by Diana Kelly
WASHINGTON (Army News Service, Aug. 10, 1999) -- The Army grounded its Chinook helicopter fleet Aug. 6 after cracked transmission gears were discovered in a CH-47D during a mechanical overhaul.
Due to this discovery, officials said all Chinooks worldwide are being checked for faulty gears. The grounding includes all CH-47 helicopters and the MH-47D and MH-47E models used for special operations.
No accidents have occurred because of this gear problem, officials said, but the Army and Chinook manufacturer Boeing are taking precautions to assure that none will, they said.
The questionable gears are being identified by a serial number search, and will be checked, officials said. A total of 466 Chinook aircraft are in the Army's helicopter fleet, including those in both active and reserve-component units. A sufficient stock of new gears is available for these aircraft if the need for replacement exists, an official said.
The most plausible cause of the problem is poor grinding of the gear's spherical bearing raceway during manufacture, according to Dan O'Boyle, a spokesman for the U.S. Army Aviation Program Executive Office at Redstone Arsenal. O'Boyle said improper grinding is a critical flaw because it could produce surface cracks and potential gear fractures. Such cracks and fractures could cause the rotor blades to come out of phase, he said, mesh with each other, lock the transmissions, and potentially lead to a crash.
Currently, only four of these gears have been found defective, but Army leaders said they are still concerned. The number one issue is the safety of the soldiers involved in the flight of the aircraft, they said.
The Army has notified foreign manufacturers so that safety precautions may be taken in the 800 H-47 aircraft worldwide.
Once the records-search is complete and all suspect gears checked, the unaffected Chinooks in the Army's fleet will be released to continue normal, routine missions and operations, officials said. They said the Chinooks will fly again as soon as potential risk to aviation soldiers is eliminated.