I85PREP
⌘ K
Guatemala DGAC TypeI aircraft-maintenance foundations study materials
Guatemala DGAC TypeI aircraft-maintenance foundations study resources

Guatemala DGAC TypeI aircraft-maintenance foundations practice questions

One question at a time. Build your Guatemala DGAC TypeI aircraft-maintenance foundations understanding.

First 50 of 190 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Inspection, measurements and maintenance evidence

A mechanic needs to torque a cylinder base nut to 150 lb-in using a torque wrench whose length (L) from handle center to drive axis is 12 inches. A special straight adapter extension adds 3 inches (E) inline directly along the wrench axis. What torque value must be set on the torque wrench dial (T_indicated)?

  1. 150 lb-in
  2. 120 lb-in Correct answer.
  3. 187.5 lb-in
  4. 100 lb-in

Explanation

When an adapter extends the effective length of the wrench inline along the handle axis, the formula is: T_indicated = T_desired * L / (L + E). Here, T_desired = 150 lb-in, L = 12 in, and E = 3 in. Therefore, T_indicated = 150 * 12 / (12 + 3) = 1800 / 15 = 120 lb-in.

Question 2Inspection, measurements and maintenance evidence

If a 3-inch adapter is attached to a 12-inch torque wrench at an angle of exactly 90 degrees relative to the longitudinal axis of the wrench handle, what torque should be set on the wrench dial to achieve a desired fastener torque of 200 lb-in?

  1. 160 lb-in
  2. 200 lb-in Correct answer.
  3. 240 lb-in
  4. 180 lb-in

Explanation

When an adapter is positioned at 90 degrees to the torque wrench handle axis, the effective lever arm from the handle to the drive axis remains unchanged. Therefore, no mathematical correction is required, and the wrench dial must be set directly to the desired torque: 200 lb-in.

Question 3Inspection, measurements and maintenance evidence

What is the primary operational limitation of Liquid Penetrant Inspection (Dye Penetrant / Líquidos Penetrantes) when examining aircraft components?

  1. It can only be used on ferromagnetic metals like carbon steel.
  2. It can only detect defects that are open to the surface; internal or subsurface flaws cannot be detected. Correct answer.
  3. It requires high-voltage radioactive isotope emitters that present severe radiation hazards.
  4. It dissolves aluminum and titanium alloys upon chemical application.

Explanation

Liquid penetrant inspection relies on capillary action to draw fluid into surface discontinuities. Consequently, it can only detect cracks, seams, and porosity that are open to the surface; entirely subsurface defects or cracks filled with foreign material will not be detected.

Question 4Inspection, measurements and maintenance evidence

Which material characteristic is strictly required for an aircraft part to be inspected using the Magnetic Particle Inspection (Partículas Magnéticas) method?

  1. The material must be an electrical insulator such as fiberglass.
  2. The material must be ferromagnetic, such as iron, carbon steel, or certain low-alloy steels. Correct answer.
  3. The material must be an austenitic stainless steel or pure copper.
  4. The material must be non-metallic and transparent to visible light.

Explanation

Magnetic particle inspection relies on establishing a magnetic field within the test part and detecting magnetic flux leakage caused by discontinuities. It can only be performed on ferromagnetic materials (such as carbon and alloy steels); it cannot be used on aluminum, magnesium, titanium, or copper alloys.

Question 5Inspection, measurements and maintenance evidence

What is a major advantage of Eddy Current Inspection (Corrientes de Foucault) when inspecting aircraft aluminum skin for surface cracks and subsurface corrosion?

  1. It requires completely stripping all protective paint and primer down to bare metal.
  2. It can detect cracks and corrosion thinning through non-conductive surface coatings such as paint and anodizing without removing them. Correct answer.
  3. It permanently magnetizes aluminum parts, providing ongoing rust prevention.
  4. It works through thick acoustic insulation blankets and heavy rubber de-ice boots without surface contact.

Explanation

Eddy current inspection uses electromagnetic induction. Because high-frequency magnetic fields penetrate non-conductive surface layers, the technique can detect surface-breaking and near-surface cracks as well as intergranular corrosion without having to remove paint or protective coatings.

Question 6Inspection, measurements and maintenance evidence

In the standard 4-digit aluminum alloy designation system, what is the primary alloying element in 2024 aluminum alloy, widely used for aircraft structural skins and stringers?

  1. Zinc
  2. Copper Correct answer.
  3. Silicon
  4. Magnesium

Explanation

In the Aluminum Association 4-digit system, 2xxx series alloys have copper as their principal alloying element (e.g., 2024 contains approx 4.4% copper). Copper provides high strength and excellent fatigue resistance, though it requires cladding (Alclad) for corrosion protection.

Question 7Inspection, measurements and maintenance evidence

What is the primary advantage and principal vulnerability of 7075-T6 aluminum alloy when used in structural aircraft applications?

  1. Extremely low tensile strength, but immune to all forms of chemical oxidation.
  2. Very high tensile and yield strength, but high susceptibility to stress corrosion cracking along grain boundaries. Correct answer.
  3. Poor machinability, but perfectly weldable with ordinary oxyacetylene equipment.
  4. Zero electrical conductivity, preventing any lightning strike damage.

