Aircraft Maintenance Practices

Cotter pins are used to secure such items as bolts, screws, pins, and shafts. They are used at any location where a turning or actuating movement takes place. The diameter of the cotter pin selected for any application should be the largest size that will fit consistent with the diameter of the cotter pin hole and/ or the slots in the castellated nut. Cotter pins, like safety wire, should never be re-used on aircraft. [Figure 2-94] Self-locking nuts are used in applications where they are not removed often. There are two types of self-locking nuts currently in use. One is all metal and the other has an insert, usually of fiber or nylon.

It is extremely important that the manufacturer’s Illustrated Parts Book (IPB) be consulted for the correct type and grade of lock nut for various locations on the aircraft. The finish or plating color of the nut identifies the type of application and environment in which it can be used. For example, a cadmium-plated nut is gold in color and provides exceptionally good protection against corrosion, but should not be used in applications where the temperature may exceed 450 °F. Repeated removal and installation causes the self-locking nut to lose its locking feature. They should be replaced when they are no longer capable of maintaining the minimum prevailing torque. [Figure 2-95] Lock washers may be used with bolts and machine screws whenever a self-locking nut or castellated nut is not applicable. They may be of the split washer spring type, or a multi-serrated internal or external star washer.

Pal nuts may be a second nut tightened against the first and used to force the primary nut thread against the bolt or screw thread. They may also be of the type that are made of stamped spring steel and are to be used only once and replaced with new ones when removed. Biplane Assembly & Rigging Biplanes were some of the very first aircraft designs. The first powered heavier-than-air aircraft, the Wright Brothers’ Wright Flyer, successfully flown on December 17, 1903, was a biplane. The first biplanes were designed with very thin wing sections and, consequently, the wing structure needed to be strengthened by external bracing wires. The biplane configuration allowed the two wings to be braced against one another, increasing the structural strength. When the assembly and rigging of a biplane is accomplished in accordance with the approved instructions, a stable airworthy aircraft is the Fine Thread Series Thread Size 7/16 - 20 1/2 - 20 9/16 - 18 5/8 - 18 3/4 - 16 7/8 - 14 1 - 14 1-1/8 - 12 1-1/4 - 12 8 inch-pounds 10 inch-pounds 13 inch-pounds 18 inch-pounds 27 inch-pounds 40 inch-pounds 55 inch-pounds 73 inch-pounds 94 inch-pounds Minimum Prevailing Torque Coarse Thread Series Thread Size 7/16 - 14 1/2 - 13 9/16 - 12 5/8 - 11 3/4 - 10 7/8 - 9 1 - 8 1-1/8 - 8 1-1/4 - 8 8 inch-pounds 10 inch-pounds 14 inch-pounds 20 inch-pounds 27 inch-pounds 40 inch-pounds 51 inch-pounds 68 inch-pounds Minimum Prevailing Torque locking nuts.

result. Whether assembling an early model vintage aircraft that may have been disassembled for repair and restoration, or constructing and assembling a new aircraft, the following are some basic alignment procedures to follow. To start, the fuselage must be level, fore and aft and laterally. The aircraft usually has specific leveling points designated 2-55 90° B1C1 C2B2D1 D2 A2A1 Firewall centerline Select easy-to-identify points from which to cross-measure. Reference point Vertical tail post (reference) Note • Make cross- measurements with a 50' steel tape. • Ideally, distances on both sides should match.

(A 1-A2 / B1-B2, etc.) Top view Rear view 90° CENTER SECTION 9 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 9 Distance “Y” same both sides Straight edge - clamp to firewall Fuselage centerline Level Top view Front view Z Z X X Plumb bob Ruler Distance “X” same both sides Both tie rods “Z” same length by the manufacturer or indicated on the plans. The fuselage should be blocked up off the landing gear so it is stable. A center line should be drawn on the floor the length of the fuselage and another line perpendicular to it at the firewall, for use as an additional alignment reference. With the horizontal and vertical tail surfaces installed, the incident angle for the horizontal stabilizer should be set.

The tail brace wires should be connected and tightened until the slack is removed. Alignment measurements should be checked as shown in Figure 2-96. Install the elevator and rudder and clamp them in a neutral position. Verify the neutral position of the control stick and rudder pedals in the flight deck and secure them in order to simplify the connecting and final tensioning of the control cables. If the biplane has a center section for the upper wing, it must be aligned as accurately as possible, because even the smallest error is compounded at the wing tip. Applicable cables and turnbuckles should be connected and the tension set as specified. [Figure 2-97] The stagger measurement can be checked as shown in Figure 2-98.

