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

Question 1: A 'Manufacturer's Maintenance Manual' (MMM) takes precedence over AC 43.13-1B because:

The FAA requires MMMs to be used exclusively
Manufacturer data is type-specific and legally part of the aircraft's approved design (Correct answer)
MMMs are always more current than ACs
AC 43.13-1B only applies to experimental aircraft

Correct answer: Manufacturer data is type-specific and legally part of the aircraft's approved design

Manufacturer maintenance manuals are type-specific approved data tied to the aircraft's type certificate, and they take precedence over the more general guidance in AC 43.13-1B.

Question 2: What is the first step in troubleshooting an aircraft system?

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

Correct answer: Identify the problem

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

Question 3: Which document serves as the authoritative source for an aircraft's certificated weight, engine model, and fuel type?

The aircraft maintenance manual (AMM)
The Type Certificate Data Sheet (TCDS) (Correct answer)
The aircraft flight manual (AFM)
The weight and balance report

Correct answer: The Type Certificate Data Sheet (TCDS)

The TCDS is the FAA's official record of the design specifications and limitations for a certificated aircraft.

Question 4: What condition causes a hydraulic pump to cavitate?

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

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 5: What is the function of a boost pump in an aircraft fuel system?

It filters fuel before delivery to the engine
It provides positive fuel pressure for starting, backup fuel pressure, and transfer between tanks (Correct answer)
It replaces the engine-driven fuel pump as the primary pump
It controls the fuel-air mixture ratio

Correct answer: It provides positive fuel pressure for starting, backup fuel pressure, and transfer between tanks

Electric boost pumps provide fuel pressure for engine starting, serve as backup if the engine-driven pump fails, and assist in fuel transfer between tanks.

Question 6: What does a landing gear squat switch (weight-on-wheels switch) do?

Activates the landing lights on touchdown
Arms the gear retraction system when airborne
Controls nosewheel steering authority
Prevents gear retraction on the ground and enables ground-only functions (Correct answer)

Correct answer: Prevents gear retraction on the ground and enables ground-only functions

The squat switch prevents inadvertent gear retraction while the aircraft is on the ground and may also enable ground spoilers, thrust reversers, or other ground-only systems.

Question 7: During a ground run, manifold pressure is 2 inches Hg higher than standard atmosphere with the throttle closed. What does this indicate?

Supercharger is engaged
Throttle plate is not fully closing (Correct answer)
Intake air filter is clogged
Manifold pressure gauge is miscalibrated

Correct answer: Throttle plate is not fully closing

A throttle plate that does not fully close allows high-pressure air to leak into the intake manifold, raising manifold pressure above atmospheric.

Question 8: 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
Filter the system fluid through progressively finer portable filters
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

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 9: What is the impact of regulatory changes on ACS professionals?

Regulations never change once established
Only government employees need to follow regulatory changes
Regulatory changes require updating practices, procedures, and documentation to maintain compliance (Correct answer)
Regulatory changes only affect large organizations

Correct answer: Regulatory changes require updating practices, procedures, and documentation to maintain compliance

Professionals must monitor and adapt to regulatory changes that affect their practice, ensuring continued compliance and effective service delivery.

Question 10: 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 11: When inspecting flexible hydraulic hose for serviceability, which condition requires immediate replacement?

Slight surface scuffing on the outer protective jacket without wire braid exposure
A small area of faded color on the outer jacket from UV exposure
Wire braid visible through the outer cover at any point (Correct answer)
Minor routing deviation of less than 10% from the installed bend radius

Correct answer: Wire braid visible through the outer cover at any point

Exposed wire braid indicates the outer protective cover is compromised, meaning the hose is susceptible to further damage and must be replaced immediately.

Question 12: The term 'continued airworthiness' under the ACS framework refers to:

An optional manufacturer maintenance program
Maintaining an aircraft to its type certificate standards throughout its operational life (Correct answer)
Flying until an aircraft breaks down
Issuing a new airworthiness certificate annually

Correct answer: Maintaining an aircraft to its type certificate standards throughout its operational life

Continued airworthiness means sustaining compliance with the aircraft's type design through ongoing maintenance and inspections throughout its life.