Explanation

7075-T6 (zinc-alloyed) offers very high tensile strength, making it ideal for upper wing skins and compression members. However, in the T6 temper, it is highly susceptible to stress corrosion cracking (SCC) under sustained tensile loads in humid environments.

Question 8Inspection, measurements and maintenance evidence

Which condition is necessary for galvanic corrosion to occur between two different aircraft structural metals?

  1. The metals must be identical in electrochemical potential and submerged in distilled de-ionized water.
  2. Two dissimilar metals must have direct electrical contact in the presence of a common conductive electrolyte. Correct answer.
  3. The metals must be exposed to pure dry nitrogen under vacuum.
  4. The metals must be heated above 1,000 degrees Celsius.

Explanation

Galvanic corrosion requires three factors: (1) two electrochemically dissimilar metals with different electrode potentials, (2) an electrical path connecting them, and (3) a conductive electrolyte (such as moisture with salt or contaminants). The more anodic (active) metal will corrode.

Question 9Inspection, measurements and maintenance evidence

What is 'Intergranular Corrosion' in aircraft aluminum alloys, and why is it considered particularly dangerous by maintenance engineers?

  1. Surface staining caused by spilled fuel that easily wipes off with a clean rag.
  2. Corrosion that attacks along the grain boundaries of the metal lattice, causing severe internal loss of structural strength with little or no surface evidence. Correct answer.
  3. A harmless cosmetic discoloration that improves structural hardness.
  4. Rapid galvanic oxidation that occurs only when plastic safety wire touches steel bolts.

Explanation

Intergranular corrosion attacks the microstructural grain boundaries of an alloy, typically caused by improper heat treatment or delayed quenching. It weakens the internal metallic bond severely without showing obvious surface corrosion products, posing catastrophic failure risks.

Question 10Inspection, measurements and maintenance evidence

In sheet metal layout and fabrication, what is 'Bend Allowance' (tolerancia de doblado)?

  1. The amount of paint allowed to flake off the metal surface during cold bending.
  2. The length of curved material consumed in forming the bend along the neutral axis. Correct answer.
  3. The gap distance between the rivet head and the bucktail.
  4. The maximum thickness of metal that can be sheared without damaging the shop brake.

Explanation

Bend allowance is the curved length of material along the neutral axis (the layer that neither stretches nor compresses) within the bend tangent lines. Calculating it accurately ensures that the finished formed sheet metal part matches the design dimensions.

Question 11Inspection, measurements and maintenance evidence

When properly driven, what should be the height and diameter of an upset rivet shop head (bucktail) relative to the original rivet shank diameter (D)?

  1. Height of 0.5D and width of 1.5D. Correct answer.
  2. Height of 1.0D and width of 2.0D.
  3. Height of 0.25D and width of 1.0D.
  4. Height of 1.5D and width of 0.5D.

Explanation

Standard aircraft riveting inspection standards require a properly formed driven head (bucktail) to have a height of 1/2 the original shank diameter (0.5D) and a width/diameter of 1-1/2 times the shank diameter (1.5D).

Question 12Inspection, measurements and maintenance evidence

In aviation maintenance human factors, what is the 'Dirty Dozen' (La Docena Sucia) developed by Transport Canada?

  1. Twelve chemical solvents that are strictly banned from aircraft cleaning.
  2. Twelve of the most common human factor error precursors or preconditions that lead to maintenance errors and aviation accidents. Correct answer.
  3. Twelve uncertified tools that mechanics must discard from their toolboxes.
  4. Twelve mandatory logging entries required on every engine overhaul.

Explanation

Developed by Gordon Dupont at Transport Canada, the Dirty Dozen represents the 12 most common human factor preconditions contributing to maintenance errors: Lack of Communication, Complacency, Lack of Knowledge, Distraction, Lack of Teamwork, Fatigue, Lack of Resources, Pressure, Lack of Assertiveness, Stress, Lack of Awareness, and Norms.

Question 13Inspection, measurements and maintenance evidence

In maintenance human factors, how is 'Complacency' (Complacencia) defined, and why is it dangerous in routine maintenance tasks?

  1. A complete lack of physical tools to finish the task.
  2. A state of overconfidence and false security arising from routine repetition, leading a technician to skip checklist steps or assume work was done correctly without verification. Correct answer.
  3. Physical fatigue caused by working night shifts.
  4. Anger and conflict between mechanics and ramp dispatchers.

Explanation

Complacency occurs when an experienced technician has performed a routine task hundreds of times without incident, leading to a false sense of security. The technician may skip reading maintenance manuals, bypass steps, or sign off items from memory, missing critical errors (such as un-torqued fittings or missing cotter pins).

Question 14Inspection, measurements and maintenance evidence

What core concept does James Reason's 'Swiss Cheese Model' illustrate regarding the breakdown of safety defenses in aviation maintenance accidents?

