FAA Aviation Mechanic – ACS Airman Certification Standards Knowledge Test — Questions and Answers

Question 1: What is the primary purpose of a hydraulic accumulator in an aircraft system?

Convert hydraulic pressure to pneumatic pressure
Regulate fluid temperature during high-load operations
Filter contaminants from the hydraulic fluid
Store hydraulic fluid under pressure to supplement the pump during peak demands (Correct answer)

Correct answer: Store hydraulic fluid under pressure to supplement the pump during peak demands

A hydraulic accumulator stores pressurized fluid to assist the pump during peak demand periods, such as when multiple systems operate simultaneously.

Question 2: An aircraft's empty weight CG is at 82.5 inches aft of datum. If the maximum forward CG limit is 78.0 inches and maximum aft CG limit is 86.5 inches, is the empty weight CG within limits?

Yes, 82.5 is between 78.0 and 86.5 (Correct answer)
Yes, but only if the aircraft is loaded to MTOW
No, 82.5 exceeds the aft limit
No, empty weight CG is always out of limits

Correct answer: Yes, 82.5 is between 78.0 and 86.5

82.5 inches falls between the forward limit of 78.0 and the aft limit of 86.5 inches, so the empty weight CG is within limits.

Question 3: How do ACS professionals contribute to organizational success?

They only perform routine tasks with no strategic impact
Professional expertise has minimal organizational value
Only executives contribute to organizational success
By applying specialized knowledge to solve problems, reduce risks, improve processes, and drive strategic outcomes (Correct answer)

Correct answer: By applying specialized knowledge to solve problems, reduce risks, improve processes, and drive strategic outcomes

Certified professionals bring specialized expertise that directly contributes to organizational goals through problem-solving, risk reduction, process improvement, and strategic decision support.

Question 4: When replacing aircraft transparent enclosures (acrylic), the fastener holes should be:

Drilled undersized and reamed to final dimension
Sealed with silicone sealant after fastener installation
Oversized to allow for thermal expansion of the acrylic (Correct answer)
The same size as the fastener diameter

Correct answer: Oversized to allow for thermal expansion of the acrylic

Acrylic plastic has a high coefficient of thermal expansion, so fastener holes must be oversized to prevent cracking as the material expands and contracts.

Question 5: What is the purpose of a fuel heat exchanger on a turbine aircraft?

To chill fuel for increased density and greater range
To increase fuel temperature for improved combustion efficiency
To use fuel to cool engine oil while also preventing fuel system icing by warming the fuel (Correct answer)
To separate water from fuel using temperature differential

Correct answer: To use fuel to cool engine oil while also preventing fuel system icing by warming the fuel

The fuel-oil heat exchanger cools hot engine oil using cooler fuel as the heat sink, simultaneously warming the fuel to prevent ice crystal formation in the fuel system.

Question 6: Which eddy current probe orientation is most effective for detecting cracks perpendicular to the surface on a flat plate?

Reflection probe
Bobbin probe
Encircling probe
Surface (pancake) probe (Correct answer)

Correct answer: Surface (pancake) probe

A surface (pancake) probe placed flat against the test surface is most effective for detecting surface cracks in flat materials because its coil orientation maximizes sensitivity to surface discontinuities.

Question 7: What documentation best practices should ACS professionals follow?

Documentation can be completed months after the work
Maintain thorough, accurate, timely records that support findings, decisions, and compliance requirements (Correct answer)
Brief notes are always sufficient
Documentation is only needed for billing purposes

Correct answer: Maintain thorough, accurate, timely records that support findings, decisions, and compliance requirements

Comprehensive documentation provides an audit trail, supports decision-making, facilitates knowledge transfer, and demonstrates compliance with professional standards.

Question 8: What causes brake fade on aircraft disc brakes during repeated hard stops?

Air in the brake lines
Worn brake pressure seals
Excessive heat buildup reducing friction between pads and disc (Correct answer)
Low hydraulic fluid viscosity

Correct answer: Excessive heat buildup reducing friction between pads and disc

Brake fade occurs when excessive heat reduces the coefficient of friction between the brake pads and disc, decreasing stopping effectiveness.

Question 9: Which 14 CFR Part governs the certification of aviation mechanics?

Part 147
Part 91
Part 43
Part 65 (Correct answer)

Correct answer: Part 65

14 CFR Part 65 covers airmen other than flight crewmembers, including the certification requirements and privileges of aviation mechanics.

