Tap an answer to reveal the correct choice and its worked rationale. Every question carries its ACS code and FAA handbook reference, so a miss tells you exactly which subject area to go and read.
When laying out a sheet metal bend, what is the bend allowance?
ACS code: AM.II.A
Correct answer: The length of material in the curved section of the bend
Rationale: Bend allowance is the length of material actually consumed in the curved portion of a bend. It must be added to the flat dimensions when computing the total developed (flat-pattern) length of a part, because the metal in the radius is neither a straight flange nor part of the setback. Setback is a separate value (the distance from the bend tangent line to the mold-point intersection), and the bend radius is the inside curvature, so those describe different quantities.
When using a wet layup repair, what does the term 'ply orientation' refer to?
ACS code: AM.II.B
Correct answer: The direction of the reinforcing fibers in each layer
Rationale: Ply orientation describes the direction in which the reinforcing fibers run in each individual layer (for example 0, 45, or 90 degrees). Maintaining the original orientation is critical because composite strength is directional. The count of layers is the ply count, and cure temperature is a separate process parameter.
On a conventional fixed-wing airplane, which primary flight control surface controls movement about the longitudinal axis?
ACS code: AM.II.C
Correct answer: The ailerons
Rationale: The ailerons control roll, which is movement about the longitudinal axis (the axis running nose to tail). The rudder controls yaw about the vertical axis, and the elevator controls pitch about the lateral axis. The three primary controls each govern one of the three axes of flight.
What document serves as the basis for the items checked during a 100-hour or annual inspection of an aircraft?
ACS code: AM.II.D
Correct answer: The scope and detail listed in 14 CFR Part 43, Appendix D
Rationale: Annual and 100-hour inspections must cover the scope and detail of items listed in 14 CFR Part 43, Appendix D, unless an approved inspection program is used. The Airframe Handbook stresses that this appendix defines the minimum checklist content for a complete airframe inspection.
What is the primary purpose of a torque link (torque arm) assembly on an oleo-pneumatic landing gear strut?
ACS code: AM.II.E
Correct answer: To keep the piston and axle aligned and prevent the wheel from rotating about the strut
Rationale: The torque links connect the upper cylinder to the lower piston of an oleo strut. They allow the piston to move up and down (telescope) while preventing it from rotating, which keeps the axle and wheel properly aligned with the direction of travel. Fluid metering is done by the metering pin/orifice, not the torque links.
What is the primary advantage that makes hydraulic systems well suited for operating aircraft components?
ACS code: AM.II.F
Correct answer: They transmit large forces with relatively little weight and low fluid friction loss
Rationale: Hydraulic systems use a confined, essentially incompressible liquid to transmit force. Because liquids do not compress appreciably, applied force is transmitted nearly undiminished, giving a high mechanical advantage with light, compact components and little friction loss. Liquids are not meaningfully compressible, so energy is not stored by compressing the fluid (that describes pneumatics), and every practical hydraulic system still requires a reservoir, pump, and relief valve.
In a vapor-cycle air conditioning system, which component compresses the low-pressure refrigerant vapor and raises both its temperature and pressure?
ACS code: AM.II.G
Correct answer: The compressor
Rationale: In a vapor-cycle system the compressor draws in low-pressure, low-temperature refrigerant vapor from the evaporator and compresses it, raising both its pressure and temperature before it flows to the condenser. The condenser only removes heat to liquefy the refrigerant, and the evaporator absorbs cabin heat to boil the refrigerant into vapor. FAA-H-8083-31 describes the compressor as the heart of the vapor-cycle loop.
Which three flight instruments are operated by the pitot-static system?
ACS code: AM.II.H
Correct answer: Airspeed indicator, altimeter, and vertical speed indicator
Rationale: The pitot-static system supplies ram (pitot) and static pressure to the airspeed indicator, altimeter, and vertical speed indicator. The attitude indicator, heading indicator, and turn coordinator are gyroscopic, and the magnetic compass is self-contained, so none of those rely on pitot-static pressure.
What does a flashing red light signal from the control tower mean to an aircraft operating on the ground?
ACS code: AM.II.I
Correct answer: Taxi clear of the runway in use
Rationale: In the FAA light-gun signal system, a flashing red light directed at a ground aircraft means 'taxi clear of the runway in use.' A steady red means stop, a flashing white means return to starting point on the airport, and a flashing green means cleared to taxi. These signals are the standard backup for radio communication failure.
In a typical aircraft reciprocating-engine fuel system, what is the primary purpose of the engine-driven fuel pump?
