What's This 'A' Check, 'C' Check Stuff?

What's This 'A' Check, 'C' Check Stuff? Aircraft inspections defined By Jack Hessburg April 2000 Jack Hessburg has over 40 years experience in aircraft maintenance. He is recently retired from The Boeing Co. where he served as...

• Visually check flight compartment escape ropes for condition and security
• Check operation of DC bus tie control unit
• Visually check the condition of entry door seals
• Operationally check flap asymmetry system
• Pressure decay check APU fuel line shroud
• Inspect engine inlet TAI ducting for cracks
• Operationally check RAT deployment and system 'D' check: This can also be referred to as the Structural check. It includes detailed visual and other non-destructive test inspections of the aircraft structure. It is an intense inspection of the structure for evidence of corrosion, structural deformation, cracking, and other signs of deterioration or distress and involves extensive disassembly to gain access for inspection. Special equipment and techniques are used. Structural checks are man-hour and calendar-time intensive. The 'D' check includes the lower checks, i.e. 'A,' 'B,' 'C,' and Daily checks. This check removes the airplane from service for 20 or more days. Examples of 'D' check items include:

• Inspect stabilizer attach bolts
• Inspect floor beams
• Detailed inspection of wing box structure

There are variations of block maintenance. One of those variations is called a phase check — don't be confused by the variety of names. The number of scheduled maintenance tasks for a large airplane like the 747 are extensive, and this is particularly true for the higher 'C' and 'D' checks. Their accomplishment can remove the airplane from service for several weeks. This is considered unacceptable as it defeats the concept of removing the airplane from service in small, manageable blocks. One solution is to divide these higher checks into segmented blocks or phases.

A typical phase check provides for a thorough visual inspection of specified areas, components, and systems as well as operational or functional checks of specified components and systems. Each check includes the requirements of traditional lower check work items and portions of 'C' and 'D' checks at the required task intervals.

Phase checks are typically accomplished at 200 to 800 flight-hour intervals, depending upon the work packaging plan and other airline operating variables.

Block maintenance is further modified when examining the special requirements of high-time/high-cycle airplanes. Older airplanes have increased maintenance tasks defined. This includes supplemental structural inspections, corrosion control programs, and aging system checks.

Executive and VIP airplanes have low utilization and represent another variation of block concepts. Task, intervals and blocks defined by the MRB are based upon the higher utilization levels of air carrier operations. They don't work for VIP airplanes. Consequently, separate packages are developed for VIP airplanes that are predominantly based upon calendar time.

Contemporary practice removes the packaging of maintenance tasks from the MRB process. When a MSG analysis is conducted only the tasks and intervals are identified. The packaging into manageable blocks is left to the operator of the airplane.

Check packages
The final item is to prepare a check package that bundles mandatory and discretionary maintenance tasks.

Mandatory tasks include:
• The scheduled check (example and 'C' check)
• AD Note accomplishment
• Certification Maintenance Requirement (CMR) inspections
• Clearance of deferred maintenance (MEL) items
• Hard time changes including such items as time/cycle-controlled or life-limited parts
• Ad Hoc maintenance such as corrosion control, structural repair, system repairs, component removal and replacement
• Special operator or manufacturer initiated inspections

Discretionary tasks include:
• Service Bulletin accomplishment to improve departure reliability
• Installing passenger acceptance, appearance, and convenience items or cost reduction items
• Sampling inspections to gather data for check escalations etc.
• Component replacement for convenience
• Replacement of Configuration Deviation List (CDL) items

Return to service The completed check package is gathered together and all the task cards, reference materials, and parts are shipped out to the hangar. The mechanics do their checks and repairs, and the airplane is returned to service.

Packaging is detailed, and there are many variations of the concept. Understanding is further complicated by the fact that packaging concepts have evolved over the past 50 years. Once an airplane uses a given packaging scheme, it is rarely changed to a more advanced technique.

Remember that blocks have numerous other names within the maintenance community, so don't let this confuse you. The exact nomenclature, composition, and number of blocks vary between operators. Thus, the maintenance packaging program for an A-340 or 777 is different from that followed by a 727/DC-8 generation airplane.

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