ANAC CEL Theoretical Exam (Airframe Group) cheat sheet

Rivet pitch (spacing) is typically 3D to 4D for single-row and up to 6D–8D for multi-row seams, where D is rivet shank diameter; edge distance is normally at least 2D.

Grip length = total thickness of the sheets being joined; the rivet shank must fill the hole through the full grip, and the manufactured head plus 1.5D of shank should protrude before bucking.

Hole size for solid rivets is generally drilled 0.1 mm (0.003 in) larger than the rivet shank diameter; oversized or elongated holes require the next larger rivet size or a repair scheme.

Bend allowance = bend angle (radians) x (inside radius + K x thickness); K-factor depends on material and radius-to-thickness ratio, typically 0.33–0.5.

Setback = (R + T) x tan(angle/2), and bend line location uses setback from the mold point; flat pattern length = sum of flange lengths minus bend deductions.

Neutral axis for bend calculations lies between 0.3T and 0.5T from the inside surface for most aircraft aluminum alloys at moderate bend radii.

Minimum bend radius for 2024-T3 sheet is roughly 2T–3T (temper and grain direction dependent); bending across the grain requires a larger radius than bending along the grain.

Repair doublers must have at least one more row of rivets than the original joint and be of the same or compatible alloy; dissimilar alloys require isolation to prevent galvanic corrosion.

Aircraft structural categories: primary structure failure is catastrophic, secondary affects flight safety indirectly, and tertiary failure does not affect safety; repairs to primary structure need approved data.

Pitot-static system: pitot pressure is total (impact) pressure, static port supplies ambient pressure; airspeed indicator uses the difference, altimeter and VSI use static pressure only.

Altimeter setting error: 1 hPa (mb) of pressure error equals about 8.5 m (28 ft) of indicated altitude near sea level; flying from high to low pressure without resetting reads higher than actual.

VSI lag is intentional; a blocked static source causes the VSI to freeze at zero after a momentary indication, the altimeter to freeze, and the airspeed indicator to act like an altimeter.

Cabin pressurization outflow valve controls cabin altitude; the safety (negative pressure) relief valve prevents cabin pressure from dropping below ambient and protects against overpressure.

Fuel system: gravity feed requires the tank outlet above the carburetor; boost pumps are used for engine starting, vapor suppression, and emergency supply when the engine-driven pump fails.

Ice protection: pneumatic deice boots inflate cyclically; thermal anti-ice uses engine bleed air or electric heaters; TKS weeping wing uses glycol fluid for both anti-ice and deice.

Oxygen systems: continuous-flow masks deliver a fixed flow regardless of altitude; diluter-demand regulators mix cabin air with oxygen and supply 100% above roughly 10,000 m.

Hydraulic reservoirs are pressurized (often with bleed air or nitrogen) to prevent pump cavitation at altitude and to ensure positive feed to the pump inlet.

Ohm's law: V = I x R; power P = V x I = I^2 x R = V^2 / R. Series circuits share current; parallel circuits share voltage.

Kirchhoff's laws: the sum of currents at a node is zero; the sum of voltage drops around a closed loop equals the source voltage.

Aircraft DC systems commonly use 28 V (24 V battery) or 14 V (12 V battery); AC systems use 115 V 400 Hz for avionics and instruments.

Wire sizing is determined by current-carrying capacity and allowable voltage drop (typically 2% or less for critical loads); longer runs need larger gauge to limit drop.

Bonding provides a low-resistance path for return current and static discharge; the main bonding jumper ties the airframe to the electrical return, and static dischargers bleed precipitation static.

A relay is an electromagnetically operated switch; a solenoid converts electrical energy into linear mechanical motion; a generator is a DC source and an alternator produces AC that is rectified.

Magneto-to-engine timing: internal timing sets the magneto breaker points to the distributor rotor; external timing aligns the magneto to the engine at the specified advance angle.

Avionics bus protection: circuit breakers must be rated to protect the wire, and critical avionics may have dedicated buses so a single failure does not remove all navigation or communication capability.

2024 aluminum is copper-alloyed, high strength, poor corrosion resistance; 7075 is zinc-alloyed, very high strength, poor corrosion resistance; 6061 is magnesium-silicon alloyed, good corrosion resistance and weldability.

2024 and 7075 are typically clad with pure aluminum (Alclad) for corrosion protection; the cladding is sacrificial and must not be removed by excessive sanding.

Anodizing builds a controlled oxide layer on aluminum for corrosion resistance and paint adhesion; it is not a conductive finish, so bonding points must be masked.

Galvanic corrosion occurs when dissimilar metals contact in the presence of an electrolyte; the anode corrodes. The galvanic series ranks metals from anodic (magnesium, zinc, aluminum) to cathodic (stainless steel, titanium, gold).

