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

Question 1: When inspecting control cable tension, you find the elevator cable is at 40 lbs when the maintenance manual specifies 50-70 lbs. What is required?

Adjust cable tension to within the specified range using the cable turnbuckles (Correct answer)
The cable tension is acceptable as long as it is above 30 lbs
Document the finding and re-check at the next 100-hour inspection
Replace the cables as worn cables cause low tension

Correct answer: Adjust cable tension to within the specified range using the cable turnbuckles

Flight control cables must be adjusted to within the manufacturer's specified tension range using the turnbuckles before the aircraft is returned to service.

Question 2: If an aircraft hydraulic system uses MIL-PRF-5606 fluid and is inadvertently serviced with MIL-PRF-83282 fluid, what action is required?

Replace only the hydraulic pump since it is most susceptible to damage
Flush the system and replace all seals, as the fluids have different seal compatibility (Correct answer)
Simply add the correct fluid to dilute the contamination
No action; the fluids are completely interchangeable

Correct answer: Flush the system and replace all seals, as the fluids have different seal compatibility

MIL-PRF-5606 and MIL-PRF-83282 have different base oils and different seal material requirements, requiring a full system flush and seal replacement if mixed.

Question 3: During engine run-up, a pilot reports intermittent engine roughness that disappears when carburetor heat is applied. What does this indicate?

Ice formation in the carburetor venturi (Correct answer)
Lean fuel-air mixture
Cracked intake manifold
Fouled spark plugs

Correct answer: Ice formation in the carburetor venturi

Carburetor ice causes rough running and partial power loss; applying carb heat melts the ice and restores smooth operation.

Question 4: Which NDT method is BEST suited for detecting subsurface delaminations in a composite honeycomb sandwich structure?

Eddy current inspection
Magnetic particle inspection
Tap test or ultrasonic through-transmission (Correct answer)
Dye penetrant inspection

Correct answer: Tap test or ultrasonic through-transmission

A coin tap test or ultrasonic through-transmission is used to detect subsurface delaminations in composite honeycomb panels, while dye penetrant only finds surface defects and magnetic particle requires ferrous material.

Question 5: When performing a scarf repair on a composite laminate, the scarf ratio is typically expressed as:

Number of plies removed divided by total ply count
Horizontal taper length divided by the laminate thickness (Correct answer)
Repair patch diameter divided by damage diameter
Depth of damage divided by the panel thickness

Correct answer: Horizontal taper length divided by the laminate thickness

Scarf ratio is the ratio of the taper length to the laminate thickness (e.g., 20:1 means 20 mm of taper per 1 mm of thickness), determining how gradually load is transferred.

Question 6: An aircraft with an expired annual inspection is considered:

Airworthy for day VFR operations only
Airworthy with a ferry permit
Unairworthy and may not be operated (Correct answer)
Airworthy if no new defects are found

Correct answer: Unairworthy and may not be operated

An aircraft whose annual inspection has expired is not in compliance with 14 CFR 91.409 and is therefore unairworthy and may not be legally operated.

Question 7: A mechanic discovers an Airworthiness Directive applies to a component already installed on an aircraft. The AD has a compliance time of 'next scheduled inspection.' What must the mechanic do?

Note it in the logbook and defer until owner requests it
Ground the aircraft immediately
Contact the FAA for an exemption
Comply with the AD at or before the next scheduled inspection (Correct answer)

Correct answer: Comply with the AD at or before the next scheduled inspection

The compliance time stated in the AD establishes the deadline; the mechanic must accomplish it no later than that time.

Question 8: What is the most common material used for aircraft skin?

Aluminum alloy (Correct answer)
Steel
Copper
Titanium

Correct answer: Aluminum alloy

Aluminum alloys are lightweight and corrosion-resistant, making them ideal for aircraft skins.

Question 9: How does continuing education benefit ACS professionals?

Only beginners benefit from additional training
Continuing education is not needed after certification
Continuing education is purely optional with no benefits
It ensures practitioners stay current with evolving standards, technologies, and best practices (Correct answer)

Correct answer: It ensures practitioners stay current with evolving standards, technologies, and best practices

Professional fields evolve constantly — continuing education ensures practitioners maintain competence and stay current with industry developments.

