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  • Writer's pictureSunil Rawat

Aircraft Manufacturer’s Documentations (Manuals) for Maintenance

Airplane Maintenance Manual (AMM)

The airplane maintenance manual (AMM) is a formal document containing all the basic information on the operation and maintenance of the aircraft and its on-board equipment.

It starts with an explanation of how each system and sub- system works (detailing description and operation) and describes such basic maintenance and serving actions as removal and installation of LRUs and various tests performed on the system and equipment, such as functional test, operational check, adjustments, the replenishing of various fluids, and other servicing tasks.

Fault Isolation Manual (FIM) / Trouble Shooting Manual (TSM)

The FIM/TMS contains a set of fault isolation trees provided by the aircraft manufacturer to help troubleshoot, isolate the section where the fault occurred, and identify and pinpoint problems related to various systems and components on the aircraft.

The aircraft faults system normally shows the fault occurrence at the flight deck on the engine-indicating and crew-alerting system (EICAS) message screen or Electronic Centralized Aircraft Monitor (ECAM).

The EICAS/ECAM shows faults in a yellow/amber colour, which alerts the flight crew that a fault has occurred.

The FIM is a block diagram that provides a reference to AMM tasks and sub-tasks. At the end of each task, it will ask, “Is the fault removed?”

The AMT must follow the subsequent arrows indicating Yes or No to further troubleshoot. If no further maintenance is required, the discrepancy has been resolved and no further action needs to be taken. The flow diagram is designed to locate many but not all problems within the various systems.

Schematic diagram manual (SDM)

The SDM contains schematic diagrams of electrical, electronic, and hydraulic systems on the aircraft, as well as logic diagrams for applicable systems. The diagrams in the AMM and other manuals are usually simplified diagrams to aid in describing the system and assist in troubleshooting.

The schematic manual, however, contains the detailed information and identifies wiring harnesses, connectors, and interfacing equipment.

Wiring diagram manual (WDM)

The WDM is an essential tool for troubleshooting. The WDM provides information on the wiring runs for all systems and components containing such elements. Due to the complexity of the modern aircraft and its electrical system, such control devices as gauges and sensors provide and relay information to the flight deck in a complicated network of wiring runs like a network system.

The WDM shows the wire routing from the aircraft’s nose to tail and from other sections to different connectors, on-board sensors, and control devices. Normally wires that are routed in bundles from the airframe side of the aircraft are also shown in the WDM.

The wiring harness is a type of wiring bundle as well, but when referring to the wiring harness, we usually are referring to the power side of the aircraft. The wiring harness normally is connected to a fire wall, which is a connection point from the engine wire harness to the aircraft airframe system.

When removing the aircraft engine, the wiring harness (bundle) stays with the aircraft engine, and only the cannon plugs are disconnected from the fire wall. (Cannon plugs are the ends of the wire bundles or harnesses where all the wires are connected by pins that provide electric current to the system when initiated).

Wire harnesses are easy to repair and troubleshoot since they do not exceed more than a few feet in length, versus the aircraft airframe side of the wires, which can be hundreds of feet in length, depending on their routing. (Wiring harness concepts are also used for automobile radios and other equipment, which makes for easy installation and troubleshooting.)

Aircraft wires are normally made from standard copper, and in some cases they are coated with different alloys to prevent corrosion.

Due to the large amount of current required for carrying longer distances, aluminum wire is frequently used. Normally it is insulated by a fiberglass braid.

Aircraft wire is measured in the American Wire Gauge (AWG) system and the largest number represents the smallest wire.

The following is an example of the AWG system found in the WDM: *** K15B-25 *** K → Alphabet letter—System in which a wire is being used 15 → Two-digit number—Individual wire number B → Alphabet letter—Wire segment/section of wire power source 25 → Two-digit number—Wire size (AWG size)

Unfortunately, there is no set standard for wire identification by the aircraft manufacturers, but there are markings on aircraft wire every 15 inches or less that indicate a wire’s location and type of circuit, which can be found in the WDM.

Illustrated parts catalog (IPC)

The IPC is produced by the airframe manufacturer and includes list and location diagrams of all parts used on the aircraft.

This includes all parts for all systems and is usually not customized to the airline’s configuration. However, when the aircraft is customized it will show parts by figure, part number, and item number with aircraft applicability.

Every aircraft is given a serial number, along with an aircraft registration number, which is used in the IPC for affectivity reason when searching for a part by using the ATA chapters.

The IPC shows assemblies, subassemblies, alternate part numbers, and part inter- changeability along with any modifications if performed on parts by the service bulletin, the IPC will show these parts as pre- or postmodification.

Structural repair manual (SRM)

The SRM is an airframe-specific manual that provides the aircraft operator with information regarding aircraft skin and other specific tolerances and procedures in the event of minor structural damage.

The SRM gives the acceptable dimensions and limits of damage to the aircraft structure so the operator knows when the damage should be fixed.

For example, when an aircraft incurs damage such as a dent, usually the dent is measured in by its depth and in relation to its surrounding area to make sure there is no damage to the ribs area and to check for any evidence of a crack.

The operator then looks into the SRM for the area where the dent is located on the aircraft to see if it will be a minor or a major repair. The SRM provides the damage tolerance which will determine if the aircraft can fly with a minor dent that can be repaired later. The SRM will also indicate the number of hours the aircraft can fly with the dent.

There are some damages beyond SRM limits, and the maintenance department will have to contact engineering in order for specific repair schemes to be issued. If the damages are beyond SRM limits, the airline engineering department is in contact with the aircraft manufacturer’s engineers.