The lower wing sections should be individually attached to the fuselage and blocked up for support while the landing wires are connected and adjusted to obtain the dihedral called for in the specifications or plans. [Figure 2-99] Next, connect the outer “N” struts to the left and right sections of the lower wing. Now, the upper wing can be attached and the flying wires installed. The slave struts can be installed and the ailerons connected using the same alignment and adjustment procedures used for the elevator and rudder. The incidence angle can be checked, as shown in Figure 2-100. 2-56 Depicted angle 4° Spar Plumb bob Stagger Lower wing hinge fittings Plumb line Ruler Level aircraft Plumb bob Stagger measured in inches Measure upper wing dihedal Plumb bobs or weights X1 X2 Dihedal Spirit board levelTo increase dihedral shorten Lower winglanding wires dihedal in inches Measuring dihedral (in inches) Wood blocks Plumb bobs (2" x 4") or weightsUpper wing with 0° dihedal - string must touch blocks LandingX1 X2wires 4° 4° can also use Use straight edge dihedal board and bevel protractor with a level Measuring dihedral (angles) 4° 57" Note: A 1" rise in 57" equals one degree of dihedral 1 Chord line Make bottom parallel with Plywood chord line Make rib template to measure incidence of acrobatic type wings Aircraft must be level when checking incidence 2 Wing Incidence angle Bevel protractor Use straight edge for flat bottom airfoils (clark Y series, etc.) Measurement for angle of incidence Spirit Levellevel Straight edge aircraftChock wheels Once this point is reached, it is a matter of measuring, checking angles, and adjusting the various components to obtain the overall aircraft symmetry and desired alignment, as shown in Figure 2-96.

Also, remember that care should be used when tightening the wing wires because extra stress can be inadvertently induced into the wings. Always loosen one wire before tightening the opposite wire. Flying and landing wires are typically set at about 600 pounds and tail brace wires at about 300 pounds of tension. When convinced the aircraft is properly rigged, move away from it and take a good look at the finished product. Are the wings symmetrical? Does the dihedral look even? Is the tail section square with the fuselage? Are the wing attaching hardware, flying wires, and control cables safetied? And the final task, before the first flight, is to complete the maintenance record entries.

As with any aircraft maintenance or repair, the instructions and specifications from the manufacturer, or the procedures and recommendations found in the construction plans, should be the primary method to perform the assembly and rigging of the aircraft. 2-57 Aircraft Inspection Purpose of Inspection Programs The purpose of an aircraft inspection program is to ensure that the aircraft is airworthy. Per 14 CFR part 3, section 3.5, “airworthy” means the aircraft conforms to its type design and is in a condition for safe operation. By this definition and according to subsequent case law relating to the term and regulations for the issuance of a standard airworthiness certificate, there are two conditions that must be met for the aircraft to be considered airworthy: 1. The aircraft must conform to its type design or properly altered condition. Conformity to type design is considered attained when the aircraft configuration and the components installed are consistent with the drawings, specifications, and other data that are part of the type certificate (TC), which includes any supplemental type certificate (STC) and field approved alterations incorporated into the aircraft.

2. The aircraft must be in a condition for safe operation. This refers to the condition of the aircraft relative to wear and deterioration (e.g., skin corrosion, window delamination/crazing, fluid leaks, and tire wear beyond specified limits). When flight hours and calendar time are accumulated into the life of an aircraft, some components wear out and others deteriorate. Inspections are developed to find these items, and repair or replace them before they affect the airworthiness of the aircraft. Performing an Airframe Conformity & Airworthiness Inspection To establish conformity of an aircraft product, start with a TCDS. This document is a formal description of the aircraft, the engine, or the propeller. It is issued by the Federal Aviation Administration (FAA) when they find that the product meets the applicable requirements for certification under 14 CFR.