Question 10: How should ACS professionals handle conflicts of interest?

Disclose potential conflicts, recuse when appropriate, and always prioritize the client's best interests (Correct answer)
Only financial conflicts matter
Conflicts of interest are normal and need not be addressed
Keep conflicts hidden to avoid complications

Correct answer: Disclose potential conflicts, recuse when appropriate, and always prioritize the client's best interests

Conflicts of interest must be identified, disclosed, and managed transparently to maintain professional integrity and client trust.

Question 11: What is the function of a hydraulic system priority valve?

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

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 12: A mechanic who suspects a fellow technician is working while impaired by alcohol should FIRST:

Immediately report it to the supervisor or safety officer (Correct answer)
Confront the technician privately and warn them
Ignore it unless the aircraft is about to fly
Annotate the maintenance log and continue working

Correct answer: Immediately report it to the supervisor or safety officer

Safety culture requires immediate escalation to a supervisor or safety officer when impairment is suspected, preventing unsafe maintenance from reaching an aircraft.

Question 13: What reading on a differential compression tester indicates a cylinder is in acceptable condition?

Equal pressure on both gauges only at TDC
Greater than 50% pressure drop
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 14: Aircraft fuel quantity gauges are required by FAR to be accurate to within what tolerance?

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

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 15: What condition causes a hydraulic pump to cavitate?

Inlet pressure is too low, causing vapor bubbles to form in the fluid (Correct answer)
System demand exceeds pump output, causing pressure fluctuations
Outlet pressure exceeds the system relief valve setting
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 16: An aircraft owner requests that a mechanic install a non-TSO'd radio as a replacement for a required navigation radio. The mechanic should:

Install it and submit a Form 337 to authorize the non-standard equipment
Install it as a temporary fix and document it as a minor repair
Refuse, because required avionics must meet TSO standards or have FAA approval (Correct answer)
Install it if the owner signs a waiver of liability

Correct answer: Refuse, because required avionics must meet TSO standards or have FAA approval

Required avionics must meet applicable TSO standards or have specific FAA approval; installing non-approved equipment on required systems is not permissible.

Question 17: What continuing education is typically required in weight & balance?

Training is only needed in the first year of certification
No continuing education is ever required
Regular training to stay current with industry standards, regulations, and best practices (Correct answer)
Only education obtained before certification matters

Correct answer: Regular training to stay current with industry standards, regulations, and best practices

Professional fields require ongoing education to ensure practitioners stay current with evolving standards, technologies, regulations, and best practices in their specialty.

Question 18: The concept of 'normalization of deviance' in aviation maintenance describes:

Using unapproved parts in low-risk applications
Documenting non-standard repairs with FAA approval
Accepting small deviations from standards as normal over time until a serious failure occurs (Correct answer)
Applying engineering judgment instead of published data

Correct answer: Accepting small deviations from standards as normal over time until a serious failure occurs

Normalization of deviance occurs when repeated minor violations of standards go uncorrected and become accepted as normal, increasing risk of catastrophic failure.

Question 19: When a sheet metal repair uses a splice plate to restore strength to a cut or damaged stringer, the splice plate must:

Be made of the same alloy and be thicker than the original to compensate
Be made of the next stronger alloy to reduce thickness and weight
Overlap the damage by exactly 1 inch on each side regardless of rivet spacing
Have a cross-sectional area equal to or greater than the original stringer and extend past the damage by the required edge distance (Correct answer)

Correct answer: Have a cross-sectional area equal to or greater than the original stringer and extend past the damage by the required edge distance

A splice plate must restore the original cross-sectional area and be long enough to develop full load through the required number of fasteners past the damaged area.

Question 20: During a structural inspection, a mechanic finds a corrosion pit in an aluminum structural member. Which measurement determines if the component remains airworthy?

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

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

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

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 22: Continuing education for a certificated mechanic is:

Not legally mandated but strongly encouraged for professional development (Correct answer)
Mandatory only for turbine-rated mechanics
Required only for IA holders
Mandatory with specific hour requirements every two years

Correct answer: Not legally mandated but strongly encouraged for professional development

While no specific continuing education hours are legally required for a basic A&P certificate, professional development and staying current with technology is strongly encouraged by the FAA.

