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Teenage twin

Demand for Boeing 777 heavy maintenance is increasing as older examples, now 17 years old, are making their second D check shop visits. Ian Goold discovers that some MROs have encountered little structural corrosion

Spills from galleys and toilets are a classic source of airliner structural corrosion at fixed locations in cabins, but even though the Boeing 777 offers flexible positioning for such equipment the twin-aisle twinjet is proving itself to be well protected from this danger. The moveable units have given rise to few or no concerns during heavy maintenance, according to sample organisations surveyed by MRO Management.


Air France Industries-KLM (AFI-KLM) has found no corrosion at all in the ‘wet/flex’ cabin zones close to such equipment, even on aircraft undergoing 12-year checks or cabin reconfiguration. “The 777 is behaving very [well] in regards to corrosion resistance,” says Thomas Sonigo, Boeing Fleet Engineering Manager at AFI-KLM Engineering & Maintenance (E&M). El Al Tech has had a similar experience, attributed to “good corrosion-inhibiting compounds”.


Gulf operator, Emirates Airline, has not seen “any heavy corrosion” on 777s, saying the flexible locations have “resulted in better prevention and control” and noting that improved corrosion measures have contributed to reduced maintenance costs. In the US, Marana Aerospace –formerly the Evergreen International Aviation maintenance centre – found no galley- or toilet-related corrosion during its single heavy-maintenance check in late 2012 on a 2006-build 777-200ER of TAAG Angola Airlines – its second 777 check was under way in January.


For its part, Boeing concedes that Airworthiness Directives (ADs) have included corrosion inspection and prevention measures: “As the fleet approached initial 16-year checks, lavatory-area corrosion became an issue.”


The MRO observations come as the US manufacturer continues to rationalise 777 maintenance procedures with further revision (usually reduction) of inspection intervals that should help to reduce engineering costs. After several rounds of maintenance schedule optimisation, Boeing’s latest moves cover 1,000 flying-hours (FH) – or less than 1,125 days’ – tasks.


“[We have] always worked to identify the optimum interval, so operators have the flexibility of planning the inspection in line with operational requirements,” says Calum Hood, Boeing Commercial Aviation Services’ (BCAS) Maintenance-Engineering Director. The latest proposed changes were accepted by the Boeing 777 Industry Steering Committee (ISC) in December 2012 before submission to the US Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA) for approval.


The changes, which address fuselage inspection work, will appear in the next 777 Maintenance Review Board Report (MRBR) revision. This is planned to complement optimisation of eight-year/3,000-day/16,000-flight-cycle (FC) wing inspection tasks that began, along with some 2,000FH jobs, in the current October 2011 edition.


Hood acknowledges that developments have included some reduced inspection intervals: “[There is] not a significant number, but very few have been ‘de-escalated’, based on fleet data with the emphasis on minimising in-service maintenance and improving despatch reliability.”


In 2007, many four-year/1,500-day/8,000FC inspection intervals had been increased to six-year/2,250-day/12,000FC periods. That change, which permitted operators to align related tasks with C or 2C inspections, resulted in an estimated overall maintenance cost reduction of about 0.5%. The next ISC meeting is expected to consider remaining four-year intervals.


In 2009, 1,000FH and 1,500FH intervals were optimised, followed by the revision of many 7,500FH tasks to 10,000FH or 15,000FH intervals in 2010. For example, Hood cites operational checks of the 777’s landing altitude manual select switch, for which the inspection period has been doubled to 15,000FH. “For many operators, [this] will allow [the work] to align with three-year/1,125-day tasks.”


Since 2010, Boeing has been using a Statistical Analysis for Scheduled Maintenance Optimisation (SASMO) tool to identify the best interval level for specific tasks, based on structured fleet maintenance and reliability data, says Hood.

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