Corrosion types: surface/general, pitting, intergranular (along grain boundaries, common in 2024 and 7075), exfoliation (layered lifting), filiform (under coatings), and stress corrosion cracking.

AN bolts are identified by head markings; a dash number after the bolt size indicates grip length in eighths of an inch. AN365 is an elastic-stop nut, AN960 a flat washer, AN310 a castle nut.

Torque values are specified dry or lubricated; a lubricated thread reaches the same clamp load at lower torque, so applying lubricant without adjusting torque can overstress the fastener.

Corrosion removal must not exceed allowable limits; blend-out depth is limited (often 10% of material thickness or per SRM), and any blend-out beyond limits requires engineering disposition.

Primary flight controls: ailerons (roll), elevators (pitch), rudder (yaw); secondary controls: flaps, slats, spoilers, trim tabs; auxiliary: leading-edge devices and speed brakes.

Differential ailerons deflect the up-going aileron more than the down-going one to reduce adverse yaw; aileron-rudder interconnect (ARI) further coordinates turns.

Hydraulic system pressure on transport aircraft is commonly 3000 psi; system pressure is regulated by a pressure regulator or an unloading valve that relieves the pump at set pressure.

Hydraulic fluid types: MIL-PRF-5606 (mineral, red), MIL-PRF-83282 (synthetic, red), and Skydrol (phosphate ester, purple, fire resistant); phosphate ester fluid attacks natural rubber seals and most paints.

Hydraulic system components: reservoir, pump, pressure regulator, accumulator (stores energy and dampens pressure pulses), selector valve, check valve, relief valve, and actuator.

Landing gear: oleo strut absorbs landing loads via compressed nitrogen (spring) and hydraulic fluid forced through an orifice (damping); servicing requires correct fluid level and nitrogen charge.

Shimmy is damped by the nosewheel steering damper or shimmy damper; a shimmy that persists after servicing indicates worn bushings, incorrect tire pressure, or improper caster.

Landing gear safety: squat switch (weight-on-wheels) prevents gear retraction on the ground; gear warning horn sounds when gear is up and power is reduced below a set value with flaps down.

Maintenance categories: scheduled (periodic inspections, servicing) and unscheduled (repairs, component replacement); line maintenance is performed on the aircraft, heavy maintenance in a shop.

Inspection methods: visual, borescope, dye penetrant (surface-breaking defects in non-porous materials), magnetic particle (ferromagnetic materials only), eddy current (surface and near-surface in conductive materials), ultrasonic (internal defects), and radiography (internal structure).

Dye penetrant steps: clean, apply penetrant, dwell, remove excess, apply developer, inspect under UV or white light; magnetic particle uses a magnetic field and iron particles to reveal discontinuities.

Maintenance documentation includes the aircraft maintenance manual (AMM), structural repair manual (SRM), illustrated parts catalog (IPC), and component maintenance manual (CMM); each repair must reference approved data.

Logbook entries must include the work performed, date, reference to approved data, and signature with certificate number; return to service requires an authorized person's signature.

Torque wrench calibration and use: apply torque smoothly, use the correct scale, and account for extensions that change effective length; torque wrenches must be calibrated periodically.

Foreign object debris (FOD) prevention: tool control, inspection of intakes and engine bays before closing, and accountability of all tools after a task.

Aircraft weighing: empty weight includes unusable fuel and full oil; maximum takeoff weight minus empty weight gives useful load; weight and balance must be within CG limits before flight.

ANAC (Agência Nacional de Aviação Civil) regulates civil aviation in Brazil; RBAC (Regulamento Brasileiro da Aviação Civil) is the national regulation series modeled on ICAO standards.

RBAC 145 governs maintenance organizations; RBAC 43 covers maintenance, preventive maintenance, and alterations; RBAC 65 covers aviation maintenance technician certification.

A Brazilian aviation maintenance technician (mecânico de manutenção aeronáutica, MMA) is certified by ANAC and may perform and certify maintenance within the ratings held.

Maintenance records must be retained and made available to ANAC; the operator is responsible for ensuring maintenance is performed by qualified personnel using approved data.

Safety management: SMS (Safety Management System) is a structured approach to identify hazards, assess risk, and implement mitigations; reporting of occurrences is encouraged and protected under just culture principles.

Human factors: the Dirty Dozen includes fatigue, complacency, lack of communication, distraction, lack of resources, pressure, lack of teamwork, lack of assertiveness, stress, lack of awareness, norms, and lack of knowledge.

Occurrence reporting in Brazil is made to ANAC and, for serious incidents and accidents, to CENIPA (Centro de Investigação e Prevenção de Acidentes Aeronáuticos).

Pre-flight and post-maintenance inspections must verify that all panels, cowlings, and access doors are secured and that no tools or debris remain before release to service.

Rivet head types: universal (AN470) for structural joints, countersunk (AN426) where flush surface is required, and brazier (AN456) for thin sheet; the rivet must match the hole and sheet thickness.