Question 23: After engine overhaul, a break-in run is performed. What oil type should NOT be used during engine break-in?

Multi-viscosity mineral oil
Ashless dispersant oil
Straight mineral oil
Synthetic oil (Correct answer)

Correct answer: Synthetic oil

Synthetic oil is too slippery during break-in and prevents cylinder walls from seating properly; mineral oil is required for new or overhauled engines.

Question 24: Which NDT method is LEAST effective for detecting defects in non-metallic composite materials?

Thermographic inspection
Magnetic particle inspection (Correct answer)
Ultrasonic testing
Radiographic inspection

Correct answer: Magnetic particle inspection

Magnetic particle inspection requires the material to be ferromagnetic; composite materials are non-metallic and non-ferromagnetic, making MPI completely ineffective for composites.

Question 25: What is the most important ethical consideration for ACS professionals in weight & balance?

Avoiding all challenging work assignments
Sharing all client information publicly
Maintaining objectivity, integrity, and confidentiality in all professional work (Correct answer)
Maximizing personal profit from each engagement

Correct answer: Maintaining objectivity, integrity, and confidentiality in all professional work

ACS professionals must maintain the highest ethical standards including objectivity, integrity, and confidentiality to protect clients and uphold professional credibility.

Question 26: The 'Swiss Cheese Model' of accident causation, as applied to aviation maintenance, illustrates that accidents occur when:

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

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 27: Which type of maintenance record entry is required after completion of a 100-hour inspection?

A Supplemental Type Certificate
A field approval form
A signed logbook entry per 14 CFR 43.11 (Correct answer)
An FAA Form 8130-3

Correct answer: A signed logbook entry per 14 CFR 43.11

14 CFR 43.11 requires a maintenance record entry including the date, aircraft total time, signature, and certificate number after each inspection.

Question 28: What is the first step in troubleshooting an aircraft system?

Disassemble the system
Identify the problem (Correct answer)
Check battery voltage
Replace suspected parts

Correct answer: Identify the problem

The first step is identifying the problem through observation or pilot reports.

Question 29: What component prevents an aircraft's structure from buckling under compressive loads?

Stringers (Correct answer)
Bulkheads
Spars
Ribs

Correct answer: Stringers

Stringers are structural elements that prevent buckling by reinforcing aircraft skin.

Question 30: Fuel flow is within normal limits but EGT is abnormally high on one cylinder. What is the most likely cause?

Clogged fuel injector on that cylinder (Correct answer)
Intake valve sticking open
Cracked exhaust valve
Incorrect spark plug gap

Correct answer: Clogged fuel injector on that cylinder

A clogged fuel injector delivers insufficient fuel to one cylinder, creating a lean mixture that raises EGT on that cylinder.

Question 31: What is the correct tube material for a high-pressure aircraft fuel line (above 1,500 PSI)?

Rigid PVC tubing
Copper tubing
Aluminum alloy 5052-O
Corrosion-resistant steel (CRES / stainless steel) or titanium (Correct answer)

Correct answer: Corrosion-resistant steel (CRES / stainless steel) or titanium

High-pressure fuel lines require CRES (stainless steel) or titanium tubing for the strength and corrosion resistance needed at pressures above 1,500 PSI.

Question 32: What is the primary purpose of an oleo strut in aircraft landing gear?

To provide electrical bonding between the gear and airframe
To lock the gear in the retracted position
To absorb landing shock through hydraulic fluid and compressed nitrogen (Correct answer)
To steer the nose wheel

Correct answer: To absorb landing shock through hydraulic fluid and compressed nitrogen

An oleo strut uses hydraulic fluid and compressed nitrogen to absorb and dissipate the energy of landing impact.

