Passengers who called 911 minutes after a Boeing 777 crashed at San Francisco International Airport said not enough help had arrived and they were doing their best to keep the critically injured alive, according to 911 calls that portray a scene of desperation.

Asiana Airlines Flight 214 crash-landed Saturday when it came in too low and too slow, killing two passengers and injuring many others as it skittered and spun 100 feet.

“We’ve been on the ground, I don’t know, 20 minutes, a half hour,” one woman said in a 911 call released late Wednesday by the California Highway Patrol. “There are people laying on the tarmac with critical injuries, head injuries. We’re almost losing a woman here. We’re trying to keep her alive.”

Another called told a dispatcher: “There’s not enough medics out here. There is a woman out here on the street, on the runway, who is pretty much burned very severely on the head and we don’t know what to do.”

The dispatcher told the caller: “OK. We do have help started that way. You said that they’re there, but there’s not enough people, correct?”

“Yes,” the caller said. “She is severely burned. She will probably die soon if we don’t get help.”

The dispatcher responded: “We are working on getting additional ambulances to you.”

San Francisco officials said ambulances could not come too close out of concern that the plane would explode.

Authorities have said that during the chaos, one of the emergency response trucks might have run over one of the two Chinese teenagers killed in the crash.

Federal investigators are examining the cockpit interaction of two Asiana Airlines pilots who had taken on new roles before the crash of Flight 214 — one of whom had seldom flown a Boeing 777 and an instructor who was on his first training flight.

There were four pilots on board but the National Transportation Safety Board is focusing on the working relationship between Lee Gang-kuk, who was landing the big jet for his first time at San Francisco International Airport, and Lee Jeong-Min, who was training him.

While the two men had years of aviation experience, this mission involved unfamiliar duties, and it was the first time they had flown together.

The pilots were assigned to work together through a tightly regulated system developed after several deadly crashes in the 1980s were blamed in part on inexperience in the cockpit, NTSB chairman Deborah Hersman said Wednesday.

“We are certainly interested to see if there are issues where there are challenges to crew communication, if there’s an authority break in where people won’t challenge one another,” she said.

Pilots are trained to communicate their concerns openly, she said, “to make sure that a junior pilot feels comfortable challenging a senior pilot and to make sure the senior pilot welcomes feedback in a cockpit environment from all members of the crew and considers it.”

Hersman said the pilot trainee told investigators he was blinded by a light at about 500 feet, which would have been 34 seconds before impact and the point at which the airliner began to slow and drop precipitously. She said lasers have not been ruled out. It was unclear, however, whether the flash might have played a role in the crash.

Hersman also said a third pilot in the jump seat of the cockpit told investigators he was warning them their speed was too slow as they approached the runway.

And she said when the plane came to a stop, pilots told passengers to stay seated for 90 seconds while they communicated with the tower as part of a safety procedure. Hersman said this has happened after earlier accidents and was not necessarily a problem. People did not begin fleeing the aircraft until 90 seconds later when a fire was spotted outside the plane.

Hersman stressed that while the trainee pilot was flying the plane, the instructor was ultimately responsible and, thus, the way they worked together will be scrutinized.

“That’s what the airline needs to do, be responsible so that in the cockpit you’re matching the best people, especially when you’re introducing someone to a new aircraft,” former NTSB Chairman James Hall said.

Massachusetts Institute of Technology aeronautics professor Mary Cummings said it’s common for two commercial pilots who have never worked together before to be assigned to the same flight. But she said the military tries to have crews work together more permanently.

“Research would tell you that crew pairing with the same people over longer periods of time is safer,” she said. “When two people fly together all the time, you get into a routine that’s more efficient. You have experience communicating.”

Details emerging from Asiana pilot interviews, cockpit recorders and control-tower communications indicate that Lee Gang-kuk, who was halfway through his certification training for the Boeing 777, and his co-pilot and instructor, Lee Jeong-Min, thought the airliner’s speed was being controlled by an autothrottle set for 157 mph.

Inspectors found that the autothrottle had been “armed,” or made ready for activation, Hersman said. But investigators are still determining whether it had been engaged. In the last two minutes, there was a lot of use of autopilot and autothrusters, and investigators are going to look into whether pilots made the appropriate commands and if they knew what they were doing, she said.

When the pilots realized the plane was approaching the waterfront runway too low and too slow, they both reached for the throttle. Passengers heard a loud roar as the plane revved up in a last-minute attempt to abort the landing.

The two pilots at the controls during the accident had also been in the cockpit for takeoff. Then they rested during the flight while a second pair of pilots took over. The two pairs swapped places again about 90 minutes before landing, giving the trainee a chance to fly during the more challenging approach phase.

Hersman cautioned against speculating about the cause of the crash. But she stressed that even if the autothrottle malfunctioned, the pilots were ultimately responsible for control of the airliner.

“There are two pilots in the cockpit for a reason,” she said Wednesday. “They’re there to fly, to navigate, to communicate and if they’re using automation, a big key is to monitor.”

Crash survivor Brian Thomson, who was returning from a martial arts competition in South Korea and walked away unscathed, said he’s not concerned about the pilot’s lack of experience with the airliner.

“At some point you have to start at hour one, hour two. It’s just natural. Everyone starts a career someway, somehow. Starts a new plane someway, somehow. They have to have training,” he said.

The flight originated in Shanghai and stopped over in Seoul before making the nearly 11-hour trip to San Francisco.

A dozen survivors remained hospitalized Wednesday, half flight attendants, including three thrown from the jet.

(AP)