Question 13: What is the maximum allowable bend radius violation that can occur when bending aluminum aircraft tubing?

The tube may be kinked if the kink is less than 10% of the tube diameter
Kinks up to 1/16 inch depth are acceptable if within 6 inches of a fitting
Minor kinks can be straightened with a tube repair tool
No kinking is acceptable — kinked tubing must be replaced (Correct answer)

Correct answer: No kinking is acceptable — kinked tubing must be replaced

Any kink in aluminum aircraft tubing significantly weakens it and creates stress concentration points — kinked tubing must always be replaced, never repaired or reused.

Question 14: When weighing an aircraft, which type of scale position provides the most accurate results?

A single scale under the CG location
Scales under each main gear and nose or tail gear with the aircraft level (Correct answer)
Scales under the tail skid only
Scales only under the main gear with tail propped up

Correct answer: Scales under each main gear and nose or tail gear with the aircraft level

Placing scales under each gear while the aircraft is level ensures all reaction forces are measured, allowing accurate calculation of weight and CG.

Question 15: When computing weight and balance, a negative moment indicates the weight is located:

At the datum
Aft of the datum
Forward of the datum (Correct answer)
Above the center of gravity

Correct answer: Forward of the datum

A negative arm (forward of datum) multiplied by a positive weight produces a negative moment, indicating weight forward of the datum.

Question 16: Moisture contamination in a composite honeycomb panel is MOST commonly found using which inspection technique?

Eddy current surface scan
Dye penetrant testing
Infrared thermography or radiographic (X-ray) inspection (Correct answer)
Magnetic particle testing

Correct answer: Infrared thermography or radiographic (X-ray) inspection

Infrared thermography detects temperature differences caused by water-filled cells, and X-ray radiography can reveal water pooling patterns inside honeycomb cells.

Question 17: What color is 100LL aviation gasoline (AVGAS) dyed, and why?

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)
Red, to distinguish it from Jet-A

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 18: Which part of the maintenance manual specifies troubleshooting steps?

Parts Catalog section
Troubleshooting section (Correct answer)
Schematics section
General Information section

Correct answer: Troubleshooting section

The Troubleshooting section of the manual provides step-by-step diagnostic guidance.

Question 19: How does technology impact modern electrical systems & avionics practices?

Technology has made professional expertise unnecessary
Only large organizations benefit from technology in this field
Technology improves accuracy, efficiency, and capabilities while requiring new skills and knowledge (Correct answer)
Technology has no impact on this field

Correct answer: Technology improves accuracy, efficiency, and capabilities while requiring new skills and knowledge

Technological advances have transformed professional practice by improving diagnostic capabilities, data analysis, documentation, and efficiency while requiring practitioners to develop new competencies.

Question 20: In ultrasonic testing, what is 'back-wall echo loss' an indication of?

Surface roughness causing signal scatter at the entry point only
Insufficient couplant application
A large internal discontinuity or severe attenuation blocking the return of the back-wall reflection (Correct answer)
Calibration error in the time base

Correct answer: A large internal discontinuity or severe attenuation blocking the return of the back-wall reflection

Loss of the back-wall echo indicates that a large internal flaw or severe attenuation is preventing the ultrasonic pulse from reaching and reflecting off the far wall of the test piece.

Question 21: 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 cylinder baffling is too effective
The fuel injector nozzle flow is too high for that cylinder
The new cylinder is not receiving ignition on both plugs (Correct answer)
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 22: 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 AC applies regardless of aircraft type
The repair method is acceptable to the FAA for that specific repair and no approved manufacturer data exists (Correct answer)

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 23: A Designated Engineering Representative (DER) has authority to:

Approve technical data for major repairs and alterations on behalf of the FAA (Correct answer)
Grant IA certificates to mechanics
Perform annual inspections on all aircraft types
Issue Airworthiness Directives

Correct answer: Approve technical data for major repairs and alterations on behalf of the FAA

DERs are delegated by the FAA to approve engineering data, which can serve as the approved data basis for major repairs and alterations.

Question 24: What is the purpose of shielding on aircraft wiring, and where must the shield be grounded?

