Cracks Noticed In Vertical Stabilizer And Bulkheads On A 'Few' Airplanes

Glasair has issued a service bulletin for all Sportsman aircraft following the discovery of cracks at the aft base of the vertical fin of a few airplanes. In some instances, there have been reports of cracking of the laminates and adhesion bond between bulkheads B and C and the vertical fin.

According to the document ... Service Bulletin 70 ... Exterior cracking is most commonly found on the right-hand side where the vertical fin meets the aft fuselage at its base. The left-hand vertical fin is molded as a part of the fuselage, whereas the right-hand vertical fin half is bonded to the fuselage and vertical fin as a separate piece during fuselage assembly. The exterior cracks are commonly showing up along the bonding joint. Minor cracking may simply indicate separation of the cosmetic filler used in paint preparation.

Some movement of the vertical fin occurs when the rudder is actuated in flight. The degree of movement is dependent upon the speed of the plane and the force exerted on the rudder controls. A lack of evidence of cracking on the exterior does not necessarily mean that disbonding between the bulkheads and the vertical fin on the inside is not occurring. A simple test of the integrity of the vertical fin is to take hold of it near the top and firmly pull it side-to-side, watching the movement and listening for any sound of separation inside.

Ultimately, a visual inspection of the bulkheads will determine the action required. Bulkhead B can be inspected by crawling into the aft fuselage. Bulkhead C can also be inspected from the inside, but is best inspected by removal of the rudder base fairing. If cracking or separation is evident in the bonding laminates between the upper portion of bulkhead C and the vertical fin, then deeper inspection will be necessary through the lower inspection hole or removal of the stabilizer.

The bulletin requires the following actions:

• An inspection is to be completed prior to the next flight.
• Repairs to interior cracks and separation are to be completed as outlined below prior to the next flight.
• Reinforcement of the attachment of the vertical fin spar to bulkhead C with part # 101-00019-01 should be completed after all composite repairs are accomplished. Installation should be completed prior to or during the next annual inspection.

Glasair says it found that while repairs to the existing structure are important, the reinforcement doubler by far is the most significant component to prevent future cracking issues in this area.

(Images provided by Glasair)

FMI: www.glasairaviation.com