The TCDS lists the limitations and information required for type certification of aircraft. It includes the certification basis and eligible serial numbers for the product. It lists airspeed limits, weight limits, control surface movements, engine make and models, minimum crew, fuel type, etc.; the horsepower and rpm limits, thrust limitations, size and weight for engines; and blade diameter, pitch, etc., for propellers. Additionally, it provides all the various components by make and model, eligible for installation on the applicable product. A manufacturer’s maintenance information may be in the form of service instructions, service bulletins, or service letters that the manufacturer publishes to provide instructions for product improvement or to revise and update maintenance manuals. Service bulletins are not regulatory unless: 1. All or a portion of a service bulletin is incorporated as part of an airworthiness directive.

2. The service bulletins are part of the FAA-approved airworthiness limitations section of the manufacturer’s manual or part of the type certificate. 3. The service bulletins are incorporated directly or by reference into an FAA-approved inspection program, such as an approved aircraft inspection program (AAIP) or continuous aircraft maintenance program (CAMP). 4. The service bulletins are listed as an additional maintenance requirement in a certificate holder’s operations specifications (OpSpecs). Airworthiness directives (ADs) are published by the FAA as amendments to 14 CFR part 39, section 39.13. They apply to the following products: aircraft, aircraft engines, propellers, and appliances. The FAA issues airworthiness directives when an unsafe condition exists in a product, and the condition is likely to exist or develop in other products of the same type design.

To perform the airframe conformity and verify the airworthiness of the aircraft, records must be checked and the aircraft inspected. The data plate on the airframe is inspected to verify its make, model, serial number, type certificate, or production certificate. Check the registration and airworthiness certificate to verify they are correct and reflect the “N” number on the aircraft. Inspect aircraft records. Check current inspection status of aircraft, by verifying: • The date of the last inspection and aircraft total time in service. • The type of inspection and if it includes manufacturer’s bulletins.

• The signature, certificate number, and the type of certificate of the person who returned the aircraft to service. Identify if any major alterations or major repairs have been performed and recorded on an FAA Form 337, Major Repair and Alteration. Review any flight manual supplements (FMS) included in the Pilot’s Operating Handbook (POH) and determine if there are any airworthiness limitations or required placards associated with the installation(s) that must be inspected. Check for a current weight and balance report, and the current 2-58 equipment list, current status of airworthiness directives for airframe, engine, propeller, and appliances. Also, check the limitations section of the manufacturer’s manual to verify the status of any life-limited components.

Obtain the latest revision of the airframe TCDS and use it as a verification document to inspect and ensure the correct engines, propellers, and components are installed on the airframe. Required Inspections Preflight Preflight for the aircraft is described in the POH for that specific aircraft and should be followed with the same attention given to the checklists for takeoff, inflight, and landing checklists. Periodic Maintenance Inspections Annual Inspection With few exceptions, no person may operate an aircraft unless, within the preceding 12 calendar months, it has had an annual inspection in accordance with 14 CFR part 43 and was approved for return to service by a person authorized under section 43.7. (A certificated mechanic with an Airframe and Powerplant (A&P) rating must hold an inspection authorization (IA) to perform an annual inspection.) A checklist must be used and include as a minimum, the scope and detail of items (as applicable to the particular aircraft) in 14 CFR part 43, Appendix D.

100-hour Inspection This inspection is required when an aircraft is operated under 14 CFR part 91 and used for hire, such as flight training. It is required to be performed every 100 hours of service in addition to the annual inspection. (The inspection may be performed by a certificated mechanic with an A&P rating.) A checklist must be used and as a minimum, the inspection must include the scope and detail of items (as applicable to the particular aircraft) in 14 CFR part 43, Appendix D. Progressive Inspection This inspection program can be performed under 14 CFR part 91, section 91.409(d), as an alternative to an annual inspection. However, the program requires that a written request be submitted by the registered owner or operator of an aircraft desiring to use a progressive inspection to the local FAA Flight Standards District Office (FSDO). It shall provide: 1. The name of a certificated mechanic holding an inspection authorization, a certificated airframe repair station, or the manufacturer of the aircraft to supervise or conduct the inspection.

2. A current inspection procedures manual available and readily understandable to the pilot and maintenance personnel containing in detail: • An explanation of the progressive inspection, including the continuity of inspection responsibility, the making of reports, and the keeping of records and technical reference material. • An inspection schedule, specifying the intervals in hours or days when routine and detailed inspections will be performed, and including instructions for exceeding an inspection interval by not more than 10 hours while en route, and for changing an inspection interval because of service experience.