  1. Accidents are always caused by a single isolated failure of the pilot on final approach.
  2. Aviation defense layers have latent weaknesses ('holes'); an accident occurs only when holes in multiple defensive layers momentarily align to create an active trajectory of failure. Correct answer.
  3. Cheese should never be consumed in aircraft maintenance hangars due to rodent hazards.
  4. Metal structures corrode in patterns identical to dairy cheese fermentation.

Explanation

The Swiss Cheese Model conceptualizes safety defenses (regulations, procedures, training, tooling, inspections) as slices of Swiss cheese, each having latent vulnerabilities ('holes'). Major accidents are rarely caused by a single human error; they occur when latent conditions and active human errors align across every defensive barrier.

Question 15Inspection, measurements and maintenance evidence

During a routine 100-hour inspection on an aircraft piston engine, the mechanic cuts open the oil filter and discovers magnetic shiny flakes in the pleats. What does this finding indicate?

  1. Normal engine break-in with no action required.
  2. Abnormal wear or impending failure of ferrous steel components (such as cylinder walls, piston rings, camshaft lobes, or gear teeth), requiring immediate grounding and thorough technical evaluation. Correct answer.
  3. The oil filter was manufactured with magnetic fibers and is functioning normally.
  4. The oil brand must simply be changed to a lower viscosity grade.

Explanation

Ferrous (magnetic) metal flakes in an oil filter or on magnetic chip detectors indicate abnormal friction, spalling, or micro-cracking of hardened steel engine parts (camshaft lobes, lifters, crankshaft gears, or cylinder barrels). The engine must be grounded immediately for oil analysis, borescope inspection, or disassembly.

Question 16Inspection, measurements and maintenance evidence

An aircraft with a reference datum located at the engine firewall is weighed on scales for a weight and balance check. The nose wheel scale records 400 lb at an arm of +20.0 inches. The two main wheel scales record a combined 1,600 lb at an arm of +80.0 inches. What is the Empty Weight Center of Gravity (CG) location aft of the datum?

  1. 50.0 inches
  2. 68.0 inches Correct answer.
  3. 75.0 inches
  4. 80.0 inches

Explanation

Center of gravity is calculated as: CG = Total Moment / Total Weight. Nose wheel moment = 400 lb * 20.0 in = 8,000 lb-in. Main wheels moment = 1,600 lb * 80.0 in = 128,000 lb-in. Total Weight = 400 + 1,600 = 2,000 lb. Total Moment = 8,000 + 128,000 = 136,000 lb-in. Empty Weight CG = 136,000 lb-in / 2,000 lb = 68.0 inches aft of datum.

Question 17Structures, controls and landing gear

How does a semi-monocoque fuselage design carry flight and landing loads compared to a pure monocoque structure?

  1. The skin carries all tensile and compressive loads with zero internal reinforcing members.
  2. The skin carries shear and tensile loads while longitudinal stringers/longerons and transverse frames/bulkheads resist bending and prevent skin buckling. Correct answer.
  3. The load is carried entirely by an internal welded steel tubing truss, with fabric covering serving only as aerodynamic fairing.
  4. The structure relies entirely on pressurized helium gas filled within sealed structural compartments.

Explanation

In a semi-monocoque fuselage, the skin carries shear stresses caused by aerodynamic and pressurization loads, while internal longitudinal stringers and longerons absorb bending stresses, and transverse formers/bulkheads maintain cross-sectional shape and prevent skin buckling under compression.

Question 18Structures, controls and landing gear

In a typical cantilever aircraft wing, which structural members are primarily responsible for carrying the aerodynamic bending and shear loads spanwise?

  1. Wing ribs
  2. Wing spars Correct answer.
  3. Trailing edge trim tabs
  4. Wing tip navigation light brackets

Explanation

Wing spars are the principal structural members running spanwise along the wing. They carry the primary aerodynamic bending moments (tension on lower cap, compression on upper cap) and vertical shear loads into the fuselage carry-through structure.

Question 19Structures, controls and landing gear

What is the aerodynamic purpose of 'Differential Ailerons' in an aircraft flight control system?

  1. To ensure both ailerons deflect downward simultaneously to act as landing flaps.
  2. To counteract adverse yaw by deflecting the up-going aileron through a greater angle than the down-going aileron. Correct answer.
  3. To lock the rudder automatically when the aircraft reaches cruising altitude.
  4. To increase the roll rate by pulsing the ailerons rapidly using hydraulic vibrators.

Explanation

Differential ailerons are designed so that the aileron deflecting upward moves through a greater angle than the aileron moving downward. The greater profile drag produced by the up-deflected aileron counteracts the induced drag of the down-deflected aileron, neutralizing adverse yaw.

Question 20Structures, controls and landing gear

Why must an aircraft mechanic use a temperature compensation chart when checking flight control cable tension with a tensiometer?

  1. Tensiometer springs expand and contract at ten times the rate of aluminum.
  2. Aluminum airframes have a higher coefficient of thermal expansion than carbon steel control cables, causing cable tension to vary significantly with ambient temperature. Correct answer.
  3. Cable tension must always be adjusted to zero whenever the outside air temperature drops below freezing.
  4. Hydraulic fluid in the cable pulleys thickens at high temperatures.

