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

Question 1: How should discrepancies be documented during inspection?

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

Correct answer: In maintenance logbooks

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

Question 2: When fuel is burned during flight, how does the CG typically shift in a high-wing aircraft with wing tanks?

CG does not shift
CG moves up
CG moves aft
CG moves forward (Correct answer)

Correct answer: CG moves forward

In most high-wing designs, wing fuel is located forward of the CG, so as fuel burns off, the CG moves forward.

Question 3: During cylinder inspection, a technician finds a barrel that is worn 0.010 inch over the maximum specified diameter. What is the correct action?

Chrome plate or replace the cylinder; it cannot be returned to service at this dimension (Correct answer)
Apply cylinder wall coating to restore the diameter
Return the cylinder to service with a note in the maintenance record
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 4: What qualifications are needed for advanced aviation mechanics practice?

Advanced certifications, specialized training, demonstrated experience, and ongoing professional development (Correct answer)
Only a college degree in any subject
No additional qualifications beyond initial certification
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 5: What is the moment index, and why is it used?

The maximum allowable moment for a given weight
A scaled-down moment value (moment ÷ a reduction factor) to simplify arithmetic (Correct answer)
A ratio of weight to drag used for performance calculations
The CG position expressed as a percentage of wing chord

Correct answer: A scaled-down moment value (moment ÷ a reduction factor) to simplify arithmetic

A moment index divides the moment by a constant (e.g., 1,000) to produce smaller, easier-to-use numbers on loading charts.

Question 6: What is a couplant used for in contact ultrasonic testing?

To eliminate the air gap between the transducer and the test surface, enabling sound transmission (Correct answer)
To magnetize the test piece
To enhance fluorescent visibility under UV light
To develop the penetrant indication

Correct answer: To eliminate the air gap between the transducer and the test surface, enabling sound transmission

A couplant (such as water, oil, or gel) fills the air gap between the transducer and test surface because ultrasonic sound waves cannot effectively transmit through air.

Question 7: A mechanic finds exfoliation corrosion on an aluminum alloy wing spar cap. What action is required?

Remove the spar cap and replace it
Clean, treat, and determine if remaining material meets minimum thickness per SRM (Correct answer)
Polish smooth, apply zinc chromate, and return to service
Treat with Alodine and apply primer immediately

Correct answer: Clean, treat, and determine if remaining material meets minimum thickness per SRM

Exfoliation corrosion causes layer-by-layer material loss; the mechanic must clean, treat, measure the remaining material, and compare it to the SRM minimum thickness allowable to determine airworthiness.

Question 8: Which component in a pneumatic system performs the same function as a hydraulic system relief valve?

Pressure relief valve (Correct answer)
Check valve
Pressure regulator
Filter/separator

Correct answer: Pressure relief valve

A pneumatic pressure relief valve protects the system from overpressure just as a hydraulic relief valve does, opening to vent excess pressure to atmosphere.

Question 9: How does technology impact modern electrical systems & avionics practices?

Technology improves accuracy, efficiency, and capabilities while requiring new skills and knowledge (Correct answer)
Technology has no impact on this field
Technology has made professional expertise unnecessary
Only large organizations benefit from technology in 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 10: 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
The landing gear uplock switch indicating a failed gear retraction
A defective gear warning horn relay
A faulty throttle position switch sending a false low-power signal (Correct answer)

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 11: During an aircraft fuel system inspection, you discover water contamination in the fuel sumps. After draining until clear fuel appears, what additional check is recommended?

Ground the aircraft for 48 hours to allow remaining water to settle
Check the fuel caps and vent systems for leaks that allowed moisture ingress (Correct answer)
Drain the entire fuel system and refuel completely
Add a water-dispersant fuel additive

Correct answer: Check the fuel caps and vent systems for leaks that allowed moisture ingress

After removing water contamination, investigate the source by checking fuel caps, vent systems, and any points where water could have entered to prevent recurrence.

Question 12: A Part 145 Certificated Repair Station differs from an individual A&P mechanic primarily in that it:

Can perform work on aircraft of any nationality without limitation
Is exempt from FAA oversight once certified
Can approve major alterations without submitting Form 337
Operates under an approved Quality Control system and may have specific ratings for complex work (Correct answer)

Correct answer: Operates under an approved Quality Control system and may have specific ratings for complex work

Part 145 repair stations must maintain an approved Quality Control system and hold specific ratings that authorize the scope of their work.

Question 13: When inspecting a riveted skin joint, you find a rivet with a shop head that is too small. What is the correct corrective action?

Apply epoxy adhesive to fill the gap around the rivet
Drill out and replace the rivet with the next larger diameter
Leave in place if the shop head diameter is at least 1.2 times the rivet diameter
Drill out and replace with the same diameter rivet driven correctly (Correct answer)

Correct answer: Drill out and replace with the same diameter rivet driven correctly

An undersized shop head indicates improper driving; the rivet must be drilled out and replaced using correct driving technique with the same specification rivet.

