FAA Aviation Mechanic Airframe (AMA)

C. An open-center system

In an open-center system, fluid circulates continuously from the pump through the selector valves and back to the reservoir when no unit is being actuated. When a selector valve is moved, the flow path is redirected to the actuator instead of back to the reservoir.

D. Follow-up (feedback) servo actuator

A follow-up (feedback) servo actuator uses a mechanical linkage from the actuator piston back to the metering valve, so the actuator stops moving once it reaches the commanded position and the valve returns to neutral. This closed-loop design provides precise, proportional control surface positioning corresponding to pilot input.

D. To allow the flight crew to visually inspect the wing leading edge for ice accumulation

A wing ice inspection light is simply an illumination device, often mounted on the fuselage or wing root, aimed at the leading edge so the flight crew can visually monitor for ice accretion at night; it provides no heating or automatic detection function itself.

B. Stress corrosion cracking from sustained tensile stress combined with a corrosive environment

Stress corrosion cracking (SCC) results from the combined effects of sustained tensile stress and a corrosive environment on susceptible high-strength alloys, producing cracks that propagate perpendicular to the stress with minimal ductile deformation, unlike fatigue cracks which require cyclic loading.

D. Outflow valve

The outflow valve modulates the amount of conditioned air leaving the pressurized cabin to maintain the desired cabin pressure schedule; the cabin pressure controller signals the outflow valve to open or close as needed.

A. Drag brace (drag strut)

The drag brace (drag strut) is positioned to resist fore-and-aft loads, transferring them from the shock strut into the airframe structure. The side brace resists lateral loads, the torque link keeps the piston aligned rotationally, and the trunnion pin serves as the pivot point for gear retraction.

C. Fretting corrosion

Fretting corrosion occurs when two tightly fitted surfaces experience small, repetitive rubbing motion, generating fine oxide powder (reddish-brown on aluminum, black on steel) and often leading to surface wear and eventual fatigue cracking. It is common at hinge points, bolted joints, and press-fit bearings subjected to vibration.

B. To carry the shear loads between the upper and lower spar caps

In a box beam spar, the spar caps (upper and lower flanges) carry the tension and compression bending loads, while the vertical web primarily carries shear loads between the caps, similar to the web of an I-beam.

B. Transformer-rectifier unit (TRU)

A transformer-rectifier unit (TRU) steps down 115-volt AC to a lower AC voltage with a transformer, then rectifies it to usable 28-volt DC power for battery charging and DC bus loads on AC-primary electrical systems.

D. Eddy current inspection

Eddy current inspection is well suited for detecting surface and subsurface cracks around fastener holes in conductive nonferrous materials like aluminum without disassembly.

B. The battery is significantly discharged and needs charging

A fully charged lead-acid battery normally reads a specific gravity of approximately 1.275 to 1.300. A reading of 1.150 is well below this range, indicating the battery is significantly discharged, since specific gravity drops as sulfuric acid is consumed during discharge.

B. 174 knots

At 8,000 feet, the correction is approximately 2% × 8 = 16% of CAS. 150 knots × 0.16 = 24 knots added to CAS, giving 150 + 24 = 174 knots TAS.

B. Distributor valve

The distributor valve (often a rotary or timer-driven valve) cycles bleed air pressure and vacuum to the different boot tube sections in the proper sequence, producing the characteristic inflate/deflate pattern that sheds accumulated ice from the leading edge.

B. To prevent a single fault, chafe point, or physical damage from affecting both systems simultaneously

Physical separation of redundant wire bundles ensures that a single event such as chafing, fire, mechanical damage, or a short circuit cannot disable both the primary and backup systems at the same time, preserving system redundancy.

C. 83.3 in-lbs

Using TW = TA x [L / (L + A)] = 100 x [10 / (10 + 2)] = 100 x (10/12) = 83.3 in-lbs. Because the extension increases the effective lever arm, the wrench must be set lower than the desired final torque so that the actual torque applied to the fastener equals 100 in-lbs.

A. Multiple-disc brake

A multiple-disc brake uses several rotating discs (keyed to the wheel) alternated with stationary discs (keyed to the torque tube), all squeezed together by hydraulic pistons to generate friction. This design is common on transport-category aircraft for greater heat capacity and braking surface.

D. All-metal (spring or deformed-thread) self-locking nut

Fiber-insert self-locking nuts are limited to about 250°F because the nylon insert degrades at higher temperatures. All-metal self-locking nuts use a spring or deformed thread design that maintains locking friction at much higher temperatures, making them suitable for hot areas such as near exhaust systems.

C. Squat switch mounted on the landing gear strut

The squat switch (also called a weight-on-wheels switch) senses strut compression to determine whether the aircraft is on the ground or airborne. This signal is used throughout the aircraft to inhibit systems such as gear retraction on the ground and to enable systems such as spoiler deployment only when the switch confirms ground contact.

D. Rectifier (diode assembly)

A rectifier, typically a set of diodes, converts the alternator's AC output into DC. The voltage regulator controls the output level, but does not perform AC-to-DC conversion; a commutator is used on brush-type DC generators, not brushless alternators.

B. 199 volts

In a Y-connected three-phase system, line voltage equals phase voltage multiplied by the square root of 3 (1.732). Calculation: 115 V × 1.732 = 199.2 V, so the line-to-line voltage is approximately 199 volts.

A. To reduce electrical load and allow ice to be shed in sections rather than melted entirely

Cycling the heating elements reduces total electrical load on the generator system while allowing accumulated ice to be loosened and thrown off by centrifugal force in sections, rather than attempting to continuously melt all ice, which would require excessive power.

C. Squat switch releases (weight off wheels), downlocks disengage, gear retracts, uplocks engage and the gear position light goes out

On a properly rigged system, liftoff removes weight from the squat switch, permitting the retraction sequence to begin: downlocks must disengage before the gear can retract, and once fully retracted the uplocks engage, extinguishing the gear position light. Any other order indicates improper rigging or a malfunction.

A. The standard sea-level pressure reference used to display pressure altitude

29.92 in Hg is the standard atmospheric pressure at sea level. Setting the Kollsman window to this value causes the altimeter to display pressure altitude, which is required above the transition altitude (18,000 feet MSL in the U.S.) so all aircraft reference a common pressure datum.

D. Diverts pump output back to the reservoir at low resistance, allowing the pump to run unloaded

Because a fixed-displacement pump cannot reduce its own output, an unloading valve senses system pressure and, at the cutout setting, redirects the pump's constant flow back to the reservoir at near-zero resistance. This lets the pump continue spinning without building further pressure, until pressure drops to the cut-in setting and normal delivery resumes.

C. Variable displacement pump

A variable displacement pump automatically adjusts the stroke (and thus output volume) of its pistons to maintain a constant system pressure as demand changes, without needing to bypass excess flow through a relief valve. A fixed displacement pump always outputs a set flow rate and requires a separate relief/regulator valve to control pressure.