It may be a year or more before national safety officials determine what sparked an in-flight fire that ended with a World War II-era B-17 bomber in flames in an Oswego farm field.
The National Transportation Safety Board released a preliminary report Thursday detailing the events of June 13 that forced the Liberty Belle B-17 to make an emergency landing just minutes after taking off from Aurora Municipal Airport en route to Indianapolis.
But the initial report does not indicate what may have sparked the fire, gives no insight into whether the plane was mechanically sound to fly, and contains no information on whether its crew followed all safety and maintenance procedures required by the Federal Aviation Administration.
That and other information is expected to be included in the final report that could take 12 to 18 months to complete. Until that report is issued, the NTSB will not speculate about the accident's cause, spokesman Keith Holloway said.
He said the NTSB will examine mechanical and maintenance issues, as well as numerous other possible factors, as a routine part of its investigation.
The Liberty Belle's operator, a Tulsa, Okla.-based nonprofit group called the Liberty Foundation, has not returned phone calls or emails concerning the accident since it occurred.
Two days before the Liberty Belle took off for the flight that ended in the farm field, the plane underwent an inspection, according to a statement the Liberty Foundation's Chief Pilot Ray Fowler posted on the group's website. Repairs were made the day before the flight, but "the maintenance performed has not been, in any way, associated to the chain of events that led to Monday's (June 13) fateful flight," according to the statement.
About six minutes after takeoff, a plane following the Liberty Belle alerted its three-member crew of an in-flight fire, according to the NTSB report. The crew already had smelled fire and shut off electrical generators. Crew members then determined the fire was on the plane's left wing and shut off engine No. 2.
Once the plane landed in the field, all three crew members and four passengers escaped, with only one passenger receiving a minor injury.
Fire crews from Sugar Grove and other area departments struggled to reach the plane in the muddy field and the fire worsened, consuming the fuselage and inside portion of both wings.
Different types of maintenance and inspections are required at different intervals for historic aircraft such as a 1940s-era B-17 than for contemporary commercial aircraft, according to the FAA.
"The bottom line, in general terms, is all aircraft are inspected on a regular basis according to use to ensure that they're safe to fly," FAA spokeswoman Elizabeth Isham Cory said.
It doesn't necessarily take more maintenance or inspections to gain permission to fly a vintage plane like the Liberty Belle -- just different procedures, Cory said.
Historic planes must apply for an experimental certificate to fly and carry passengers. The application requires a statement of the aircraft's planned use, photos and an inspection to ensure the plane meets regulations and is in working order to fly.
Once the experimental certificate is in place, keeping a historic aircraft in working order becomes a "labor of love," said Dick Knapinski, spokesman for the Experimental Aircraft Association, a nonprofit group of recreational pilots based in Oshkosh, Wis., that owns and operates its own World War II B-17.
When historic planes or new jets need repairs, all fixes must be completed by an FAA-licensed mechanic, Cory said.
Finding replacement parts can be one the biggest -- and most expensive -- challenges in keeping an antique plane airworthy, Knapinski said. All parts need to meet the original military specifications or be approved by the FAA.
And the FAA inspects maintenance logs at least once a year, Cory said.
"We're continually developing new patterns of inspection for different systems on those aircraft to ensure that they're inspected on a regular basis as needed," she said.
The Experimental Aircraft Association's B-17 gets an inspection after every 25 hours of flight and a more in-depth inspection every 125 hours.
"Certain things are required to inspect at each hour time frame," Knapinski said. "Engines come apart, the wing structure is inspected to make sure it's all up to specifications."
Inspection schedules are not determined based on a plane's age, but on how other planes of that type are performing and what problems have been noticed in the past, Cory said.
Chief pilot Fowler's statement on the Liberty Foundation's website says Boeing B-17s have an "exceptional safety record," with the Liberty Belle successfully flying 20,000 people across the nation since December 2004.
"The aircraft's safety record is spectacular and I am certain the overall cause of our issue, which is under investigation, will not tarnish that safety record," the statement says.
About 50 of the 12,713 B-17s built during World War II remain and fewer than 15 can fly, according to the Experimental Aircraft Association.
"The goal is when you have an aircraft that's a museum piece like that, you want to ensure the fitness to fly," the FAA's Cory said. And organizations like the Experimental Aircraft Association and the Liberty Foundation "love to keep these museum pieces flying, and they're working on them constantly."