Inspection and Maintenance - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 195

Table 13.5 Example of the inspection events of an airplane a

Time
Event

Interval Time on ground Man hours

Trip check Before every flight 35 min 0.5

Service check Weekly 4 h 20

A check 250 flight hours (4 weeks) 6 h 40

B check 900 flight hours (3 months) 12 h 150

C check 3,000 flight hours (12 months) 30 h 700

IL check b

First interval 12 500 flight hours (5 years)
Following interval 6,500 flight hours (3 years)

2 weeks 12,000

D check c First interval 25,000 flight hours (9 years)

Following interval 12,500 flight hours (5 years)

4 weeks 30,000

a

Designed in the 1970s and 1980s
b, c

The prime aim of the IL and the D check is the maintenance of the structure

Association (ATA) of America in 1980. Its forerunners, MSG-1 (1968) and
MSG-2 (1970), were used to encourage the industry to move away from the
overhaul mindset. The basic overhaul is done to almost everything on an airplane
at a fixed time interval, e.g., every 6 years. The MSG system has an engineering
plan that determines the most appropriate maintenance task and interval for an
aircraft's major components and structure [ 31 ].
The definitions of the most important elements are in the MSG-2 memorandum:

• Hard-Time limit (HT) which is the maximum interval for performing mainte-
nance tasks. The intervals usually apply to overhaul, but are also used for the
total life of parts;
• On Condition (OC) means repetitive inspections or tests to determine the con-
dition of systems or structural parts; and
• Condition Monitoring defines items that have neither ''Hard Time'' limits nor
''On Condition'' maintenance as their primary maintenance process. It is

responsible for finding and resolving problem areas [ 32 ].

13.3 Engine Deteriorations

An aircraft's lifespan is measured in pressurization cycles. An aircraft is pres-
surized during flight each time therefore, its fuselage and wings are stressed. In jet
engines, gas turbine compressor blades are easily affected by pollutants, water
droplets, and other particles in the air. Both are made of large, plate-like parts
connected with fasteners and rivets, and over time, cracks develop around the
fastener holes due to metal fatigue [ 33 ].
Erosion in the compressor and the carbonization of nozzles are the main sources
of wear in engines during flight (see. Fig. 13.7 ).