Piper J4 Cub Coupe

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 4 type certificates. The FAA has issued 9 airworthiness directives (orders that owners must comply with) that name this model, most of them about landing gear. Operators and repair shops have filed 1 failure report with the FAA since 2006, 1 of them in the last ten years: about 0.5 a year for every 100 aircraft on the register; the system most often named is landing gear. 35 approved modifications exist for it, the most by F Atlee Dodge Aircraft Service.

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.