Explanation

Aluminum airframes expand and contract at roughly twice the rate of carbon steel cables. As temperature rises, the fuselage expands faster than the cables, increasing cable tension; as temperature drops, tension decreases. Cable rigging charts specify required tension relative to ambient hangar temperature.

Question 21Structures, controls and landing gear

What is the primary danger of returning an aircraft to service with an aileron, elevator, or rudder that is dynamically out of balance or tail-heavy after repainting?

  1. The aircraft will instantly stall at cruising speed.
  2. Destructive aeroelastic control surface flutter can occur at high airspeeds, potentially tearing the surface off the aircraft. Correct answer.
  3. The autopilot servos will refuse to power on during ground testing.
  4. The pitot-static system will indicate reverse airspeed.

Explanation

Control surfaces must be balanced within manufacturer limits. Adding paint or repairs behind the hinge line shifts the center of gravity aft. At high speeds, an aft CG allows aerodynamic turbulence to initiate aeroelastic flutter, where self-reinforcing oscillations can lead to catastrophic structural failure within seconds.

Question 22Structures, controls and landing gear

If an oleo shock strut bottoms out (reaches metal-to-metal contact) during an ordinary landing impact but maintains proper chrome extension height while parked on the ramp, what is the most probable cause?

  1. Excessive nitrogen gas pressure.
  2. Low hydraulic fluid level. Correct answer.
  3. The nose wheel tire is over-inflated.
  4. The emergency gear release handle is engaged.

Explanation

If an oleo strut holds proper extension height on the ramp, the nitrogen gas charge is adequate. However, if it bottoms out during landing impact, it lacks sufficient hydraulic fluid to meter through the orifice to absorb the dynamic kinetic energy of the landing.

Question 23Structures, controls and landing gear

A mechanic must energize the hydraulic system on a jacked aircraft to troubleshoot a landing gear fault. What protection do landing gear ground safety locks (pasadores de seguridad, 'ground lock pins') provide, and what must be done with them afterwards?

  1. They apply the parking brake hydraulically so the aircraft cannot roll off the jacks, and they remain installed throughout the next flight.
  2. They mechanically block the retraction linkage so an inadvertent gear selection or a pressurized system cannot retract the gear onto personnel working beneath the aircraft; fitted with REMOVE BEFORE FLIGHT streamers, they must be removed and accounted for before flight. Correct answer.
  3. They seal the shock strut air/oil charging valve so nitrogen cannot escape while the aircraft is supported on jacks.
  4. They isolate the gear position indicating lights so cockpit annunciators do not distract maintenance personnel during the test.

Explanation

Ground safety locks are pins or sleeves inserted through the side brace, drag brace, or actuator to hold the gear mechanically down and locked, independently of hydraulic pressure. They are the barrier that keeps a wrong selection or a pressurized system from collapsing the gear onto anyone working under the aircraft. Because they are flight-critical if left in place, they carry REMOVE BEFORE FLIGHT streamers and must be removed, counted, and stowed before the aircraft is released.

Question 24Structures, controls and landing gear

In an aircraft multiple-disc brake assembly, what is the role of the automatic adjusters (retractor pins)?

  1. To dump brake fluid overboard if the brakes overheat.
  2. To maintain a uniform running clearance between the rotating discs and stationary stators as brake linings wear. Correct answer.
  3. To prevent the pilot from applying differential braking during crosswind taxiing.
  4. To lock the brake pedals permanently when parking chocks are removed.

Explanation

Automatic adjusters (retractor assemblies) retract the pressure plate a precise, fixed distance when brake hydraulic pressure is released. This maintains a constant running clearance and pedal travel throughout the service life of the brake discs, regardless of friction lining wear.

Question 25Structures, controls and landing gear

How does an electro-hydraulic Anti-Skid system detect and prevent a wheel skid during heavy braking on a slippery runway?

  1. Wheel speed transducers detect an abnormal deceleration rate indicating an impending skid, causing the anti-skid control valve to release hydraulic pressure to that brake. Correct answer.
  2. Optical cameras look at the tire tread and cut off engine power if smoke is observed.
  3. Pressure sensors in the cockpit pedals vibrate to warn the pilot to pump the brakes manually.
  4. The system automatically deploys tail parachutes whenever runway water is detected.

Explanation

Wheel speed transducers generate AC signals proportional to wheel rotational speed. An anti-skid computer monitors the deceleration rate; if a wheel decelerates rapidly compared to aircraft reference speed (skid onset), the controller energizes an anti-skid valve to release brake pressure, allowing the wheel to spin up before reapplying pressure.

Question 26Structures, controls and landing gear

If the primary hydraulic system fails on a retractable landing gear aircraft, what is the typical emergency extension method provided on transport aircraft?