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 adds mechanical protection; ground at both ends always
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 25: What effect does increasing the frequency of an ultrasonic transducer have on inspection capability?

Increases both penetration depth and sensitivity equally
Increases sensitivity to small defects but reduces penetration depth (Correct answer)
Increases penetration depth but reduces sensitivity to small defects
Has no effect on penetration or sensitivity

Correct answer: Increases sensitivity to small defects but reduces penetration depth

Higher ultrasonic frequencies produce shorter wavelengths, improving resolution and sensitivity to small defects, but are attenuated more rapidly, reducing penetration depth in the material.

Question 26: 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
Spark plug gap on that cylinder
Cylinder baffling and cooling fins for that cylinder (Correct answer)
Fuel injector flow rate for 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 27: Which method is primarily used to detect corrosion on aircraft structures?

X-ray imaging
Magnetic field mapping
Visual inspection (Correct answer)
Ultrasonic inspection

Correct answer: Visual inspection

Visual inspection is the first method to identify corrosion before using specialized tests.

Question 28: Under an SMS framework, a 'just culture' policy primarily aims to:

Standardize disciplinary procedures across all maintenance stations
Differentiate between honest mistakes and reckless behavior to encourage reporting (Correct answer)
Eliminate punishment for all maintenance errors
Transfer liability for errors to the operator rather than the mechanic

Correct answer: Differentiate between honest mistakes and reckless behavior to encourage reporting

Just culture distinguishes between unintentional errors and willful violations so that honest mistakes are treated with support and coaching, encouraging open reporting of safety concerns.

Question 29: FAA Form 337 (Major Repair and Alteration) must be submitted to the FAA within:

Immediately before the first flight after the work
90 days of work completion
24 hours of return to service
30 days of work completion (Correct answer)

Correct answer: 30 days of work completion

14 CFR 43.9 and related regulations require Form 337 to be submitted to the FAA Aircraft Registration Branch within 30 days after the work is approved for return to service.

Question 30: How should ACS professionals approach client or stakeholder communication?

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

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 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 surface area of the corroded region
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 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: When inspecting aircraft tires for continued airworthiness, what condition mandates immediate removal from service?

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

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 33: When servicing an oleo strut, the correct fluid level is verified by:

Using a pressure gauge on the Schrader valve
Measuring strut extension with a ruler only
Deflating the strut fully, adding fluid to the specified level, then re-inflating with nitrogen (Correct answer)
Checking the fluid reservoir sight glass

Correct answer: Deflating the strut fully, adding fluid to the specified level, then re-inflating with nitrogen

The correct procedure is to fully deflate the strut, fill it with the specified hydraulic fluid to the proper level, then re-inflate with dry nitrogen to the manufacturer's specified pressure.

Question 34: What is the scope of practice for ACS certification in composite materials & repair?

Defined boundaries of competence and authority established by the certifying body and applicable regulations (Correct answer)
Only the employer defines the scope of practice
The scope is determined individually by each professional
There are no limits on what certified professionals can do

Correct answer: Defined boundaries of competence and authority established by the certifying body and applicable regulations

Scope of practice defines the activities, procedures, and processes that a certified professional is authorized to perform based on their education, training, and certification level.

Question 35: 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, but only if the aircraft is loaded to MTOW
No, 82.5 exceeds the aft limit
Yes, 82.5 is between 78.0 and 86.5 (Correct answer)
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 36: Which NDT method is most appropriate for detecting delaminations in a carbon fiber reinforced polymer (CFRP) aircraft panel?

Eddy current surface probe testing
Magnetic particle inspection
Ultrasonic testing (pulse-echo or through-transmission) (Correct answer)
Dye penetrant 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 37: How does technology impact modern hydraulic & pneumatic systems practices?

Only large organizations benefit from technology in this field
Technology improves accuracy, efficiency, and capabilities while requiring new skills and knowledge (Correct answer)
Technology has made professional expertise unnecessary
Technology has no impact on this field

Correct answer: Technology improves accuracy, efficiency, and capabilities while requiring new skills and knowledge

Question 38: What is the importance of peer review in aviation mechanics?

