The Boeing 737-800 was launched in September 1994, earned FAA certification in March 1998 and first flew with Germany’s Hapag-Lloyd that same year. It became the biggest-selling member of the 737NG family and has been continually enhanced, for example with the option of blended winglets. The aircraft’s cabin also has had multiple upgrades.

At the start of this year, 3,831 -800s were flying; 383 more are due for delivery before year-end. Deliveries will continue at a similar pace though 2017, after which they will drop off sharply to barely 18 aircraft delivered in 2019. By the end of that year, more than 4,640 will have entered service.

One characteristic that makes the type popular with airlines is that hangar visits are less frequent and lengthy. In developing all 737NGs, Boeing aimed to reduce airframe maintenance cost by 15%, compared with 737 Classics.

Several innovations helped reduce MRO costs. NGs’ new wings have nearly one-third fewer parts than Classic wings. Its leading edge was also redesigned for easier maintenance. The main landing gear on NGs is simpler, and the time required for brake changes was cut by 30%. Access to many NG line replaceable units (LRUs) was made easier, and quick-disconnect line fittings were used wherever possible.

In addition, better ground-support equipment was provided, halving the time required for engine removal and installation. NG auxiliary power units were made easier to access and maintain, as were bays for electronics and other equipment. Boeing improved NGs’ built-in test equipment (BITE) user interfaces to reduce troubleshooting time and errors.

Boeing NGs use digital cabin-pressure controls instead of analog systems, reducing the number of mechanical parts. This redesign helped BITE more quickly identify problem LRUs or wiring defects, reducing troubleshooting time. BITE also cut this system’s mean time between unscheduled removals by three-quarters.

Another NG upgrade integrated stall management and yaw-damper computers in a single unit, improving reliability and reducing maintenance costs. On NG flight decks, Boeing enhanced systems, reliability, redundancy and BITE to increase mean time between failures by 62%.

Even though the 737-800s now require less maintenance, there are still a lot of them out there. Moreover, the first -800s have been flying for 18 years, so this next-generation aircraft is starting to become a senior jet, the kind that usually needs a little more care in the hangar. So maintenance of the 737-800—like that of the more popular members of the A320 family—is big business.

The upshot, according to Aviation Week’s MRO Prospector, is that the 737-800 will require about $31 billion in total MRO spending from the start of 2015 through the end of 2019. Of that, $2.1 billion, or less than 7%, will be spent on heavy airframe checks, with the vast majority of outlay for engines, components, line maintenance and modifications. The 737NGs are still, according to Boeing’s plan, stingy with the touch labor in C and D checks.

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