In most cases, the 717-200 is being operated by airlines smaller than Boeing has traditionally dealt with. To handle this it created an innovative customer support philosophy in which airlines openly share maintenance problems or operational issues. Boeing 717 fleet support chief Dan Meadows says. "Most don't have the large organisations that slow down the flow of information. It's been relatively easy for us to go in and suggest things, and they are willing and able to adapt. We asked them all what they thought about distributing data on other fleets and they said 'fine.'"
Boeing's 717 support team, chief engineers and fleet chiefs now meet every two weeks to discuss issues affecting aircraft in service around the world. The resulting list covers every system and sub-system. "We look to see if it is a premature failure of the part, and search for trends - either in failures of components or the way a particular airline is operating the aircraft," says Meadows.
The system has unearthed new issues and access to the list was requested by Hawaiian several months before it became a 717 operator. "They wanted to know in advance what was going on with the fleet in service, which helped them prepare," says 717 chief project engineer Tom Croslin. Meadows adds that the effort is necessarily intense: "Although they're all entrepreneurial, the downside is they need a lot of support." The results, however, appear to make it worthwhile. Fleet average dispatch reliability was at 97% with the first few aircraft shortly after entry into service in October 1999, and having dipped below this the following winter subsequently began a continuous recovery. It has stayed above 98% since February 2000, and is on track for Boeing's design target of 99.1% by the end of the third year in service. As Flight International went to press the fleet was nearing its 14th consecutive week at more than 99%.
The big threat to maintaining this standard, warns Boeing, is "the winter dip." To offset this primarily ice-related series of problems seen in two successive northern winter seasons, Boeing is working to ensure three key improvements with fleet-wide retrofits, upgrades and replacements. "We have resolutions for all three problems, and we have plans to get the fleet retrofitted before next winter," says Croslin. The three key areas are a redesigned engine starter air valve, a modified air cycle machine (ACM) and further modifications to the APU inlet ice-protection screen.
Improvements to the starter valve include an upgraded, more robust design with a higher torque capability rotor and a redesigned butterfly valve. Boeing says the changes will prevent the sudden build up of air pressure in the valve which was sticking in the closed position during engine start-up due to ice accumulation.
Icing issues also dogged the ACM which suffered from "flash freezing" on start-up. The problem is thought to be responsible for at least half of the failures on the unit which has nothing like the 4,500h mean time between failures (MTBF) enjoyed on a virtually identical design used in the 737, says Croslin. The redesign will raise air temperature around the air bearing which "locked up" when ambient air dropped below 35í, and is adding a drain to get rid of any water that might collect close to the bearing area. The upgraded ACM will also have revised plumbing to prevent back pressure. This caused tip fatigue in the fan blades of the third wheel of the ACM, and the revised design will be introduced into the production line in July, Croslin adds. Retrofit kits are also being issued this summer.
A fleet retrofit and production line change is also in place for what Boeing believes is a final cure for a nagging 'soft' FOD (foreign object damage) impact to blades in the Hamilton Sundstrand APIC APS 2100 APU. "Ice was forming in the duct, so we put a conical screen on the outside of the inlet to the impellor. But the issues didn't go away, because ice formed on the struts beyond the inlet screen. So we've moved the screen to the inside [of the support ]. We're cutting it into the line now, and we're doing a fleet retrofit," says Croslin.
Boeing's main focus is on continued software improvements, including the engine electronic control, proximity electronic sensor units (flaps, slats, doors etc), pneumatic systems controller, spoiler electronic control unit, engine vibration monitoring system, PCDU and electric power control unit. Increased avionics functionality, including Cat 3B autoland was introduced in October with the second certification upgrade of the Honeywell versatile integrated avionics (VIA) processors. The upgrade, which included new software loads for the flight control computers, also gave the 717 full Vnav capability.
Boeing and Honeywell are working on a Block 02 software update that will increase FCC functionality, eliminating some hardware and "take some weight, cost and complexity out of the aircraft". The upgrade will also help meet US Federal Aviation Administration mandated requirements for the VIA to record force sensor parameters from August 2002 onwards. It will also help support the optional addition of head-up-displays on the aircraft, in line with other Boeing types. Honeywell meanwhile, says the MTBF of the main systems it supplies (VIA, FCC and air data inertial reference unit) are "all at least three times over the target we planned for," says the company's vice- president and general manager of air transport programmes, Scott Starrett.
Rolls-Royce has increased production of the BR715 to 10 per month to match the Boeing 717 assembly rate of five per month, and by the end of May expects to have delivered almost 130, including spares. Engines are available at three thrust ratings: 18,500lb (82kN), 20,000lb and 21,000lb, with most selecting the lowest thrust setting. By early May the engines had accumulated almost 204,000 flight hours and close to 86,000 cycles.R-R is also introducing a redesigned second stage high pressure turbine blade into new engines and as a retrofit, to counter root cracking discovered on a testbed.
Software glitches with the EEC, which led to uncommanded engine shut downs, have now been corrected, says manager of sales and marketing support, John Taylor. Other issues have included case cracking and failures of the Line 12 bearing driving the permanent magnet generator, the latter being addressed with gearbox manufacturer Hispano Suiza.
Overall, however, Taylor says operators are pleased with the engine's low fuel burn, emissions and noise performance. Average engine mechanical dispatch reliability has reached 98% with individual operators achieving higher figures including AirTran (99.89%), Olympic Aviation (99.89%), TWA (99.96%) and ABEL (100%).
Source: Flight International
