The worst icing conditions in at least 15 months hung above University Park Airport on Saturday afternoon, prompting emergency crews to go on alert three times in five hours, airport Director Bryan Rodgers said Monday.
It started at 1:32 p.m. Saturday, when the crew of an inbound plane declared an emergency because of exterior ice buildup. That aircraft landed safely.
Less than 30 minutes later, a $2.5 million propeller plane en route to land crashed two miles short of the runway, killing the six people aboard. It was the most deadly aviation calamity in Centre County history, federal records show.
The plane's pilot, Jeffrey Jacober, of Providence, R.I., did not report any problems to air-traffic controllers before the crash.
Investigators have not determined the cause of the crash.
But at 2:21 p.m., just a half-hour after the plane went down, another incoming aircraft declared an emergency -- again because of ice. And it happened once more about 6:45 p.m., Rodgers said.
Those planes touched down without incident.
Rodgers said the emergencies reflected the most intense spurt of icing the airport has seen since he took over in January 2004. While icing is a common woe around springtime, it's rare to face such a fierce outbreak in such a short period, he said.
Bob Dannaker, who retired in 2004 after 16 years as airport director, said he couldn't recall seeing so many ice-related emergency declarations in one day.
"There must have been some unusual and unpredicted weather conditions that would cause that," Dannaker said. "To have so many on the same day is really extraordinary."
Rodgers said he would not speculate about whether icing was a factor in the fatal crash.
The National Transportation Safety Board, which is handling the investigation, reported Sunday that it had found nothing definitive to suggest what caused the crash. Its preliminary report is expected in April, but findings may not be final until early 2006, an investigator said.
It wasn't clear Monday whether air-traffic controllers had advised pilots on incoming flights, including Jacober, of the ice reports from other aircraft. If any advisories were issued, they would have come from a flight center in Long Island, N.Y., that monitors and directs regional air traffic, Rodgers said.
Efforts to contact the NTSB and the Federal Aviation Administration to see if any advisory was issued were unsuccessful late Monday.
FAA records indicate that both Jacober, 51, and the 1999 Pilatus PC-12/45 he was flying had "clean" records -- no accidents or violations -- before the crash, FAA spokesman John Clabes said.
Jacober's third-class medical certificate, which is required for private pilots and must be renewed every two years, was renewed last month, Clabes said.
Jacober was flying north from Florida on Saturday with his wife, Karen, and son Eric and three family friends: Gregg and Dawn Weingeroff and their son, Leland.
All six died on impact when the plane crashed within about 25 yards of the new Centre County Correctional Facility.
The Swiss-built aircraft had a high-powered, Canadian-made engine and a range of at least 1,600 nautical miles. By air, the distance between University Park Airport and Naples, Fla., where it took off Saturday, is 1,040 miles.
Gail Cureton, director of communications for the City of Naples Airport Authority, said she did not know how much fuel the PC-12 took off with, but she said 100 gallons of fuel were pumped into it Saturday morning.
The plane can hold 402 gallons, according to published performance specifications.
By most accounts, it has a solid record.
Of more than 11,300 other fatal airplane crashes reported in the United States since 1982, just six involved aircraft manufactured by Pilatus Aircraft Ltd. One involved a PC-12/45.
That fatal crash, which claimed two lives, happened in October in Westphalia, Mo. The NTSB said pilot disorientation probably caused it.
Of six total crashes involving a PC-12/45, one has been linked to mechanical failure, according to NTSB records.
Since July, federal authorities have issued two orders for modifications to PC-12s, The Providence Journal reported Monday. One involved wiring for windshield de-icing equipment.
In 2000, the Federal Aviation Administration called for a modification to the PC-12's flight manual.
The manual should tell pilots to activate a part of the de-icing system as soon as they see ice buildup, the FAA said.
Still, Dannaker said, Pilatus models are like the Range Rovers of the sky -- and no stranger to University Park Airport.
"Sometimes you won't see any for a month, and then you'll see two or three the next month, sometimes in the same day," Dannaker said. He said one Big Ten university -- not Penn State -- uses a fleet of Pilatus planes to transport its athletes.
University Park Airport annually hosts about 68,000 landings and take-offs, about 15,000 of which are for scheduled commercial flights. The rest involve chartered aircraft, corporate and private planes and Federal Express flights. FedEx has three or four flights a day, Rodgers said.
Hubert C. "Skip" Smith, professor emeritus of aerospace engineering at Penn State, said there's nothing unusually tricky about flying into the airport.
"It's a very standard approach," said Smith, also a flight instructor. "The airport has gone through many, many updates in recent years, and it's first-class as far as safety."