Peer review is unnecessary for experienced professionals
Peer review undermines professional confidence
Peer review ensures quality, catches errors, provides learning opportunities, and maintains professional standards (Correct answer)
Only management should review professional work

Correct answer: Peer review ensures quality, catches errors, provides learning opportunities, and maintains professional standards

Peer review is a cornerstone of professional quality assurance, providing independent verification, knowledge sharing, and continuous improvement opportunities.

Question 39: What career advancement paths exist for ACS certified professionals?

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

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 40: What career advancement paths exist for ACS certified professionals?

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

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 41: What is the purpose of a diode installed in parallel with a relay coil in an aircraft electrical circuit?

To increase the relay switching speed
To suppress the voltage spike (back-EMF) generated when the relay de-energizes (Correct answer)
To provide redundant power to the relay coil
To reduce current draw during relay operation

Correct answer: To suppress the voltage spike (back-EMF) generated when the relay de-energizes

A flyback (snubber) diode connected across a relay coil absorbs the inductive voltage spike that occurs when coil current is interrupted, protecting other circuit components.

Question 42: What is the primary purpose of ballast in an aircraft weight and balance context?

To increase structural load capacity
To reduce fuel consumption
To shift the CG to within approved limits (Correct answer)
To increase gross weight capacity

Correct answer: To shift the CG to within approved limits

Ballast is temporary or permanent weight added to move the aircraft CG into the approved operating range.

Question 43: The glass transition temperature (Tg) of a cured composite resin is important because:

It defines the temperature at which the fibers begin to melt
It specifies the lowest operational temperature for the composite
It determines the maximum cure temperature allowed during manufacturing
Above Tg, the resin softens significantly and loses stiffness and strength (Correct answer)

Correct answer: Above Tg, the resin softens significantly and loses stiffness and strength

The glass transition temperature is the point above which an amorphous polymer transitions from a rigid glassy state to a rubbery state, causing a dramatic drop in structural properties.

Question 44: Which type of inspection checks for internal engine cracks?

Ultrasonic inspection
Visual inspection
Dye penetrant inspection
Magnetic particle inspection (Correct answer)

Correct answer: Magnetic particle inspection

Magnetic particle inspection detects surface and subsurface cracks in ferrous materials.

Question 45: What qualifications are needed for advanced aviation mechanics practice?

No additional qualifications beyond initial certification
Advanced certifications, specialized training, demonstrated experience, and ongoing professional development (Correct answer)
Only a college degree in any subject
Advanced practice requires no formal credentials

Correct answer: Advanced certifications, specialized training, demonstrated experience, and ongoing professional development

Advanced practice requires building upon foundational knowledge through specialized certifications, targeted training, and demonstrated competence in specific areas.

Question 46: What does a hydraulic snubber do in a pressure gauge line?

Dampens pressure surges to protect the gauge and provide a steady reading (Correct answer)
Prevents fluid from flowing backward through the gauge during pressure drops
Filters contamination out of the fluid sample going to the gauge
Amplifies small pressure changes to improve gauge sensitivity

Correct answer: Dampens pressure surges to protect the gauge and provide a steady reading

A snubber is a small orifice or restriction that dampens rapid pressure pulsations, protecting the gauge bourdon tube from fatigue damage and providing a readable steady indication.

Question 47: During a preflight fuel check, a pilot/mechanic finds a small amount of water in the fuel sample. The correct action is:

Ground the aircraft indefinitely until the tank is removed
Add fuel system icing inhibitor and return to service
Continue sampling and draining until no water is found, verifying the sample is clear (Correct answer)
Drain only the affected sump and continue

Correct answer: Continue sampling and draining until no water is found, verifying the sample is clear

When water is found in a fuel sample, continue draining and sampling from all sumps until all samples are consistently clear and free of water, then verify the quantity before flight.

Question 48: What is a borescope used for?

Internal visual inspections (Correct answer)
Measuring airspeed
Removing corrosion
Cleaning components

Correct answer: Internal visual inspections

A borescope allows internal inspection of engines and airframes without disassembly.

