Planeload of problems continue to dog path of Rockwell's B-1B plane.

Nearly seven years after it went into service, the Rockwell International Corp.-built B-1B still is plagued by problems and questions about its value to the United States Air Force.

The latest incident reflecting the plane's structural and systems problems occurred last summer when an engine overheated, grounding the entire fleet of 96 aircraft for three weeks.

Also, the aircraft has had a series of lingering problems that have included what the Air Force calls "stand downs."

On at least nine occasions since the aircraft went into service in the mid-1980s, part or all of the fleet has been grounded because of various problems that have included three fires, a dropped engine, a fuel spill and a system failure, according to Air Force officials.

Now, with the demise of the Soviet threat, the purpose of controversial aircraft -- designed to penetrate Soviet air space undetected -- seems to be unclear, said Washington, D.C.-based military analysts.

Because of its problems the $28 billion B-1B fleet is a sensitive subject to both the Air Force and Seal Beach-based Rockwell. Unlike other projects, information released on the B-1B must be approved by a chain of command at both Rockwell and the Air Force.

"It's no secret that it's received a lot of criticism, so answers to questions about the B-1 must be approved before going out," said Air Force Capt. Tracy O'Grady at the aeronautical systems division in Dayton, Ohio.

Questions about the aircraft at Rockwell also had to go to high company officials. At presstime last week, Rockwell officials were unavailable to answer most questions about the aircraft and the $28 billion project that in the 1980s employed about 10,000 Southland workers.

Rockwell, an international conglomerate that in 1991 had almost $12 billion in sales, continues to collect revenues from maintenance work on the stealth bomber in Palmdale. Rockwell revenues from the B-1B continue to decline from $1.3 billion four years ago and $530 million in 1990 but that trend could be reversed because of continuing problems with the aircraft and its uncertain future.

Company officials were unavailable to discuss a potential increase in revenues from the B-1B but government and military officials have said it could take up to $3 billion to make "modifications" in the 97-aircraft fleet. In the current defense budget, $120 million -- about one-third what was requested by the Air Force -- has been allocated for work on the B-1B.

Late in September, the Air Force completed what it called a "summit meeting" to determine what fixes and modifications have to be made to the B-1B fleet over the next decade. The changes are required to correct problems and enable the aircraft to carry conventional as well as nuclear weapons, the Air Force said.

Work on the B-1B fleet could include improvements to the radar warning system, addition of precision-guided weapons capability and upgrades to the fleet's electronic defensive measures to block attacks and detection.

The Air Force officials concluded the bombers' stealth capability and ability to survive undetected in enemy territory is still questionable.

Most of the work, they said, would be designed to accommodate conventional weapons. In the 1980s, under President Ronald Reagan, the B-1B was designed as a low-altitude, high-speed bomber carrying nuclear weapons that could penetrate Soviet Union air space undetected.

Last year, hairline cracks were found on longerons in 37 B-1Bs, which resulted in restricted flight operations for at least 14 of the aircraft. Longerons are structural components that run along the length of an aircraft's fuselage and are part of its frame.

In late 1990, just before the start of the Persian Gulf War, the entire B-1B fleet was grounded following what the Air Force said at the time were "two catastrophic engine failures."

Other groundings of the entire fleet have followed a wing malfunction and an incident in which one or more pelicans penetrated the skin of one of the aircraft, causing a crash that killed three crew members and one Rockwell test pilot in September 1987.

In a statement, the Air Force said the other stand downs "caused minimal impact to flying schedules. Upon completion of inspections, individual aircraft returned to service, as required. Some returned to service the next day."

Independent defense industry and military analysts said it's difficult to say whether nine stand downs are a significant number.

"It's a unique aircraft so it's hard to compare it to anything else," said John Pike of the Federation of American Scientists, a Washington D.C. think tank. "But there's no doubt it's had problems and I think it was the wrong plane to build."

The B-1B was born in controversy during the mid-1970s. Then known as the B-1, it was designed to be a bridge aircraft between the B-52 and the then-contemplated B-2 bomber that is now being made by Century City-based Northrop Corp.

Shortly into his term that began in 1977, President Jimmy Carter canceled the project but it was later resurrected by Reagan and renamed the B-1B.