Ownership: Back to full strength

Spar mods revive T–34s

October 1, 2012

t-34

The fatal 1999 in-flight failure of a T–34 wing spar during a mock dogfight over Georgia was the start of a long nightmare for owners of the stalwart airplanes in which two generations of U.S. Air Force and Navy pilots learned to fly.

The two-seat Mentor is based on a beefed-up Bonanza airframe and has been in military service since 1953. Until that day in 1999, however, the airplanes had been regarded as nearly indestructible. Some airframes had logged many thousands of hours in the harshest imaginable conditions: aerobatic and formation flight training, student takeoffs and landings, all while being parked outside for years in coastal locations prone to corrosion.

After their military service, the punishing work continued. Some T–34s were used for pipeline patrols where they flew thousands more hours at low altitude in turbulence, and others went to Top Gun-style aerial combat businesses where high speeds, unusual attitudes, and heavy Gs were the norm. Other T–34s enjoyed more pampered semi-retirements in which civilian owners restored them to gleaming condition and flew them well within their Aerobatic category limits of plus-6 and minus-3 Gs.

But in the aftermath of the 1999 breakup of a T–34 near Atlanta—and two subsequent, nearly identical wing failures in airplanes formerly operated by the same air combat business—the FAA imposed strict limits on all T–34s. And there was great concern that the airplanes, about 400 of which were in private hands, would be grounded permanently.

t-34The T–34 Association and AOPA argued that the airplanes were safe if properly maintained and flown within their normal limits. But the FAA insisted there was no reliable way to determine whether any particular airframe had been abused and imposed a blanket solution. Raytheon, which owned Beech at the time, recommended costly and burdensome magnetic eddy current inspections of T–34 spars every 80 flight hours.

The value of T–34s fell sharply as the future of the once sought-after airplanes suddenly seemed doubtful. The fate of Beech Bonanzas that share the same wing design and construction also was called into question. And well-known T–34 airshow performers such as the six-airplane Lima Lima team and Julie Clark faced more uncertainty—even though they had no doubts about the strength and durability of their airplanes.

Fortunately, four companies studied the problem, did their own research and engineering, and came up with alternate means of compliance that addressed the root of the problem and avoided the draconian and recurring inspection requirements. These fixes have returned T–34 fleet to full strength.

“Every airplane that’s currently flying has had a spar mod done,” said Curtis Boulware, owner of George Baker Aviation in New Smyrna Beach, Florida, a firm that performs the full spectrum of T–34 modifications—ranging from external spar straps to installing brand-new spars that are far stronger than the originals.

Prices for the mods range from about $13,000 to $35,000 per aircraft.

  • The Saunders Strap is the simplest and least expensive of the T–34 spar mods. A stainless steel strap reaching from one outer wing panel to the other takes some of the load off the spar and had been used successfully in other Beech designs such as the Model 18, Queen Air, King Air, and Beech 99.
  • The Parks Jig replaces the original spar and associated attachments and shims with a newer and stronger one made from a solid piece of aluminum.
  • The GAMI Cable stretches across the T–34 center section and, like the Saunders Strap, lightens the loads on the spar itself. GAMI also uses an internal doubler plate and reinforces the bolt and rivet holes at critical portions of the wing support structure.
  • Nogle & Black Aviation of Tuscola, Illinois, is the most extensive solution in that it completely eliminates the original T–34 wing spars and associated webbing and replaces them with newer, stronger spars of its own design and additional supports.

Each method has advantages. The Saunders Strap is a proven method used on a variety of Beech aircraft; the GAMI mod doesn’t change the airplane’s external appearance and can be done with a minimum of aircraft down time, and the Nogle & Black spar replacement is the gold standard in that it provides completely new spars that are stronger than the originals.

“The GAMI mod is the most popular,” Boulware said. “It’s the least intrusive.”

Boulware said he’s seen very little metal fatigue or corrosion inside the many T–34 wings he’s inspected, even those that were subject to the most hours flown and the hardest use. All of the parts were primed at the factory during construction in preparation for long periods outdoors and flying in coastal, salt air.

“The fleet is in very, very good shape,” he said. “Even the airplanes that had been subjected to the toughest conditions and had logged the most flying hours, we found very few problems.”

The findings are good news for owners of other Beech products such as Bonanzas, which share similar wing designs. And perhaps more important than the T–34 wing modifications themselves has been the realization among owners that no airplane, no matter how well built, is indestructible.

“We’re confident the ADs and the spar issues are behind us,” Boulware said. “The general aviation community has learned a great deal from this process about the issues regarding aging aircraft, and how to maintain and fly them safely.”

Tim Roehl, a GAMI founder and T–34 owner, said the company spent five years developing its spar STC, and he expects the modifications to give the T–34 fleet decades of additional life—although he still believes the ADs and required modifications were largely unnecessary.

“We spent a lot of time and went to a lot of effort to fix something that really wasn’t broken,” Roehl said. “But after all the inspections and modifications, there can be no doubt that the T–34 fleet today is in excellent health.”

GAMI is best known for developing precise fuel metering systems and popularizing lean-of-peak engine operations, and the company performed much of its early flight testing for Continental engines in a T–34. Both Roehl and GAMI cofounder George Braly own and fly T–34s as personal aircraft.

By coming up with a relatively cost-effective solution to a serious situation that threatened to ground the T–34 fleet, as well as preserving their ability to fly their own aircraft without additional limitations, Roehl says he and Braly take great satisfaction.

“We feel like we did some good for a really wonderful airplane,” he said. “And I’m reminded every time I fly one that the T–34 is an absolutely wonderful airplane.”

Email dave.hirschman@aopa.org

Dave Hirschman

Dave Hirschman | AOPA Pilot Senior Editor , AOPA

AOPA Pilot Senior Editor Dave Hirschman joined AOPA in 2008. He has an airline transport pilot certificate and instrument and multiengine flight instructor certificates. Dave flies vintage, historical, and Experimental airplanes and specializes in tailwheel and aerobatic instruction.