September 3, 2005
AOPA is continuing its efforts with the T-34 community and the FAA to get these vintage warbirds back in the air. Two members of AOPA's technical staff are in Kansas City this week, talking to key contacts at the FAA's Small Airplane Directorate about many issues, including the T-34 and the larger related issue of aging aircraft.
T-34s, former military trainers similar to the Beechcraft Bonanza, were grounded late last year following the third in-flight breakup of a T-34 used in mock aerial combat. The FAA considers the T-34s to be the "canaries in the coal mine," the very early indicators of problems that might crop up with other aging aircraft years from now.
"But we also must be careful not to extrapolate from failures in aircraft flown under the extremely demanding and repetitive high G-load environment of simulated combat," said Andy Cebula, AOPA senior vice president of Government and Technical Affairs. "That kind of flying imposes an exponentially greater number of fatigue cycles on an aircraft than normal or utility category flying."
Aircraft structures do wear out. Every landing, every jolt of turbulence, flexes critical structures and causes metal fatigue. Eventually, something will break.
Two years ago, AOPA, the FAA, several aircraft type clubs, and other aviation organizations collaborated to publish the FAA's Best-Practice Guide for Maintaining Aging General Aviation Airplanes. It was sent to the owners of all aircraft built before 1974.
Most GA aircraft flying today were certified under the old CAR 3 standards, which did not set a life-limit for aircraft components. Newer aircraft (such as the Commander 112 and 114 and the offerings from Cirrus and Lancair) are certified under FAR Part 23, which requires the manufacturer to establish a life-limit - in flight hours - for critical structures such as wing spars. For example, the pressurized P58 Baron (unlike its siblings in the Beechcraft line) is Part 23 certified and has a 10,000-hour wing spar limit. Cirrus aircraft have a 12,000-hour limit on the wing. The Commander single-engine models range from 6,945 to 19,284 hours maximum life on the wing.
So does that mean that 10,000 hours would be a ballpark figure for the life of CAR 3 aircraft? Not necessarily. For Part 23-certificated aircraft, the life-limit is what the manufacturer has chosen to prove to the FAA - the structure actually has a much greater safety margin built in. So 10,000 hours might be very conservative. (And for a point of reference, the average single-engine aircraft in the United States flies about 120 hours a year, so even a 50-year-old aircraft might have around 5,000 hours total time.)
And of course, the whole system of repetitive aircraft inspections, service difficulty reports, airworthiness concern process, and airworthiness directives is designed to catch problems before they become catastrophic. For the fleet as a whole, the system has been very effective.
"Even though we believe that our older aircraft are still safe, there is no question that the FAA is going to be changing the way it deals with aging general aviation aircraft," said Cebula. "But we'll insist that whatever they do is based on solid, scientific safety data. Arbitrary airframe life limits would be unacceptable.
"As always, AOPA's goal is to keep our aircraft safe, affordable, and flying."
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