A Delta Airlines flight from Atlanta to New York skid off the runway at LaGuardia on landing during a snowstorm this morning.  The airplane hit a fence and berm which may have prevented it from going into the waters of Flushing Bay.  No life-threatening injuries were reported among the 125 passengers and five crew members, although 3 passengers were reportedly taken to the hospital.  The airport was closed immediately following the accident but one runway has recently been re-opened.  The NTSB has announced that it is sending investigators to retrieve the black boxes and document the accident.

The NTSB’s initial steps following an accident are to document the so-called perishable evidence – any evidence that could be lost or destroyed if not gathered at the scene.  This would include, in a situation like this, the runway conditions, including any skid marks or ground scars (such as scrapes or gouges which could indicate that the wings or other parts of the aircraft had struck the ground).   The NTSB will also gather any information regarding weather conditions at the airport at the time of landing, as well as reported conditions, including pilot braking reports from previous flights.  Of particular significance, will be wind speed and direction.  While airplanes normally land into the wind, they can also land safely with crosswinds and tail winds.  A tail wind would typically make a landing roll-out longer.  The wind speed and direction are included in the calculations made by pilots to determine landing distance and whether a landing can be made safely given existing conditions, including the condition of the runway (wet, snow-covered or icy, for example) and its length.

The NTSB will secure the cockpit and voice data recorders – the black boxes – and send them to its lab in Washington, DC for analysis.  This will include information such as airspeed on landing and engine performance – in particular, at what point were the thrust reversers deployed.  The thrust reversers change the direction of the engine exhaust to aid in slowing down the airplane.  Data will also include the performance of the anti-skid system.  This system, which is much like the anti-skid system in modern cars, prevents the plane’s wheels from locking up and negatively affecting braking distance.  In addition, the data will indicate how the ground spoiler system worked, which is critical to assisting the aircraft in stopping.  The ground spoilers are panels on top of the wing that pivot up, destroying any lift, and putting the entire weight of the airplane on the wheels, increasing braking efficiency.

The NTSB will also review the cockpit voice recorder and air traffic control tapes, as well as information including the experience and training of the flight crew.  The NTSB will look at any other relevant factors, including the decision to keep the airport open and the decision to use that particular runway.  While it is easy to assume that weather was a factor, there are many things to consider before any conclusion can be reached on why this flight skid off the runway.