Had fog, lightning or equipment failure been a factor, the crash landing of an Asiana Airlines flight at San Francisco International Airport that left two dead Saturday would have been no less tragic. But it might have been more understandable.

That it occurred on a clear day with no apparent contributing technical factors makes it all the more perplexing — and maddening.

Now comes this. San Francisco fire officials say one of the two people killed, both 16-year-old girls from China, may have died not because of the plane crash but because she was hit by an emergency vehicle, a fire truck, arriving at the scene.

If true, it's an unthinkable outcome — the possibility that the girl may have survived the crash only to be hit and killed by those who were coming to save her.

It raises a host of new questions: How did the girls get outside the aircraft after the crash landing and where were they? What was the visibility like when emergency crews arrived? What are the protocols for first-responders in chaotic situations such as this, and were they followed?

These come on top of many other questions that revolve around what caused the crash landing in the first place.

All preliminary evidence suggests pilot error. Officials from the National Transportation Safety Board said the pilot, who had 10,000 hours of flight experience but only 43 hours on a Boeing 777, was making his first landing in San Francisco.

Officials say the aircraft was traveling far below the 137 knots per hour required for landing at SFO. In the final moments before the crash, the jetliner began to stall and the pilot attempted to abort the landing. But it was too late. Witnesses say the aircraft's tail clipped a seawall at the end of the runway, the fuselage then slammed into ground and spun off the runway. Later, it caught fire.

Officials say the first sign of problems was about seven seconds before the crash when pilots recognized the need for speed. But why was it not apparent earlier to those in the cockpit? Witnesses both on the flight and on the ground say they observed the jetliner was having problems even before the seven-second mark.

Given that there were pilots with more 777 flight experience on board, was there a breakdown in communication between the pilot and other members of the crew that may have contributed to the crash?

While federal investigators look to answer these and other questions, they also should evaluate and shed light on why this tragedy was not far worse. Given the severity of the landing, it's remarkable that there are not more casualties.

Officials say research into past incidents like this have led to improvements in aviation safety, including stronger aircraft, stronger seats, less flammable materials, easier to open doors, etc.

That 305 out of 307 passengers and crew members survived an accident like this is remarkable. But unfortunately, when so much of the evidence suggests that these tragedies were preventable, it's cause for short celebration.