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ATPL · illustrated course

ATPL airframe, systems and power plant course: 14 illustrated chapters

The ATPL airframe, systems and power plant course follows the syllabus in 14 chapters: 118 key points explained in a few paragraphs, often with a diagram, what to remember and, for many, the classic exam trap. The first chapter, « Structures, loads and certification », can be read in full on this page.

Contents

Each chapter explains, point by point, what the questions of the bank ask, with a « Remember » box and often the classic exam trap. The first chapter is free, below and in the app; the next ones are for ATPL subscribers.

  1. Basic stresses, fuselage and wing, bending and torsion, design philosophies, materials and CS-25 failure categories.

    9 key points · 84 questions of the bank

  2. 2.Flight controls

    Subscribers

    Primary and secondary flight controls, spoilers, tabs, flutter, irreversible servo controls and artificial feel, electrical flight controls and protection devices.

    9 key points · 72 questions of the bank

  3. 3.Hydraulic systems

    Subscribers

    Pascal's principle, hydraulic power, fluids, reservoir, pumps, accumulators, actuators, check valves and emergency sources.

    9 key points · 63 questions of the bank

  4. 4.Landing gear, brakes and tyres

    Subscribers

    Gear types, oleo-pneumatic shock absorbers, operation and emergency extension, indications, brakes, anti-skid and tyres.

    7 key points · 56 questions of the bank

  5. 5.Pneumatics, air conditioning and pressurisation

    Subscribers

    Bleed air, bootstrap air conditioning packs, temperature control, pressurisation principle and modes, differential pressure calculations and safety devices.

    7 key points · 69 questions of the bank

  6. 6.Ice and rain protection

    Subscribers

    Anti-icing and de-icing: hot air, pneumatic boots, electrical heating, windshield, ice detectors and rain protection.

    6 key points · 31 questions of the bank

  7. 7.Fuel system

    Subscribers

    Fuels, tanks and venting, low-pressure pumps, cross-feed, refuelling, fuel quantity gauging and fuel jettisoning in flight.

    8 key points · 73 questions of the bank

  8. 8.Electricity: basics, direct current and batteries

    Subscribers

    Electrical quantities, series and parallel circuits, magnetism and induction, batteries, DC generators, protection, bonding and digital logic.

    11 key points · 155 questions of the bank

  9. 9.Alternating current and aircraft electrical systems

    Subscribers

    AC quantities and three-phase power, brushless alternators, CSD and IDG, paralleling, systems and buses, AC/DC conversion, protections and AC motors.

    9 key points · 114 questions of the bank

  10. 10.Piston engine: cycle, lubrication and ignition

    Subscribers

    Engine construction, the four-stroke cycle and the actual cycle, lubrication, cooling and magneto ignition.

    7 key points · 85 questions of the bank

  11. 11.Fuel supply, mixture and supercharging

    Subscribers

    Carburettor, icing, richness and mixture adjustment, detonation, manifold pressure, power at altitude and turbocharger.

    7 key points · 106 questions of the bank

  12. 12.Propellers

    Subscribers

    Pitch angle and angle of attack, fixed-pitch propeller, forces on the blades, constant-speed propeller, feathering and reverse, free-turbine turboprop.

    6 key points · 37 questions of the bank

  13. 13.Gas turbine engines and APU

    Subscribers

    Principle of propulsion, architecture and stations, bypass ratio, air intake, compressors, surge, combustion chamber, turbine, thrust reversers, parameters, FADEC, starting, oil and APU.

    13 key points · 160 questions of the bank

  14. 14.Fire protection, oxygen and emergency equipment

    Subscribers

    Overheat, fire and smoke detection, engine and APU fire extinguishing, portable extinguishers, crew and passenger oxygen systems, evacuation equipment.

    10 key points · 103 questions of the bank

Chapter 1: Structures, loads and certification

Basic stresses, fuselage and wing, bending and torsion, design philosophies, materials and CS-25 failure categories.

Basic stresses

← Faites glisser le schéma →

The five modes of loading on a part

© ForAllPilots

Every structural part works in one of five basic modes:

  • tension: two opposing forces tend to lengthen the part;
  • compression: the forces tend to crush it;
  • shear: two parallel, opposite forces make one section slide over the other (rivet, spar web);
  • bending: the part curves; one side is compressed, the other stretched;
  • torsion: a torque tends to twist the part about its axis.

Bending and torsion combine several stresses: they are effects "of more than a simple force".

Remember

Tension = stretch, compression = crush, shear = slide, torsion = twist (torque).

Exam trap

On the annex diagrams, a curved arrow around an axis represents a torque (torsion), not tension.