Question 10: According to FAA AC 43.13-1B, which statement about NDT method selection is correct?

Visual inspection alone is sufficient for all primary structural inspections if performed by a certificated A&P mechanic
The NDT method used must be specified in the manufacturer's maintenance manual or approved equivalent data for that inspection (Correct answer)
Any NDT method may be substituted for another without engineering approval if the inspector has been trained in both
NDT is only required on powerplant components, not airframe structures

Correct answer: The NDT method used must be specified in the manufacturer's maintenance manual or approved equivalent data for that inspection

FAA AC 43.13-1B requires that the NDT method and procedure must be those specified in the manufacturer's approved maintenance data; substituting methods without engineering approval is not acceptable.

Question 11: What is the purpose of a flow control valve in a hydraulic system?

Prevent reverse fluid flow through a hydraulic line
Block fluid flow completely when a system is not in use
Control the rate of actuator movement by limiting fluid flow regardless of pressure differential (Correct answer)
Reduce system pressure to a lower value for downstream components

Correct answer: Control the rate of actuator movement by limiting fluid flow regardless of pressure differential

A flow control valve meters fluid flow rate to an actuator, controlling movement speed independently of the pressure differential across the valve.

Question 12: An engine cylinder head temperature (CHT) gauge shows one cylinder consistently 50°F hotter than the others in level cruise. What should be inspected first?

Valve timing on that cylinder
Fuel injector flow rate for that cylinder
Cylinder baffling and cooling fins for that cylinder (Correct answer)
Spark plug gap on that cylinder

Correct answer: Cylinder baffling and cooling fins for that cylinder

Damaged or missing baffling disrupts cooling airflow to individual cylinders and is the most common cause of a single cylinder running consistently hotter.

Question 13: What career advancement paths exist for ACS certified professionals?

Only changing careers provides advancement
Leadership roles, specialized consulting, education and training, and executive management positions (Correct answer)
Advancement requires leaving the field entirely
No advancement is possible beyond initial certification

Correct answer: Leadership roles, specialized consulting, education and training, and executive management positions

Certified professionals can advance through specialization, leadership roles, consulting, academic/training positions, and executive management within their field.

Question 14: A landing gear warning horn sounds in flight with the gear retracted and the throttle not reduced. What should the technician investigate?

A short circuit in the gear position indicator lights
A faulty throttle position switch sending a false low-power signal (Correct answer)
The landing gear uplock switch indicating a failed gear retraction
A defective gear warning horn relay

Correct answer: A faulty throttle position switch sending a false low-power signal

The landing gear warning system activates when a throttle position switch signals low power; a faulty switch can trigger this warning even with full power applied.

Question 15: What is the purpose of a fuel crossfeed system on a multi-engine aircraft?

To preheat fuel in cold weather
To feed both engines from either tank to manage fuel load or feed a live engine from any tank after an engine failure (Correct answer)
To transfer fuel only to the landing gear hydraulic reservoir
To dump fuel overboard in an emergency

Correct answer: To feed both engines from either tank to manage fuel load or feed a live engine from any tank after an engine failure

A crossfeed system allows either engine to draw from any tank, balancing fuel loads and enabling a surviving engine to draw from the opposite side's tank after an engine failure.

Question 16: An aircraft with a Continental fuel-injected engine experiences engine roughness after takeoff that smooths out as power is reduced. This symptom most closely suggests:

A rich mixture condition, possibly caused by a malfunctioning fuel control unit (Correct answer)
A cracked cylinder head affecting compression
A lean condition caused by a blocked injector nozzle
Magneto timing retarded beyond limits

Correct answer: A rich mixture condition, possibly caused by a malfunctioning fuel control unit

Roughness at high power that smooths at reduced power suggests an over-rich condition, as excess fuel is more problematic at higher power where flow is greatest.

Question 17: When using a dial indicator to check crankshaft runout, the total indicated reading (TIR) is 0.006 inches. If the maximum allowable runout is 0.004 inches, what action is required?

The crankshaft is within limits and may be returned to service
Polish the crankshaft journals to correct the runout
The crankshaft can be re-indexed to reduce runout
The crankshaft must be replaced or sent to an overhaul facility for evaluation (Correct answer)

Correct answer: The crankshaft must be replaced or sent to an overhaul facility for evaluation

When TIR exceeds the manufacturer's maximum allowable limit, the crankshaft must be replaced or sent for overhaul evaluation—it cannot be returned to service as-is.

