Piper PA-18 Super Cub

The fuselage is a welded steel-tube frame covered in fabric, with metal or wooden wing spars under fabric-covered wings; the fabric is replaced every few decades. The design is held under 2 type certificates. The FAA has issued 25 airworthiness directives (orders that owners must comply with) that name this model, most of them about airframe structure. Operators and repair shops have filed 136 failure reports with the FAA since 1995, 8 of them in the last ten years: about 0.1 a year for every 100 aircraft on the register; the system most often named is engine. 554 approved modifications exist for it, the most by Cub Crafters INC.

Sources: the FAA's type certificate data sheets, airworthiness directives, supplemental type certificates, special conditions and special airworthiness information bulletins (Dynamic Regulatory System), and the FAA's service difficulty reports. A failure report is what an operator or repair station chose to file; the counts show reporting as much as reliability, and larger and commercial fleets report more. How the systems are grouped.