DC-10s to Get Valves That Curb Hydraulic Fluid Loss

McDonnell Douglas Corp. said Friday it will install hydraulic safety valves in DC-10 jetliners designed to prevent the kind of massive failure that led to the July 19 crash in Sioux City, Iowa. That crash killed 112 and renewed concerns about the plane’s safety record.

The United Air Lines DC-10 was crippled when the tail engine exploded and hurled shrapnel through the fuselage, severing all three hydraulic lines. Company officers said the new valve would preserve at least one of the plane’s hydraulic systems in the event of a similar airborne catastrophe.

Other jumbo jets manufactured by Lockheed and Boeing already are equipped with similar safety valves. McDonnell Douglas estimated that the cost of retrofitting DC-10s will be about $10,000 per plane.

Others Not Copied

Dale Warren, vice president of the Douglas division, said that no moves were made to copy the safety valve designs on other jetliners because the company believed “up until Sioux City that the DC-10’s redundancies (in its hydraulic system) were sufficient.”

He said the company still regards chances of complete hydraulic failure as “one in a billion.”

Friday’s announcement was made as an FAA task force continued to investigate possible design flaws related to hydraulic systems in all jumbo jets, including Lockheed’s L-1011 and Boeing’s 747.

James B. Busey, chief of the Federal Aviation Administration, called the company’s decision “a solid step forward.” In a statement issued from Washington, Busey endorsed the much-criticized DC-10.

“Once these design changes are in place, they will raise the already high safety standards of the DC-10, and in effect, make a good airplane even better,” Busey said.

Briefly Grounded

The DC-10 was briefly grounded in 1979 after a series of accidents that raised concerns about the jetliner’s design. Since late July, the International Airline Passengers Assn. has lobbied for another grounding of the fleet.

McDonnell Douglas spokeswoman Elayne Bendel said the safety improvements will take an estimated 21 months to complete, including time to design, deliver and install the devices in the more than 400 DC-10s in commercial service worldwide. The modifications will also be made in the military variant, the KC-10, an Air Force jet cargo and mid-air refueling aircraft.

Bendel said that the engineers have not yet decided whether to recommend changes for the new jumbo jetliner, the MD-11, which is essentially an updated version of the DC-10 that was designed with a similar hydraulic arrangement.

As proposed, McDonnell Douglas engineers want to install two valves behind the rear wall of the DC-10 passenger cabin, just forward of the horizontal stabilizers. If the tail engine explodes, sensors would detect a sudden drop in hydraulic pressure and close the valves to stop the loss of fluid in one of the redundant hydraulic systems, in much the way a tourniquet reduces uncontrolled bleeding in a severely injured person.

Warning Light

The corporation proposes also to install a warning light on the flight engineer’s panel that would indicate whether the valve closes.

“We have never seen the kind of extreme damage to a DC-10’s multiple redundant hydraulic systems that we saw in the Sioux City case, and we certainly don’t expect to see it again,” said Warren. “We view the new enhancements as extra safety equipment similar to the installation of air bags in automobiles.”

Bendel said the corporation is yet to decide whether it will bear the costs of the installations or whether they would be left to the planes’ owners.

A spokesman for the Lockheed Aeronautical Systems Co., maker of the L-1011 three-engine jetliner, said that aircraft has always had fast-acting valves protecting two of the plane’s four hydraulic systems. Spokesman Richard Stadler said that, although there have been reports of L-1011s that have landed safely with loss of three systems, he said there have been none that has lost all four.

“It’s not unusual for lines to get nicked by shrapnel (in event of an engine explosion) no matter how well protected they are,” Stadler said. “You try to protect it as much as possible, but there are no guarantees.”