  1. Manually unlatching the mechanical uplocks to allow the landing gear to free-fall by gravity and airflow slipstream into the down-and-locked position. Correct answer.
  2. Firing an explosive pyrotechnic charge that jettisons the landing gear overboard.
  3. Inverting the aircraft into a negative-G dive so centrifugal force pushes the gear out.
  4. Injecting high-pressure fuel into the hydraulic retract lines.

Explanation

Emergency landing gear extension systems commonly use a manual mechanical release that disengages uplocks, allowing the gear to free-fall under gravity and aerodynamic airflow. Downlock springs and over-center linkages then lock the gear in place. Alternate systems may use pneumatic nitrogen bottles or manual hand pumps.

Question 27Structures, controls and landing gear

What is the primary function of a Flap Asymmetry Protection System (Sistema de Protección de Asimetría de Flaps)?

  1. To deploy the left flap during left turns to assist the ailerons.
  2. To immediately stop or disconnect flap drive motion if one wing's flap moves faster or further than the other, preventing an uncontrollable rolling moment. Correct answer.
  3. To automatically retract all flaps if engine exhaust temperature increases.
  4. To dump wing fuel overboard whenever flaps are extended beyond 15 degrees.

Explanation

Flap asymmetry occurs if mechanical drive failure causes flaps on one wing to extend while the other remains stationary or lags behind. The resulting large lift and drag differential creates a severe rolling moment that can exceed available aileron control authority; asymmetry sensors immediately detect the mismatch and shut down the flap drive.

Question 28Structures, controls and landing gear

How does an Anti-Servo Tab differ in operation and purpose from a standard Balance Tab on a flight control surface?

  1. An anti-servo tab moves in the opposite direction of the control surface to reduce control stick forces.
  2. An anti-servo tab moves in the same direction as the control surface trailing edge, increasing control stick resistance to prevent over-controlling and flutter on stabilators. Correct answer.
  3. An anti-servo tab is an electronic spoiler that only deploys upon wheel touchdown.
  4. An anti-servo tab is used exclusively on rudder pedals to adjust pilot leg reach.

Explanation

An anti-servo tab moves in the same direction as the control surface trailing edge (commonly used on all-moving stabilators). By deflecting with the surface, it creates an aerodynamic force opposing surface deflection, providing natural artificial feel and increasing dynamic stability to prevent pilot over-controlling.

Question 29Fluid power, cabin environment and water systems

Which of the following statements correctly identifies the color, base, and seal compatibility of mineral-base aircraft hydraulic fluid MIL-PRF-5606?

  1. It is dyed purple, has a synthetic phosphate-ester base, and requires butyl rubber seals.
  2. It is dyed red, has a petroleum (mineral) base, and is compatible with synthetic rubber (Buna-N / Nitrile) and Neoprene seals. Correct answer.
  3. It is clear and colorless, has a vegetable oil base, and requires natural rubber seals.
  4. It is dyed bright blue, has a water-glycol base, and is incompatible with any elastomer seals.

Explanation

MIL-PRF-5606 is a petroleum (mineral) based hydraulic fluid dyed red for identification. It uses synthetic rubber (Nitrile / Buna-N) or fluorocarbon (Viton) seals. It is flammable and must never be mixed with synthetic phosphate-ester fluids.

Question 30Fluid power, cabin environment and water systems

What are the primary operational functions of an accumulator in an aircraft hydraulic system?

  1. To filter solid dirt particles down to 3 microns from the hydraulic fluid.
  2. To damp hydraulic pressure surges, store energy under pressure for auxiliary or emergency operation, and supplement the pump during peak flow demands. Correct answer.
  3. To cool the hydraulic fluid by circulating it through external wing heat exchangers.
  4. To convert 28V DC electrical power into hydraulic flow.

Explanation

A hydraulic accumulator stores energy in the form of compressed gas, serves as a hydraulic shock absorber against pressure pulses from pumps or actuator cycling, supplements the pump when flow demand exceeds pump output, and provides emergency pressure to operate brakes or gear.

Question 31Fluid power, cabin environment and water systems

What is the function of a System Pressure Relief Valve in an aircraft constant-pressure hydraulic system?

  1. To maintain system pressure at zero whenever the landing gear is extended.
  2. To serve as a safety backup device that vents fluid back to the reservoir if the main pump pressure regulator or compensator fails in the high-pressure mode. Correct answer.
  3. To allow the pilot to vent hydraulic fluid overboard to reduce landing weight.
  4. To automatically fill the nitrogen chamber in the brake accumulator.

Explanation

A pressure relief valve is installed as a safety backup. If the variable-displacement pump compensator or unloader valve fails to limit pressure, the relief valve cracks open at a set pressure (typically 10-15% above system operating pressure) to divert fluid back to the reservoir, preventing blown lines or cylinder ruptures.

Question 32Fluid power, cabin environment and water systems

How do pneumatic de-icer boots on the leading edges of aircraft wings and stabilizers remove accumulated structural ice?

  1. Electric heating elements inside the rubber melt the ice completely into liquid runoff.
  2. Engine bleed air or vacuum/pressure pump air inflates alternating inflatable rubber tubes, expanding the leading edge profile to crack and break ice so slipstream carries it away. Correct answer.
  3. Chemical glycol is sprayed through micro-pores in the rubber surface to dissolve ice.
  4. High-frequency acoustic vibrations shatter the ice crystals at the atomic level.