ACS code: AM.II.J
Correct answer: To supply fuel under pressure to the carburetor or fuel injection system during normal engine operation
Rationale: The engine-driven fuel pump is the main pump in a gravity-independent system; it delivers fuel under pressure to the metering device (carburetor or injection unit) whenever the engine is running. Venting is handled by the tank vent system, and metering of the air-fuel ratio is the job of the carburetor or fuel injection system, not the pump.
What is the main functional difference between a circuit breaker and a fuse?
ACS code: AM.II.K
Correct answer: A circuit breaker can be reset after a fault, while a fuse must be replaced
Rationale: Both devices open a circuit on an overcurrent condition to protect wiring. The key difference is that a circuit breaker uses a mechanical trip mechanism that can be reset and reused, whereas a fuse contains a metal element that melts and must be replaced after it opens. Neither is voltage- or AC/DC-specific in the way the distractors state.
On a typical pneumatic deicing system, what causes the inflatable boots on the wing and tail leading edges to expand?
ACS code: AM.II.L
Correct answer: Engine bleed air or pump pressure directed into the boot tubes
Rationale: Pneumatic deicing boots use rubber tubes that are inflated with regulated pressurized air (from engine bleed air on turbine aircraft or an engine-driven pump on reciprocating aircraft). The inflation flexes the boot, cracking accumulated ice so airflow sheds it. Heating elements are used in anti-icing, not pneumatic boots; hydraulic fluid is not routed into boots.
In a thermal switch fire detection system, how are the individual thermal switches and the warning light wired?
ACS code: AM.II.M
Correct answer: The switches are wired in parallel with each other and in series with the warning light.
Rationale: Thermal switches are heat-sensitive units that close their contacts at a set temperature. They are wired in parallel with one another so that any single switch can complete the circuit, but that switch network is wired in series with the warning light. Closing any switch energizes the light. The handbook describes this parallel-switch, series-light arrangement for spot-type thermal switch systems.
In a typical single main rotor helicopter, what is the primary purpose of the tail rotor?
ACS code: AM.II.N
Correct answer: To counteract the torque produced by the main rotor and provide directional control
Rationale: The spinning main rotor applies a torque to the fuselage that tends to rotate it in the opposite direction. The tail (anti-torque) rotor produces sideward thrust to counteract this torque and, through pedal inputs, allows the pilot to control the helicopter's heading about the vertical axis. Lift is produced by the main rotor, not the tail rotor.
In a typical transport-category potable water system, how is water normally forced from the storage tank to the faucets and other outlets?
ACS code: AM.II.O
Correct answer: By air pressure applied to the top of the water tank
Rationale: Most potable water systems are pressurized: regulated air (from a compressor or engine bleed air through a pressure regulator) is applied to the top of the storage tank, pushing water out to the lavatory and galley outlets. Gravity is not relied upon, and a venturi is not the motive source.
The neutral axis (neutral line) of a piece of sheet metal that is being bent is the location where the metal
ACS code: AM.II.A
Correct answer: is neither compressed nor stretched
Rationale: During bending, metal on the inside of the radius is compressed and metal on the outside is stretched. Between these zones lies the neutral axis, where the material is neither compressed nor stretched and its length does not change. Bend-allowance formulas are based on the length of this neutral line, which for practical purposes lies near 0.445 of the material thickness from the inside surface.
A nondestructive method that uses sound to detect delamination or disbond in a composite panel is the:
ACS code: AM.II.B
Correct answer: Coin tap test
Rationale: The coin-tap (ring) test relies on the difference in sound between a solid bonded area (sharp ring) and a delaminated or disbonded area (dull thud). Dye penetrant is used for surface cracks in nonporous metals, and magnetic particle inspection works only on ferromagnetic materials, so neither is suitable for composites.
Which set of surfaces is classified as the primary flight controls of an airplane?
ACS code: AM.II.C
Correct answer: Ailerons, elevator, and rudder
Rationale: Primary flight controls are the ailerons, elevator, and rudder, which provide control about the three axes. Flaps, slats, and spoilers are secondary (auxiliary) controls, and trim tabs are devices used to relieve control pressures rather than to maneuver the aircraft directly.
When performing a visual inspection of an aircraft structure, adequate lighting and the use of a mirror and flashlight are important because they help the technician
ACS code: AM.II.D
Correct answer: detect defects in areas that are not directly visible
Rationale: Visual inspection is the most widely used method, and the handbook notes that mirrors, flashlights, and magnifiers extend the inspector's reach into hidden or shadowed areas. These aids reveal cracks and damage that would otherwise be missed, but they do not measure depth or alloy.
In an oleo-pneumatic (air-oil) shock strut, how is the energy of landing impact primarily absorbed?
