Aircraft Maintenance Technician Study Guide - Vocabulary

FAA Eligibility Requirements and Certification Procedures

• To qualify for an Airframe and/or Powerplant (A&P) rating, an applicant must present a certificate of completion from an FAA-approved aviation maintenance school (FAR 147) or provide written proof of past experience.
• Experience requirements for those not utilizing school certificates:
  • 18 months of documented experience for a single rating (either Airframe or Powerplant).
  • 30 months of documented experience for both ratings.
• Documentation methods include letters, DD-214 forms, and training certificates. Applicants are advised to contact their local Flight Standard District Office (FSDO) and an Aviation Maintenance Inspector (ASI) for specific documentation requirements.
• General requirements:
  • Minimum age of 18 years.
  • Ability to read, write, speak, and understand the English language.
  • Must pass all required tests within a 24-month period.
• FAA Form 8610-2 (Airmen Certificate and Rating Application) must be completed in two original copies and signed by an ASI before taking tests.

FAA Written (Computerized) Testing

• Written exams must be passed before the oral and practical exams.
• Tests are administered by Computerized Test Designees (CTD) selected by the FAA.
• Testing fees typically range from $90$ to $100$.
• Required materials for testing day: Signed 8610-2 forms and two forms of identification (one with a photo).
• Simple electronic calculators are permitted.
• FAA-approved reference material is provided by the CTD.

Oral and Practical Examinations

• These exams are administered by a Designated Mechanic Examiner (DME).
• Computerized test reports are valid for two years; if the oral and practical exams are not passed within this timeframe, the written tests expire.
• The exam covers 43 subject areas across General, Airframe, and Powerplant sections.
• Failure and Retesting Policy:
  • Failed sections are listed on the back of Form 8610-2.
  • Retesting with the same DME within 30 days requires a signed letter from a certified mechanic stating additional instruction was given.
  • Retesting with a different DME may require retaking the entire examination.
• A temporary certificate is issued the same day the exam is passed.

Section I: General Subjects

Basic Electricity

• Ohm’s Law: The fundamental law of electricity, expressed as $I = E "/ " R$.
• Elements: Voltage ($E$), Current ($I$), and Resistance ($R$).
• Power Sources: Mechanical (generator), chemical (battery), photoelectric (light), and thermal (heat).
• Power Measurement: In DC circuits, power is measured in Watts ($P = I "\times" E$). One horsepower equals $746"""W$.
• Capacitance and Inductance:
  • Capacitors (condensers) store electricity.
  • Inductance ($L$) induces a voltage in a coil that opposes changes in alternating current.
  • Impedance ($Z$) is the combined effect of resistance, inductive reactance, and capacitive reactance in AC.
• Batteries:
  • A $24-volt$ lead-acid battery contains 12 cells, each rated at $2"""V$.
  • Lead-acid electrolyte specific gravity: $1.275$ to $1.300$.
  • Nickel-cadmium (Ni-cad) batteries cannot be checked via hydrometer because specific gravity does not change significantly during charge/discharge.
  • Ni-cad and lead-acid batteries must not be stored together as lead-acid fumes contaminate Ni-cad electrolyte.
• Maintenance:
  • Battery compartments are coated with acid-resistant paint, such as bituminous paint.
  • Electrolyte level should be approximately $3/8"""inch$ above plates.
  • A trip-free (no-trip) circuit breaker cannot be reset while a fault exists or in-flight if so designed.

Weight and Balance

• Purpose: Ensures flight safety and efficiency.
• Definitions:
  • Datum: An imaginary vertical plane for measuring longitudinal distances (arms).
  • Arm: The distance in inches an item is located from the datum.
  • Moment: The rotational force obtained by $Weight "\times" Arm$, expressed in inch-pounds.
  • Tare: Weight of weighing equipment (chocks, jacks) that must be subtracted from scale readings.
• Fuel Considerations:
  • Residual/Unusable Fuel: Fuel remaining after draining; part of the empty weight.
  • Minimum Fuel (FAR 23): Amount needed for 1/2 hour of operation at maximum continuous power ($"""1/12"""lb$ per METO horsepower).
• Computation: CG is located by dividing total moment by total weight ($CG = "\frac{Total"""Moment}{Total"""Weight}$).

Fluid Lines and Fittings

• Sizing:
  • Metal tubing: Sized by outside diameter in $1/16"""inch$ increments and wall thickness.
  • Flexible hose: Sized by inside diameter in $1/16"""inch$ increments.
• Installation:
  • Fluid lines should be routed below electrical wiring with at least $6"""inches$ clearance (minimum $1/2"""inch$ if clamped).
  • Flexible hoses require $5"""to"""8"""percent$ slack for movement under pressure.
  • Identification stripes (lay lines) on hoses indicate if the hose has twisted.
• Fittings:
  • AN fittings: Blue or black color, coarse threads, shoulder between threads and flare cone.
  • AC fittings: Gray or yellow, threads extend to the flare cone.
  • Flareless fittings (MS): Consist of a body, sleeve, and nut. Overtightening weakens the tube by cutting too deep.

Section II: Airframe Structures

Wood Structures

• Standard Species: Sitka Spruce is the reference for strength.
• Plywood vs. Laminated Wood: Plywood grain runs at $90^\circ$ between layers; laminated wood grains are parallel.
• Glues: Casein and synthetic resins (resorcinol formaldehyde).
• Maintenance:
  • Scarf joints are the preferred method for splicing structural members.
  • Scarf patches for plywood use a $12:1$ slope (splayed patches use $5:1$).
  • Compression wood (high specific gravity, excess summer wood growth) is a rejectable defect.
  • Moisture content formula: $Percent"""Moisture = "\frac{W_1 - W_2}{W_2} "\times" 100$ (where $W_1$ is original weight and $W_2$ is oven-dry weight).

