The FAA has made final an Airworthiness Directive (AD) for certain models of Hartzell Propellers installed on Pitts aircraft, stipulating that their certified service life is limited to 2,000 hours, and has extended the comment period. on its final rule regarding Aging Airplane Safety. The rule applies to multiengine aircraft older than 14 years used in Part 121 operations. Comments will be accepted until May 5. The FAA says the prop change is necessary to prevent failure of the original hub and blades in flight. The one comment received had no impact on the rulemaking, the FAA said, since the commenter claimed that there is no documentation of the hours on props, which the FAA refutes. Also, at the request of the Air Transport Association and the Regional Airline Association, the FAA has extended the comment period.