JUSTIN WASTNAGE / LONDON
DATA COMPILED BY BRANDON NOTHNAGEL
The advent of digital technology has made aircraft maintenance faster and cheaper
Fly-by-wire technology is considered by many to be the single biggest advance in aviation of the last two decades. Like other major advances in technology - the jet engine, supersonic flight - the shift to electronics has required a step change in the way aircraft are maintained.
In the early 1970s Pan American Airways had teams of 40 ready to complete line maintenance on its fleet of Boeing 747-100s. Today, four people can complete the same level of checks on Airbus A340-600s. Meanwhile, Boeing Next generation 737s require 30% less maintenance than their Classic brothers.
As a result, maintenance, repair and overhaul (MRO) facilities, the largest of which are still owned by the major airlines, now rationalise how they organise their teams to deliver much quicker turnaround times for aircraft. Reducing delays due to technical faults is key to delivering satisfied customers, says Thor Johansen, Boeing's technical director for Europe. Design changes that allow MROs to cut the man hours spent on each aircraft also deliver cost savings for the airlines.
In general terms, the number of people employed per aircraft in maintenance has been halved. Airlines are approaching 4h of maintenance time for every hour flying, compared with 8h 20 years ago. This means the average short-haul aircraft now spends 12h a day in the air, compared with 10h in 1980.
Thanks to advances in aircraft technology, the world's MROs have clearly achieved huge productivity gains. Part of this stems from far better data exchange between the manufacturers and maintenance facilities. Much data is gleaned from aircraft accidents. The Aircraft Accident Investigation Branch (AAIB) of the UK's transport ministry says that pinpointing any technical fault with an aircraft involved in an incident has been made simpler by the vast wealth of data available. However useful this centralised maintenance check may be to airlines, Airbus says it is purely "a useful tool", but "no substitute for MROs".
The flight data recorder of a 737-800 records more than 7,000 parameters - compared with seven parameters mandated by the AAIB and its counterparts. This is based on the standard altitude, engine thrust and temperature readings available on 1970s aircraft designs, many of which still fly. When data was still etched onto silver foil tachographs, weight was a prohibitive factor. Advances in silicon technology have increased the feasibility of recording minute details, but most data is sent back by accident investigators to the original equipment manufacturer for analysis. Manufacturers know within weeks of an incident any areas of weakness on the fuselage and can request additional checks on these points in worldwide fleets.
Consistent feedback
Boeing customers have also contributed to design enhancements. Norway's Braathens operates in far harsher conditions than the Seattle-based engineers envisaged. Large deposits of grit and sand required to keep runways clear of ice in some of Norway's further extremities led to faster undercarriage corrosion for Braathens' 737s than for most other airlines.
Norwegian engineers advised the Boeing team on repositioning the corrosion prevention units, using different compounds and thinning the components to allow them to be slid into tighter corners. Boeing used the resulting design changes to swing a deal with Alaska Airlines.
Similarly, Bombardier had consistent feedback from its early CRJ100 customers on the positioning of access points to certain junction boxes in the forward fuselage. Servicing required hours of extra manpower to remove panels prior to simple checks, but the company "learned vital lessons" and changed the design on later aircraft, says Jim Sorokan, Bombardier's director of airline support analysis.
Advances in aircraft structural technology have also occurred, making heavy maintenance easier. Airbus points to extended fatigue testing, which allows it to predict weak spots in fuselages and recommend remedies ahead of time. Boeing, which uses fewer composite materials on its aircraft than its European rival, has, over 40 years, built a comprehensive database of aluminium crack patterns for its aircraft. MROs use these statistics to strengthen joints ahead of time.
Airlines with long-term maintenance contracts with General Electric and other engine makers can have regular servicing while the engine is on the wing, reducing the time each aircraft spends out of action.
More mundane aspects of MRO work are also being speeded up. Plastics conglomerate 3M, for example, has developed a polymer film that can be applied in place of paint. Applying this film cannot only be done in a third of the time typically taken to paint a widebody, but it can also reduce drag. Even conservative estimates provided by Singapore Airlines, which has one such coated airliner, point to drag reductions of 0.5%. This could save up to $300,000 for its long-haul fleet over the five-year life of a coat of paint.
Change of emphasis
Boeing's Johansen says that airlines have driven a shift from proscribed deadlines for several maintenance checks, or "hard time" to what he calls reliability-centred maintenance: "Typically, 20% of an airline's maintenance programme is now customised to its own conditions." A new methodology to checking components, permitted under chapter three of the US FAA maintenance steering group recommendations of the mid-1980s, uses predictions and data from centralised maintenance systems to monitor the condition of individual units. Rather than having to remove components and overhaul them after a specified time, MROs can do bench tests on components and check them against OEM performance targets to ensure airworthiness. Bench tests can take as little as 2h and can be done on an overnight stop, rather than the aircraft having to return to the hangar for a 7h check.
Changes in work practice, too, have passed time savings on to the MROs. Boeing has moved to zonal practices,placing the responsibility for every check in a certain part of the aircraft to one team, rather than different teams working through the aircraft carrying out thesame checks.
Similarly, complete integration of corrosion checkers and heavy maintenance teams have saved duplication of effort. Equally, only critical components, such as landing gear and flight control balancing now require a second signature at time of inspection, as the aircraft is double checked by a team leader, who holds responsibility for the entire aircraft.
Bombardier, meanwhile, has found that among US regionals, where staff turnover is high, technical dispatch reliability has suffered. To counter some lack of experience, Bombardier has developed (with Atlantis Aerospace) intuitive software called Spotlight which guides engineers through a series of questions until any glitch is found. The system is being beta-tested by airlines including Northwest Airlines and Air Canada on their CRJ fleets to improve check consistency.
Bombardier, whose regional jets typically operate much shorter cycle times than their mainline counterparts, have specifically engineered their aircraft to handle the stress demands of 1h cycles on landing gear. It has developed completely interchangeable parts across its product range, so smaller operators can maintain to the same standards as flag carriers.
Source: Flight International