Bucktail height after driving should be about 1.5D and diameter about 1.5D; a properly driven rivet fills the hole and shows no cracking or excessive sheet deformation.

Aircraft sheet metal repair: cracks stop-drilled at the tip with a hole of at least 1/8 in (3 mm) or 2T diameter to relieve stress concentration before repair.

Stress concentration is highest at sharp corners and holes; repairs should avoid abrupt changes in section and use generous radii to reduce stress concentration.

Riveted lap joints: the number of rivets per row and row spacing affect load transfer; a repair doubler must restore the original strength and stiffness of the structure.

Corrosion protection after repair: apply primer to bare aluminum, seal faying surfaces, and restore the finish to prevent future corrosion.

Air conditioning: vapor-cycle machines use refrigerant (R-134a) with an evaporator, compressor, condenser, and expansion valve; air-cycle machines use bleed air through a compressor, heat exchanger, and turbine.

Pressurization controllers modulate the outflow valve; cabin pressure differential is limited by the pressure relief valves and structural design limits.

Fuel quantity indicating: float-type, capacitance-type (measures dielectric change), and ultrasonic; capacitance systems compensate for fuel density changes.

Fire detection: thermocouple, rate-of-rise, and optical (infrared/UV) detectors; fire extinguishing agents include Halon 1301 and, increasingly, Halon alternatives.

Anti-ice for pitot and static ports uses electric heaters; windshield anti-ice uses electric heating or hot bleed air.

Battery capacity is rated in ampere-hours (Ah); a 24 V lead-acid battery has 12 cells at about 2.1 V each, and a 12 V battery has 6 cells.

Aircraft wiring: wire is identified by gauge (AWG), and the smaller the AWG number the larger the wire; 10 AWG is larger than 20 AWG.

Circuit protection: a fuse is a one-time device; a circuit breaker is resettable; a current limiter protects large feeder circuits and is not resettable in flight.

Grounding and bonding resistance is typically measured with a micro-ohmmeter or bonding meter; values are usually specified in milliohms per the maintenance manual.

Navigation and communication antennas must be bonded and located to avoid interference; VHF communication uses the 118–137 MHz band, and VOR/ILS uses 108–118 MHz.

Titanium is highly corrosion resistant and strong but difficult to machine; it is used in high-temperature and high-strength applications.

Stainless steel (e.g., 304, 316) is used for firewalls and exhaust components; it is cathodic to aluminum and can drive galvanic corrosion of adjacent aluminum.

Composite materials: carbon fiber reinforced polymer is strong and light but galvanically incompatible with aluminum; isolation plies and sealant are required at joints.

Corrosion prevention: wash regularly, keep drain paths clear, apply protective coatings and sealants, and inspect for corrosion at faying surfaces and under insulation.

Hardware identification: AN (Air Force-Navy) and MS (Military Standard) hardware; a bolt with a drilled head is for safety wire, and a self-locking nut must be replaced when it can be turned by hand on the bolt.

Trim tabs: a trim tab moves opposite the control surface to trim the aircraft; an anti-servo tab moves with the surface to increase control feel (common on stabilators).

Flap types: plain, split, slotted, Fowler; Fowler flaps increase both wing area and camber and are common on transport aircraft.

Hydraulic pump types: gear, vane, and piston; a variable-displacement piston pump can regulate output and reduce power consumption at low demand.

Hydraulic system inspection: check fluid level, filter condition, leaks, and pressure; air in the system causes spongy operation and must be bled.

Landing gear retraction: the gear is locked up by uplocks and down by downlocks; the gear position and warning system uses proximity switches and a squat switch.

Work order and task card: each task must identify the aircraft, the work to be done, the approved data reference, and the sign-off.

Calibration: measuring tools such as torque wrenches, micrometers, and pressure gauges must be calibrated and traceable to a standard.

Aircraft jacking: use the correct jack points, ensure the aircraft is level, and install safety locks before working under the aircraft.

Fuel system safety: ground the aircraft and fuel equipment, use bonding cables, and avoid ignition sources during fueling and defueling.

Weight and balance: the datum is a reference point; arm is the distance from the datum; moment = weight x arm; CG = total moment / total weight.

ANAC issues and renews certificates and licenses; the maintenance organization must have an approved quality system and qualified personnel.

RBAC 43 requires that maintenance be performed using methods, techniques, and practices acceptable to ANAC, and that the person signing off be authorized.

Safety reporting: voluntary reporting systems encourage the reporting of hazards and errors without fear of punishment, supporting a just culture.

Human factors in maintenance: fatigue, complacency, and pressure are common causes of maintenance errors; use of checklists and independent inspection reduces risk.

Emergency response: know the location of fire extinguishers, first aid, and emergency exits; report accidents and serious incidents promptly to the appropriate authorities.