Ian Goold, MRO Management, June 2010

Requirements for Boeing 767 heavy maintenance services each year are expected to  have increased by almost a third by 2020.  Nevertheless, annual numbers of heavy checks will continue to reflect original delivery cycles, with peaks and troughs; Ian Goold discovers that about 140 D checks next year will grown in volume to about 180 two years later.

Demand for Boeing 767 heavy maintenance D-check capacity in the coming decade, based on cyclic aircraft-delivery trends and an assumed six-year inspection interval, will peak in 2019 at about 190.  That is 30% higher than this year’s expected requirements for around 145, according to Boeing.

“Knowing that major checks are spread out more evenly, it is more appropriate to take a five-year rolling-average view,” says director of maintenance economics at Boeing, K.M. Ali. “This indicates that demand is expected to rise 10% during the next 10 years.”

Boeing puts the 2015-20 five-year annual average at some 175 aircraft. This will follow a steep increase in such work from just over 140 next year to 180 in 2013. TIMCO Aviation Services says the demand crest in three years’ time will precede an overall retraction in the size of the fleet, producing a gradual downward trend for the duration of the decade. Nevertheless, overall size of the 767 market will remain large relative to other fleets, says marketing and business development vice-president Leonard Kazmerski.

For American Airlines (AA), increased 767 maintenance demand is linked to ageing-aircraft inspections and a higher incidence of corrosion uncovered during structural inspections. “[The] predicted span time for these inspections increases as [aircraft] age past their fourth heavy check.”

A factor in extended 767 operational lives is the industry’s wait for the Boeing 787, according to Ireland’s Shannon Aerospace (SAL): “We see a continuing demand for 767 heavy maintenance as the aircraft [are] remaining in service longer than anticipated. As the overall fleet age grows, the airframe will generate more maintenance,” says marketing & sales head Paul Murray. “Continued delays in the 787 had a positive effect on residual aircraft values and operators have had to extend the operation of these aircraft and, in some cases, ‘source’ additional 767 capacity.”

In the much longer term, Frankfurt-based Lufthansa Technik Maintenance International (LTMI) foresees “stagnation” in check events, driven by “significantly reduced deliveries” of more recent new-build 767s. Boeing’s Ali is confident there is adequate capacity in all regions. “We have not heard reports of shortage to perform [C and D] checks on the 767. Being a mid-sized airplane, the hangar space requirement is common to many other airplanes and the few [demand] peaks are easily met by space and labour capacity."

MRO providers AMECO, Aveos, SAL and TIMCO agree, although the latter warns: “A return of high fuel prices could mean fewer options in some regions as the cost of ferrying aircraft exceeds labour or currency exchange economies, but these will likely be exceptional.” LTMI points out that there might even be some over-capacity, while SAL sees “occasional demand for a winter slot at short notice,” but insufficient “to warrant a second [767] line.”

Operations with the 767 – Boeing’s first twin-aisle design – began almost 28 years ago, in August 1982, the oldest example having logged a relatively modest 76,901 flight-hours (FH) and 19,290 flight-cycles (FC) by 1 April this year. The fleet-leaders have recorded almost 102,000 FH (a Series 300EREM) and some 46,450 FC (a ‘vanilla’ 767-300), respectively, according to Boeing.

Over the life of the 767, the maintenance schedule, which applies to all 767 models and sub-variants, has evolved as operators reported their inspection findings. For aircraft systems, the original 3,-000-FH C check interval has grown in stages to the 6,000 FC per 18 months frequency introduced in 2007. On the airframe structure, the initial 3,000-FC interval remains today, but the related maximum 15-month frequency was extended to 18 months in 1990. The 4C check is a straight four-times multiple of the C check values.

In line maintenance, structural A check inspections have always been required at 300-FC intervals. Equivalent systems check requirements have been relaxed steadily from every 250 FC to the 750 FC adopted three years ago.

