A pilot needs to reach the end of the runway at the right height and speed. Too slow and the aircraft could stall and crash. Too fast and the aircraft will run off the far end.

As an approach to landing progresses, the pilot watches the runway and constantly reassesses whether the aircraft is going to come up short or, instead, float too far down. The pilot needs to adjust his power settings and pitch all along the way to end up in the landing zone at the right speed and height. Things work out best if the pilot flies down a gradient of about 3 degrees. That profile allows the pilot to keep his speed and altitude in check.

So where did Asiana Flight 214 go wrong? We don’t know yet but here’s what the pilot had working against him:

Surrounded by water. San Francisco airport is surrounded by water. The lack of visual cues impairs depth perception and makes it a bit tricky to tell whether the approach is going to work out properly. Not impossible by any means. Just a little tricky.

Slam dunk. Air traffic control kept the aircraft higher than normal as it neared the airport. The approach, sometimes called a “slam dunk” approach, requires the pilot to descend more steeply than he might otherwise be comfortable with. Again, just a little bit more difficult approach than normal.

ILS inoperative. In bad weather, the pilots use instruments in the cockpit to guide the aircraft down the proper glidepath. In fact, the autopilot will generally keep the aircraft on the proper descent – not too shallow, not too steep. Yesterday, the weather was nearly perfect and the aircraft had not been instructed to fly the electronic glide path. The crew was to fly by looking out the window. Nonetheless, most pilots keep the electronic glide path tuned in and engaged, just for additional help.PAPI's were inoperative Unfortunately, the electronic system (called an “ILS” or Instrument Landing System) was not operating at the airport yesterday. Certainly, it wasn’t needed given the weather, but it would have helped.

No PAPI lights. At the end of the runway is a series of colored lights. If the aircraft is too low, the lights turn red. Too high, and they turn white. The lights (called Precision Approach Path Indicators or "PAPIs") are an aid to flying the proper glide path when making a visual approach. Unfortunately, those lights weren’t working.

So the pilot made a slam dunk approach into an airport that can be a bit tricky. He had no ILS to help him, and no PAPI. He had one other thing working against him:

43 Hours. The co-pilot had only 43 hours of 777 time. With so little experience, it’s unlikely he would have felt comfortable telling the pilot that things just didn’t look right.