Engineer Aircraft cheat sheet

Limit load is the maximum load expected in service; ultimate load equals limit load multiplied by the 1.5 factor of safety, and the structure must withstand ultimate load for 3 seconds without failure.

Fail-safe (damage-tolerant) design uses redundant load paths and crack-stopping features so that a discrete damage or single failure does not cause catastrophic loss; safe-life design retires a component after a calculated fatigue life.

Shear flow in a thin-walled closed section is q = T/(2A), where A is the area enclosed by the median line; this underlies torsion analysis of fuselage and wing boxes.

Bending stress follows sigma = M·y/I; the neutral axis passes through the centroid, so stringers placed far from the neutral axis carry the greatest axial load.

Aircraft structural loads are classified as flight loads (maneuver, gust), ground loads (landing, taxi), pressurization loads, and inertia loads from mass distribution.

The wing spar caps take bending, the webs take shear, and ribs maintain airfoil shape and transfer loads; fuselage frames carry concentrated loads while stringers react pressurization and bending.

Buckling of stiffened panels depends on skin thickness, stringer spacing, and end fixity; crippling strength of short columns is a local failure mode independent of overall column length.

Pressurized fuselage hoop stress is sigma = p·r/t (twice the longitudinal stress of p·r/2t), which is why longitudinal cracks are more critical than circumferential ones.

Corrosion-prone areas include lap joints, bilge areas, and faying surfaces; structural inspection programs target fatigue-critical and corrosion-critical locations defined by the design authority.

Brayton cycle efficiency rises with pressure ratio and turbine inlet temperature; specific thrust falls as bypass ratio increases, improving propulsive efficiency at moderate speeds.

Thrust is F = m_dot·(V_exit − V_inlet) plus the pressure term (p_exit − p_ambient)·A_exit; turbofan thrust splits between core and bypass streams.

A gas turbine has cold-section limits on compressor materials and hot-section limits on turbine blades; turbine inlet temperature is the dominant constraint on power output.

Surge and stall in axial compressors are avoided by variable inlet guide vanes, bleed valves, and casing treatment; surge is a full-annulus flow breakdown, rotating stall is a localized cell.

Engine pressure ratio (EPR) and N1 fan speed are the primary thrust parameters for turbofans; N1 is typically used for the fan-speed-based rating and EPR where a pressure-based rating is approved.

Specific fuel consumption (SFC) is fuel flow per unit thrust; improvements come from higher bypass ratio, higher overall pressure ratio, and higher turbine temperature.

On a turboprop, power is measured as shaft horsepower plus residual jet thrust; propeller efficiency peaks at a design advance ratio and falls at high Mach.

Engine fire detection zones are typically divided into fan, core, and pylon; the fire handle closes fuel, hydraulic, and bleed valves and arms the extinguisher bottles.

FADEC controls fuel metering and variable geometry, and provides fault reporting; the FADEC is normally dual-channel with one channel active and one in standby.

Aircraft DC systems are typically 28 V DC (14 V on light aircraft); AC systems are 115 V AC at 400 Hz, and 235 V AC is used on some transport aircraft for high-power loads.

Generator paralleling requires matching voltage, frequency, and phase sequence; a generator control unit (GCU) provides over/under voltage, overfrequency, and differential fault protection.

A bus tie breaker connects or isolates DC buses; essential and emergency buses are fed from the battery or a standby generator through a static inverter or transformer-rectifier.

ARINC 429 is a unidirectional, 32-bit word, twisted-pair bus; ARINC 629 and AFDX are bidirectional and use different framing and redundancy schemes.

Airdata parameters are computed from pitot and static pressure plus total air temperature; airspeed is indicated airspeed corrected for position and instrument error, and calibrated airspeed is the basis for most performance data.

Aircraft antennas require a counterpoise or ground plane; VHF communication uses the 118–137 MHz band and VOR/ILS uses 108–118 MHz, so antenna spacing and cable routing affect interference.

Bonding and grounding provide a low-impedance return path and lightning protection; a bonding resistance above the specified limit can cause EMI and unsafe fault currents.

