Par 12-58 Page 12-22
d. After 1 minute, check to see that the leak has not exceeded the equivalent of 100 ft of altitude (decrease in differential pressure of approximately 0.0105 inHg or 1.43 inches of water).
12-59. TEST PITOT SYSTEM. Tests should be in accordance with the aircraft manufacturer’s instructions. If the manufacturer has not issued instructions for testing pitot systems, the following may be used:
a. Seal the drain holes and connect the pitot pressure openings to a tee to which a source of pressure and manometer or reliable indicator is connected.
b. Restrain hoses that can whip due to applied pressure.
c. Apply pressure to cause the airspeed indicator to indicate 150 knots (kts) (differential pressure 1.1 inHg or 14.9 inches of water), hold at this point and clamp off the source of pressure. After 1 minute, the leakage should not exceed 10 kts (decrease in differential pressure of approximately 0.15 inHg or 2.04 inches of water).
CAUTION: To avoid rupturing the diaphragm of the airspeed indicator, apply pressure slowly and do not build up excessive pressure in the line.
Release pressure slowly to avoid damaging the airspeed indicator.
d. If the airspeed indicator reading declines, check the system for leaky hoses and loose connections.
e. Inspect the hoses for signs of deterioration, particularly at bends and at the connection points to the pitot mast and airspeed indicator. Replace hoses that are cracked or hardened with identical specification hoses. Any time a hose is replaced, perform a pressure check.
WARNING: Do not apply suction to pitot lines.
12-60. MAINTENANCE PRECAUTIONS. Observe the following precautions in all pitot-static system leak testing:
a. Before any pitot/static system is tested, determine that the design limits of instruments attached to it will not be exceeded during the test. To determine this, locate and identify all instruments attached to the system.
b. A system diagram will help to determine the location of all instruments as well as locate a leak while observing instrument indications. If a diagram is not available, instruments can be located by tracing physical installation.
c. Be certain that no leaks exist in the test equipment.
d. Run full range tests only if you are thoroughly familiar with the aircraft instrument system and test equipment.
Par 12-60 Page 12-23
e. Make certain the pressure in the pitot system is always equal to, or greater than, that in the static system. A negative differential pressure across an airspeed indicator can damage the instrument.
f. The rate of change or the pressure applied should not exceed the design limits of any pitot or static instruments connected to the systems.
g. When lines are attached to or removed from the bulkhead feed through fitting or at a union, ensure the line attached to the opposite end is not loose, twisted, or damaged by rotation of the fitting. Such fittings normally are provided with a hex flange for holding the fitting.
12-61. REPLACING LINES. If necessary to replace lines, observe the following installation:
a. Attach lines at regular intervals by means of suitable clamps.
b. Do not clamp lines at end fittings.
c. Maintain the slope of lines toward drains to ensure proper drainage.
d. Check the lines for leaks.
12-62. RELOCATION OF PITOT TUBE. If pitot tube relocation is necessary, perform the relocation in accordance with approved data and consider the following:
a. Freedom of aerodynamic disturbances caused by the aircraft.
b. Location protected from accidental damage.
c. Alignment with the longitudinal axis of the aircraft when in cruising flight.
12-63. TROUBLESHOOTING THE PITOT/STATIC PRESSURE SYSTEM.
a. If instruments are inoperative or erratic operation occurs, take the following action:
(1) Check for clogged lines. Drain lines at the valves (especially after aircraft has been exposed to rain). Disconnect lines at the instruments and blow them out with low-pressure air.
(2) Check lines for leaks or looseness at all connections. Repair as required.
b. If the pitot heating element(s) are operative, check the following:
(1) Are circuit breaker(s) tripped?
(2) Reset the circuit breaker to determine if:
(a) The system is OK, or
(b) The circuit breaker trips again, if so:
Par 12-63 Page 12-24
1. Check the wiring continuity to the ground. If the switch(s) is defective, repair as necessary.
2. Check the heating element; replace it if it is defective.
TABLE 12-1. COLOR CODES FOR PITOT-STATIC SYSTEMS CODE ABBR. DEFINITION COLOR
PP PITOT PRESSURE NATURAL
SP STATIC PRESSURE (PILOT) RED
STATIC PRESSURE (CO-PILOT) GREEN
STATIC PRESSURE (CABIN) YELLOW
STATIC PRESSURE (STANDBY) BLUE
12-64.–12-69. [RESERVED.]