Question 14: When installing a new wheel bearing on aircraft landing gear, the bearing should be:

Heated in an oven to 300°F for press fit
Bonded with Loctite to the axle
Installed dry to prevent contamination
Packed with the correct grease per the AMM specification before installation (Correct answer)

Correct answer: Packed with the correct grease per the AMM specification before installation

Wheel bearings must be thoroughly packed with the specific grease type specified in the AMM to ensure proper lubrication and prevent corrosion.

Question 15: The ASRS (Aviation Safety Reporting System) offers reporters immunity from FAA certificate action primarily to:

Replace mandatory accident reporting requirements
Reward mechanics financially for reporting
Provide legal immunity in civil lawsuits
Encourage candid, voluntary disclosure of safety hazards (Correct answer)

Correct answer: Encourage candid, voluntary disclosure of safety hazards

ASRS immunity protects reporters so they will voluntarily disclose safety-relevant incidents without fear of certificate action, improving overall system safety.

Question 16: What is the importance of professional networking in aviation maintenance?

Networking only benefits entry-level professionals
Networking is a waste of time for established professionals
Only online networking has value
Building relationships with peers enables knowledge sharing, professional development, and career advancement (Correct answer)

Correct answer: Building relationships with peers enables knowledge sharing, professional development, and career advancement

Professional networks provide opportunities for knowledge exchange, mentorship, collaboration, and staying informed about industry trends and opportunities.

Question 17: When is a Form 337 (Major Repair and Alteration) required to be submitted to the FAA?

For every scheduled maintenance inspection
When performing any repair listed in AC 43.13
Upon completion of a major repair or major alteration (Correct answer)
Only when the repair involves powerplant components

Correct answer: Upon completion of a major repair or major alteration

FAA Form 337 must be completed and submitted to the FAA Flight Standards District Office within 48 hours after a major repair or major alteration is completed.

Question 18: What documentation is required when performing electrical systems & avionics work?

Detailed records of methods used, findings, conclusions, and supporting evidence (Correct answer)
Only a verbal summary to the supervisor
No documentation is required for professional work
Documentation is only needed if problems are found

Correct answer: Detailed records of methods used, findings, conclusions, and supporting evidence

Thorough documentation protects both the professional and the client, provides an audit trail, and ensures work can be reviewed, verified, or continued by others.

Question 19: Which part of the maintenance manual specifies troubleshooting steps?

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

Correct answer: Troubleshooting section

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

Question 20: During a borescope inspection of a turbine engine combustion section, you observe hot spots and discoloration on the combustion liner. The next step should be:

Compare findings to engine manufacturer's limits and serviceable criteria (Correct answer)
Apply a protective coating to the discolored area
Continue operating with increased monitoring intervals
Immediately replace the combustion liner without further analysis

Correct answer: Compare findings to engine manufacturer's limits and serviceable criteria

Borescope findings must be compared against the manufacturer's inspection criteria to determine if the component is serviceable, requires repair, or replacement.

Question 21: Which type of inspection checks for internal engine cracks?

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

Correct answer: Magnetic particle inspection

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

Question 22: What does a hydraulic snubber do in a pressure gauge line?

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

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 23: 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)
Confirmation bias
Complacency
Normalization of deviance

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 24: Ethics in aviation maintenance requires that a mechanic who is pressured by a supervisor to approve an unairworthy aircraft should:

Complete the task but file an anonymous ASRS report after the flight
Follow supervisor instructions since they carry final authority
Approve with a written note limiting personal liability
Refuse to sign off and escalate to higher authority or the FAA if necessary (Correct answer)

Correct answer: Refuse to sign off and escalate to higher authority or the FAA if necessary

A mechanic's signature on a return-to-service constitutes a personal safety certification; no supervisor can legally override this, and escalation to the FAA is always available.

Question 25: What is the scope of practice for ACS certification in electrical systems & avionics?

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

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 26: When must a maintenance log entry be made?

Only after engine overhauls
Every time maintenance is performed (Correct answer)
At the end of the year
Only after inspections

Correct answer: Every time maintenance is performed

A maintenance log entry must be made anytime maintenance, preventive maintenance, or alteration is performed.

Question 27: 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)
A malfunctioning magneto
Incorrect ignition timing

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

Tighten the fitting incrementally until seepage stops, regardless of torque limits
Apply an external sealant compound to stop the seepage temporarily
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

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.

Question 29: What is the primary purpose of a fuel strainer (gascolator) in a reciprocating aircraft engine fuel system?