Question 33: An aircraft's altimeter was found to be inaccurate during a transponder/altimeter inspection. Under 14 CFR 91.411, the aircraft may be flown in controlled airspace under IFR:

Only if the discrepancy is within 75 feet
With an inoperative altimeter placard and the MEL applied
After the pilot verifies accuracy using GPS altitude
Not until the altimeter is repaired and the system retested and found within tolerances (Correct answer)

Correct answer: Not until the altimeter is repaired and the system retested and found within tolerances

14 CFR 91.411 prohibits flight in controlled airspace under IFR with an altimeter system that does not meet accuracy requirements; it must be repaired and retested.

Question 34: Under the ACS quality framework, which document provides the minimum standards for evaluating whether aviation maintenance meets regulatory requirements?

OSHA safety guidelines
The local FSDO's operations specifications
14 CFR Parts 43 and 65, applicable ADs, and approved manufacturer data (Correct answer)
The aircraft owner's manual

Correct answer: 14 CFR Parts 43 and 65, applicable ADs, and approved manufacturer data

Regulatory compliance in aviation maintenance is governed by 14 CFR Parts 43 and 65 together with applicable ADs and FAA-approved manufacturer data.

Question 35: What does a hydraulic system ground test unit (GTU) allow a technician to do?

Operate aircraft hydraulic systems using external ground power without running the engines (Correct answer)
Test hydraulic systems with engines running at high power settings safely on the ground
Measure hydraulic fluid contamination levels during system operation
Pressurize only the brake system independently from the main hydraulic system

Correct answer: Operate aircraft hydraulic systems using external ground power without running the engines

A ground test unit provides external hydraulic pressure and flow, allowing full system operation and testing without starting the aircraft engines.

Question 36: A turbocharged engine's manifold pressure continues to rise after the throttle is advanced to a set position. What component has likely failed?

Wastegate controller (Correct answer)
Fuel control unit
Throttle body seal
Intercooler bypass valve

Correct answer: Wastegate controller

A failed wastegate that sticks closed prevents exhaust from bypassing the turbine, causing uncontrolled manifold pressure rise (overboosting).

Question 37: What is the correct torque technique when installing AN/MS flareless tube fittings?

Thread until metal-to-metal contact, then add 1/4 turn
Tighten until resistance is felt, then tighten 1/16 turn more
Use the 'finger-tight plus turns' method specified in the applicable maintenance manual (Correct answer)
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 38: What is the primary purpose of a peel ply in composite layup?

To provide a sacrificial surface layer that creates a bondable texture when removed (Correct answer)
To distribute resin evenly across the laminate
To reinforce the outer skin of the composite panel
To seal the vacuum bag against air leaks

Correct answer: To provide a sacrificial surface layer that creates a bondable texture when removed

Peel ply is a woven fabric applied as the last layer during layup; when peeled off after cure it leaves a clean, textured surface ready for secondary bonding.

Question 39: The 'fail-safe' design concept in aircraft structures means:

The structure will never fail under any load condition
All structural repairs must restore the part to original factory dimensions
Every structural member has a 4:1 safety factor above ultimate load
Alternate load paths exist so that failure of one member does not cause catastrophic failure of the entire structure (Correct answer)

Correct answer: Alternate load paths exist so that failure of one member does not cause catastrophic failure of the entire structure

Fail-safe design provides redundant or alternate load paths so that a single structural failure (crack, fracture) is arrested or redistributed without causing sudden catastrophic collapse.

Question 40: Which instrument uses a Wheatstone bridge circuit to measure fuel quantity?

The capacitance-type fuel quantity system (Correct answer)
The resistor-type fuel quantity system
The pressure-differential fuel system
The float-type fuel quantity system

Correct answer: The capacitance-type fuel quantity system

Capacitance-type fuel quantity systems use a Wheatstone bridge to compare capacitance values and determine fuel quantity accurately.

Question 41: What is the correct procedure if a hydraulic system fluid sample indicates particle contamination above allowable limits?

Add a chemical dispersant to the fluid to dissolve the particles
Replace the hydraulic fluid and clean or replace contaminated components per maintenance manual (Correct answer)
Continue operation but reduce system pressure by 10% to compensate
Filter the system fluid through progressively finer portable filters

Correct answer: Replace the hydraulic fluid and clean or replace contaminated components per maintenance manual

Contamination above allowable limits requires fluid replacement and inspection/cleaning of components because dispersants are not approved and portable filtering may not address the contamination source.

