Boeing is expecting, on 21 January, the results of a US Federal Aviation Administration audit of its quality control which was triggered - along with inspections of 211 Boeing 737s - by the unexplained crash of a SilkAir 737-300 on 19 December.
The FAA's quality-assurance audit is focused on the 737-300/400 and -500 horizontal-stabiliser assembly processes. Completed tail units were also inspected after the FAA issued an airworthiness directive on 8 January calling for inspections of 211 aircraft delivered after 20 September, 1995.
The inspections, like the audit itself, were prompted when investigators probing the wreckage of the SilkAir crash in Indonesia discovered that 26 fasteners on the horizontal stabiliser and one bolt from the elevator attachment may have been missing before impact.
As Flight International closed for press, only two aircraft remained to be inspected. Initial results indicate that five aircraft had missing fasteners and one had a missing bolt, although the FAA says omission of the fasteners would not have affected the structural integrity of the horizontal stabiliser.
"So far the findings do not represent a threat to safety," says Boeing. "We expect that the FAA audit will validate our quality assurance and the aircraft certification standards."
The FAA criticised Boeing late last year over quality control issues that arose during a period of sharply increasing production.
Four screws were found to be missing on a 737-500 delivered to Continental in August, and Southwest found a screw missing on one stabiliser leading-edge, as well as a loose elevator-hinge bolt. An unidentified Japanese carrier discovered one missing elevator-hinge bolt and nut, and four other non-US operated aircraft were found to have loose elevator-hinge bolts. One of these aircraft was also missing four stabiliser leading-edge flush head screws.
The leading edge of each horizontal stabiliser of the 737-300/400/500 family is attached with 66 flush head screws (33 top and 33 bottom) on the inboard section, and 223 on the outboard (111 top and 112 bottom). Each stabiliser also contains eight elevator attachment bolts. About 75% of the stabilisers are fabricated in Wichita, Kansas, with the rest produced by Xian Aircraft in China. Apart from the identity of the Continental model, none of the others has yet been divided into type or vintage.
The scrutiny over safety issues affecting the 737 is threatening to eclipse two major milestones for the family later this month. The last of the Next Generation family, the 737-600, is scheduled to have its first flight around 22 January to begin a six-month certification effort before deliveries begin to launch customer Scandinavian Airline System.
Within days, Boeing will also celebrate the delivery of the 3,000th 737, easily making it the best-selling jet airliner ever built. The aircraft is believed to be a 737-400 for Alaska Airlines and marks a landmark in commercial-aviation history.
Source: Flight International
