The verdict is in. It was FOD, or "foreign object debris," that fractured at least 21 front and side windshields on 14 planes at Denver International Airport on Feb. 16, according to air safety investigators.
The pilots of one plane reported taxiing through "some dirt and debris" before the cracking occurred, said Denver-based National Transportation Safety Board investigator Jennifer Kaiser, who led the probe of the bizarre DIA incident.
Wind gusts at the airport reached 48 mph, said Kyle Fredin of the National Weather Service. While winds of that intensity are at the "high end," they are not that unusual.
Cracks showed up on 14 planes - from SkyWest Airlines, Frontier Airlines and Great Lakes Airlines - within about three hours in the early afternoon.
"The only commonality across aircraft type, operator, location, time and phase of flight was the wind and weather," Kaiser said.
She said windshield fractures developed on six planes as they were taking off, some of which aborted; on one just after it had landed; on two as they were taxiing to the terminal after landing; on three as they were parked at the gate; on one as it was being pushed back from the gate; and on one while it was at 19,000 feet.
The cracking was on the outer of the three layers of the windshields. Microscopic analysis showed fine particles caused pitting that in turn caused cracking, Kaiser said.
It is possible that the high winds blew back sand that may have been put down on DIA's runways and taxiways during the December and January storms.
The airport's snow and ice plan says "sand used in the air operations area will be washed, sharp sand, and screened" to a fine-grained product.
Investigators were not able to determine the precise nature of the debris because there were no "transfer" marks of the material onto the windshields, Kaiser said. "We have nothing at the impact sites to say this is definitively what it is."
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