Question 42: What is the primary function of an aircraft hydraulic system?

To provide drinking water to passengers
To cool the engine compartment
To transmit force for operating flight controls, landing gear, brakes, and other high-load mechanisms (Correct answer)
To fuel the aircraft engines

Correct answer: To transmit force for operating flight controls, landing gear, brakes, and other high-load mechanisms

Aircraft hydraulic systems use pressurized fluid to operate heavy-duty mechanisms like flight controls, landing gear retraction/extension, brakes, nose wheel steering, and thrust reversers.

Question 43: What is the most important ethical consideration for ACS professionals in hydraulic & pneumatic systems?

Maximizing personal profit from each engagement
Sharing all client information publicly
Avoiding all challenging work assignments
Maintaining objectivity, integrity, and confidentiality in all professional work (Correct answer)

Correct answer: Maintaining objectivity, integrity, and confidentiality in all professional work

ACS professionals must maintain the highest ethical standards including objectivity, integrity, and confidentiality to protect clients and uphold professional credibility.

Question 44: What type of hydraulic pump is most commonly used in high-performance aircraft as an engine-driven pump due to its variable output capability?

Gear pump
Vane pump
Variable displacement piston pump (Correct answer)
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 45: What does a sudden drop in fuel flow during an engine operational test with no corresponding change in throttle position indicate?

Fuel pump pressure exceeding regulator limits
Idle cutoff valve partially engaging
Fuel vapor lock or cavitation in the fuel system (Correct answer)
Mixture control moved inadvertently

Correct answer: Fuel vapor lock or cavitation in the fuel system

Vapor lock causes intermittent fuel starvation as fuel vaporizes in the fuel lines, creating a pocket that temporarily reduces liquid fuel flow.

Question 46: What is the minimum dwell time typically specified for dye penetrant inspection of standard discontinuities in aluminum alloy parts?

1 minute
30 seconds
5 to 30 minutes (Correct answer)
1 to 2 hours

Correct answer: 5 to 30 minutes

For most aluminum alloy parts, penetrant dwell times typically range from 5 to 30 minutes to allow adequate capillary action into discontinuities, as specified by the applicable process specification.

Question 47: How should ACS professionals approach client or stakeholder communication?

Only communicate in writing, never verbally
Use technical jargon regardless of the audience
Communication skills are unimportant for technical professionals
Use clear, professional language appropriate to the audience, confirm understanding, and document key communications (Correct answer)

Correct answer: Use clear, professional language appropriate to the audience, confirm understanding, and document key communications

Effective communication tailored to the audience's knowledge level is essential for building trust, ensuring understanding, and achieving professional objectives.

Question 48: What constitutes 'approved data' for performing a standard repair on a certificated aircraft?

ASTM standards only
Any data referenced in an aviation maintenance textbook
Any current manufacturer service bulletin
FAA-approved manufacturer data, FAA Advisory Circulars with approved methods, or DER-approved data (Correct answer)

Correct answer: FAA-approved manufacturer data, FAA Advisory Circulars with approved methods, or DER-approved data

Approved data sources include FAA-approved manufacturer manuals, AC 43.13-1B for standard practices, and data approved by a DER.

Question 49: During a top overhaul, a technician finds chrome cylinder walls. What special consideration applies?

Chrome cylinders require higher-viscosity oil for break-in
Chrome cylinders must use cast iron piston rings, not chrome rings (Correct answer)
Chrome cylinders require a longer break-in period than steel cylinders
Chrome cylinders cannot be re-honed and must be replaced

Correct answer: Chrome cylinders must use cast iron piston rings, not chrome rings

Chrome-plated cylinders must be fitted with cast iron piston rings because two chrome surfaces together will not seat properly and will cause excessive wear.

Question 50: What is the significance of a 'return to service' signature by a certificated mechanic?

It authorizes the next scheduled maintenance
It certifies that the work was performed per approved data and the aircraft is airworthy (Correct answer)
It transfers liability to the aircraft owner
It satisfies all AD requirements automatically

Correct answer: It certifies that the work was performed per approved data and the aircraft is airworthy

The return to service signature is the mechanic's professional certification that work was accomplished per approved standards and the aircraft is airworthy.

