging employees to be resolute in the face of any criticism.

During a meeting attended by nearly 700 staff at the company’s headquarters near Delhi, Chandrasekaran said it was the most heartbreaking crisis of his career. “We need to use this incident as an act of force to build a safer airline,” he said.

“We need to wait for the investigation … It’s a complex machine, so a lot of redundancies, checks and balances, certifications, which have been perfected over years and years. Yet this happens, so we will figure out why it happens after the investigation.”

An Air India 787 bound for New Delhi from Hong Kong turned back as a precautionary measure on Monday after the pilot suspected a technical issue, a source told Reuters.

Flight AI315 landed safety in Hong Kong at 1.15pm local time and was undergoing checks.

Boeing has further scaled back its presence at the Paris airshow, one of the global aerospace industry’s leading commercial events, cancelling a media reception on Monday. Its chief executive, Kelly Ortberg, had already pulled out and a Boeing team has been sent to Ahmedabad to offer assistance to the investigation.