Par 12-70 Page 12-25 SECTION 5. AVIONICS TEST EQUIPMENT
12-70. GENERAL. Certificated individuals who maintain airborne avionics equipment must have test equipment suitable to perform that maintenance. Test equipment such as meters, torque wrenches, static, and transponder test equipment should be checked at least once a year.
12-71. TEST EQUIPMENT CALIBRATION STANDARDS.
a. The test equipment calibration standards must be derived from and traceable to one of the following:
(1) The National Institute of Standards and Technology (NIST).
(2) Standards established by the test equipment manufacturer.
(3) If foreign manufactured test equipment, the standards of the country, where it was manufactured, if approved by the Administrator.
b. The technician must make sure that the test equipment used for such maintenance is the equipment called for by the manufacturer or equivalent.
(1) Before acceptance, a comparison should be made between the specifications of the test equipment recommended by the manufacturer and those proposed by the repair facility.
(2) The test equipment must be capable of performing all normal tests and checking all parameters of the equipment under test. The level of accuracy should be equal to or better than that recommended by the manufacturer.
(3) For a description of avionics test equipment used for troubleshooting, refer to the equipment or aircraft manufacturing instruction manual.
c. NIST traceability can be verified by reviewing test equipment calibration records for references to NIST test report numbers. These numbers certify traceability of the equipment used in calibration.
d. If the repair station uses a standard for performing calibration, that calibration standard cannot be used to perform maintenance.
e. The calibration intervals for test equipment will vary with the type of equipment, environment, and use. The accepted industry practice for calibration intervals is usually one year.
Considerations for acceptance of the intervals include the following:
(1) Manufacturer’s recommendation for the type of equipment.
(2) Repair facility’s past calibration history, as applicable.
Par 12-71 Page 12-26
f. If the manufacturer’s manual does not describe a test procedure, the repair station must coordinate with the manufacturer to develop the necessary procedures, prior to any use of the equipment.
12-72–12-83. [RESERVED.]
Par 13-2 Page 13-1 CHAPTER 13. HUMAN FACTORS
13-1. HUMAN FACTORS INFLUENCE ON MECHANIC’S PERFORMANCE. To accomplish any task in aviation maintenance at least three things must be in evidence. A mechanic must have the tools, data, and technical skill to perform maintenance. Only recently has the aviation industry addressed the mechanic job functions, pressures, and stress, by identifying those human factors (HF) that impact the mechanics performance.
13-2. THE FAA AVIATION SAFETY PROGRAM has condensed these HF reports into a personal minimums checklist, which asks the mechanic to answer 10 ‘yes or no’ questions before the maintenance task is begun and 10 ‘yes or no’ questions after the task is completed. If the mechanic answers “NO” to any of the 20 questions, the aircraft should not be returned to service.
We have provided the checklist in Figure 13-1 for your evaluation and review. A color copy of the checklist is available from any Flight Standards District Office (FSDO). Just ask for the Airworthiness Safety Program manager.
Par 13-2 Page 13-2 FIGURE 13-1. PERSONAL MINIMUMS CHECKLIST Do I have the knowledge to perform the task?
Do I have the technical data to perform the task?
Have I performed the task previously?
Do I have the proper tools and equipment to perform the task?
Have I had the proper training to support the job task?
Am I mentally prepared to perform the job task?
Am I physically prepared to perform the task?
Have I taken the proper safety precautions to perform the task?
Do I have the resources available to perform the task?
Have I researched the 14 CFRs to ensure compliance?
Did I perform the job task to the best of my abilities?
Was the job task performed to be equal to the original?
Was the job task performed in accordance with appropriate data?
Did I use all the methods, techniques, and practices acceptable to industry?
Did I perform the job task without pressures, stress, and distractions?
Did I reinspect my work or have someone inspect my work before returning to service?
Did I make the proper record entries for the work performed?
Did I perform the operational checks after the work was completed?
Am I willing to sign on the bottom line for the work performed?
Am I willing to fly in the aircraft once it is approved for the return to service
Appendix 1 APPENDIX 1. GLOSSARY The following words and terms represent some of those that are often encountered in the field of aviation. For a more complete list of definitions, a mechanic or technician should consult an aviation dictionary.
-A- Abrasion resistant PTFE — A solid insulation wall of PTFE with hard, nonconductive grit positioned midway in the wall thickness, and significantly improves the resistance of the PTFE material to damage from wear.
Acetylene — Gas composed of two parts of carbon and two parts of hydrogen. When burned in the atmosphere of oxygen, it produces one of the highest flame temperatures obtainable.
