Commuter airlines and their suppliers are conducting ultrasonic inspections of more than 8,500 propeller blades under an expanded Federal Aviation Administration airworthiness directive. An Embraer EMB-120 turboprop aircraft using the blades crash-landed Aug. 21 near Carrollton, Ga., killing five people on an Atlantic Southeast Airlines flight. National Transportation Safety Board investigators said part of one of the propeller blades broke in midflight and may have been damaged earlier.
Blades consists of a forged aluminum spar, nonstructural polyurethane to define the airfoil and a fiberglass-cloth wrapping. The structure is injected with epoxy resin in a vacuum mold and cured. An erosion-resistant coating is applied for an outside cover. Hamilton Standard, a division of United Technologies Corp., makes the blades.
``We're sending out inspectors and reimbursing [users] for the inspection procedure,'' said John Mayo, a spokesman for Hamilton Standard in Windsor Locks, Conn.
Worldwide, more than 200 operators of some 1,500 aircraft use 13,000 Hamilton Standard propeller blades. The FAA directive applies to U.S.-based aircraft. Per-blade inspection takes about 15 minutes.
In an initial directive Aug. 25, the FAA ordered operators of EMB-120s to remove from service Hamilton Standard 14RF-9 blades that had been repaired and returned to service after failing an ultrasonic inspection.
On Aug. 28, the FAA ordered inspection of blades on all Embraer EMB-120 aircraft within 50 flights and on other aircraft equipped with blades that have not been shot peened - a process that increases resistance to fatigue and cracking - within 150 flights. About two-thirds of the affected in-service blades were made before shot peening became part of the process.