The repair is usually done by using an engineering order (EO) that will guide the aircraft maintenance department and inspection department on how to repair and sign off, bringing the aircraft back to an airworthy condition.

Component Maintenance Manuals (CMM)

Any component built by the airframe manufacturer will be accompanied by a component maintenance manual (CMM) written by the manufacturer.

Normally, the aircraft manufacturers make the aircraft, while other systems, such as engines, landing gears, flight crew seats, and passenger seats, are purchased from outside vendors, but when the aircraft manufacturer sells the aircraft, the other vendors’ CMMs accompany these items, in case parts need to be repaired or replaced.

The CMM shows the breakdown of all components that make a complete part. The components installed on the aircraft are chosen by the airlines and are installed during or after the aircraft is completed.

Storage and Recovery Document (SRD)

The SRD contains information needed to address maintenance and servicing of aircraft that are to be out of service and stored for long periods of time.

This includes the procedures for draining certain fluids, moving the aircraft so that tires will not go flat, and protecting components from the weather. In the older model aircraft, this document was produced separately by the airframe manufacturer.

Maintenance Planning Document (MPD)

This document provides the airline operator with a list of maintenance and servicing tasks to be performed on the aircraft.

It contains all items of the Maintenance Review Board (MRB) report along with other information. Some of these tasks are identified as certification maintenance requirements (CMRs) and are required by the FAA in order to maintain certification of the aircraft.

All other tasks, which were developed by the Maintenance Steering Group (MSG) process are included along with other tasks recommended by the manufacturer.

The tasks are divided into various groupings for older aircraft models—daily, transit, letter checks, hourly limits, and cycle limits—and are used for planning purposes by the airline. Later models do not group the tasks by letter checks, only by hours, cycles, and calendar time.

Component location manual (CLM)

The CLM provides the location of all the major equipment items of the aircraft. Normally, AMTs know how to locate a component when replacing it, but the CLM is a great tool for finding the part number of the component and its location as well.

Master minimum equipment list (MMEL)

The MMEL is issued by the airframe manufacturer and developed by the manufacturer’s flight engineering group.

Prior to issuing the MMEL, the aircraft manufacturer submits a proposed master minimum equipment list (PMMEL) to the type certificate office of the aircraft manufacturing country. Once it is approved by the authority it becomes an MMEL.

The MMEL is used to identify the equipment that may be degraded or inoperative at the dispatch time of the aircraft. These are the systems that the flight crew, under certain circumstances, may agree to accept at dispatch in degraded or inoperative condition, provided the system is fixed within the prescribed time limit set by the MMEL.

The MMEL contains information on all equipment available on the aircraft model to which it applies. It is the airline’s responsibility to develop its own manual tailored to its specific equipment. This document, called the MEL.

Dispatch Deviation Guide (DDG)

Some of the MMEL items that are inoperative or degraded at dispatch require maintenance action prior to the deferral and dispatch. This may be the need to pull and placard certain circuit breakers, disconnect power, tie up loose cables for removed equipment, and various other actions to secure the aircraft and the system against inadvertent operation.

The instructions necessary for these actions are provided in the DDG. This guide is written by the manufacturer’s AMM staff and is coordinated with the MMEL.

Configuration deviation list (CDL)

The CDL is similar to the DDG but involves configuration of the aircraft rather than the aircraft’s system and equipment. The CDL identifies any external part of an aircraft’s panels, gear doors, flap hinge fairings, cargo doors, and all door indication and warning systems. These items could have been inoperative, cracked, broken, or missing.

Normally, these items are discovered during the line checks or at pre- or post flight checks of the day. The CDL items do not affect the airworthiness and safety of the aircraft, and scheduled flight operation can be resumed. Some CDLs, when applied or issued, may have icing conditions or flight speed restrictions (e.g., gear door, flap hinge fairing, etc.).

The CDL system normally has category C placement, where it needs to be fixed in 10 flight days, excluding the day of discovery. This cycle of repair is customized by the aircraft operator.

Nonessential equipment and furnishing (NEF) items

The NEF contains the most commonly deferred items, such as paneling (flight deck, cabin), cup holders, missing paint off panel in flight deck or cabin area— cosmetic items which could be broken, cracked, chipped, or missing. NEF items are located throughout the aircraft and do not affect the safety or airworthiness of the aircraft.

The NEF uses a deferral program customized from the MMEL as a basis for air carriers to develop their air carrier-specific items. NEF items do have a tran- sitioning period or a repair interval, which means that they must be fixed at the first available opportunity, depending on parts availability, or no later than what is described in the NEF manual, which normally does not exceed the next A check.

Task cards (TC)

Certain tasks in the AMM for removal/installation, testing, servicing, and similar maintenance items are extracted from the AMM and produced on separate cards or sheets so that the mechanic can perform the action without carrying the entire maintenance manual to the aircraft.

These task cards can be used “as is” or they can be modified by the operator for reasons discussed in the section Airline-Generated Documentation.

Service bulletins, service letters, and maintenance tips

Whenever the airframe manufacturer or the engine manufacturer have modifications or suggestions for improving maintenance and/or servicing, they issue appropriate paperwork to the affected airlines.

A service bulletin (SB) is usually a modification of a system that will provide improved safety or operation of a system and includes a detailed description of the work and parts required.

An SB is usually optional and the airline makes the choice, except in certain cases involving an FAA airworthiness directive (AD) which is mandatory.

A service letter (SL) usually provides information to improve maintenance actions without equipment modification.

The maintenance tip is a suggestion for maintenance personnel to assist in their work or improve conditions.

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