Guy Norris/SEATTLE
BOEING PLANS TO MAKE changes to the 777 gust-response system as part of efforts to eliminate a slow yawing motion, or "tail-wag", experienced by crews on the first few United Airlines aircraft.
"We sent a team out to fly with the aircraft on revenue service and confirmed the problem," says 777 service-engineering director Dean Muncey. The tail-wag is exhibited in a cyclic motion of around 4Hz, which has been enough to cause some air-sickness in both passenger and crew seated in the aft area.
"We will be doing some flight-testing to confirm exactly what the mode is and to see how we can redesign our gust-response system," says Muncey. Flight-tests will be conducted using one of the two Rolls-Royce-powered Cathay Pacific test aircraft. A long-term fix, involving changes to the flight-control software, will be available "probably in a year or so", he adds.
Few other in-service problems have arisen, apart from isolated breakages in the guide rails and locks of the cargo-handling system, and some cabin-comfort issues. One of these, related to moist air condensing into "snow" inside areas of the cabin, has been cured by the fitting of ice screens in the outlets.
"We've had lots of the little problems that are normal for a new airliner, but, overall, the reliability has been very good," says Muncey. In its first three months of revenue service, United's six-strong fleet experienced a cumulative schedule reliability of 97.7%. The October figure dipped to 97.6%, mainly as a result of United scheduling too little time for turn-arounds at airports. "It usually drops significantly during the first few months as aircraft age and problems stack up," cautions Muncey.
"This programme is much better than the 767 was at the same stage," he says, citing reliability levels of below 90% for the 767 and 747-400 at their entries into service. The 767 did not achieve the current levels of 777 reliability until 18 months into service, while the 747 took 38 months to reach similar levels. The company hopes to see 777 reliability levels of 98% by May 1996, the end of the first year in service, and is aiming for 98.4% by the end of the first three years.
Significant reductions in delays caused by prolonged trouble-shooting and wrongly identified problems have been achieved by the central maintenance computer. "It has been excellent," says Muncey. Another software-intensive system which has performed well is the aircraft information-management system (AIMS), which "...everyone thought of as a monster to start with, but we've had very few problems", he says.
New AIMS software will be loaded and certificated when the first R-R-powered 777 enters service with Thai Airways International in mid-January 1996.
Source: Flight International