Question 18: Which risk assessment model used in aviation maintenance identifies likelihood and severity to prioritize hazards?

Risk matrix (likelihood × severity) (Correct answer)
5M model
PAVE checklist
DECIDE model

Correct answer: Risk matrix (likelihood × severity)

A risk matrix that evaluates both the likelihood of an event and its potential severity is the standard tool for prioritizing hazards in SMS and maintenance risk management.

Question 19: What condition causes a hydraulic pump to cavitate?

Outlet pressure exceeds the system relief valve setting
System demand exceeds pump output, causing pressure fluctuations
Inlet pressure is too low, causing vapor bubbles to form in the fluid (Correct answer)
Fluid temperature drops below the pour point, increasing viscosity

Correct answer: Inlet pressure is too low, causing vapor bubbles to form in the fluid

Cavitation occurs when fluid pressure at the pump inlet drops below the fluid's vapor pressure, causing vapor bubbles to form and then violently collapse, damaging pump internals.

Question 20: AC 43.13-1B is best described as:

A legally binding regulation for all aircraft maintenance
FAA-accepted methods, techniques, and practices for aircraft inspection and repair (Correct answer)
A mandatory training curriculum for A&P schools
The type certificate data sheet reference manual

Correct answer: FAA-accepted methods, techniques, and practices for aircraft inspection and repair

AC 43.13-1B provides FAA-accepted (not mandatory) methods, techniques, and practices for aircraft inspection and repair, commonly used when no manufacturer data exists.

Question 21: When checking ignition timing using a timing light on a running engine, the light should flash at what point relative to the crankshaft?

At the intake valve opening point
At TDC on the compression stroke
At the specified degrees before TDC (Correct answer)
At BDC on the power stroke

Correct answer: At the specified degrees before TDC

Ignition timing is set to fire the spark plug at a specified number of degrees before TDC to allow the fuel-air mixture to reach peak pressure at the optimal piston position.

Question 22: When a maintenance technician completes a required inspection entry, the record must include all of the following EXCEPT:

Signature and certificate number of the approving person
Description of the work performed
Owner's written authorization to perform the work (Correct answer)
Date of completion

Correct answer: Owner's written authorization to perform the work

14 CFR 43.9 requires the work description, date, and approving technician's signature/certificate number—owner authorization is not a required element of the maintenance entry itself.

Question 23: What is the correct procedure when stop-drilling a crack in aluminum aircraft skin?

Drill two holes, one at each end, through the crack tips
Drill the hole through the center of the crack tip
Drill the hole just ahead of the visible crack tip (Correct answer)
Drill the hole 1/2 inch behind the crack tip

Correct answer: Drill the hole just ahead of the visible crack tip

The stop-drill hole must be placed just ahead of (beyond) the visible crack tip to eliminate the stress concentration at the crack tip and arrest crack propagation.

Question 24: During a magneto timing check, the engine is rotated to find the firing position. What tool is commonly used to locate top dead center (TDC)?

Timing light
Piston stop tool (Correct answer)
Compression tester
Feeler gauge

Correct answer: Piston stop tool

A piston stop tool is threaded into the spark plug hole to precisely locate TDC by stopping piston travel at a known point.

Question 25: What is the primary purpose of a drain hole in an aircraft control surface?

To prevent moisture accumulation that can cause corrosion and balance issues (Correct answer)
To allow pressure equalization during altitude changes
To reduce the weight of the surface
To provide access for internal inspection without disassembly

Correct answer: To prevent moisture accumulation that can cause corrosion and balance issues

Drain holes prevent moisture buildup inside control surfaces, which can cause corrosion and shift the balance of the surface, affecting flight characteristics.

Question 26: A mechanic using AC 43.13-1B for a structural repair must verify that:

The AC supersedes all manufacturer data
The repair is approved by the owner
The repair method is acceptable to the FAA for that specific repair and no approved manufacturer data exists (Correct answer)
The AC applies regardless of aircraft type

Correct answer: The repair method is acceptable to the FAA for that specific repair and no approved manufacturer data exists

AC 43.13-1B provides acceptable methods only when no approved manufacturer data exists; manufacturer data takes precedence when available.

Question 27: What is the correct torque technique when installing AN/MS flareless tube fittings?

