NEW YORK — As the National Transportation Safety Board begins its investigation into a Delta jetliner that slid off a runway while landing during a snowstorm at LaGuardia Airport, there is no shortage of questions to pursue:
How big a factor was the snow? Was the runway too slippery? Could it have been a mechanical problem? Did the pilot come in too fast?
Thursday's accident of Flight 1086 from Atlanta caused only minor injuries to six passengers, but it was a scary case of what could have been at an airport notorious for its relatively short runways and proximity to water. The plane packed with 130 people smashed through a perimeter fence and came to rest just feet from the icy waters of Flushing Bay.
Aviation safety experts interviewed by The Associated Press give their take on the possible scenarios:
Maintaining a runway during bad weather is similar to maintaining a highway, except an aircraft is operating at a much higher speed than a motor vehicle, said Jim Hall, former chairman of the NTSB.
"You know, it's a piece of concrete," Hall said. "You've got to maintain the friction in order for the aircraft tires to engage and stop the plane."
Airports rely on reports on runway conditions from pilots as they land to continually monitor safety. On Thursday, Port Authority Executive Director Patrick Foye said the runway had been plowed "literally minutes" before the Delta flight arrived, and two pilots who landed before had reported "good braking conditons."
There's no rule about how much snow or ice leads to a runway closing. Instead, the Federal Aviation Administration requires airports to measure runways during winter storms to assure planes can safely brake: A specially equipped vehicle races down the runway with a computer checking braking action, and if the runway fails the test it must be closed.
Steve Hull, an accident-investigation consultant with RTI Forensics, says U.S. airports need to start providing more information themselves about the conditions of runways.
"Relying on aircraft crews is an unreliable method," Hull said. "Runway patrols to positively identify the braking action is what is required."
The plane could have been coming in too fast or drifting to the left or the right. There was a slight tail wind and crosswind at the time, but safety experts say both were well within the capabilities of such a jet.
Normally, pilots prefer to land facing the wind, rather than having it at their back. A headwind slows a jet down while a tail wind gives it a push, making it slightly harder to stop. It is up to a pilot to decide when a landing is too risky and to abort the approach, climb, circle around and try it again.
"Runway overruns are the accident that never goes away," said Steven Wallace, who was director of the FAA's accident-investigations office from 2000 to 2008. "There has been a huge emphasis on runway safety and different improvements, but landing too long (too far down the runway) and too fast" can result in an overrun.
There was no indication of any issue prior to landing. Passengers weren't told to brace. So if something did happen, it would have occurred during touchdown. Todd Curtis, a former Boeing safety engineer and director of Airsafe.com Foundation, said a few things could have led to the pilots losing the ability to steer the plane.
The rudder — part of the tail that steers the jet inflight — could have failed. Upon landing, the jet's engines reverse their thrust to help slow the plane down. They might have malfunctioned or one of the two failed, causing the plane to unexpectedly turn. Another scenario could have had the brakes on the plane's wheel fail or incorrectly apply more pressure to one side than the other.
In 2008, a United Airlines Airbus A320 skidded off the right side of the runway and into a snowbank after landing in Jackson Hole, Wyoming. In preliminary findings, the National Transportation Safety Board determined that the brake system had been wired incorrectly. "That made all the brakes on one side of the plane fail, essentially, and then the plane departed (the runway) off the other side," Wallace said. "That sort of thing is pretty rare."
Besides having an effect on the runway, bad weather makes the pilots' job more difficult. There are instruments in the cockpit showing the plane's speed, the angle it is approaching the runway and if it is lined up with the centerline.
But pilots pair that data with what they are seeing out the cockpit windows. There are normally visual clues that help them tell if they are lined up with the runway and how fast the plane is approaching.
According to the National Weather Service, Thursday's snowstorm that dumped about 7 inches on the New York City area cut visibility to a quarter mile.
"It's an additional set of information that the flight crew has to make a decision," Curtis said. The preponderance of information would allow them to make a decision: should we continue this landing or should we abort this landing."
Associated Press writers Meghan Barr in New York and David Koenig in Dallas contributed to this report.