Why did so many passengers survive Asiana crash?*

Part of it was the use of flame-resistant materials used on the Boeing 777. Part of it were passenger seats that could withstand tremendous force. Part of it was the flight crew that was able to get everyone off quickly (despite one of the evacuation chutes being activated inside the cabin.) One of the flight attendants is being singled out for carrying out passengers piggyback. From the WSJ:

The Asiana crash "is the culmination of what has been done over more than 20 years to help more and more passengers survive crashes," according to Kevin Hiatt, president and chief executive of the Flight Safety Foundation, a nonprofit group in Alexandria, Va., that advocates for safety improvements world-wide. Regulators in the late 1980s mandated all-new passenger planes must have seats able to withstand stronger impacts than in the past--practices that the Federal Aviation Administration ordered in 2005 be applied to nearly all passenger planes by October 2009. As part of those rules, seats on jetliners must be able in tests to survive collisions that slam them forward at 16 times the force of gravity, or 16g, to ensure the seats don't collapse or detach from the floor. A Boeing spokesman said the company has been delivering all its jets with 16g-rated seats since 2009. Before the advent of such stronger seats, Mr. Hiatt said, the intense vertical and horizontal force generated by a crash like Saturday's "would have caused many more seats to break free and pancake into each other, probably blocking exit paths."

From Bloomberg:

Introduced in 1995, the jet features seats that can withstand 16 times the force of gravity, compared with the previous standard of 9 times, according to Boeing. All new aircraft designed and built after 1998 have the 16G seats, according to the Chicago-based planemaker. The jet that crashed in San Francisco was delivered in March 2006, Boeing said. Modern aircraft also are required to have non-flammable material for seat cushions, carpet, walls and other interior parts. Insulation blankets in aircraft walls are designed to slow the spread of flames, and along with the jet's skin can provide at least four minutes for evacuation before a fuel-fed post-crash fire can burn through, according to documents on Boeing's website. "These new 16G seats stay firmly bolted into the floor system, whereas in the past the seats would break free and pancake into each other and cause fatalities or more severe injuries," said Kevin Hiatt, chief executive officer of the Flight Safety Foundation in Alexandria, Virginia, and a former Delta Air Lines Inc (DAL). pilot who flew 777s among other jets.

Happenstance also played a huge role. The plane didn't have much fuel remaining and was flying at a very low speed, limiting the force on impact. It was the middle of the day and the weather was perfect. SFO is a modern facility, with emergency personnel quickly available (the first EMS technicians arrived within a minute or two of the crash). Of course, none of that clears up the matter of why this happened - specifically, why the pilot of the Asiana plane had so little experience flying 777's? And why didn't anyone else in the flight deck recognize that the aircraft was coming in too low and too slow?

*Update: Pilot error may turn out to be the cause of the crash, but aviation experts point out that it's not at all unusual for a pilot transitioning to a new aircraft to be at the controls. From Air Transport World:

As US National Transportation Safety Board (NTSB) chairman Deborah Hersman said Monday morning on NBC's Today Show, it is typical for pilots to move to new aircraft types. When they do, after going through simulator training, the pilots then go through an initial "training" period in which they are part of crews with more experienced pilots on the aircraft type to which the pilot is transitioning. At some point, these pilots make their first landing with an aircraft type at a given airport. Gang-Guk Lee had landed at SFO before in other aircraft, including the 747, and he had landed the 777 already at, among other airports, London Heathrow and Los Angeles International. Allowing an experienced pilot who has landed a 747 at SFO and a 777 at Heathrow and LAX to land a 777 at SFO does not sound out of line at all.