Investigators probing the July 6 crash of Asiana Airlines Flight 214 at San Francisco International Airport (SFO) are working to understand what caused the Boeing 777-200ER to make a slow, steady descent into a sea wall just short of its assigned runway, and why the flight crew did not detect a problem until just seconds before the plane hit.

While it is too soon to draw firm conclusions, information released by NTSB officials paints a clear picture of what happened just before the accident. The aircraft slowed below its minimum safe landing speed well before touchdown, and hit a sea wall just short of the airfield. The crew did not indicate any trouble with the plane or the approach until seconds before the plane hit, and investigators have not revealed anything that points to a mechanical malfunction.

Based on what investigators have confirmed, all seemed normal as Flight 214 approached SFO following a routine flight from Incheon International Airport. The crew, cleared for a visual approach, verified that the 777’s landing gear was down and the flaps set to 30 deg., says NTSB Chairman Deborah Hersman explained. The pilots set 137 kt. as a target speed for crossing the runway threshold, Hersman confirmed today at a media briefing. A “very early read” of flight data recorder (FDR) information shows the aircraft’s airspeed declined steadily as it approached the airfield. Airspeed dropped below the targeted landing speed to 134 kt. when the plane was about 500 ft. above ground at 34 sec. before impact, she says. Airspeed continued to decline until just before impact, reaching a minimum speed of 103 kt. 3 sec. before the plane hit. Airspeed was 105 sec. when the plane hit the sea wall, she says.

Based on the cockpit voice recorder (CVR), Hersman says at 7 sec. before impact, one crewmember called for an increase in speed, and at 4 sec. before hitting the sea wall, the stick shaker—indicating an imminent stall—is heard. At 1.5 sec. before impact, Hersman says a crewmember called for a go-around, and both Pratt & Whitney PW4090 engines “appear[ed] to respond normally.”

On-site inspection of the engines turned up no anomalies, Hersman says. Indications are that both were producing power with “high rotation” when they hit the ground. Pratt & Whitney will perform more detailed teardowns as part of the investigation.

CVR evidence reveals the crew did not discuss a problem with the aircraft, and did not declare an emergency prior to touching down, Hersman notes. A preliminarily FAA review of the plane’s approach did not show anything abnormal, such as an unusually steep descent, she adds.

Investigators found correct navigational charts for SFO in the appropriate places in the cockpit, Hersman says.

Various working groups are digging more deeply into the FDR, CVR, and operational aspects of the accident. Hersman says investigators planned to interview all four pilots onboard later today.

She confirmed that one of the two pilots operating the aircraft was “working on his initial [777] operations experience,” while the second pilot was a check airman. She would not confirm which pilot was flying the approach, though Asiana executives have said that the pilot with less 777 experience was in command as the plane headed into SFO.

Hersman says investigators will seek “a lot more details” about the flight crew’s activities during the flight and in the 72 hr. prior to departing Seoul. Information from the interviews will be “correlated” with CVR and FDR data, she says. “We want understand what [the pilots] knew, and what they understood,” she says.

The crash ripped the plane’s tail off, leaving its tail cone in the sea wall and scattering parts in the water and along the airfield. Pieces of the sea wall were knocked “several hundred feet” up the runway, Hersman says, and both engines separated from the airframe.

The plane was carrying 291 passengers and 16 crewmembers. Two passengers died. Hersman says that reports of an emergency response vehicle striking and killing one of the passengers are premature.