Acetylene regulator — Manually adjustable device used to reduce cylinder pressure to torch pressure and to keep the pressure constant. They are never to be used as oxygen regulators.
Adherend — One of the members being bonded together by adhesive.
Airworthiness Directive— A regulation issued by the FAA that applies to aircraft, aircraft engines, propellers, or appliances, when an unsafe condition exists and that condition is likely to exist or develop in other products of the same type design.
Airworthy — Is when an aircraft or one of its component parts meets its type design and is in a condition for safe operation.
Ambient light — The visible light level measured at the surface of the part.
Ampere (amp) — The basic unit of current flow. One A is the amount of current that flows when a difference of potential of 1 V is applied to a circuit with a resistance of 1 Ω. One coulomb per second.
Antenna — A device designed to radiate or intercept electromagnetic waves.
Anti-tear strips — Strips of fabric of the same material as the airplane is covered with, laid over the wing rib under the reinforcing tape.
Apparent power — The product of volts and amperes in AC circuits where the current and voltage are out of phase.
Appliance — Any instrument, mechanism, equipment, part, apparatus, appurtenance, or accessory, including communications equipment, that is used or intended to be used in operating or controlling an aircraft in flight, is installed in or attached to the aircraft, and is not part of an airframe, engine or propeller.
Appendix 1 Arm — A measurement of distance, in inches, feet, etc., used in weight and balance calculations. Normally only the longitudinal arm is of practical importance. The three axial arms are longitudinal arm, lateral arm, and vertical arm.
Automatic direction finder (ADF) — A radio receiver utilizing a directional loop antenna that enables the receiver to indicate the direction from which a radio signal is being received; also called a radio compass.
Automatic flight control system (AFCS) — A flight control system incorporating an automatic pilot with additional systems such as a VOR coupler, an ILS approach coupler, and an internal navigation system that is fully automatic, so the aircraft can be flown in a completely automatic mode.
Avionics — The science and technology of electronics as applied to aviation.
Azimuth — Angular distance measured on a horizontal circle in a clockwise direction from either north or south.
-B- Balance — The condition of stability which exists in an aircraft when all weight and forces are acting in such a way as to prevent rotation about an axis or pivot point.
Base metal — The metal to be welded, brazed, soldered, or cut.
Black light — Electromagnetic radiation in the near ultraviolet range of wavelength.
Blade station — Is a reference position on a blade that is a specified distance from the center of the hub.
Bond — The adhesion of one surface to another, with or without the use of an adhesive as a bonding agent.
Bonding — A general term applied to the process of electrically connecting two or more conductive objects. In aircraft, the purpose of bonding (except as applied to individual connections in the wiring and grounding systems) is to provide conductive paths for electric currents. This is accomplished by providing suitable low-impedance connections joining conductive aircraft components and the aircraft structure. Another purpose of bonding is to ensure the safe passage of current caused by lightning or static electricity through the aircraft structure.
Borescope — A long, tubular optical instrument designed for remote visual inspection of surfaces.
Brashness — A condition of wood characterized by low resistance to shock and by an abrupt failure across the grain without splintering.
Appendix 1 Braze welding — A welding process variation in which a filler metal, having a liquidus above 450 °C (840 °F) and below the solidus of the base metal is used. Unlike brazing, in braze welding the filler metal is not distributed in the joint by capillary action.
Brazing — The joining of two pieces of metal by wetting their surface with molten alloy of copper, zinc, or tin.
Bus or bus bar — Solid copper strips to carry current between primary and secondary circuits;
also used as jumpers.
Butt joint — A joint between two members aligned approximately in the same plane.
Butyrate dope — A finish for aircraft fabric consisting of a film base of cellulose fibers dissolved in solvents with the necessary plasticizers, solvent, and thinners.
-C- Cable (electrical) — Assembly of one or more conductors within an enveloping protective sheath so constructed as to permit use of conductors separately or in a group.
Calibration — A set of operations, performed in accordance with a definite document procedure, which compares the measurements performed by an instrument or standard, for the purpose of detecting and reporting, or eliminating by adjustment, errors in the instrument tested.
Center of gravity — That point about which the aircraft would balance if suspended. For field weight and balance purposes/control, the center of gravity is normally calculated only along its longitudinal axis (nose to tail), disregarding both the lateral and vertical location.
Certification — Implies that a certificate is in existence, which certifies or states a qualification.
Check — A lengthwise separation of the wood, the greater part of which occurs across the rings of annual growth.