Question 51: What is the purpose of shielding on aircraft wiring, and where must the shield be grounded?

Shielding adds mechanical protection; ground at both ends always
Shielding reduces electromagnetic interference; grounded at one end only to prevent ground loop currents (Correct answer)
Shielding provides redundancy; grounded at the load end only
Shielding increases current capacity; grounded at the power source end

Correct answer: Shielding reduces electromagnetic interference; grounded at one end only to prevent ground loop currents

Coaxial cable and shielded wire shields are grounded at one end only to prevent ground loops that would introduce noise into the shielded circuit.

Question 52: Which tool measures cylinder wear in an engine?

Cylinder bore gauge (Correct answer)
Micrometer
Feeler gauge
Dial indicator

Correct answer: Cylinder bore gauge

A cylinder bore gauge measures wear inside the engine cylinders.

Question 53: Under the ACS framework, 'risk management' is best described as:

Documenting all repairs in the aircraft logbook
Following manufacturer inspection intervals exactly
Avoiding all non-standard maintenance tasks
The process of identifying hazards, assessing risk, and mitigating it to an acceptable level (Correct answer)

Correct answer: The process of identifying hazards, assessing risk, and mitigating it to an acceptable level

ACS risk management involves a systematic process of identifying, assessing, and mitigating hazards before performing maintenance tasks.

Question 54: A mechanic completes a 100-hour inspection and finds several discrepancies. The aircraft owner declines repairs. What must the mechanic do?

Ground the aircraft permanently
Contact the FAA immediately
Refuse to sign off the inspection and note discrepancies in writing to the owner (Correct answer)
Return the aircraft to service anyway

Correct answer: Refuse to sign off the inspection and note discrepancies in writing to the owner

The mechanic must not approve an unairworthy aircraft for return to service and must advise the owner in writing of discrepancies found.

Question 55: What is the purpose of a desiccant in an aircraft pneumatic system?

Filter particulate contamination larger than 10 microns
Regulate downstream pressure to a constant value
Remove moisture from compressed air before it enters system components (Correct answer)
Lubricate moving components within the pneumatic valves

Correct answer: Remove moisture from compressed air before it enters system components

A desiccant absorbs moisture from compressed air, preventing ice formation at altitude and corrosion within system components.

Question 56: A suspected unapproved part (SUP) is discovered during maintenance. The correct action is to:

Return it to the supplier for a refund
Tag it, remove it from service, and report it to the FAA (Correct answer)
Install it if it fits correctly
Test it and install if it passes

Correct answer: Tag it, remove it from service, and report it to the FAA

FAA Order 8120.10 directs mechanics to remove SUPs from service, quarantine them, and report to the FAA's Suspected Unapproved Parts Program.

Question 57: What is the purpose of a fuel heat exchanger on a turbine aircraft?

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

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 58: Which NDT method is most appropriate for detecting delaminations in a carbon fiber reinforced polymer (CFRP) aircraft panel?

Eddy current surface probe testing
Ultrasonic testing (pulse-echo or through-transmission) (Correct answer)
Dye penetrant inspection
Magnetic particle inspection

Correct answer: Ultrasonic testing (pulse-echo or through-transmission)

Ultrasonic testing is the preferred method for detecting delaminations in CFRP composites because delaminations create internal interfaces that reflect ultrasonic energy, and the method works on non-conductive materials.

Question 59: What color is 100LL aviation gasoline (AVGAS) dyed, and why?

Red, to distinguish it from Jet-A
Clear/colorless, undyed for purity
Green, per FAA standard
Blue, to identify it as 100 octane low lead and prevent misfueling with other grades (Correct answer)

Correct answer: Blue, to identify it as 100 octane low lead and prevent misfueling with other grades

100LL AVGAS is dyed blue to identify it as 100 octane low lead fuel and prevent misfueling with Jet-A or other grades.

Question 60: 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 allow fuel vapors to escape for fire prevention
To equalize pressure between wing tanks
To enable fuel cross-feed between 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.

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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