The Boeing Co. said Friday it has notified all its 767-300 customers that parts of the wing structure near the central fuel tank may be susceptible to cracking.
Before the affected planes can fly again, the FAA said, electrical cables must be coiled and stowed between the glare-shield and the standby display to further isolate the display from other instruments and revise operational procedures.
Boeing is inspecting 16 model 767-300 jets in various stages of production for cracks in "stringers," which run the width of the fuel tank and help support the wing.
No cracks have been reported in planes currently in service with carriers, and it's not clear how many planes could be affected, Boeing spokeswoman Debbie Heathers said.
Boeing said the problem came to light recently when an 8-inch crack was found in a stringer on a 767-300 in production at the company's widebody jetliner plant in Everett. The company blamed one shipment of improperly heat-treated parts from a supplier, and said Friday that only a single lot of 32 parts was affected.
Boeing said it did not consider the matter an immediate safety-of-flight issue. It is inspecting all of its 767-300s in production for similar problems. The Federal Aviation Administration said it was awaiting further analysis by Boeing before it determines what should be done with planes that are already in service.
"The airplanes in service are safe to fly," Boeing spokeswoman Yvonne Leach told the Seattle Post-Intelligencer, which first reported on the stringer problem in Friday's editions.
The problem comes as Boeing is trying to get back on schedule following a 40-day strike by engineers and technical workers that resulted in delivery delays for a number of aircraft.
Leach said the company believes the suspect parts can be removed and replaced in the 767s in production, without delaying any deliveries. The next 767 is scheduled to be delivered Monday, she said, and the suspect parts have already been removed and replaced in that plane.
The FAA was notified by Boeing last week and is working with the company to better understand the nature and scope of the problem, as well as to determine a corrective action plan for planes in service, said FAA spokesman Mitch Barker.
"We are waiting for Boeing to do an assessment of the size of the problem, what effect this might have and what needs to be done," Barker said.
This is the second supplier problem that has complicated Boeing production in recent weeks. Production had to be slowed in early March on all but one of Boeing's commercial models after the company discovered substandard fasteners had been used on its assembly lines in Everett and in Renton since last December.
The fasteners wre made from an alloy that made them prone to cracking. The latest problem involves 194-inch-long aluminum stringers that help carry the wing load and serve as an attachment to the metal skin of the center wing fuel tank.
There are 28 stringers on top of the tank and 28 on the bottom. Only two of the 28 upper stringers are suspect, Leach said. Engineers have calculated that even if the two stringers failed, the others could carry the wing load with adequate safety margins, she said.
Leach said the problem occurred with the supplier of raw material used in the stringers. She would not identify the supplier.
"Our investigation found that the material was heat-treated at too high a temperature at the raw material supplier's facility," Leach said. He said only one bad lot of parts came from that supplier.
Though Boeing said only 32 parts were affected, the FAA's Barker said there were 40 jets now in service with airlines that were built during delivery of the suspect parts, and all of those will be thoroughly inspected for cracks.