• Sample routine and detailed inspection forms and instructions for their use. • Sample reports and records and instructions for their use. 3. Enough housing and equipment for necessary disassembly and proper inspection of the aircraft. 4. Appropriate current technical information for the aircraft. The frequency and detail of the progressive inspection program shall provide for the complete inspection of the aircraft within each 12 calendar months and be consistent with the manufacturer’s recommendations and kind of operation in which the aircraft is engaged. The progressive inspection schedule must ensure that the aircraft will be airworthy at all times. A certificated A&P mechanic may perform a progressive inspection, as long as they are being supervised by a mechanic holding an Inspection Authorization.

If the progressive inspection is discontinued, the owner or operator must immediately notify the local FAA FSDO in writing. After discontinuance, the first annual inspection will be due within 12 calendar months of the last complete inspection of the aircraft under the progressive inspection. Large Airplanes (over 12,500 lb) Inspection requirements of 14 CFR part 91, section 91.409, to include paragraphs (e) and (f). Paragraph (e) applies to large airplanes (to which 14 CFR part 125 is not applicable), turbojet multiengine airplanes, turbo propeller powered multiengine airplanes, and turbine- powered rotorcraft. Paragraph (f) lists the inspection programs that can be selected under paragraph (e).

The additional inspection requirements for these aircraft are 2-59 placed on the operator because the larger aircraft typically are more complex and require a more detailed inspection program than is provided for in 14 CFR part 43, Appendix D. An inspection program must be selected from one of the following four options by the owner or operator of the aircraft: 1. A continuous airworthiness inspection program that is part of a continuous airworthiness maintenance program currently in use by a person holding an air carrier operating certificate or an operating certificate issued under 14 CFR part 121 or 135.

2. An approved aircraft inspection program approved under 14 CFR part 135, section 135.419, and currently in use by a person holding an operating certificate issued under 14 CFR part 135. 3. A current inspection program recommended by the manufacturer. 4. Any other inspection program established by the registered owner or operator of the airplane or turbine- powered rotorcraft and approved by the FAA. This program must be submitted to the local FAA FSDO having jurisdiction of the area in which the aircraft is based. The program must be in writing and include at least the following information: (a) Instructions and procedures for the conduct of inspections for the particular make and model airplane or turbine-powered rotorcraft, including the necessary tests and checks. The instructions and procedures must set forth in detail the parts and areas of the airframe, engines, propellers, rotors, and appliances, including survival and emergency equipment, required to be inspected.

(b) A schedule for performing the inspections that must be performed under the program expressed in terms of the time in service, calendar time, number of system operations (cycles), or any combination of these. This FAA approved owner/operator program can be revised at a future date by the FAA, if they find that revisions are necessary for the continued adequacy of the program. The owner/operator can petition the FAA within 30 days of notification to reconsider the notice to make changes. Manufacturer’ s Inspection Program This is a program developed by the manufacturer for their product. It is contained in the “Instructions for Continued and including, but not limited to, the following content: • A description of the airplane and its systems and installations, including its engines, propellers, and appliances.

• Basic information describing how the airplane components and systems are controlled and operated, including any special procedures and limitations that apply. • Servicing information that covers servicing points, capacities of tanks, reservoirs, types of fluids to be used, pressures applicable to the various systems, lubrication points, lubricants to be used, equipment required for servicing, tow instructions, mooring, jacking, and leveling information. • Maintenance instructions with scheduling information for the airplane and each component that provides the recommended periods at which they should be cleaned, inspected, adjusted, tested, and lubricated, and the degree of inspection and work recommended at these periods.

• The recommended overhaul periods and necessary cross references to the airworthiness limitations section of the manual. • The inspection program that details the frequency and extent of the inspections necessary to provide for the continued airworthiness of the airplane. • Diagrams of structural access plates and information needed to gain access for inspections when access plates are not provided. • Details for the application of special inspection techniques, including radiographic and ultrasonic testing where such processes are specified. • A list of special tools needed. • An Airworthiness Limitations section that is segregated and clearly distinguishable from the rest of the document. This section must set forth: 1. Each mandatory replacement time, structural inspection interval, and related structural inspection procedures required for type certification or approved under 14 CFR part 23 or part 25.

