Special Cracks Check Ordered for Older Jets
Boeing Co. began advising airlines in 1983 to increase inspections for structural cracks in their aircraft fleets, including 747s, as a result of concern that potentially dangerous airframe deterioration could go undetected.
The special inspections were required by the Federal Aviation Administration after an exhaustive analysis of a 1977 crash--in which a Boeing 707 jet came apart in the air--revealed that traditional inspection techniques were not capable of ensuring the integrity of aircraft.
The inspection was “developed to take care of airplanes that have been aging,” said Bill Zenker, an FAA inspector in San Franciso. The Boeing 747 was included “because the 747 reaches back to the very early ‘70s. It is old now.”
Old Planes Kept
Many U.S. airlines have chosen in recent years not to replace their fleets of aircraft purchased in the 1970s, meaning that existing jet aircraft are being called on for many more years of service than any previous generation of jets.
To comply with the FAA requirement, Boeing issued a series of “supplementary inspection documents” to operators of the Boeing 747, instructing them to look for deterioration in parts of the aircraft’s metal structure that had never before been subject to inspection. The airlines were given one year under FAA regulations to implement the inspection program. Not all airlines have begun their inspections, and the results obtained by those that have are unknown.
Airlines were instructed to conduct the supplemental inspections for cracks, corrosion and fatigue in virtually all areas of the Boeing 747, including the tail assemblies, one of the focal points of the investigation of this week’s still-mysterious crash of a Japan Air Lines 747. “At this point, virtually anything is possible,” one aviation accident specialist said in discussing the reasons for the JAL crash.
While some domestic and foreign carriers have started doing the additional inspections, the JAL airliner that crashed had not yet been inspected--at least in the tail section that broke off before the aircraft crashed. Two parts of the tail section were found at sea, 100 miles from the crash site.
“The fin-support bulkhead was not inspected yet on this particular (aircraft)--JA8119,” said Tadao Fujimatsu, JAL director of public relations in New York City. A large section of the fin, or vertical stabilizer, was one of the pieces found at sea.
Airline Quotes Boeing
JAL officials said they were told by Boeing that the additional inspections were not necessary for the 747 SR (for short range) versions operated by the airline on its domestic routes. It was a short-range version of the 747, fitted with extra seats, that crashed Monday in the Japanese Alps. However, Fujimatsu said, the airline developed its own inspection program.
“Japan Air Lines asked Boeing, ‘Why don’t you do it for SR?’ and they said it is not necessary,” Fujimatsu said.
Boeing spokesman Dave Jimenez said that Boeing had developed a special inspection program for the 747 SR in mid-1984.
Even before the FAA-ordered inspection program went into effect, instances of structural deterioration in tail sections of U.S.-based Boeing 747s were being reported to the FAA. Computer summaries of these reports obtained by The Times show 11 such instances in the past five years.
Cracks, Sheared Bolts
Ten involved evidence of deterioration such as cracks, sheared bolts and corrosion in components related to the horizontal stabilizer. One report cited two cracks, one 4 1/2 inches long and the other 7 inches long, in a rib of the upper rudder.
In the computer summaries, The Times also found 16 reports to the FAA of problems with flight-control components in tail sections of the 747 aircraft during the past five years.
Among the reports were six involving cracks in elevator-control rods and seven relating to problems with the hydraulic system.
The problems are described in Service Difficulty Reports filed with the FAA by air carriers, maintenance stations, plane manufacturers and FAA inspectors. The total number of maintenance problems with Boeing 747 tail sections might be higher than the number of reports indicate, because not all of those required to report are equally conscientious.
The new, FAA-mandated inspection program included small parts, such as forgings and castings, which in the past had not received the emphasis put on larger structures that were presumed more important. But aeronautics experts found that such smaller assemblies could cause catastrophic failure.
Until the new inspection criteria were issued, aircraft inspections were based solely on metal stress fatigue, which is the weakening that metal undergoes in normal long-term use. The new criteria, based on so-called “damage-tolerance ratings,” included the effect that corrosion and contact with foreign objects such as birds or maintenance tools could have.
The heightened concern grew out of the May, 1977, crash of a Boeing 707 cargo jet, operated by Dan-Air Services Ltd., during a landing at Lusaka, Zambia. A British investigation of that accident revealed that the 707’s tail and horizontal stabilizer assembly broke off in flight and sent the aircraft into a nose dive.
The investigation revealed that a whole series of small parts in the tail assembly had collectively failed, largely because of corrosion and metal fatigue.
British authorities pressed a sometimes acrimonious crusade to force more complete inspections of older aircraft. At one point, the British Civil Aviation Authority had threatened to ground aircraft after they had flown a specified number of hours.
The dispute eventually forced the FAA to dramatically alter its design criteria for new aircraft and to revise the methods used to inspect existing aircraft.
‘A Key Turning Point’
“Dan-Air was an accident that never should have occurred, because from the inspections we had in place at that time, it was unbelievable,” said a technical service engineer at United Airlines. “That incident was a key turning point in structural design and inspection technique.”
Metal fatigue is “like a time bomb, and you never know when it will go off,” said John Galipault, head of the Aviation Safety Institute in Worthington, Ohio. He declined to speculate whether metal fatigue may have been a factor in the JAL crash.
But a Japanese metallurgical expert who examined the tail fin, or vertical stabilizer, recovered Tuesday from Sagami Bay discounted metal fatigure and said it would take “a powerful force to have ripped the part off.” Loss of the vertical stabilizer would have made the plane difficult, but not impossible, to fly.
Other experts also believe that metal fatigue played no part in the JAL crash. They have theorized that if--as some news reports have suggested--the fuselage of the JAL aircraft had a hole in it, perhaps it was hit and weakened or punctured by a heavy object.
One said that if a hole developed in the fuselage, the pressure differential between the inside and outside of the aircraft could have caused near-explosive conditions. Sudden depressurization could also have occurred as control valves failed and blew apart in the plane’s air-conditioning system, he said.
Additional damage to vital flight-control cables in the 747’s ceiling also could have contributed to the pilot’s inability to control the aircraft, one U.S. expert said.
Meanwhile, other safety specialists discounted earlier speculation that a section of the tail fin could have been the object that punctured the fuselage. They explained that because the tail fin is located above the rear fuselage, it would have had to defy the laws of aerodynamics to fall forward.
Moreover, they say, if part of an engine had fallen off, pilot Masami Takahama would have reported engine problems.
At Boeing, Jimenez said the company had run fatigue tests on 747s in the early 1970s, when the airplane was introduced, that were equivalent to flying the planes 60,000 hours--or about 20 years. The company also has tested the tail fin skin, the stabilizer skin and other parts for an additional 12,000 hours, he said.
Times staff writers David Holley, Penny Pagano and J. Michael Kennedy contributed to this story.