LTMI chief commercial officer Altfried Nessel points out that several operators have increased C check interval to 24 months. El Al Israel Airlines, for example, has established 767 A checks every 500 FH and C checks every 5,500 FH, or 18 months (whichever comes first). Nessel says that for low-utilisation aircraft, such as those in corporate operations, A and C checks are normally driven by respective 90-day or 24-month calendar limits.

Another element of 767 maintenance evolution has been the incorporation of corrosion protection and control and structural-inspection programmes, says SAL engineering and planning head Mick O’Dwyer. This “most notable change” has resulted in “a significant reduction in the number of tasks required, with many repeat inspections having been removed.”

According to Boeing Commercial Aviation Services (BCAS) maintenance-engineering director Lynne Thompson, 767 operators generally package checks “in line with the Boeing maintenance-planning document (MPD), but [over time] have added inspection requirements and optimized existing requirements beyond [the] MPD.”

The manufacturer can provide high-or low-utilisation packages, says TIMCO’s Kazmerski.  “Operators [are free] to move more routine work to smaller line checks or special route visits due to the decoupling of a specific check.” He concedes that such adjustment brings attendant risk: “Operators and maintenance providers need to exercise increased responsibility and management of the overall maintenance programme.”

In developing 767 maintenance procedures, AA has followed the Industry Steering Committee (ISC) requirements that use the MSG-3 philosophy when adjusting increments for the required inspections and also utilise the ISC’s Reliability Programme to make necessary adjustments.

For China’s Ameco Beijing, there is no general rule as to how operators plan maintenance: “[We] can’t judge this. Each work package we receive is different.” No current LTMI customer’s 767 makes use of MSG-3 packaged maintenance, while SAL has found “a small number have packages designed to optimize requirements – usually aligned along extended-range twin-engine operations (ETOPS) and critical tasks. As [most] have one or two 767s, it usually makes more sense to utilise the MPD.”

MROs found early-build 767s in generally good condition at initial heavy checks, although some problem areas emerged subsequently. El Al reports no special “issues”, while AMECO says there are “always cracks” in floor beams at body station (BS) 246.

For LTMI, early work was “rather smooth”, although major findings at later checks included “pylon migrated shims, corrosion in wet areas, [and] cracks at STA246.” SAL cites “corrosion relating to [the] floor and aft galleys “as being among more-frequent occurrences. “Engines on the 767 experienced [early] vibration, but this has been resolved.” Early aircraft suffered “significant corrosion and stress cracks under the [cabin] monuments [for which] inadequate Mylar installation seemed to be the root cause”, according to TIMCO, which has had few lower-lobe concerns.

Considering later-build 767s, the newest AA machines’ initial heavy checks (in the past two years) have been “consistent with light maintenance and can be generalised as wear and tear. Some ‘issues’ [were] identified with wiring bundles that are not exposed during light and intermediate maintenance.” AA says the volume of non-routine write-ups with the first two heavy visits was comparable. Nevertheless, older 767s undergoing third and fourth heavy checks around the same time “had 13% and 65% more non-routine write-ups, respectively.”

TIMCO also identifies flap-fitting cracks as seeming “more abundant in later models that with earlier versions,” while tail and cowling delamination appears “almost routinely.” Cabin corrosion and stress cracks also remain a characteristic.

Newer aircraft with in-flight entertainment systems introduce further potential defects, such as in software, which can generate “difficulties in sourcing parts,” says SAL. The Irish MRO also reports that inspection of the engine-pylon mid-spar closeout angle often requires unscheduled pylon removal during C checks and consequent extended ground- times. SAL has found a way to apply the approved repair on-wing without pylon removal, for which it claims a significant advantage in cost and ground-time.

For Singapore Technologies (ST) Aerospace, there has not been as much change between older and younger airframes as it has seen on alternative designs. “The Boeing 767 has a more straightforward configuration, which results in lesser variance between the earlier models and the newer ones compared with other aircraft types.” Modifications available for the 767 that are typically introduced during heavy-maintenance checks include winglets and cabin-crew rest modules.

