By the end of this year there will be more than 5,000 of the world’s most popular aircraft, the Boeing 737-800, in service.

Aviation Week Network’s Commercial Aviation Fleet & MRO Forecast also predicts that 737-800 num

This is obviously great news for maintenance providers, which receive a steady stream of work from an aircraft produced in consistently high numbers for almost two decades.

“The 737NG fleet is large and drives a lot of maintenance requirements,” Troy Jonas, vice-president, global sales and marketing for US MRO provider AAR, tells Inside MRO, adding: “It has and will continue to drive a significant share of MRO requirements for the foreseeable future.”

Aviation Week Network expects the maintenance market for all 737 types to reach $21.7 billion in 2018. Of that total, 41% is for component work, 27% for engine maintenance, 22% for line maintenance, 5% for airframe work and 5% for modifications.

Most of that MRO demand is for the 737-800, which will provide $14.7 billion of maintenance value in 2018, rising to almost $16.6 billion in 2022.

Lithuanian MRO provider FL Technics reports that 737NGs entering its hangars are on average 9.5 years old, the age when aircraft of that type approaching their first heavy check.

Common faults found during such checks are vapor barrier cracking and corrosion near wet areas such as galleys and lavatories.

“Cracks are often found in the wing root structure and they require reinforcing repair involving repairs to the fuel tank structure,” says Kestutis Jasutis, head of production planning, base maintenance, FL Technics.

One of the most time-consuming aspects of 737 heavy checks is fuel tank inspections, which require “many hours to remove the sealant inside the fuel tanks so we can access the structure to do both visual and NDT inspections”, says Jonas.

“The irony is it takes all that effort but we very rarely find defects –it’s just part of the inspection requirements.”