To remove water and sediment from fuel before it reaches the carburetor or fuel injector (Correct answer)
To regulate fuel pressure to the engine
To prevent vapor lock in the fuel lines
To measure fuel flow rate

Correct answer: To remove water and sediment from fuel before it reaches the carburetor or fuel injector

A fuel strainer (gascolator) filters water and particulate contamination from the fuel before it enters the engine fuel metering system.

Question 30: 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
Annotate the maintenance log and continue working
Ignore it unless the aircraft is about to fly

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 31: What is the advantage of a brake-by-wire (electro-hydraulic) braking system compared to a conventional hydraulic brake system?

Allows the pilot to apply greater mechanical advantage to brake pedals
Reduces aircraft weight by using smaller diameter brake lines
Eliminates the need for hydraulic fluid entirely by using electric motors
Provides faster and more precise brake pressure modulation for anti-skid performance (Correct answer)

Correct answer: Provides faster and more precise brake pressure modulation for anti-skid performance

Electro-hydraulic brake systems use electronic control to modulate hydraulic pressure with greater speed and precision than mechanical inputs alone, improving anti-skid performance.

Question 32: During engine run-up, a pilot reports intermittent engine roughness that disappears when carburetor heat is applied. What does this indicate?

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

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

Throttle body seal
Fuel control unit
Wastegate controller (Correct answer)
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 34: An EGT gauge shows all cylinders rise normally during leaning except one which rises sharply then drops off. What does this indicate?

That cylinder has a leaking exhaust valve
That cylinder has high compression
That cylinder is misfiring
That cylinder has a partially clogged fuel injector (Correct answer)

Correct answer: That cylinder has a partially clogged fuel injector

A clogged injector delivers less fuel, so that cylinder reaches peak EGT much earlier in the leaning process and then goes excessively lean before the others.

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)
Pressurize only the brake system independently from the main hydraulic system
Test hydraulic systems with engines running at high power settings safely on the ground
Measure hydraulic fluid contamination levels during system operation

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: When inspecting a pressurized fuselage, fatigue cracks most commonly originate at:

Longitudinal seams on the bottom of the fuselage
Window and door cutouts, fastener holes, and areas of stress concentration (Correct answer)
Smooth, unpierced skin panels away from all fasteners
Painted exterior surfaces that have not been touched

Correct answer: Window and door cutouts, fastener holes, and areas of stress concentration

Stress concentrations at fastener holes, window frames, and door cutouts create the highest cyclic stress levels during pressurization cycles, making them the most common fatigue crack initiation sites.

Question 37: Under the ACS standards, a mechanic must demonstrate knowledge of quality assurance by understanding that an Inspection Authorization (IA) is required to:

Perform routine oil changes on turbine engines
Sign off on 100-hour inspection records
Approve an aircraft for return to service after an annual inspection (Correct answer)
Install PMA parts

Correct answer: Approve an aircraft for return to service after an annual inspection

Annual inspections can only be approved for return to service by a mechanic holding an IA, per 14 CFR 65.95.

Question 38: Under 14 CFR 65.83, a certificated mechanic must have performed or supervised work in the aviation maintenance field within the preceding how many months to exercise certificate privileges?

12 months
24 months (Correct answer)
36 months
6 months

Correct answer: 24 months

14 CFR 65.83 requires mechanics to have performed or supervised at least 6 months of work within the preceding 24 months to exercise certificate privileges.

Question 39: An A&P mechanic with an Inspection Authorization (IA) may perform which of the following that a basic A&P may not?

Perform sheet metal repairs
Sign off 100-hour inspections
Approve major repairs and alterations for return to service (Correct answer)
Replace aircraft engines

Correct answer: Approve major repairs and alterations for return to service

An IA holder can approve major repairs and major alterations for return to service on certificated aircraft.

Question 40: 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)
Issuing a new airworthiness certificate annually
Flying until an aircraft breaks down

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

Chrome cylinders require a longer break-in period than steel cylinders
Chrome cylinders require higher-viscosity oil for break-in
Chrome cylinders must use cast iron piston rings, not chrome rings (Correct answer)
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 42: When inspecting flexible hydraulic hose for serviceability, which condition requires immediate replacement?

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

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 43: An aircraft engine exhibits black smoke from the exhaust. This symptom most likely indicates:

Oil burning due to worn piston rings
Rich fuel-air mixture or excessive fuel flow (Correct answer)
Ignition timing advanced too far
Lean fuel-air mixture

Correct answer: Rich fuel-air mixture or excessive fuel flow

Black exhaust smoke is a classic indicator of a rich mixture or excessive fuel flow resulting in incomplete combustion.

Question 44: According to FAA regulations, who may perform NDT inspections on certificated aircraft?