ST Aerospace, whose work includes passenger-to-cargo conversions for Japan’s All Nippon Airways, under Boeing’s 767-300 converted freighter programme, performs a number of commonly requested modifications during maintenance. These include pylon, cockpit-security door and emergency locator transmitter work. The most frequent AD-compliance activities for ST Aerospace are mandatory modifications to the floor beam at BS246 and the fail-safe strap at the BS955 bulkhead.

The BS246 floor beam is a double-depth unit forming the step up from the passenger-cabin floor to the flightdeck floor, a consequence of the adoption of a common cockpit for the 767 and smaller 757 single-aisle jetliner. According to the relevant service bulletin, ‘stiffeners, clips, pulley-bracket clips, the mid-chord, and webs common to this floor beam have been found cracked on airplanes with as few as 1,140 flight-cycles.’

Boeing analysis indicated that these cracks had been caused by fatigue from higher-than-anticipated fore and aft deflection of the beam. Since all flying-control cables need disconnection, the modification leads to intensive functional checks later, advises Boeing. ST Aerospace suggests that the BS955 fail-safe strap inspection/termination exercise “tends to be a problem for Boeing 767 aircraft that have not been properly maintained.”

Recent developments promulgated by the 767 ISC or the Maintenance Review Board have included integration of the zonal structure and corrosion-prevention and control programme (CPCP). TIMCO says increased inspection intervals have been accompanied by increased sampling following “insignificant” findings, while LTMI notes the development of a new online forum whereby operators may exchange 767 experiences. The forum gives vendors reading access to vendor-specific posting items to enhance the flow of information. LTMI says a “working-together-team” has been founded to cover ATA36 problems.

Notable developments for SAL include airworthiness limits and certification maintenance requirements, which it sees mainly “in relation to fuel-tank systems. Fuel-quantity indicating systems are an example [that] often results in a large number of findings.”

Boeing’s Ali says that the advent of 767ETOPS flights in the 1980s saw engine maintenance and reliability set new standards. Fleet-wide, Ali says the 767 has “shown improved engine removal rates of 20 to 30% in the past five to 10 years” across the aircraft’s four engine types: General Electric (GE) CF6-80, Pratt & Whitney (P&W) JT9D-7R4 and PW40000, and Rolls-Royce (R-R) RB211-524H. “Engine on-wing work has been reduced for routine and non-routine maintenance with the increase of servicing and inspection intervals.”

As a heavy-maintenance provider, TIMCO reports that all 767 variants have performed well. “We’ve found this in traditionally problematic areas, as well as with the frequency and extent of non-routine [jobs].” LTMI confirms that maintenance increases with age, but has seen no “abnormal rise in findings,” with average engine on-wing of 18,000 to 22,000 FHs. SAL agrees, but notes one difference among customers: “End-of-lease aircraft tend to require a lot of work, while [customer-owned] aircraft will arrive in better overall condition.”

How well did 767 direct maintenance costs (DMCs) meet targets at entry into service (EIS) in 1982, and later on mature aircraft? Boeing’s Ali explains that 767 design was initiated in the days before deregulation in 1978, at a time when there were no specific maintenance-cost improvement targets.

“The 767 was certainly designed to get the lowest maintenance cost. Industry feedback has shown that the actual maintenance cost was lower than expected. We have seen a 20% reduction of airframe maintenance cost in the last 28 years. There have been continuous reductions due to [product] improvements, modifications, reliability of components, and the maintenance programame,” according to the maintenance-economics director.

What 767 developments arising from in-service experience have contributed most to reduced maintenance costs? Boeing attributes the greatest reduction to increased inspection intervals and fewer check tasks, a view endorsed by SAL. “Some new [work was] added to allow early detection and rectification of defects before costs became too high,” says Ali. “Another factor has been increased competition among [maintenance] suppliers and MROs [which] allows airlines to get the best possible cost without compromising reliability.”

The manufacturer acknowledges initial corrosion problems reported around the 767’s landing-gear pivot points and bushings – resolved by changes in bushing design, increased lubrication, and better greases and processes. “This resulted in significant reductions in [landing-gear] overhaul costs during the last 15 years.”