Explanation

Pneumatic de-icing boots consist of segmented inflatable rubber tubes bonded to the leading edges. When inflated alternately with low-pressure air (approx 15-20 psi), the rubber expands, cracking the brittle ice accumulation; the aerodynamic slipstream then peels the ice fragments away.

Question 33Fluid power, cabin environment and water systems

What is the function of a Bleed Air Pre-Cooler in an aircraft pneumatic environmental control system?

  1. To freeze moisture out of the fuel before it enters the engine fuel nozzles.
  2. To cool extremely hot engine bleed air (which can exceed 400 degrees Celsius) using engine fan air or ram air before distributing it to cabin air conditioning packs and wing anti-ice ducts. Correct answer.
  3. To refrigerate avionics bay computers using liquid freon coils.
  4. To warm up engine oil prior to starting on cold mornings.

Explanation

Engine compressor bleed air exits at temperatures often exceeding 400 degrees C (750 degrees F). The bleed air pre-cooler is an air-to-air heat exchanger located in the engine pylon that uses cool fan bypass air to lower bleed air temperature to a manageable 200 degrees C before ducting it through the airframe.

Question 34Fluid power, cabin environment and water systems

An aircraft is cruising at 35,000 feet, where ambient atmospheric pressure is 3.46 psi. The cabin pressurization system maintains a cabin pressure altitude of 8,000 feet, corresponding to an internal pressure of 10.91 psi. What is the cabin differential pressure (Delta P)?

  1. 14.37 psi
  2. 7.45 psi Correct answer.
  3. 3.15 psi
  4. 10.91 psi

Explanation

Cabin differential pressure is the difference between internal cabin air pressure (P_cabin) and external ambient atmospheric pressure (P_ambient): Delta P = P_cabin - P_ambient. Here, Delta P = 10.91 psi - 3.46 psi = 7.45 psi.

Question 35Fluid power, cabin environment and water systems

What is the primary governing component that controls cabin altitude and differential pressure in a pressurized aircraft by regulating the discharge of conditioned air?

  1. The cabin outflow valve Correct answer.
  2. The engine high-pressure turbine nozzle
  3. The ram air scoop on the vertical fin
  4. The cabin baggage door handle

Explanation

Conditioned bleed air enters the pressure cabin at an approximately constant rate. The cabin pressure controller regulates internal pressure by modulating the opening of the cabin outflow valve, controlling how much exhaust air escapes from the sealed fuselage vessel.

Question 36Fluid power, cabin environment and water systems

Why are aircraft pressurization systems equipped with a Negative Pressure Relief Valve (Válvula de Alivio de Presión Negativa)?

  1. To prevent internal cabin pressure from exceeding structural maximum limits during climb.
  2. To prevent ambient outside air pressure from exceeding inside cabin pressure during rapid descents, which could crush the fuselage inward. Correct answer.
  3. To dump cabin air if smoke is detected in the lavatory.
  4. To blow warm air over the windshield to prevent fogging.

Explanation

Aircraft fuselages are designed as pressure vessels to withstand internal pressure pushing outward. They are structurally weaker against external pressure pushing inward. A negative pressure relief valve opens inward if outside pressure exceeds cabin pressure (e.g., during rapid emergency descent), equalizing pressure to prevent structural collapse.

Question 37Fuel, fire, oxygen and ice protection

When draining and inspecting fuel sumps during maintenance or preflight inspections, where will entrained free water settle in the fuel sample, and how is it detected visually?

  1. Water is lighter than aviation fuels and will float as a clear layer on top of the fuel.
  2. Water is denser than both Avgas (100LL) and Jet-A, and will settle to the bottom of the container, appearing as clear bubbles or a distinct lower layer separated by an interface line. Correct answer.
  3. Water dissolves completely in aviation fuel, turning it bright fluorescent orange.
  4. Water immediately evaporates into gaseous vapor as soon as it exits the drain valve.

Explanation

Water has a specific gravity of 1.0, while Avgas is approximately 0.72 and Jet-A is approx 0.80. Because water is denser, it sinks to the lowest points in fuel tanks (sumps). In a clear sample cup, water appears as a clear layer or beads at the bottom, beneath colored Avgas (blue for 100LL) or straw-colored Jet-A.

Question 38Fuel, fire, oxygen and ice protection

What is the primary cause and hazard of microbiological growth (such as Cladosporium resinae) in aircraft turbine fuel tanks?

  1. Microbes feed on aviation gasoline lead additives and turn the fuel into lubricating grease.
  2. Fungi and bacteria thrive at the fuel-water interface in jet fuel, producing acidic sludge that clogs fuel filters, corrodes aluminum tank structure, and causes fuel transmitter malfunctions. Correct answer.
  3. Microbes create combustible hydrogen gas that overpressurizes the fuel tank vents during climb.
  4. Microbiological growth is beneficial because it consumes dissolved water without any maintenance concerns.

