As it turned out, it was both, probably because the technology required for big-fan engines had yet to be proved for long-range, heavy aircraft. Six months later, in April 1992, the smaller A340-200 variant took to the skies, eventually beating its larger sibling into service by a month, in January 1993. Both variants have proved popular and, up to August 2005, some 244 had been ordered of which 236 are in service.

More recent demand for bigger aircraft has seen Airbus stretch the A340 design to its limits, both in size and weight. Its -600 variant is still the world's longest airliner at 75.3 meters (one inch shy of 247 feet) while the ultra-long-range -500 is the heaviest Airbus currently in service with a MTOW of 372 tonnes (820,000 lbs). In addition, the -500 and -600 have benefited greatly from the in-service experience gained by their older siblings and the large contribution that has been made to their evolved maintenance programs and longer check intervals.

One of the features of early A340s (and narrowbody A320s) was their central on-board maintenance system, which Christian Fremont, director of avionics systems for Airbus Customer Services Engineering, described as a "big step forward at the time," because predecessor aircraft, like the A300 and A310, had only basic test equipment to monitor on-board functions and no ground-desk connection to help line maintenance.

That said, the A310 had built-in test equipment (BITE) in 90% of its avionics systems, including a BITE connection from the auto-flight system to the maintenance test panel (MTP). According to Fremont, the A340 systems designers quickly saw the potential in extending MTP connections to all flight systems and collating their data centrally. The result was the Central Maintenance System (CMS), from which line engineers could test the aircraft systems from a single point in the cockpit.

"The A320 and A340 revolutionized system monitoring," said Fremont, "while on-board data-links allowed in-flight maintenance messages and warnings to be transmitted to the ground in real-time and compared against manuals and databases - the first step toward proactive and preventative maintenance."

Maintenance Program Evolution

When the A340 entered service in 1993, A-check intervals were baselined at 400 flight hours and C check intervals at 15 months. A checks were increased to 500 flight-hours in 1998 and subsequently increased to 600 flight-hours in 2002 when C checks were moved to 18-month intervals. Heavy-check intervals still remain at five years (4C check) and 10 years (8C check). However, because the A340-500 and -600 were introduced after these interval updates were approved, both variants benefited from the new intervals from their first days in service.

"When we applied to increase the A check intervals to 600 flight hours in 2002, we technically justified intervals of 700 flight hours," explained Christian Delmas, director maintainability and maintenance engineering for Airbus. "But, at that time, the aviation authorities who approve the MRB Report (Maintenance Review Board) said the 40% increase was too high. They preferred to wait until operators proved they gained experience with the smaller increase to 600 flight hours. In principle, this was not unreasonable, as the intervals published in the MRB Report apply from day one to any start-up operator."

Despite the cautious approach of the MRB, Airbus still believes greater A and C check intervals are possible and has proposed that the A340's C check intervals move to a "usage parameter" (UP) in 2007. Depending upon potential component degradation trends, the UP would be flight hours, flight cycles or calendar time. This move would be based upon an exercise Airbus carried out last year for the A320 family that specifically looked at changing its maintenance intervals from a letter interval to a UP concept.