Use the 'finger-tight plus turns' method specified in the applicable maintenance manual (Correct answer)
Thread until metal-to-metal contact, then add 1/4 turn
Tighten until resistance is felt, then tighten 1/16 turn more
Torque to the manufacturer's value using only a calibrated torque wrench

Correct answer: Use the 'finger-tight plus turns' method specified in the applicable maintenance manual

Flareless fitting installation requires presetting the ferrule on the tube first, then during final assembly using the turns method specified in the maintenance manual.

Question 28: Which NDT method is most effective for detecting surface and near-surface cracks in ferromagnetic aircraft components?

Magnetic particle inspection (Correct answer)
Dye penetrant inspection
Eddy current testing
Ultrasonic testing

Correct answer: Magnetic particle inspection

Magnetic particle inspection (MPI) is specifically designed for ferromagnetic materials and can reveal both surface and subsurface discontinuities by applying a magnetic field and iron particles.

Question 29: When inspecting aircraft tires for continued airworthiness, what condition mandates immediate removal from service?

Uneven tread wear of less than 1/16 inch
Minor weather checking on the sidewalls
Tread depth at the wear indicators
Fabric cord showing through the tread (Correct answer)

Correct answer: Fabric cord showing through the tread

Exposed fabric cords in aircraft tires represent a critical safety hazard requiring immediate removal from service regardless of remaining tread depth.

Question 30: Which formula correctly expresses the relationship used to find CG from weight and moment data?

CG = Total Moment ÷ Total Weight (Correct answer)
CG = Weight × Moment
CG = Total Weight ÷ Total Moment
CG = Total Moment × Total Weight

Correct answer: CG = Total Moment ÷ Total Weight

CG arm = Total Moment divided by Total Weight, giving the CG location in inches from the datum.

Question 31: During a structural inspection, a mechanic finds a corrosion pit in an aluminum structural member. Which measurement determines if the component remains airworthy?

The depth of the pit compared to the material thickness and manufacturer's allowable limits (Correct answer)
The distance of the pit from the nearest fastener
The surface area of the corroded region
The color and type of corrosion products present

Correct answer: The depth of the pit compared to the material thickness and manufacturer's allowable limits

Corrosion pit depth relative to material thickness is the critical measurement because excessive pitting reduces structural cross-section below allowable limits.

Question 32: FAA Form 337 is used to document which of the following?

Major repairs and major alterations (Correct answer)
Engine time between overhauls
Routine scheduled maintenance
Annual inspection results

Correct answer: Major repairs and major alterations

FAA Form 337 is the Major Repair and Alteration form required to document and approve major repairs and alterations under 14 CFR Part 43.

Question 33: When curing a composite repair using a heat blanket, which parameter is MOST important to monitor continuously?

Color change of the laminate during the cure cycle
Ambient relative humidity at the repair site
Vacuum bag pressure at the pump inlet only
Cure temperature ramp rate and hold temperature at the part surface (Correct answer)

Correct answer: Cure temperature ramp rate and hold temperature at the part surface

Incorrect ramp rates can cause residual stress or incomplete cure; hold temperature must be verified at the part surface because heat blankets can overshoot.

Question 34: What career advancement paths exist for ACS certified professionals?

No advancement is possible beyond initial certification
Advancement requires leaving the field entirely
Only changing careers provides advancement
Leadership roles, specialized consulting, education and training, and executive management positions (Correct answer)

Correct answer: Leadership roles, specialized consulting, education and training, and executive management positions

Certified professionals can advance through specialization, leadership roles, consulting, academic/training positions, and executive management within their field.

Question 35: When inspecting a hydraulic actuator for internal leakage, what is the most reliable method?

Pressurize the extend port and check for fluid weeping at the retract port with both ports open
Measure the time it takes the actuator rod to drift under a known load with ports blocked (Correct answer)
Visually inspect the cylinder bore for scoring using a borescope
Check the fluid level drop in the reservoir over a 24-hour period

Correct answer: Measure the time it takes the actuator rod to drift under a known load with ports blocked

Applying a load and timing rod drift with ports blocked reveals internal seal bypass, which is the definitive test for internal actuator leakage.

Question 36: During cylinder inspection, a technician finds a barrel that is worn 0.010 inch over the maximum specified diameter. What is the correct action?