Explanation

Microorganisms (fungi/bacteria like Hormoconis resinae / Cladosporium resinae) live in water droplets at the bottom of jet fuel tanks, consuming hydrocarbon fuel for food. Their metabolic waste forms thick, corrosive brown/black slime that clogs fuel filters, coats quantity probes, and produces organic acids that pit aluminum skins.

Question 39Electrical power, instruments and avionics

An aircraft 28-volt direct current (DC) electrical bus powers a landing light circuit with a total circuit resistance of 4 ohms. What is the current flowing through the circuit, and how much electrical power is consumed?

  1. Current = 112 A, Power = 3,136 W
  2. Current = 7 A, Power = 196 W Correct answer.
  3. Current = 0.14 A, Power = 3.92 W
  4. Current = 14 A, Power = 392 W

Explanation

According to Ohm's Law: I = V / R. Here, I = 28 V / 4 ohms = 7 Amperes. Electrical power is calculated as P = V * I. Therefore, P = 28 V * 7 A = 196 Watts (or P = I^2 * R = 49 * 4 = 196 W).

Question 40Electrical power, instruments and avionics

A continuous DC load draws 10 Amperes through a 20-foot single copper wire run. The wire has a resistance of 0.02 ohms per foot (total wire resistance R = 0.4 ohms). What is the voltage drop across the wire, and what voltage reaches the load on a 28-volt bus?

  1. Voltage drop = 0.4 V, load receives 27.6 V
  2. Voltage drop = 4.0 V, load receives 24.0 V Correct answer.
  3. Voltage drop = 2.0 V, load receives 26.0 V
  4. Voltage drop = 8.0 V, load receives 20.0 V

Explanation

Voltage drop across a conductor is calculated using Ohm's Law: V_drop = I * R_wire. Here, total resistance R = 20 ft * 0.02 ohms/ft = 0.4 ohms. Voltage drop = 10 A * 0.4 ohms = 4.0 Volts. Voltage reaching the load = 28 V - 4.0 V = 24.0 Volts.

Question 41Electrical power, instruments and avionics

What is the defining safety operational characteristic of a 'Trip-Free' circuit breaker installed in an aircraft electrical system?

  1. It can be reset by applying a permanent magnetic field to the faceplate.
  2. It allows its internal contacts to trip open during an electrical overload even if the operating push-button is held in by the crew. Correct answer.
  3. It trips only when the outside air temperature exceeds 100 degrees Celsius.
  4. It automatically bypasses the short circuit and powers the load through the airframe skin.

Explanation

AC 43.13-1B and aviation electrical certification rules require circuit breakers to be 'trip-free.' This means that during an overcurrent or short-circuit condition, the thermal/magnetic mechanism will trip and open the circuit even if the mechanical button is held depressed manually, preventing thermal fires.

Question 42Electrical power, instruments and avionics

Why must the maximum allowable current capacity (ampacity) of an aircraft electrical wire be derated when the wire is bundled with multiple other wires in a tight wire harness?

  1. The bundle creates high magnetic friction that slows down electron velocity.
  2. Restricted air circulation within the bundle reduces convective heat dissipation, causing higher operating temperatures for a given current. Correct answer.
  3. Copper wires absorb nitrogen from the cabin air when tied together.
  4. The voltage automatically doubles when wires touch one another.

Explanation

Electrical current generates heat (I^2 * R). A single wire in free air dissipates heat easily. In a bundle, adjacent wires also generate heat and insulate each other, severely reducing heat dissipation. To prevent the insulation from melting, wires in bundles must be derated to lower current limits.

Question 43Electrical power, instruments and avionics

How is the state of charge of an aircraft lead-acid battery determined during routine shop maintenance?

  1. By measuring the open-circuit voltage with an ordinary uncalibrated test light.
  2. By measuring the specific gravity of the liquid electrolyte in all cells using a temperature-corrected hydrometer. Correct answer.
  3. By counting the number of bubbles formed on the terminal posts.
  4. By weighing the battery on a bathroom scale.

Explanation

In a flooded lead-acid battery, sulfuric acid is consumed during discharge and regenerated during charging. Measuring electrolyte specific gravity with a hydrometer (temperature corrected to 80 degrees F) provides an accurate assessment of state of charge: 1.275 to 1.300 indicates full charge, while 1.150 indicates discharged.

Question 44Electrical power, instruments and avionics

What is 'Thermal Runaway' in an aircraft Nickel-Cadmium (Ni-Cad) battery, and why does it occur?

  1. The battery becomes completely cold and ceases to produce any voltage below 0 degrees C.
  2. Ni-Cad cells have a negative temperature coefficient of resistance; high temperature decreases internal resistance, drawing higher constant-voltage charging current, causing further heating in an uncontrollable destructive cycle. Correct answer.
  3. The electrolyte boils into solid ice due to endothermic reactions during rapid discharge.
  4. The battery casing expands and creates an acoustic siren warning.

