PRIOR FAILURES. Type of engine in plane crash was targeted for safety check

Investigators analyzing the crash of Northwest Flight 255 are expected to focus, at least initially, on the plane's two engines. Federal Aviation Administration officials say the Northwest Airlines jet that crashed near Detroit on Sunday had engine problems in the past involving turbine blade failures and oil pressure.

The problems were severe enough that the original engines on the McDonnell Douglas MD-82 jet had to be replaced with two Pratt & Whitney JT8D-217 engines, an FAA official said.

Yesterday, FAA spokeswoman Joann Sloane said one of the two engines was damaged July 23 by a foreign object. The engine was repaired and returned to service subject 500 hours of monitoring, she said. At the time of the crash, 139 hours had elapsed.

Months before the crash of Northwest Flight 255, a federal agency strongly recommended safety inspections and changed maintenance procedures for the type of engines involved because of several prior engine failures.

Although investigators have not yet assigned a cause to the Detroit crash, an air traffic controller and witnesses on the ground reported flames coming out of the engine area prior to the crash.

But until the engines are physically inspected, and other data taken into account, experts say it cannot be determined what caused the crash that killed at least 153 passengers and two people on the ground.

Following at least four incidents in which similar Pratt & Whitney 200 series engines failed, the National Transportation Safety Board told the FAA on April 28 that there was a problem requiring safety inspections.

``Our concern was that there were these failures,'' says Michael Benson, an NTSB spokesman. ``Because the potential for an uncontained engine failure and possible airplane damage exists, the safety board believes the FAA should take immediate and appropriate action.''

In a May 29 response, the FAA agreed with the NTSB recommendations and said it would study the issue and recommend new inspections of JT8D-200 series engines. Last month, the FAA told airlines it would require the engines to undergo radioisotope inspection because of concerns growing out of the NTSB findings. The inspections are scheduled to take effect this fall.

According to the Associated Press, Eunice Burnham, a Northwest spokeswoman, said Monday night that the inspections prompted by the NTSB findings ``had been done and corrections had been made prior to any suggestion by the FAA.''

The safety board's recommendations followed its recent investigation of a Pratt & Whitney JT8D-217A engine that lost power on March 23 as American Airlines Flight 241 from Chicago approached an airport in Minneapolis. Pilots shut the engine down and landed the MD-82 safely.

The recurring problem in Pratt & Whitney 200 series engines was identified by the NTSB in its investigation of the American Airlines incident in March, as well as by the engine company. In an April 24 notice, Pratt & Whitney notified all airlines that it was possible for ``locking pins'' within the low-pressure stage of the compressor to fracture. The company has since offered a beefed-up, redesigned locking pin.

``Do I know if they had those pins in the engine?'' asked Robert Weiss, a Pratt & Whitney spokesman. ``I don't know. But based on information from our experts, there's no indication that the pin was the cause, or that there was any damage to the pins based on data they've analyzed so far.''

Mr. Weiss said the preliminary analysis used data on the engines supplied by the airline.

There are currently 816 JT8D-200 series engines flying on MD-80 aircraft, according to Pratt & Whitney. The JT8D is one of the most popular engine types in history, with more than 9,000 in service in the US.

Although popular, the JT8D has had some bad history in the past few years. An engine failed on a Midwest Express DC-9 jet in September 1985 in Milwaukee. That plane crash killed 31 people.

Severe cracking in the engine's combustion chamber was blamed for the breakup of a JT8D engine on a British AirTours aircraft in Manchester, England, in August 1985 in which 55 people died when the plane caught fire.