by Gerry J. Gilmore
WASHINGTON (Army News Service, Nov. 17, 1999) - The Army's AH-64 Apache helicopters are undergoing inspections to determine the serviceability of the aircraft's tail-rotor system and gearbox components.
The inspections involve all 743 Apaches - to include older "A" and newer "D" models - in service across the force, said Col. Fred Naigle, the chief of the Aviation Division, Office of the Deputy Chief of Staff for Logistics in the Pentagon.
The Army estimates that up to half of the aircraft inspected may require replacement parts to return them to flyable status, said Naigle.
The tail-rotor inspections, announced by Army officials Nov. 5, concentrate on the hanger bearing assemblies, or flanges, which act as connectors between the tail rotor and the power drive.
The gearbox inspections were announced Nov. 12, and center on two clutches in the accessory gearbox, a component of the helicopter's transmission, said Army officials, who noted there is concern about excessive wear of the clutches.
A recent Apache crash at Fort Rucker, Ala., which totaled the aircraft and injured its two-man crew, was traced to failure of the hanger bearing assembly, said officials. Investigators determined the helicopter's hanger bearing assembly had developed corrosion-stress cracks, due to a tempering treatment, which caused the metal to become brittle.
Officials said the Army modified the hanger bearing assembly's manufacturing process in 1993; such parts produced after the change aren't susceptible to similar corrosion-stress fractures. Suspect hanger bearing assemblies would be replaced as part of the inspection process, officials said.
The crash of an Israeli Air Force AH-64 this June prompted the gearbox inspection order, officials said.
Six clutch failures have recently plagued Army Apaches - while they were still on the ground, said officials, who noted analysis of the clutches involved showed excessive wear. Army and contractor officials are seeking to determine why the wear is occurring and methods to prevent it.
As part of the gearbox inspections, officials said all Apache accessory gearboxes found with more than 1,000 flight hours will be replaced.
Both rotor assembly and gearbox inspections are taking place "as soon as practicable" and "no later than one week from notification," according to Army news releases. Helicopters assigned to high-readiness combat arms units receive priority to be inspected first.
Naigle said he wasn't certain when both Armywide inspections would be complete.
All unaffected aircraft will be immediately returned to service, said officials.