ACS code: AM.II.E
Correct answer: By forcing hydraulic fluid through a metering orifice while compressing the air charge
Rationale: An oleo-pneumatic strut absorbs energy in two stages: hydraulic fluid is forced through a small metering orifice (dissipating energy as heat), and the trapped air/nitrogen charge is compressed, acting as a spring. Coil springs and rubber donuts are used in other shock-absorbing designs, not in oleo-pneumatic struts.
Which basic physical principle explains how a hydraulic system multiplies an applied force?
ACS code: AM.II.F
Correct answer: Pascal's law, stating pressure is transmitted equally throughout a confined fluid
Rationale: Pascal's law states that pressure applied to a confined fluid is transmitted undiminished in all directions and acts equally on all areas. By applying the same pressure to a larger piston area, a larger output force is produced (force equals pressure times area). Bernoulli's principle relates velocity and pressure in moving fluids, and Boyle's law applies to gases, not the force multiplication in hydraulics.
In a vapor-cycle air conditioning system, the receiver-dryer is primarily used to perform which function?
ACS code: AM.II.G
Correct answer: Store liquid refrigerant and remove moisture
Rationale: The receiver-dryer acts as a reservoir for liquid refrigerant leaving the condenser and contains a desiccant and filter that remove moisture and contaminants from the system. Compressing vapor is the compressor's job, and metering flow into the evaporator is the expansion valve's job. FAA-H-8083-31 lists moisture removal and storage as the receiver-dryer's roles.
The altimeter, airspeed indicator, and vertical speed indicator each receive static pressure, but which one also requires pitot (ram air) pressure?
ACS code: AM.II.H
Correct answer: The airspeed indicator
Rationale: The airspeed indicator measures the difference between ram (pitot) pressure and static pressure, so it is the only one of the three connected to the pitot line. The altimeter and vertical speed indicator use static pressure alone, which is why a blocked static port affects all three but a blocked pitot tube affects only the airspeed indicator.
When installing or troubleshooting a VHF communications antenna, why is the bonding of the antenna base to the aircraft structure important?
ACS code: AM.II.I
Correct answer: It provides a proper ground plane for the antenna
Rationale: A VHF antenna requires a low-resistance bond to the metal skin so the airframe acts as the ground plane that the antenna radiates against. Poor bonding raises resistance, degrades the radiation pattern, and causes weak transmission and reception. Bonding does not increase transmitter power or change the operating frequency.
What is the purpose of the fuel tank sump and its drain valve?
ACS code: AM.II.J
Correct answer: To collect water and sediment at the lowest point of the tank so they can be drained off
Rationale: The sump is a low point in the tank where water (heavier than fuel) and sediment settle and collect. A drain valve at the sump lets the mechanic or pilot drain off the contaminants during preflight or maintenance. It is not a pressure-relief device, and the vent connects to the top of the tank, not the sump.
What is the primary function of a voltage regulator in an aircraft generator system?
ACS code: AM.II.K
Correct answer: To maintain a constant generator output voltage as load and speed vary
Rationale: A voltage regulator controls field excitation so that the generator's output voltage stays within a set range despite changing rotational speed and electrical load. Rectification is performed by a rectifier, and protection against excessive current is the job of a current limiter or circuit protection device, not the regulator.
What is the fundamental difference between an anti-icing system and a deicing system?
ACS code: AM.II.L
Correct answer: Anti-icing prevents ice from forming; deicing removes ice after it forms
Rationale: Anti-icing systems operate continuously to keep ice from accumulating in the first place (for example, heated leading edges or weeping-wing fluid). Deicing systems allow a small amount of ice to build up and then break or shed it, as with pneumatic boots. The distinction is prevention versus removal, not flight versus ground.
On what principle does a thermocouple fire detection system operate?
ACS code: AM.II.M
Correct answer: The rate of temperature rise at the thermocouple location.
Rationale: A thermocouple fire detection system depends on the rate of temperature rise, not on a specific temperature value. A rapid temperature increase creates a temperature difference between the active and reference junctions, generating a voltage that closes a sensitive relay. Because it responds to rate of rise, it will not give a warning for a slow, gradual overheat. This distinguishes it from thermal switch (set-temperature) and continuous-loop (resistance) systems.
Which control changes the pitch of all main rotor blades simultaneously and by an equal amount?
ACS code: AM.II.N
Correct answer: The collective pitch control
Rationale: The collective changes the pitch angle of all main rotor blades at the same time and by the same amount, which changes total rotor thrust and governs the helicopter's climb and descent. The cyclic changes blade pitch individually as the blades rotate, tilting the rotor disc; the pedals control tail rotor thrust.
How does a vacuum-type (vacuum flush) lavatory waste system move waste from the toilet bowl to the holding tank?
