DC-10 fleet to undergo hydraulic system changes

By DAVE McNARY, UPI Business Writer

LONG BEACH -- McDonnell Douglas Corp. announced Friday that all DC-10s will undergo three design changes in the plane's vital hydraulic system aimed at preventing a repeat of the Sioux City, Iowa, disaster that killed 112 people.

James B. Busey, head of the Federal Aviation Administration, said the design changes on the wide-body jet 'are a solid step foward in assuring' that there will be no recurrance of the July 19 United Air Lines DC-10 crash in Sioux City.


'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 ever better,' Busey said in a statment.

The DC-10 involved in the Iowa disaster crashed after the tail engine blew apart, hurtling debris that severed the plane's hydraulic lines, which enable the pilot to control the craft.


Dale Warren, vice president of Douglas Aircraft Co., said, '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 certainly don't expect to see it again.'

He likened the design changes to the installation of air bags in automobiles, saying they were 'additional measures to protect occupants.'

Douglas, a unit of McDonnell Douglas, said it plans to have the new equipment installed in all DC-10s within 21 months. There are about 400 DC-10s worldwide. Warren said that the cost to airline companies would be about $10,000 per plane.

One of the three new safety features involves installation of an electrically operated shutoff valve in the supply line and a check valve in the return line in one of the plane's three hydraulic systems.

The shutoff valve will be located behind the back wall of the aircraft cabin and in front of the horizontal stabilizer.

The other new features are a sensor switch in the hydraulic reservoir of that system and an annuciator light in the cockpit that will go on if the shutoff valve is activated.

The shutoff valve, which is normally open, will close if it detects hydraulic fluid dropping below normal levels. 'It will detect the smallest leaks,' Warren said.


Even if all three hydraulic systems are damaged, the new valve should preserve enough pressure in the one system for flight crews to have enough control to land a damaged plane safely, Warren said.

Warren said Douglas, using the new equipment, was able to develop procedures that consistently led to safe landings in flight simulator tests on a DC-10 with damage similar to that in the Sioux City crash.

Douglas said it has started meeting with suppliers and airlines to negotiate installation of the new equipment. 'This is a very inexpensive improvement from the standpoint of the airline industry,' Warren said.

Warren said Douglas' action is voluntary, but he said there is a 'good probability' that the FAA will issue a directive to require the equipment.

The new equipment may be installed on Douglas's new MD-11 jetliner, which is scheduled for FAA certification next year, Warren said.

Warren said the Boeing Co. had installed a similar valve in its 747, 757 and 767 jets after the 1985 Japan Air Lines crash of a Boeing 747 in which 520 people died. But since the Boeing and Douglas hydraulic systems are designed differently, Warren said, no move was made to copy Boeing's action.


'We felt up until Sioux City that the DC-10's redundancies (in its hydraulic system) were sufficient,' Warren said.

Warren said about 10 other minor modifications to the DC-10's hydraulic system have been made since 1978.

McDonnell Douglas has been under pressure since the Sioux City crash because of critics' charges that the jet, which began flying in 1971, is less safe than similar wide-body aircraft, including the Boeing 747 and the Lockheed L-1011. The International Airline Passengers Association in late July called on the FAA to ground the jet.

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