Chemical conversion coating (Specification MIL-C-81706) — Is a chemical surface treatment used on aluminum alloys to inhibit corrosion and to provide a proper surface for paint finishing.
Chord — An imaginary straight line joining the leading and trailing edges of an airfoil.
Circuit — A closed path or mesh of closed paths usually including a source of EMF.
Circuit breaker — A protective device for opening a circuit automatically when excessive current is flowing through it.
Close-grained wood — Wood with narrow and inconspicuous annual rings. The term is sometimes used to designate wood having small and closely spaced pores, but in this sense the term “fine-textured” is more often used.
Coil shot — Production of longitudinal magnetization accomplished by passing current through a coil encircling the part being inspected.
Appendix 1 Compass — A device used to determine direction on the Earth’s surface. A magnetic compass utilizes the Earth’s magnetic field to establish direction.
Compression wood — Identified by its relatively wide annual rings, usually eccentric, and its relatively large amount of summer wood, usually more than 50 percent of the width of the annual rings in which it occurs. Compression wood shrinks excessively lengthwise as compared with normal wood.
Conductor — A wire or other material suitable for conducting electricity.
Conduit — A rigid metallic or nonmetallic casing, or a flexible metallic casing covered with a woven braid or synthetic rubber used to encase electrical cables.
Contact — Electrical connectors in a switch, solenoid or relay that controls the flow of current.
Control panel — An upright panel, open or closed, where switches, rheostats, meters, etc., are installed for the control and protection of electrical machinery.
Corrosion — The electrochemical deterioration of a metal resulting from chemical reaction to the surrounding environment.
Crack — Is a partial separation of material caused by vibration, overloading, internal stresses, nicks, defective assemblies, fatigue, or rapid changes in temperature.
Creepage — Is the conducting of electrical current along a surface between two points at different potentials. The current’s ability to pass between two points increases with higher voltage and when deposits of moisture or other conductive materials exist on the surfaces.
Cross grain — Grain not parallel with the axis of a piece. It may be either diagonal or spiral grain or a combination of the two.
Cross coat — A double coat of dope or paint. It is sprayed on in one direction, and then immediately after the solvent flash-off, it is sprayed at right angles to the first coat.
Cure — To change the properties of a thermosetting resin irreversibly by vulcanization or chemical reaction. May be accomplished by the addition of curing (cross-linking) agents, with or without a catalyst, and with or without heat or pressure.
Curing temperature — Temperature to which a resin or an assembly is subjected in order to cure the resin.
Cutting torch — A device used in gas cutting of metals.
Appendix 1 -D- Damping — Limiting the duration of vibration by either electrical or mechanical means.
Data — Information that supports and/or describes the original aircraft design, alteration or repair, including the following: (1) drawings, sketches, and or photographs; (2) engineering analysis; (3) engineering orders; and (4) operating limitations.
Datum — Imaginary vertical plane from which all horizontal measurements are made or indicated when the aircraft is in level flight attitude.
Derating — Is a technique whereby a part is stressed in actual usage at values well below the manufacturer’s rating for the part. By decreasing mechanical, thermal, and electrical stresses, the probability of degradation or catastrophic failure is lessened.
Direct current electrode negative — The arrangement of direct current arc welding leads in which the work is the positive pole and the electrode is the negative pole of the welding arc.
Direct current electrode positive — The arrangement of direct current arc welding leads in which the work is the negative pole and the electrode is the positive pole of the welding arc.
Discontinuity — An interruption in the normal physical structure or configuration of a part, such as a crack, lap, seam, inclusion, or porosity.
Distal tip — The tip, lens end, of a borescope.
Dope — Liquid applied to fabric to tauten it by shrinking, strengthen it, and render it airtight by acting as a filler.
Dope-proofing — Protecting a surface from the chemicals and chafing qualities of dope and doped fabrics.
Drape — The ability of tape and broad goods to conform to a contoured shape.
Drip loop — A bundle installation method used to prevent water or other fluid contaminants from running down the wiring into a connector.
Dry rot — A term loosely applied to many types of wood decay but especially to that which, when in an advanced stage, permits the wood to be easily crushed to a dry powder. The term is actually a misnomer for any decay, since all fungi require considerable moisture for growth.
Dwell time — The total time that a penetrant, emulsifier (or remover), or developer remains on the surface of the test part.
Dye penetrant inspection — An inspection method for surface cracks in which a penetrating dye is allowed to enter any cracks present and is pulled out of the crack by an absorbent developer. A crack appears as a line on the surface of the developer.