Apply cylinder wall coating to restore the diameter
Return the cylinder to service with a note in the maintenance record
Chrome plate or replace the cylinder; it cannot be returned to service at this dimension (Correct answer)
Hone the cylinder to the next oversize and fit oversized pistons

Correct answer: Chrome plate or replace the cylinder; it cannot be returned to service at this dimension

A cylinder worn beyond the manufacturer's maximum allowable diameter must be chrome plated to restore dimensions or replaced; operating beyond limits is not airworthy.

Question 37: A 100-hour inspection is being performed on an aircraft used for flight instruction. During the inspection the mechanic discovers the engine has exceeded its manufacturer's TBO. What action is required?

Document the TBO status and return to service since TBO is advisory for Part 91 operations
Overhaul or replace the engine before return to service since TBO limits are mandatory for commercial operations (Correct answer)
Apply for an FAA extension waiver before continuing flight operations
Ground the aircraft immediately; TBO exceedance is an automatic airworthiness violation

Correct answer: Overhaul or replace the engine before return to service since TBO limits are mandatory for commercial operations

For aircraft used in commercial operations (such as flight instruction for hire), manufacturer TBO limits are mandatory per 14 CFR 91.409 and applicable operating rules.

Question 38: What type of seal is most commonly used in aircraft landing gear actuating cylinders?

Labyrinth seals
Teflon tape-wrapped pipe thread seals
Mechanical carbon face seals
Lip-type dynamic seals (O-rings with backup rings) (Correct answer)

Correct answer: Lip-type dynamic seals (O-rings with backup rings)

O-ring seals with backup rings are the standard dynamic seals in hydraulic actuating cylinders, preventing fluid bypass past the piston and rod.

Question 39: After replacing a cylinder on a reciprocating engine, the cylinder head temperature on the new cylinder is abnormally low compared to adjacent cylinders at the same power setting. What does this most likely indicate?

The fuel injector nozzle flow is too high for that cylinder
The new cylinder is not receiving ignition on both plugs (Correct answer)
The cylinder baffling is too effective
The new cylinder has excessive compression

Correct answer: The new cylinder is not receiving ignition on both plugs

A cylinder with no ignition (both plugs misfiring) will not combust fuel normally, resulting in low CHT because little or no combustion heat is being generated.

Question 40: What are composite materials in aircraft construction?

Recycled materials from decommissioned aircraft
Paint and coating materials for aircraft exteriors
Engineered materials combining two or more constituents (like carbon fiber and resin) for superior strength-to-weight ratio (Correct answer)
Standard aluminum alloys used in all aircraft

Correct answer: Engineered materials combining two or more constituents (like carbon fiber and resin) for superior strength-to-weight ratio

Aircraft composites typically combine reinforcing fibers (carbon, glass, aramid) with a resin matrix, creating materials that are lighter and stronger than traditional metals for many applications.

Question 41: How do ACS professionals contribute to organizational success?

They only perform routine tasks with no strategic impact
Only executives contribute to organizational success
Professional expertise has minimal organizational value
By applying specialized knowledge to solve problems, reduce risks, improve processes, and drive strategic outcomes (Correct answer)

Correct answer: By applying specialized knowledge to solve problems, reduce risks, improve processes, and drive strategic outcomes

Certified professionals bring specialized expertise that directly contributes to organizational goals through problem-solving, risk reduction, process improvement, and strategic decision support.

Question 42: After completing a composite skin repair, what is the FIRST post-cure inspection step before returning the aircraft to service?

Install all removed panels and fasteners and conduct a functional flight test
Apply primer and topcoat paint immediately to seal the repair
Perform a tap test and visual inspection of the repair area to verify consolidation and surface quality (Correct answer)
Measure the total repair weight to update the aircraft weight and balance record

Correct answer: Perform a tap test and visual inspection of the repair area to verify consolidation and surface quality

A post-cure tap test and visual inspection verify that the repair is void-free, properly consolidated, and bonded before any finish work or return-to-service is authorized.

Question 43: How should discrepancies be documented during inspection?

By verbal communication only
In maintenance logbooks (Correct answer)
Only after repairs
On personal notes

Correct answer: In maintenance logbooks

All discrepancies should be clearly recorded in the maintenance records/logbooks.

Question 44: How should an aircraft mechanic test a repaired fuel system for leaks before returning the aircraft to service?

