Investigators consider whether powerful ‘wind shear’ or ‘microburst’ caused Bali crash in which all 108 on board survived

The Lion Air pilot whose jet fell into the sea while trying to land in Bali has reportedly described how he felt it “dragged” out of its trajectory and into the water. Investigators are considering whether a powerful downdraft of wind caused the crash in which all 108 passengers and crew survived despite the Boeing 737 cracking in half on impact.

The newly built plane undershot the tourist island’s main airport runway in Denpasar and belly-flopped in water on Saturday. Authorities from Indonesia, the US and Boeing are investigating.

Initial debriefings, witness comments and weather reports have focused attention on the possibility of “wind shear” or a downdraft from storm clouds known as a “microburst”. Experts say such violent and unpredictable gusts are rare but can leave even the most modern jet helpless if they are stronger than the plane’s ability to fly out of trouble – with the critical moments before landing among the most vulnerable.

“If you have a downdraft which exceeds the performance of the plane, then even if you put on full thrust you will go downhill and you can’t climb out,” said Hugh Dibley, a former British Airways captain and expert on loss-of-control events.

The cause of the crash has potential implications for the reputation of one of the world’s fastest-growing airlines, which is fighting to be removed from a European Union safety blacklist just as it buys record volumes of Airbus and Boeing jets.

According to initial pilot debriefings, details of which have been described to the Reuters news agency, flight JT-904 was on an eastwards approach to Bali’s Ngurah Rai airport at mid-afternoon on Saturday following a normal flight from Bandung, West Java.

The co-pilot, an Indian national with 2,000 hours of relevant flying experience, was in charge for the domestic trip, which was scheduled to last one hour and 40 minutes.

As the Lion Air plane was coming in to land, with an aircraft of national carrier Garuda following behind and another about to take off on the runway just ahead, the co-pilot lost sight of the runway as heavy rain drove across the windshield. The captain, an Indonesian citizen with about 15,000 hours’ experience and an instructor’s licence, took the controls.

Between 122 metres and 61 metres altitude (400-200ft) pilots described flying through a wall of water, according to the source. Bursts of heavy rainfall and lost visibility are not uncommon in the tropics but the aircraft’s low altitude meant the crew had little time to react.

With no sight of the runway lights or markings the captain decided to abort the landing and perform a “go around”, a routine manoeuvre for which all pilots are well trained. But the captain told officials afterwards that instead of climbing the 737 started to sink uncontrollably and their well-practised routines unravelled quickly.

“The captain says he intended to go around but that he felt the aircraft dragged down by the wind; that is why he hit the sea,” said the source, who was briefed on the crew’s testimony. “There was rain coming east to west; very heavy,” the source said, asking not to be named because no one is authorised to speak publicly about the investigation while it is under way.

A passenger on board the jet painted a similar picture of an aircraft getting into difficulty only at the last minute. “There was no sign at all it would fall but then suddenly it dropped into the water,” Tantri Widiastuti, 60, told Metro TV.

Lion Air declined to comment on the cause of the crash.

According to the Flight Safety Foundation, bulletins for pilots at around that time indicated a few storm clouds at 518 metres (1,700ft) and a wind blowing moderately but varying in its direction from east-south-east to the west.

The aircraft itself was delivered in February and there had been only one technical problem: a landing light that had to be replaced.

According to Boeing, the 737-800, its most popular current model, is equipped with a system that detects wind shear ahead and warns the pilot audibly to go around.