Sheet Metal Structures

• Riveting Standards:
  • Grip length: Combined thickness of materials to be joined.
  • Shop head dimensions: One-and-one-half times diameter ($1.5 "\times" D$) wide and one-half diameter ($0.5 "\times" D$) thick.
  • Minimum Edge Distance: $2 "\times" D$.
  • Minimum Rivet Spacing: $3 "\times" D$ (single row).
  • Drill sizes: #40 for $3/32"""inch$, #30 for $1/8"""inch$, #21 for $5/32"""inch$.
• Rivet ID (e.g., AN470AD4-4):
  • AN: Standard (Airforce-Navy).
  • 470: Universal head type.
  • AD: 2117-T aluminum alloy.
  • 4: Diameter in $32nds$ ($4/32"""inch$).
  • 4: Length in $16ths$ ($4/16"""inch$).
• Special Constructions:
  • Bonded Honeycomb: Laminar construction using materials like titanium, stainless steel, or resin paper. Potted repair or glass fabric cloth overlay are common repair methods.
  • Anodizing: Electrolytic bath forming a hydroxide film on aluminum for corrosion resistance and paint bonding.

Section III: Airframe Systems and Components

Landing Gear Systems

• Power Sources: Electrical or hydraulic.
• Maintenance:
  • Retraction checks: Required during annual inspections, after component replacement, or hard landings.
  • Strut inflation: Use high-pressure dry air or nitrogen.
  • Shimmy damper: Hydraulic unit preventing nose wheel vibration.
  • Fusible plugs: Relieve tire pressure in case of overheating (e.g., heavy braking) to prevent wheel explosion.
• Alignment: Maintained by torque links.

Cabin Atmosphere Control

• Pressurization:
  • Principal control: Cabin outflow valve.
  • Negative pressure relief valve: Prevents cabin altitude from exceeding aircraft altitude.
  • Source: Bleed air from engine compressor (turbine) or independent compressors.
• Cooling Systems:
  • Air Cycle: Uses expansion turbines to drop air temperature.
  • Vapor Cycle: Uses Freon ($R-12$ or similar), compressor, condenser, and evaporator. Bubbles in the sight glass indicate low charge.

Ice and Rain Control

• Deicing:
  • Inflatable boots: Rubber tubes cycled with air to break ice. Clean with mild soap and water.
  • Pneumatic rain removal: Blows high-pressure bleed air across the windshield to form a barrier.
• Anti-icing:
  • Thermal systems: Use bleed air or combustion heaters to prevent ice formation.
  • Overheat protection: Thermal switches shut off air at approximately $185^\circ F$.

Section IV: Powerplant Theory and Maintenance

Reciprocating Engines

• Classification: Cylinder arrangement (V-type, Radial, In-line, Opposed) or cooling method (liquid or air-cooled).
• Piston Rings: Compression, oil control, and scraper rings. Incorrect installation leads to high oil consumption.
• Valve Train:
  • Valve overlap: Improves volumetric efficiency and cooling.
  • Sodium-filled valves: Improve heat dissipation from the head to the stem (sodium melts at $208^\circ F$).
• Maintenance:
  • Sudden stoppage: Requires checking propeller drive shaft for runout and misalignment.
  • Detonation: Instantaneous explosive burning of fuel-air mixture due to temperature/pressure limits exceeded.

Turbine Engines

• Major Components: Air inlet, compressor, combustion, turbine, exhaust, and accessory sections.
• Compressor Types: Centrifugal flow and axial flow.
• Combustion Chambers: Can, can-annular, and annular.
• Thrust Reversers: Mechanical blockage or aerodynamic blockage.
• Turbine Nozzle: Converts heat/pressure to velocity and directs gases at the optimal angle to strike rotor blades.

Section V: Powerplant Systems and Components

Ignition and Fuel Systems

• Magnetos: Engine-driven AC generators.
  • E-gap: Position where magnet poles are a few degrees past neutral; breaker points open to collapse primary field.
  • Impulse coupling: Retards spark and increases rotation speed for starting.
• Fuel Metering:
  • Venturi functions: Proportions fuel-air mixture, lowers pressure at discharge nozzle, and limits total airflow.
  • Economizer system: Provides extra fuel for cooling at high power settings (above $60-70"""percent$).
• APUs (Auxiliary Power Units):
  • Usually consistent speed regardless of load.
  • Shutdown involves a cooling period (closing bleed air valve).

Maintenance Forms and Records

• Time in Service: From the moment the aircraft leaves the surface until it touches down.
• 100-Hour Inspection:
  • Recorded in maintenance records with date, total time, certification statement, and signature.
  • Records kept until work is repeated/superseded or for one year.
• Major Alterations/Repairs:
  • Recorded on FAA Form 337.
  • Distribution: One copy to owner, one to local FSDO.
• Airworthiness Directives (ADs):
  • Regulatory notices of unsafe conditions. Frequencies are issued every two weeks (bi-weekly updates).

Appendices and Calculations

• Temperature Conversions:
  • $F = (C "\times" 1.8) + 32$
  • $C = "\frac{F - 32}{1.8}$
• Physics:
  • Standard Sea Level Pressure: $14.7"""psi$ or $29.92"""inches"""Hg$.
  • Speed of Sound at Sea Level: $662"""knots$ ($761"""mph$).
  • Absolute Zero: $-273^\circ C$.
• Rivet Layout Problem:
  • For two $3-inch$ pieces of metal with $1/8"""inch$ rivets (AN470AD4-4):
  • Edge distance ($2D$) = $1/4"""inch$.
  • Spacing ($3D$) = $.375"""inch$.
  • Calculations show $7$ rivets are needed for a straight single row on a $3-inch$ piece.