ACS code: AM.II.O
Correct answer: A pressure differential draws the waste into the tank
Rationale: Vacuum waste systems use the differential pressure between the cabin and the holding tank (provided by cabin pressurization in flight or a vacuum generator on the ground) to draw waste into the tank with a small amount of rinse water. This eliminates the large fluid charge and pump of a recirculating system.
What is the primary purpose of an aircraft sheet metal stop drill at the end of a stress crack?
ACS code: AM.II.A
Correct answer: To prevent the crack from spreading farther
Rationale: A crack acts as a stress concentrator with a very sharp tip. Drilling a small hole precisely at the end (tip) of the crack blunts that sharp point and spreads the load over the larger radius of the hole, which arrests the crack's progress. It is a temporary measure to stop further growth until a proper repair is made; it does not relieve panel-wide stress or serve as a rivet pilot.
When storing pre-impregnated (prepreg) composite material, why is it kept in a freezer?
ACS code: AM.II.B
Correct answer: Low temperature slows curing and extends shelf life
Rationale: Prepreg already contains the resin in a partially uncured state, so the chemical cure reaction is continuously progressing. Freezer storage slows that reaction, preserving the material's working life and tack. The freezer does not stiffen the fibers for cutting or dry out the resin; in fact, frozen prepreg must be thawed sealed to avoid moisture condensation.
What is the primary purpose of wing flaps when they are extended?
ACS code: AM.II.C
Correct answer: Increase lift and drag for lower-speed flight
Rationale: Flaps increase the camber of the wing, raising both lift and drag, which permits flight at lower airspeeds for takeoff and landing. They do not control roll (that is the ailerons), and they increase rather than reduce camber.
A magnetic particle inspection method can be used to detect surface and subsurface discontinuities in
ACS code: AM.II.D
Correct answer: ferromagnetic materials such as steel
Rationale: Magnetic particle inspection relies on magnetizing the part, so it only works on ferromagnetic materials like iron and steel. The handbook notes nonmagnetic materials such as aluminum, magnesium, and composites cannot be inspected by this method.
An oleo shock strut on a parked aircraft is compressed more than the published exposed-piston dimension. The most likely cause is that the strut is
ACS code: AM.II.E
Correct answer: low on air charge or hydraulic fluid
Rationale: Strut inflation is checked by measuring the exposed (shiny) portion of the piston against the manufacturer's specification. A strut compressed below the correct dimension indicates insufficient air charge and/or low fluid. Over-servicing with air would produce an over-extended strut, not a compressed one.
What is the primary function of a pressure relief valve in a hydraulic system?
ACS code: AM.II.F
Correct answer: To limit system pressure and protect components from excessive pressure
Rationale: A pressure relief valve is a safety device that opens to route fluid back to the reservoir when pressure exceeds a preset maximum, protecting lines, seals, and components from damage. Maintaining a constant flow to actuators is the role of a flow control valve, and preventing reverse flow is the role of a check valve.
In a vapor-cycle system, the thermostatic expansion valve controls the refrigerant by performing which action?
ACS code: AM.II.G
Correct answer: Metering high-pressure liquid into the evaporator
Rationale: The thermostatic expansion valve meters high-pressure liquid refrigerant from the receiver-dryer into the low-pressure evaporator, where it expands and boils to absorb heat. Condensing vapor to liquid is the condenser's function, and drawing vapor from the evaporator is the compressor's function. FAA-H-8083-31 identifies the expansion valve as the metering device dividing the high and low sides of the system.
An aircraft altimeter measures aircraft altitude by sensing which of the following?
ACS code: AM.II.H
Correct answer: Ambient atmospheric (static) pressure
Rationale: An altimeter is an aneroid barometer that senses ambient static (atmospheric) pressure, which decreases with altitude. The difference between ram and static pressure is what the airspeed indicator senses, and the rate of change of static pressure is what the vertical speed indicator senses.
What is the primary purpose of an emergency locator transmitter (ELT) installed in an aircraft?
ACS code: AM.II.I
Correct answer: Transmit a signal to aid search and rescue after a crash
Rationale: An ELT automatically transmits a distress signal on designated emergency frequencies to help search-and-rescue forces locate an aircraft after an accident; it is activated by the impact forces of a crash or manually. It is not a two-way voice radio and does not provide cockpit navigation displays.
During a fuel system pre-flight check, water contamination in a tank is most reliably detected by
ACS code: AM.II.J
Correct answer: draining a fuel sample from the lowest sump and checking for separated water
Rationale: Water is heavier than aviation fuel and settles to the lowest point in the tank, the sump. Draining a sample from the sump drain lets the mechanic see water as a separate layer or clear globules at the bottom of the sample. Fuel quantity gauges and line temperature are not reliable indicators of water contamination.