Any FAA-certificated pilot with instrument rating
Only FAA inspectors
Only FAA-certificated airframe and powerplant mechanics with appropriate training and authorization (Correct answer)
Any person supervised by a licensed mechanic

Correct answer: Only FAA-certificated airframe and powerplant mechanics with appropriate training and authorization

NDT inspections on certificated aircraft must be performed by FAA-certificated A&P mechanics who have received specific training and authorization in the applicable NDT method per the manufacturer's approved data.

Question 45: What type of material is prohibited for use in aircraft fuel system tubing due to incompatibility with aviation fuels?

Aluminum alloy 5052
Galvanized steel tubing (Correct answer)
Stainless steel
titanium

Correct answer: Galvanized steel tubing

Galvanized steel is prohibited in fuel systems because zinc from the galvanizing reacts with tetraethyl lead in AVGAS to form lead compounds that clog filters and damage fuel system components.

Question 46: During a preflight fuel check, a pilot/mechanic finds a small amount of water in the fuel sample. The correct action is:

Continue sampling and draining until no water is found, verifying the sample is clear (Correct answer)
Ground the aircraft indefinitely until the tank is removed
Add fuel system icing inhibitor and return to service
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 47: A Designated Engineering Representative (DER) has authority to:

Perform annual inspections on all aircraft types
Grant IA certificates to mechanics
Approve technical data for major repairs and alterations on behalf of the FAA (Correct answer)
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 48: What career advancement paths exist for ACS certified professionals?

No advancement is possible beyond initial certification
Leadership roles, specialized consulting, education and training, and executive management positions (Correct answer)
Only changing careers provides advancement
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 49: During an annual inspection, you find a crack in an aircraft's aluminum skin near a rivet hole. What is the correct procedure?

Immediately ground the aircraft and replace the entire panel
Measure the crack, determine if it exceeds limits, and consult manufacturer's structural repair manual (Correct answer)
Apply a patch and return to service without documentation
Report it in the maintenance log and defer repair

Correct answer: Measure the crack, determine if it exceeds limits, and consult manufacturer's structural repair manual

The mechanic must measure the defect, compare it against the manufacturer's allowable limits in the SRM, and follow approved repair procedures.

Question 50: Which NDT method is LEAST effective for detecting defects in non-metallic composite materials?

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

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 51: What qualifications are needed for advanced aviation mechanics practice?

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

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

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

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 53: What is the purpose of an Airworthiness Directive (AD)?

To mandate corrective action for unsafe conditions (Correct answer)
To recommend optional upgrades
To approve new parts for installation
To document scheduled maintenance intervals

Correct answer: To mandate corrective action for unsafe conditions

ADs are legally enforceable regulations issued by the FAA to correct unsafe conditions found in aircraft, engines, propellers, or appliances.

Question 54: Which type of hydraulic seal is most commonly used between two parts that have relative motion (dynamic application)?

Metal crush washer
Anaerobic sealant
O-ring used as a static seal
O-ring or lip seal in a dynamic groove (Correct answer)

Correct answer: O-ring or lip seal in a dynamic groove

Dynamic seals such as O-rings installed in dynamic grooves or lip seals are designed to prevent leakage between moving components.

Question 55: What is the function of a hydraulic power transfer unit (PTU)?

Maintain equal pressure in both main and backup hydraulic systems
Convert hydraulic energy to electrical energy for emergency power
Transfer fluid between two separate hydraulic systems without cross-contaminating the fluids (Correct answer)
Pump fluid when the engine-driven pump fails

Correct answer: Transfer fluid between two separate hydraulic systems without cross-contaminating the fluids

A PTU allows one hydraulic system to power another using a hydraulic motor/pump combination, transferring power but keeping the fluids isolated.

Question 56: 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 equalize pressure between wing tanks
To allow fuel vapors to escape for fire prevention
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.

Question 57: What reading on a differential compression tester indicates a cylinder is in acceptable condition?

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

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 58: What document governs the minimum bend radii and tube material specifications for aircraft fluid lines?

AC 43.13-1B Chapter 9 and the applicable aircraft maintenance manual (Correct answer)
MIL-SPEC-5015 only
FAR Part 21
NFPA 407

Correct answer: AC 43.13-1B Chapter 9 and the applicable aircraft maintenance manual

AC 43.13-1B Chapter 9 provides the FAA-accepted data for aircraft plumbing including bend radii, materials, flare types, and installation standards, supplemented by the AMM.

Question 59: When making a flared tube fitting for an aircraft fuel line, the correct flare angle for AN (Army-Navy) fittings is:

37 degrees (double flare equivalent per AN standard) (Correct answer)
90 degrees
45 degrees
60 degrees

Correct answer: 37 degrees (double flare equivalent per AN standard)

AN (Army-Navy) standard fittings use a 37-degree flare angle, which is different from the 45-degree flare used in automotive applications.

Question 60: When a maintenance technician completes a required inspection entry, the record must include all of the following EXCEPT:

Description of the work performed
Signature and certificate number of the approving person
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.

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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