Pressure test or operational test per the AMM with fuel system pressurized and all connections checked for leaks (Correct answer)
Dye penetrant test on all fittings
Run the engine to operating temperature and inspect
Visual inspection alone with the fuel caps open

Correct answer: Pressure test or operational test per the AMM with fuel system pressurized and all connections checked for leaks

After repair, the fuel system must be leak-tested per the AMM procedure, typically by pressurizing the system and inspecting all connections, fittings, and repaired areas for any leakage.

Question 45: Aircraft fuel quantity gauges are required by FAR to be accurate to within what tolerance?

No tolerance is specified — they are advisory only
They must only be accurate when reading empty (zero fuel) (Correct answer)
±5% of total capacity
±10% of indicated reading at all fuel levels

Correct answer: They must only be accurate when reading empty (zero fuel)

FAR 23.1337 requires fuel quantity gauges to be accurate only at the empty (zero) position; at all other quantities, accuracy is advisory and may vary.

Question 46: Which document is the primary reference for an aircraft's approved weight and balance limits?

The aircraft maintenance logbook
The FAA-approved Airplane Flight Manual (AFM) or Pilot's Operating Handbook (POH) (Correct answer)
The repair station's work order
The type certificate data sheet only

Correct answer: The FAA-approved Airplane Flight Manual (AFM) or Pilot's Operating Handbook (POH)

The FAA-approved AFM or POH contains the official CG envelope, weight limits, and loading instructions for the aircraft.

Question 47: What type of hydraulic pump is most commonly used in high-performance aircraft as an engine-driven pump due to its variable output capability?

Variable displacement piston pump (Correct answer)
Gear pump
Vane pump
Centrifugal pump

Correct answer: Variable displacement piston pump

Variable displacement piston pumps can adjust their output flow based on system demand, maintaining constant pressure while reducing heat generation and power consumption when demand is low.

Question 48: Why must aircraft fuel tanks be vented to atmosphere?

To prevent tank collapse or pressure differential as fuel is consumed and altitude changes (Correct answer)
To enable fuel cross-feed between tanks
To allow fuel vapors to escape for fire prevention
To equalize pressure between wing tanks

Correct answer: To prevent tank collapse or pressure differential as fuel is consumed and altitude changes

Tank venting prevents vacuum buildup as fuel is consumed and compensates for atmospheric pressure changes with altitude, preventing tank deformation and fuel flow interruption.

Question 49: What type of fuel is used in most turbine-powered aircraft operated in the United States?

Jet-A (kerosene-based turbine fuel) (Correct answer)
100LL AVGAS
MOGAS (automotive gasoline)
Jet-B wide-cut turbine fuel

Correct answer: Jet-A (kerosene-based turbine fuel)

Jet-A is the standard turbine fuel used in most US turbine aircraft, with a flash point above 100°F and freeze point around -40°C.

Question 50: What is the purpose of a pneumatic system bootstrap reservoir?

Cool pneumatic fluid before it enters actuators
Store excess bleed air for use during engine failure
Pressurize the reservoir above atmospheric pressure to prevent pump cavitation at altitude (Correct answer)
Act as an expansion chamber for thermal growth of pneumatic tubing

Correct answer: Pressurize the reservoir above atmospheric pressure to prevent pump cavitation at altitude

A bootstrap reservoir is pressurized above the fluid inlet pressure so the hydraulic or pneumatic pump receives adequate inlet pressure, preventing cavitation at high altitudes.

Question 51: What is the function of a hydraulic system priority valve?

Prevent two hydraulic systems from operating at the same time
Regulate pump output pressure to a constant predetermined value
Ensure flight-critical systems receive hydraulic pressure before non-critical systems during low-pressure conditions (Correct answer)
Switch automatically from one hydraulic system to another if pressure drops

Correct answer: Ensure flight-critical systems receive hydraulic pressure before non-critical systems during low-pressure conditions

A priority valve ensures that flight-critical hydraulic consumers (such as flight controls) are served first, with non-essential systems receiving flow only when adequate pressure exists.

Question 52: The 'Swiss Cheese Model' of accident causation, as applied to aviation maintenance, illustrates that accidents occur when:

A single catastrophic component failure overwhelms all safety systems
Maintenance errors are not caught by quality assurance inspection
Multiple layers of defenses each have gaps that align to allow a hazard to reach an outcome (Correct answer)
An individual mechanic ignores established procedures

Correct answer: Multiple layers of defenses each have gaps that align to allow a hazard to reach an outcome

James Reason's Swiss Cheese Model shows that accidents result from multiple aligned failures across defensive layers (procedures, inspections, design), not a single cause.