Explanation

Ni-Cad batteries possess a negative temperature coefficient: as cell temperature rises, internal resistance decreases. On a constant-voltage bus, lower resistance draws higher current, generating more I^2*R heat. This positive feedback loop causes boiling electrolyte, melting separator nylon, cell shorting, and battery fire.

Question 45Electrical power, instruments and avionics

What is the primary difference in function between an aircraft Inverter and a Transformer-Rectifier Unit (TRU)?

  1. An inverter converts AC into DC, while a TRU converts DC into AC.
  2. An inverter converts Direct Current (DC) into Alternating Current (AC), while a TRU converts Alternating Current (AC) into Direct Current (DC). Correct answer.
  3. Both units perform identical functions and can be interchanged directly.
  4. An inverter stores mechanical energy in a flywheel, while a TRU is a pneumatic vacuum pump.

Explanation

An inverter takes DC battery or bus power (e.g., 28V DC) and produces AC power (e.g., 115V AC, 400 Hz). Conversely, a Transformer-Rectifier Unit (TRU) steps down high-voltage AC from engine-driven alternators and rectifies it into 28V DC power to feed DC buses and charge batteries.

Question 46Electrical power, instruments and avionics

If an aircraft's pitot tube ram air opening becomes completely blocked by ice in flight while its drain hole remains open, how will the Airspeed Indicator (ASI) react during level cruise flight?

  1. It will immediately peg at maximum airspeed (Vne).
  2. The indicated airspeed will drop to zero as trapped ram air bleeds out through the open drain hole. Correct answer.
  3. It will continue to read the exact true airspeed accurately forever.
  4. The needle will rotate backward counter-clockwise.

Explanation

When the ram air impact hole is blocked while the drain hole remains open, pressure inside the pitot line vents out through the drain until it equals ambient static pressure. Because the pressure on both sides of the airspeed indicator diaphragm is now equal (both static pressure), the instrument reads zero airspeed.

Question 47Electrical power, instruments and avionics

If both the pitot tube ram impact opening AND the drain hole freeze completely shut during flight, how will the Airspeed Indicator behave as the aircraft climbs to a higher altitude?

  1. It will drop to zero immediately.
  2. It will act like an altimeter, falsely indicating an increase in airspeed as the aircraft climbs. Correct answer.
  3. It will freeze at exactly 100 knots regardless of aircraft pitch.
  4. It will oscillate between zero and 300 knots.

Explanation

If both the impact opening and drain hole are blocked, a fixed mass of ram air is trapped inside the diaphragm. As the aircraft climbs, ambient static pressure inside the instrument casing decreases. The trapped pitot pressure expands the diaphragm against the dropping casing pressure, causing the ASI to falsely indicate increasing airspeed.

Question 48Electrical power, instruments and avionics

What are the two fundamental physical properties of a spinning gyroscope that enable its use in attitude indicators, directional gyros, and turn coordinators?

  1. Centrifugal expansion and magnetic resonance
  2. Rigidity in space (gyroscopic inertia) and Precession Correct answer.
  3. Capillary action and aerodynamic lift
  4. Thermal expansion and electrical capacitance

Explanation

Gyroscopic flight instruments operate based on two physical principles: (1) Rigidity in space, where a spinning rotor maintains its plane of rotation fixed in space unless acted on by an external torque, and (2) Precession, where an applied deflecting force causes a reaction 90 degrees later in the direction of rotation.

Question 49Electrical power, instruments and avionics

What is the function of Static Discharger Wicks (Descargadores de Estática) mounted on the trailing edges of wings, ailerons, and elevators?

  1. To discharge wing fuel overboard during landing emergencies.
  2. To dissipate accumulated electrostatic charge quietly into the slipstream at a controlled rate, preventing corona discharge that interferes with VHF, VOR, and ADF radio navigation receivers. Correct answer.
  3. To measure aircraft true airspeed using piezoelectric crystals.
  4. To attract lightning strikes away from the engines directly into the cockpit.

Explanation

Aircraft moving through precipitation, dust, or clouds accumulate high electrostatic charges (precipitation static / P-static). Static wicks have high-resistance carbon fibers that bleed off this charge smoothly from sharp trailing-edge points into the airflow, preventing noisy corona discharges that blind aircraft radio receivers.

Question 50Powerplant and propeller foundations

In a four-stroke aircraft reciprocating engine, what is 'Valve Overlap' (traslape de válvulas) and what is its primary thermodynamic purpose?

  1. The mechanical error when valves collide with the top of the piston.
  2. The period at the end of the exhaust stroke and start of the intake stroke when both intake and exhaust valves are simultaneously open, using exhaust gas inertia to help draw in the fresh fuel-air charge. Correct answer.
  3. The time when all valves remain closed during the entire compression stroke.
  4. The delay caused by stretched pushrods at high engine oil temperatures.

Explanation

Valve overlap occurs when the intake valve opens several degrees before Top Dead Center (BTDC) while the exhaust valve does not close until several degrees after Top Dead Center (ATDC). This allows the scavenging momentum of exiting exhaust gases to create a low-pressure area that draws in the fresh intake charge, improving volumetric efficiency.