NEWARK, N.J. — Seconds before a Continental Airlines DC-10 lifted off at Newark International Airport last April, pilots heard a "boom" as their left engine partly disintegrated. Like shrapnel from an artillery shell, shards of metal bounced off the runway and smashed into the right engine, damaging it, too. Only the tail engine was functioning normally as the big jet thundered into the sky.
What followed was a chilling 34-minute flight as the pilots circled over New Jersey, dumping tons of fuel to get the crippled plane down to landing weight. In the cabin, flight attendants had the 220 passengers chanting "bend over, heads down; bend over, heads down" in preparation for the emergency landing. As the jet came in — smoothly and safely — Newark's tower controller radioed to the pilots: "Continental . . . beautiful job."
The engine that came apart was a General Electric Co. CF-6. Continental's close call, it turned out, was only one of the more-dramatic episodes resulting from recent problems with GE's CF-6 engines.
In June, a CF-6 engine partly disintegrated on a Varig Airlines Boeing 767 in Sao Paulo, Brazil, forcing the pilot to abort his takeoff. And in September, two more GE engines on Continental DC-10s partly disintegrated, again forcing aborted takeoffs. In a third case that month, one blew apart on a taxiway during maintenance.
The incidents have alarmed safety officials. GE's CF-6 is one of the most widely used engines in the world. Nearly 5,000 of them power a broad range of Boeing Co. and Airbus Industrie planes. The fear is that a CF-6 engine on another plane will disintegrate at the critical moment of takeoff and cause a crash.
The Federal Aviation Administration, the National Transportation Safety Board and GE have all launched investigations. The engine faults, the NTSB has said, could result in a "catastrophic accident." The FAA has issued emergency airworthiness directives intensifying engine inspections, and it says several more directives are to come.
Despite the close calls, CF-6 engine failures are still rare. By one measure — rate of in-flight engine shutdowns — the average CF-6 engine will fly 30 years before suffering a shutdown, says GE spokesman Rick Kennedy. But while all kinds of jet engines are subject to occasional failure, most failures are contained within the engine casing. What is troubling about the CF-6 failures is that they have been uncontained, with pieces flying out to pose a risk to passengers, to other engines and to aircraft structures critical to flight.
"These incidents, particularly Continental's flight at Newark, are ones we don't want to see repeated, and we're going to make sure they're not," says Jay Pardee, chief of the FAA's engine directorate in Burlington, Mass.
GE is taking the matter seriously. It has developed better inspections of engines to catch faults. It is redesigning certain parts to eliminate the faults and, in the meantime, making devices to insert into engines to prevent faults from leading to disintegration. "I can't afford another engine failure," says Roger Seager, CF-6 project manager at GE's sprawling jet-engine plant near Cincinnati. The company's huge aircraft-engine division contributes more than $10 billion of annual revenue, which is more than 9 percent of GE's total. The CF-6, one of three engines GE makes for big airliners, has a nearly 60 percent share of the widebody-jet market.
Inspections mandated by the FAA have become so time-consuming that they threaten to force planes out of regular service, disrupting airline schedules. To prevent this, GE is setting up special "engine hospitals" around the world to inspect and doctor ailing engines quickly. A a few of them serve particular customers, such as one at New York's Kennedy airport for American Airlines, a big user of the GE engines.
Two problems have been plaguing the CF-6 engine, one identified a decade ago and one just this year. GE has developed fixes for both of them. However, GE says engineers so far can't figure out what went wrong in an incident on Sept. 22, when an engine on a US Airways jet blew apart on a taxiway at Philadelphia International during maintenance, throwing parts into the nearby Delaware River. That case prompted the NTSB on Dec. 12 to call for a review of part of the engine's design, racheting up the pressure on the company.
The first of the two known CF-6 engine faults surfaced in 1991. Inspectors of a Korean Air A300 were astonished to find a crack caused by a new kind of metal fatigue. Called "dwell-time fatigue," it can arise when crystals that form within metal during forging are aligned, permitting cracks along the alignment.
The cracks were in the engines' titanium spools. These big parts — 3.5 feet long and looking a little like a beer keg — hold the spinning blades that compress incoming air. A cracking spool will release blades that then shoot through the engine casing, possibly damaging the aircraft enough to cause a crash.
This type of metal fatigue was causing cracks "much faster than we had ever seen before," says Pardee of the FAA, which ordered frequent inspections to find any bad part before it could fail. Safety authorities considered the problem solved.
But in 1993, the GE engine on an American Airlines Boeing 767 taking off from Los Angeles partly disintegrated, spewing parts into the Pacific. After the plane limped safely back to the airport, inspectors found that the new type of cracking was again at fault.
The FAA ordered that inspections be still more frequent.
Then in June of this year, a spool fractured again, on the Varig 767 taking off from Sao Paulo. Although rolling at 100 knots, the captain was able to slam on the brakes and bring the jet to a stop. "I thought we had this problem under control, and then we had Varig," says GE's Seager.
Spool inspections, it turned out, were inadequate. Cracks were developing in new places even faster than expected, and the configuration of the spool made it hard to detect every crack. In September, the FAA took Draconian steps. It sharply increased the frequency of inspections, required an ultrasonic test to probe for cracks more thoroughly and cut spools' service life to 12,500 takeoffs from 15,000.