Question 53: The FAA's Aviation Safety Hotline (1-800-255-1111) is used to report:

Weather hazards to ATC
Lost or stolen airman certificates
Near-midair collisions only
Alleged violations of aviation regulations or safety concerns (Correct answer)

Correct answer: Alleged violations of aviation regulations or safety concerns

The FAA Safety Hotline allows anyone to anonymously report suspected regulatory violations or safety hazards to the FAA.

Question 54: What is the correct method for splicing aircraft wiring when a connector is not available?

Twist the wires together and wrap with electrical tape
Solder the splice without any additional protection
Use a wire nut connector
Use a solderless crimp splice with approved heat-shrink tubing (Correct answer)

Correct answer: Use a solderless crimp splice with approved heat-shrink tubing

FAA-approved crimped splices with heat-shrink tubing are the correct method; wire nuts and tape are not approved for aircraft.

Question 55: What condition does a 'hung start' describe in a turbine engine?

Fuel flow is interrupted during the start sequence before light-off occurs
The engine achieves start but then surges repeatedly above and below idle
The engine lights off and runs but stabilizes at an RPM below idle due to insufficient power from the starter (Correct answer)
The starter motor fails to disengage after the engine reaches self-sustaining speed

Correct answer: The engine lights off and runs but stabilizes at an RPM below idle due to insufficient power from the starter

A hung start occurs when the turbine engine lights and reaches a self-sustaining condition but RPM stabilizes below normal idle because the starter cannot supply enough energy to accelerate the engine further.

Question 56: What reading on a differential compression tester indicates a cylinder is in acceptable condition?

Greater than 50% pressure drop
Equal pressure on both gauges only at TDC
Differential pressure greater than 80/80
Less than 25 psi differential between reference and cylinder pressure (Correct answer)

Correct answer: Less than 25 psi differential between reference and cylinder pressure

FAA guidance generally accepts cylinders with no more than a 25% (about 20 psi on an 80 psi tester) differential pressure drop as serviceable.

Question 57: An aircraft fuel-injected engine that runs rough at cruise power but smoothly at full throttle most likely has:

An air leak in the intake manifold
A partially blocked fuel injector nozzle causing a lean condition at cruise (Correct answer)
Incorrect ignition timing
A malfunctioning magneto

Correct answer: A partially blocked fuel injector nozzle causing a lean condition at cruise

A partially blocked injector creates a lean mixture in one cylinder that is more pronounced at cruise power settings where fuel flow is lower, causing rough running.

Question 58: Which human factors concept describes a mechanic's tendency to complete a task as originally planned despite new information suggesting a change is needed?

Plan continuation error (Correct answer)
Normalization of deviance
Confirmation bias
Complacency

Correct answer: Plan continuation error

Plan continuation error (get-there-itis equivalent for maintenance) occurs when a technician proceeds with an original plan even after cues indicate it should change.

Question 59: What does 'maximum landing weight' refer to?

The maximum certificated weight at which the aircraft can land without exceeding structural limits (Correct answer)
The weight including all passengers but no cargo
The same value as maximum takeoff weight
The weight after a minimum fuel load is consumed

Correct answer: The maximum certificated weight at which the aircraft can land without exceeding structural limits

Maximum landing weight is the highest weight at which the landing gear and structure can absorb landing loads without damage.

Question 60: What is the correct procedure when a hydraulic system component is found to have a minor external seepage (not a drip) at a fitting?

Clean the area and monitor for progression; replace if seepage becomes a drip or increases (Correct answer)
Immediately ground the aircraft and replace all seals in the affected component
Apply an external sealant compound to stop the seepage temporarily
Tighten the fitting incrementally until seepage stops, regardless of torque limits

Correct answer: Clean the area and monitor for progression; replace if seepage becomes a drip or increases

Minor seepage that forms no drips is typically acceptable per maintenance manuals — it should be cleaned, identified, monitored, and addressed if it worsens to an active leak.

FAA Aviation Mechanic – ACS Airman Certification Standards Knowledge Test

The FAA Aviation Mechanic knowledge test evaluates candidates on general aviation maintenance principles, airframe systems, fuel/hydraulic systems, and NDT inspection skills required to earn an FAA Mechanic Certificate under the Airman Certification Standards (ACS) framework.

Questions

150 min

Time Limit

70%

To Pass

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