2. Each mandatory replacement time, inspection interval, related inspection procedure, and all critical design configuration control limitations approved under 14 CFR part 23 or part 25, for the fuel tank system. Airworthiness” required under 14 CFR part 23, section 23.1529 The Airworthiness Limitations section must contain a and part 25, section 25.1529. It is in the form of a manual, or legible statement in a prominent location that reads: “The manuals as appropriate, for the quantity of data to be provided Airworthiness Limitations section is FAA-approved and 2-60 specifies maintenance required under 14 CFR part 43, sections 43.16 and part 91, section 91.403, unless an alternative program has been FAA-approved.” Any operator who wishes to adopt a manufacturers’ inspection program should first contact their local FAA Flight Standards District Office, for further guidance.

Altimeter & Static System Inspections in Accordance with 14 CFR Part 91, Section 91.411 Any person operating an airplane or helicopter in controlled airspace under instrument flight rules (IFR) must have had, within the preceding 24 calendar months, each static pressure system, each altimeter instrument, and each automatic pressure altitude reporting system tested and inspected and found to comply with 14 CFR part 43, Appendix E. Those tests and inspections must be conducted by appropriately rated persons under 14 CFR. Air Traffic Control (ATC) Transponder Inspections Any person using an air traffic control (ATC) transponder must have had, within the preceding 24 calendar months, that transponder tested and inspected and found to comply with 14 CFR part 43, Appendix F, and part 91, section 91.411.

Additionally, following any installation or maintenance on an ATC transponder where data correspondence error could be introduced, the integrated system must be tested and inspected and found to comply with 14 CFR part 43, Appendix E, and part 91, section 91.411 by an appropriately rated person under 14 CFR. Emergency Locator Transmitter (ELT) Operational & Maintenance Practices in Accordance with Advisory Circular (AC) 91-44 This AC combined and updated several ACs on the subject of ELTs and receivers for airborne service. Under the operating rules of 14 CFR part 91, most small U.S. registered civil airplanes equipped to carry more than one person must have an ELT attached to the airplane. 14 CFR part 91, section 91.207 defines the requirements of what type aircraft and when the ELT must be installed. It also states that an ELT that meets the requirements of Technical Standard Order (TSO)-C91 may not be used for new installations.

The pilot-in-command of an aircraft equipped with an ELT is responsible for its operation and, prior to engine shutdown at the end of each flight, should tune the VHF receiver to 121.5 MHz and listen for ELT activations. Maintenance personnel are responsible for accidental activation during the actual period of their work. Maintenance of ELTs is subject to 14 CFR part 43 and part 91, section 91.413 and should be included in the required inspections. It is essential that the impact switch operation and the transmitter output be checked using the manufacturer’s instructions. Testing of an ELT prior to installation or for maintenance reasons, should be conducted in a metal enclosure in order to avoid outside radiation by the transmitter. If this is not possible, the test should be conducted only within the first 5 minutes after any hour.

Manufacturers of ELTs are required to mark the expiration date of the battery, based on 50 percent of the useful life, on the outside of the transmitter. The batteries are required to be replaced on that date or when the transmitter has been in use for more than 1 cumulative hour. Water activated batteries, have virtually unlimited shelf life. They are not usually marked with an expiration date. They must be replaced after activation regardless of how long they were in service. The battery replacement can be accomplished by a pilot on a portable type ELT that is readily accessible and can be removed and reinstalled in the aircraft by a simple operation.

That would be considered preventive maintenance under 14 CFR part 43, section 43.3(g). Replacement batteries should be approved for the specific model of ELT and the installation performed in accordance with section 43.13. AC 91-44 also contains additional information on: • Airborne homing and alerting equipment for use with ELTs. • Search and rescue responsibility. • Alert and search procedures including various flight procedures for locating an ELT. • The FAA Frequency Management Offices, for contacting by manufacturers when they are demonstrating and testing ELTs. Although there is no regulatory requirement to install a 406 ELT, the benefits are numerous, regardless of regulatory minimums. All new installations must be a 406 MHz digital ELT. It must meet the standards of TSO C126. When installed, the new 406 MHz ELT should be registered so that if the aircraft were to go down, search and rescue could take full advantage of the benefits the system offers. The digital circuitry of the 406 MHz ELT can be coded with information about the aircraft type, base location, ownership, etc. This coding allows the search and rescue (SAR) coordinating centers to contact the registered owner or operator if a signal is detected to determine if the aircraft is flying or parked. This type of identification permits a rapid SAR response in the event of an accident, and will save valuable resources from a false alarm search.

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