Indonesian investigators indicate that the crew of a Lion Air Boeing 737-800 continued to descend below minimum altitude despite not having visual contact with the runway during a non-precision approach to Bali.

The National Transportation Safety Committee, in its preliminary report into the 13 April accident, says the first officer, who was flying, mentioned that the runway was not in sight as the aircraft descended through 900ft.

Although the aircraft's automated systems issued a "minimum" warning at 550ft the crew disengaged the autopilot and autothrottle, and continued the descent.

Within a minute the 737 had descended to just 150ft and the captain took control of the aircraft, while the first officer again said that he could not see the runway.

The enhanced ground-proximity warning system called a 20ft height alert and the pilot commanded a go-around but, just 1s later, the aircraft impacted the water.

Approach charts show the missed-approach point is 2nm west of the Bali VOR, giving the altitude as 465ft.

While the 737 was severely damaged as it struck, short of runway 09, all seven crew and 101 passengers survived, although four passengers were seriously injured.

NTSC says the 48-year old Indonesian pilot had logged 15,000h in total, with 7,000h on type, but the 24-year old Indian co-pilot had 1,200h and 923h on type.

Surveillance camera images indicate it was raining at the time of the ill-fated aircraft's approach. Indonesian investigators have sought additional information from other pilots about weather conditions at the time.

A pilot holding short of runway 09 corroborates that it was raining, with visibility reduced to 1-2km, and he was unable to see the 737 when his collision-avoidance system informed that the flight was 3nm away.

Another crew, approaching the airport 5nm behind the Lion Air jet, stated that they could not see the runway at the published minima and decided to execute a go-around.

Flight JT904 from Bandung appeared to be uneventful until the final seconds. The NTSC's timeline of the accident reads as follows:

06:48UTC: While 80nm from Bali VOR, the pilot makes first contact with the Bali controller. The flight is cleared for descent to 17,000ft.

06:52: The pilot is cleared to descend to 8,000ft and proceed to the Kuta waypoint, which lies west of runway 09 over the sea.

06:59: The aircraft is vectored for a VOR/DME approach for runway 09, and cleared to descend to 3,000ft.

07:04: Pilot tells Bali tower that he is leaving Kuta waypoint. The tower tells the crew to reduce speed to ensure sufficient separation with another aircraft.

07:08: Bali tower sees the Lion 737 on final and gives clearance to land, informing the pilot of a 5kt wind from the south-east.

07:08:56: At a height of 900ft, the first officer says he is unable to see the runway.

07:09:33: The enhanced ground proximity warning system calls "minimum" at 550ft. The pilot disengages the autopilot and autothrottle and continues to descend.

07:09:53: Captain takes control at 150ft, first officer says he cannot see the runway.

07:10:01: Ground-proximity system calls "twenty" and captain orders a go-around, but aircraft hits the water short of the runway. The 737 comes to rest 20m from shore and 300m southwest of the beginning of runway 09.

Source: Air Transport Intelligence news