Aircraft batteries are typically lead-acid or NiCd; NiCd cells exhibit voltage depression and thermal runaway risk, and require capacity checks and electrolyte level checks.

Instruments are classified as pitot-static, gyroscopic, or magnetic; a standby attitude indicator and standby airspeed indicator are required on transport-category aircraft.

Hydraulic system pressure is typically 3000 psi on transport aircraft; system pressure is regulated by a pressure regulator or pump compensator, and relief valves protect against overpressure.

Hydraulic fluid types are mineral-based (MIL-PRF-5606), phosphate ester (Skydrol), and polyalphaolefin; seals and hoses must match the fluid, and mixing types is prohibited.

A hydraulic reservoir is pressurized by bleed air or by a bootstrap system to prevent pump cavitation at altitude; the reservoir also accommodates thermal expansion.

Pneumatic system bleed air is taken from the engine compressor stages; precoolers limit bleed temperature before it reaches the pneumatic manifold, and a bleed-air leak is detected by overheat or leak-detection loops.

Fuel system components include boost pumps, check valves, crossfeed valves, and a fuel quantity indicating system; unusable fuel is the fuel that cannot be delivered under the most adverse conditions.

Fuel tanks are vented to prevent overpressure and to allow expansion; a flame arrestor in the vent line prevents ignition propagation.

Fuel jettison systems must be designed so that jettisoned fuel does not impinge on the aircraft; fuel dumping is prohibited below a specified altitude and airspeed.

Hydraulic filters are rated by micron rating and beta ratio; a bypass valve opens when the element is clogged, allowing unfiltered flow to protect the system from loss of pressure.

Pneumatic system valves include pressure-regulating valves, shutoff valves, and check valves; a failed open pressure-regulating valve can overpressure downstream ducts.

Primary flight controls are ailerons, elevators, and rudder; secondary controls are flaps, slats, spoilers, and trim tabs, which modify lift or trim rather than primary attitude.

A fly-by-wire system uses computers to convert pilot inputs to surface commands; normal law, alternate law, and direct law define the level of envelope protection available after failures.

The landing gear consists of the shock strut, torque links, wheel and brake assembly, and retraction mechanism; the shock strut uses nitrogen and hydraulic fluid to absorb landing energy.

A shimmy damper prevents nosewheel oscillation; shimmy is a self-excited oscillation caused by tire and strut dynamics and is corrected by damping and correct tire pressure.

Anti-skid systems modulate brake pressure to maintain wheel slip near the optimum; a locked wheel produces lower braking force than a wheel at the slip peak.

Landing gear warning systems activate on gear-up approach when flaps are extended or power is reduced below a set threshold.

Trim systems include elevator, rudder, and aileron trim; a runaway trim condition is countered by the trim cutout switch and manual reversion.

Flap asymmetry protection stops flap drive when the left and right flaps disagree beyond a set limit; flap overspeed can cause structural damage to the flap and tracks.

Landing gear retraction is interlocked with weight-on-wheels sensors so that gear cannot retract on the ground; squat switches also control pressurization and anti-skid logic.

Maintenance is categorized as line maintenance, base maintenance, and workshop maintenance; line maintenance covers pre-flight, transit, and daily checks, while base maintenance covers heavy checks.

A check (or letter check) intervals are set by the maintenance review board and the operator's approved maintenance program; intervals are expressed in flight hours, flight cycles, or calendar time.

The MSG-3 process defines scheduled maintenance tasks by failure consequence: lubrication, inspection, and functional checks are selected for each significant item.

A borescope inspection allows internal examination of engine compressor and turbine sections without disassembly; findings are compared with limits in the engine manual.

Torque values are specified in the maintenance manual; a calibrated torque wrench is used, and torque is applied in the sequence and increments specified to avoid uneven loading.

Lockwire and cotter pins are safetying methods; lockwire must be installed with the correct twist direction and tension, and self-locking nuts are replaced when the locking feature is degraded.