Operators very often have their own philosophies in dealing with incidental maintenance tasks, according to TIMCO’s Kazmerski. “Some drive significant find-and-fix events, mainly cabin-oriented, during overnight checks, [which] reduces the frequency of non-routine [jobs to be performed] during heavy visits. Others, drive by their respective reliability-analysis groups, tack on numerous [tasks] with shorter checks to prevent major issues during [heavy checks].”

LTMI says the extended check intervals reduced aircraft ground time and “enabled maintenance packages to be adjusted to [make] most efficient use of resources.” The MRO provides an example of investment in new equipment paying dividends.  “An installed fuel system was replaced with [one] from a different vendor. The new system is much more reliable and allows [the operator] to check the amount of loaded fuel after refueling.”

Overall, the 767 is not associated with a large volume of component change work, says SAL. “The issue of monitoring is more relevant, with the aircraft cabin being the most costly. An operator can achieve significant savings by ‘tweaking’ and staggering its cabin modifications and updates over the aircraft’s lifetime.”

What reduction in DMC can be expected by an operator replacing mature 767s with new (or much younger) 767s? One way to reduce airframe maintenance cost, of course, is to buy a new 767, for which Boeing says costs would “be less than half of a 25-year-old 767 (10-year average).” Other cost considerations for airlines replacing older fleets or converting passenger aircraft into freighters are said to include higher fuel-burn due to drag, engine deterioration, and weight increase. AA received its 767s in three distinct delivery batches, but variations in operational performance among these groups are “not statistically significant.” The airline confirms that operating cost and days lost to maintenance do increase, but “the operational performance is generally similar.”

A major positive for any operator, and an incentive to replace mature 767s with newer examples, is offered by SAL: “A younger 767 would avoid a Body Station 955 inspection and strut-improvement programme in the near future, both of which involve high costs and extended ground times.”

How do maintenance requirements differ among 767s powered by respective GE, P&W, or R-R powerplants? Boeing says that individual maintenance requirements do not vary greatly among 767s powered by the different engines available. “The routine inspections, filter replacements, and such like, are done at about the same intervals. Off-wing engine maintenance is performed in accordance with an operator’s approved maintenance programme, in conjunction with the respective engine OEM work-scope planning document,” says Ali.

Aveos perceives an unspecified advantage for Pratt & Whitney-powered aircraft, but “all [fare] pretty much the same” otherwise. TIMCO also sees no major differences. “Tooling availability can sometimes be an issue, depending on the scope of an operator’s maintenance programme,” says Kazmerski.

Documents covering 767 maintenance have also evolved over time, most obviously with digital technology replacing paperwork. ‘My Boeing Fleet’ has introduced Fleet Team Digests (FTD), a search engine useful when investigating non-routine tasks, reports Aveos. Maintenance training has evolved with tools such as computer-based training, a point also noted by El Al.

TIMCO says the “rules surrounding documentation of maintenance have remained stable,” with [customer] operators adding requirements for their specific fleets as regulatory requirements have dictated.” Many 767 maintenance-programme changes have been driven by factors applied to other aircraft types as well, according too Kazmerski.

On MRO 767 maintenance-training programmes, he says adjustments have been made “to the basic general familiarization courses as trend data has become available, or as regulatory changes have dictated.”

LTMI sees the switch from microfiche data as having been a milestone. “In addition, introduction of communication with Boeing internet and web-based training contributes to an improvement in quality.”

Similarly, SAL appreciates the changes: “Previously, it was up to the customer to supply the MRO provider with a large volume of paperwork to include every task card and associated service-bulletin documentation. Now, as Boeing has gone online, we can access all relevant materials for a project via the internet, on CD-Rom, or even directly via the customer’s own computer server.

“Our ability to access the work package early means that we can ensure [we are] fully prepared ahead of a maintenance event. Crucially, the customer is also saved a lot of work in advance of the aircraft’s arrival at the [maintenance] facility,” concludes SAL.