WASHINGTON -- One morning last month, a Marine Corps CH-46D Sea Knight helicopter crashed into the Atlantic some 30 miles off the Georgia coast while scouring the waters for a downed civilian aircraft.
Four Marines were pulled from the chilly waters after the helicopter went down March 9. Two days later, the body of a Navy corpsman serving with the Marines, Petty Officer 1st Class Kevin J. Frank, 39, of Ocean City, Md., was found next to the helicopter, 90 feet below the surface.
The Sea Knight is one of 18 Navy and Marine Corps aircraft, helicopters and fixed-wing warplanes, that crashed between October and the end of last month, resulting in 19 deaths.
Investigators suspect mechanical or structural failures as a cause of the Sea Knight crash and 10 others, which killed a half-dozen servicemen, including two in Afghanistan. That is a far greater percentage than in any of the previous five years, according to a Navy official.
As a result, some officials suspect that the root cause of the deadly and costly crashes may be an aging aircraft fleet.
The Navy and Marine Corps aviation force is the oldest ever, with the average plane or helicopter 18 years old. The Sea Knight helicopter that went down off Georgia was 37 years old, officials said. And, even with new aircraft joining the fleet, the average age of the force is scheduled to increase to 20 years during the next five years.
"This might be symptomatic of an aged force with material problems," said the Navy official, who asked not to be named. "As the airplanes get older, they're going to require more care and attention and more inspections."
The corrosive maritime environment in which the Navy and the Marines operate is particularly hard on aircraft, officials said.
The initial suspicions may not be borne out in all of the crash investigations. They can take up to a year and often lay the blame on the pilot, officials note. And Navy Secretary Gordon R. England said in a recent interview that he has yet to see any evidence of a trend in the recent crashes of Navy and Marine Corps aircraft, cautioning, "You don't know until you do the actual analysis."
But the steadily rising age of naval aircraft is a growing concern for top officers, including Gen. James Jones, commandant of the Marine Corps and a decorated Vietnam veteran, who raised the issue last month before the House subcommittee that oversees defense spending.
"We have CH-53Ds which are 31 years old, well past their service life," he told the lawmakers. "The CH-46 predates me in active service, and look what I look like after 35 years."
Navy and Marine officials stress that no aircraft is allowed to fly without strict inspections and proper maintenance. Still, a Pentagon official said, "you don't know what's going to break on an old airplane." And with the aviation fleet rising in age, "you could expect more problems, not less."
Moreover, the replacements for these older fixed-wing planes and helicopters are sometimes years off because of budget constraints and the search for suitable substitutes. More and more money that could be used for replacements is being sapped by steadily rising maintenance costs for aging aircraft, officials said.
Bernard S. Loeb, former director of the Office of Air Safety for the National Transportation Safety Board, agreed that aging aircraft could suffer more mechanical problems.
"The older it gets, the more times you have to put your hands on the airplane" for maintenance, he said. And more maintenance means a greater likelihood for error or oversight. "It becomes even more of a problem if the airplane is in an environment that facilitates corrosion or similar kinds of problems," he said.
"Corrosion is the main thing. If you want to fix it, it's costly because of the maintenance," said Ramana Pidaparti, professor of mechanical engineering at Purdue University, who is trying to develop a system to predict structural failures on aging aircraft to aid maintenance workers.
Richard L. Perry, a retired Air Force colonel who is a manager for airworthiness assurance at Sandia National Laboratories in Albuquerque, N.M., a federal government research and development facility, said word of the suspected Navy and Marine Corps crash trend had reached him through his Air Force contacts. Perry was director of engineering and system safety at the crash-investigating Air Force Safety Center until 1996.
"The Navy is at least seeing the appearance of a trend this year," said Perry. "Older airplanes can be managed effectively, as long as you're careful in assessing the environment and the inspection process," he said.
The concern over the recent Navy and Marine Corps crashes comes against a downward trend in mechanical and structural failures. In the past 10 years, the number of such problems -- so-called material failures -- contributing to a crash has been 0.86 per 100,000 flight hours. In the past five years, it dropped to 0.71 per 100,000 flight hours, according to Navy statistics.