737 Heavy Maintenance

One of the advantages of the 737 NG over the 737 Classic is that Boeing allow for intermediate base C checks before the D check to reduce the time, work and expense required at the D check. Operators that have a maintenance programme with a P48 check can have a base check interval of eight phases (hence the name P8), where one phase = 500FH, and so have six base checks in the base maintenance cycle. These will be P8, P16, P24, P32, P40 and P48 checks, often referred to as C1, C2, C3, C4, C5 and C6 checks. The P8 check will have an interval of 4,000FH and up to 18 months. The maintenance cycle will therefore have an interval of 24,000FH and up to nine years.

A typical P48 check or (D check) can take 20-30,000 man-hours, 2 months to complete and cost several million dollars. Most operators will also use opportunity of the D check to incorporate other tasks such as incorporating EO’s, AD’s, SB’s, changing or refurbishing the interior and making any desired modifications to the aircraft eg installing Satcom for on-board Wi-Fi, TCAS 7.1, FANS B+, etc.

In the photo above you can see from the inside of door 1L that the interior has been removed, the seats are on the right of the photo. The airstairs have been removed and are on trestles near door 1L. The engines were removed but have been reinstalled and some of the cowlings can be seen in a stack. There is a cherry-picker up to the fin which may be working on the rudder. The leading edge devices have bene removed. The main undercarriage has been removed for servicing as well.

In the article linked to here on 737NG maintenance, it looks at three different maintenance programs and summarises as follows:

“The three programmes collectively demonstrate that the 737NG has lower base maintenance requirements than the A320 family. The A320 utilises at least 10,000MH more and has higher associated material costs than the 737NG in its first base check. Moreover, the A320 has a shorter cycle interval. The 737NG has clearly benefited from a modern maintenance programme, the main advantage of which has been long check intervals.”

The interior during a D check

In the photo above, the seats have been removed showing the many floor panels. The black circle in the middle of the cabin floor is the main gear downlock viewer. Most of the sidewall panels have been removed to expose the insulation blankets (see photo below). The panels are made from a crushed-core composite and are purely for aesthetics.

A 737-800 during a P check in May 2017

Aircraft Commerce article on 737 NG maintenance programs here

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