Question 49: Which NDT method is LEAST effective for detecting defects in non-metallic composite materials?

Magnetic particle inspection (Correct answer)
Ultrasonic testing
Radiographic inspection
Thermographic 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 50: Which tool is commonly used to check continuity in electrical circuits?

Caliper
Torque wrench
Rivet gun
Multimeter (Correct answer)

Correct answer: Multimeter

A multimeter is used to check continuity and diagnose electrical faults.

Question 51: What is the purpose of 'lapping' valves during engine overhaul?

Create a precise, gas-tight seal between the valve face and the valve seat (Correct answer)
Harden the valve seat surface by work-hardening with abrasive compound
Measure the exact thickness of the valve head margin
Remove corrosion from the valve stem for smooth operation in the guide

Correct answer: Create a precise, gas-tight seal between the valve face and the valve seat

Lapping uses fine abrasive compound to create a matched, gas-tight contact surface between the valve face and seat, ensuring no compression or combustion gases escape past the valve.

Question 52: What is the scope of practice for ACS certification in weight & balance?

Defined boundaries of competence and authority established by the certifying body and applicable regulations (Correct answer)
There are no limits on what certified professionals can do
Only the employer defines the scope of practice
The scope is determined individually by each professional

Correct answer: Defined boundaries of competence and authority established by the certifying body and applicable regulations

Scope of practice defines the activities, procedures, and processes that a certified professional is authorized to perform based on their education, training, and certification level.

Question 53: What is the purpose of a fuel crossfeed system on a multi-engine aircraft?

To preheat fuel in cold weather
To dump fuel overboard in an emergency
To transfer fuel only to the landing gear hydraulic reservoir
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)

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 54: What is the main purpose of the carburetor in an aircraft engine?

Lubricate engine parts
Mix air and fuel (Correct answer)
Increase engine temperature
Control exhaust gases

Correct answer: Mix air and fuel

The carburetor mixes air and fuel in the correct ratio for combustion.

Question 55: When is it mandatory to bond and ground an aircraft during fueling?

Only when fueling in dry climates with low humidity
Grounding is optional if fueling from a bonded fuel truck
Always, before fueling begins, to prevent static discharge ignition of fuel vapors (Correct answer)
Only when fueling turbine aircraft

Correct answer: Always, before fueling begins, to prevent static discharge ignition of fuel vapors

Bonding and grounding are always required before fueling to equalize static electrical charges and prevent sparks that could ignite fuel vapors.

Question 56: What type of fuel is used in most turbine-powered aircraft operated in the United States?

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

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 57: 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 58: What is the primary function of an aircraft hydraulic system?

To transmit force for operating flight controls, landing gear, brakes, and other high-load mechanisms (Correct answer)
To cool the engine compartment
To provide drinking water to passengers
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 59: An aircraft engine has a magneto drop of 175 RPM on one magneto and 50 RPM on the other during run-up. The maximum allowable drop is 125 RPM. What does this indicate?

Both magnetos are functioning normally
The magneto showing 175 RPM drop has an ignition problem requiring investigation (Correct answer)
The magneto showing 50 RPM drop indicates a timing issue
The engine should be run longer to warm up before re-checking

Correct answer: The magneto showing 175 RPM drop has an ignition problem requiring investigation

A magneto drop exceeding the maximum allowable limit (175 RPM vs. 125 RPM limit) indicates a faulty ignition component such as spark plugs, ignition leads, or the magneto itself.

Question 60: What is the scope of practice for ACS certification in hydraulic & pneumatic systems?

Only the employer defines the scope of practice
Defined boundaries of competence and authority established by the certifying body and applicable regulations (Correct answer)
There are no limits on what certified professionals can do
The scope is determined individually by each professional

Correct answer: Defined boundaries of competence and authority established by the certifying body and applicable regulations

Scope of practice defines the activities, procedures, and processes that a certified professional is authorized to perform based on their education, training, and certification level.

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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These practice questions were written with AI tools. They are not real exam questions. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy

Sources & references

Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy

faa.gov — Score release, score validity, eligibility, passing score, retake policy, time limit, exam format, exam information · verified Oct 2026
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