A maintenance record must include the work performed, the date, the identity of the person signing, and the reference to approved data; a certificate of release to service is issued after maintenance.

Aircraft jacking requires the aircraft to be within weight and balance limits and the jack points to be correctly engaged; control locks and ground locks are removed before flight.

Foreign object debris (FOD) control is a continuous process; inspection of engine intakes and flight control surfaces for FOD is part of every pre-flight and post-maintenance check.

ICAO Annex 8 sets the minimum airworthiness standards for international operations; national authorities implement them through type certification and continued airworthiness rules.

A type certificate approves the design of an aircraft type; a certificate of airworthiness confirms that a particular aircraft conforms to the approved type design and is safe to operate.

Airworthiness Directives (ADs) are mandatory; compliance is required within the stated interval, and an AD can require inspection, modification, or operational limitations.

Service Bulletins are issued by the manufacturer and are not mandatory unless made so by an AD or by the operator's approved maintenance program.

A supplemental type certificate (STC) is required for a major modification to a type-certified product; a minor modification may be approved as a minor change.

The aircraft maintenance manual, illustrated parts catalog, structural repair manual, and wiring diagram manual are approved or accepted data; maintenance must be performed to approved data.

A minimum equipment list (MEL) allows dispatch with specified equipment inoperative, subject to conditions and placards; the MEL is approved by the authority and cannot be less restrictive than the master MEL.

Weight and balance documentation includes the empty weight, empty weight center of gravity, and the loading envelope; exceeding the forward or aft CG limit affects controllability and performance.

Continued airworthiness includes corrosion prevention and control programs, aging aircraft inspections, and mandatory reporting of defects and unairworthy conditions.

The SHEL model describes the interfaces between software, hardware, environment, and liveware; mismatch at an interface is a source of human error.

The dirty dozen human factors include fatigue, complacency, distraction, lack of communication, and lack of resources; each contributes to maintenance error.

The Swiss cheese model describes accident causation as aligned holes in multiple defensive layers; safety management focuses on strengthening defenses rather than blaming individuals.

A safety management system (SMS) has four components: safety policy, safety risk management, safety assurance, and safety promotion.

Threat and error management (TEM) identifies threats before flight, errors during flight, and undesired aircraft states; countermeasures are applied at each stage.

Fatigue risk management limits duty and rest periods; circadian low points and cumulative sleep debt reduce vigilance and increase error rates.

Just culture distinguishes human error from at-risk and reckless behavior; reporting is encouraged, but reckless conduct is subject to disciplinary action.

Crew resource management (CRM) covers communication, leadership, workload management, and decision-making; it applies to maintenance teams as well as flight crews.

A safety occurrence report should be factual, timely, and confidential where a reporting system exists; the purpose is to identify hazards, not to assign blame.

Aluminum alloys 2024 and 7075 are common airframe materials; 2024 has good fatigue resistance, while 7075 has higher strength but lower corrosion resistance.

Titanium alloys are used in high-temperature and high-strength areas; titanium is susceptible to galvanic corrosion when coupled with aluminum in the presence of an electrolyte.

Composite structures use carbon or glass fibers in an epoxy matrix; impact damage can cause delamination that is not visible on the surface, so tap testing and ultrasonic inspection are used.

Heat treatment of aluminum includes solution treatment, quenching, and artificial aging; the T6 temper is solution treated and artificially aged.

Dye penetrant inspection detects surface-breaking defects in nonporous materials; magnetic particle inspection detects surface and near-surface defects in ferromagnetic materials only.

Eddy current inspection detects surface and near-surface cracks in conductive materials; it is fast and does not require contact but is affected by coating thickness.

Ultrasonic inspection uses high-frequency sound waves to detect internal defects and measure thickness; a couplant is required to transmit sound into the part.

Radiographic inspection uses X-rays or gamma rays to detect internal defects; it requires access to both sides of the part and radiation safety controls.

Galvanic corrosion occurs when dissimilar metals are in contact with an electrolyte; the anodic metal corrodes, and the risk increases with the potential difference between the metals.