The FAA has issued an Emergency Airworthiness Directive (AD) that addresses a safety problem with Great Lakes aircraft produced in the 1970s and 1980s.
In an email sent out by WACO Classic Aircraft Corp., company officials note that while the affected aircraft were not produced by WACO Classic 
Aircraft, “as the new Type Certificate Holder, we take seriously the issue of continued airworthiness of the Great Lakes fleet of aircraft serial numbers 501 through 1012.”
The AD does not apply to new production aircraft manufactured by WACO Classic Aircraft, as the affected area has been redesigned to prevent this condition from recurring, company officials add.
The AD can be found at the FAA website or at the WACO Classic Aircraft website.
Background: In March 2011, a Great Lakes 2T-1A-2 was substantially damaged when the right horizontal stabilizer failed as the airplane completed some aerobatic maneuvers, and separated from the airplane while it was on final approach for landing. The pilot was able to continue to a landing at the airport, but due to the damage to the rudder, was unable to maintain directional control, and the airplane ground looped to the right.
Examination of the right stabilizer revealed evidence of a pre-existing crack in the front spar at the rivets securing the steel attach fitting tube. The spar moved outward and disengaged from the fitting. At least one maintenance facility familiar with this aircraft type has reported finding similar cracks in the stabilizer front spar on a number of occasions during routine maintenance.
Great Lakes Aircraft Service Bulletin #15, issued May 1, 2000, points out the possibility of front spar failure inside the attach fitting as a result of excessive torque loads, due to improperly rigged tail brace wires. It also notes that a frozen Front Center Beam may be a contributing factor. Broken front stabilizer spar tubes inside the attach fitting was also the subject of a Service Alert published by Phoenix Aircraft Co. on Dec. 24, 1988.
Both the service bulletin by Great Lakes and the service alert by Phoenix Aircraft emphasize that the tail brace wire fitting attach bolt through the rear stabilizer spar should be free to move when the stabilizer trim is adjusted up and down.
Although previous known instances of stabilizer spar cracking and suggested inspections have been limited to the front spar, WACO Classic Aircraft considers it prudent to inspect both front and rear stabilizer spars and to ensure that both the front and rear center beams turn freely and are well lubricated.
In addition, the known cases of cracking and failure have occurred in aircraft used in aerobatic flight, and because these aircraft are certificated in the Aerobatic category it must be assumed that they will be subjected to aerobatic maneuvers. For this reason, the FAA is requiring that this be a recurring inspection, unless the aircraft is fitted with the newly designed replacement parts.
For more information: WACOAircraft.com
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