Truss, monocoque, semi-monocoque

← Faites glisser le schéma →

The three fuselage structural principles

© ForAllPilots

Three main families of fuselage:

  • truss of welded steel tubes covered with fabric: used only on light aircraft;
  • monocoque: the skin carries all the loads, with no significant internal framework;
  • semi-monocoque: a stressed skin supported by a light framework (frames, stringers, spars). This is the structure of all pressurised transport aircraft.

The materials most used in monocoque and semi-monocoque structures remain aluminium and its alloys, increasingly supplemented by composites.

Remember

Transport aircraft fuselage = semi-monocoque: skin + frames + stringers.

Role of the fuselage elements

← Faites glisser le schéma →

Differential pressure stretches the fuselage skin

© ForAllPilots

In a semi-monocoque fuselage:

  • the frames give the shape and the transverse stiffness;
  • the stringers (longitudinal stiffeners) help the skin carry the longitudinal tension and compression loads due to fuselage bending;
  • the skin carries the shear and, on the cylindrical section, the loads created by pressurisation cycles (hoop tension).

Each pressurised flight is one loading cycle: it is the number of cycles, not the hours, that wears out the airframe through fatigue.

Exam trap

The question "what carries the pressurisation loads on the cylindrical section" expects the skin, not the frames.

Wing structure

← Faites glisser le schéma →

Cross-section of a two-spar wing box

© ForAllPilots

A wing consists of:

  • front and rear spars, made of a web (shear) and caps (tension/compression); they carry the bending when the skin is not load-bearing;
  • ribs: they give the wing its aerofoil profile and transmit the loads to the box;
  • stiffeners and skin, which together with the spars form the wing box.

A cantilever wing is attached only at the root, with no external support. A non-cantilever wing is supported by struts, which carry it on the ground and in flight (light high-wing aircraft).

Remember

Spar = web + caps. Rib = shape of the profile.

Wing bending in flight and on the ground

← Faites glisser le schéma →

Lift creates a bending moment that increases towards the wing root

© ForAllPilots

In flight, the distributed lift bends the cantilever wing upwards: the upper surface is in compression and the lower surface in tension; the upper spar cap works in compression, the lower one in tension. The bending moment is greatest at the wing root.

On the ground (parking, hangar), the weight of the wing and engines reverses the effect: tension on the upper surface, compression on the lower surface.

To relieve the wing root, fuel is kept as long as possible in the outer tanks and the ailerons may be deflected upwards (load alleviation). This is also what sets the maximum zero fuel mass (MZFM): beyond it, the moment at the root would be too great.

Remember

In flight: upper surface in compression, lower surface in tension. On the ground: the opposite.

Exam trap

To reduce the loads on the wing, the fuel in the outer tanks is kept (not "used first") and the ailerons are deflected upwards.

Torsion and in-plane loads

← Faites glisser le schéma →

Top view: thrust and drag bend the wing in its plane

© ForAllPilots

The wing undergoes significant torsion under the effect of aileron deflection: at high speed, an outboard aileron can twist the wing to the point of reversing its effect. Hence the inboard ailerons, used at high speed to reduce wing twisting, the outboard ailerons being active only with flaps extended (low speed).

In the horizontal plane, a jet engine under the wing pulls it forward, while drag pushes it rearward: the front spar works in compression between the root and the engine, then in tension towards the tip.

Remember

Front spar, from root to tip: compression then tension.

Safe life, fail safe, damage tolerance

← Faites glisser le schéma →

Three structural design philosophies

© ForAllPilots

  • Safe life: the part is designed for a defined life (cycles or hours) and then replaced, whether damaged or not.
  • Fail safe: the load is shared between several elements in parallel; if one breaks, the others carry a reasonable load until the failure is detected.
  • Damage tolerance: the structure withstands weakening (a crack) without catastrophic failure, the crack growing slowly enough to be found during inspection.

Fatigue is the failure of a material subjected to repeated loads, even below its static breaking load. Life is calculated for a given load spectrum: a long-haul aircraft used on short-haul routes undergoes many more cycles and uses up its fatigue life much faster.

Remember

Safe life = scheduled replacement. Fail safe = redundancy, parallel load paths.

Materials, composites and sandwich

← Faites glisser le schéma →

Cross-section of a honeycomb sandwich panel

© ForAllPilots

  • Duralumin: aluminium-copper alloy (2024 family), light and strong, a good thermal conductor, difficult to weld (it is riveted).
  • Titanium and stainless steel: hot areas (nacelle firewalls) and highly loaded parts.
  • Composite: fibres (carbon, glass, aramid) embedded in a matrix (resin). Excellent strength-to-mass ratio and no corrosion, but damage can sometimes be invisible.
  • Sandwich: two thin skins separated by a light core (honeycomb, foam). Very light and stiff, but unsuited to concentrated loads (fittings, impacts).

Exam trap

Sandwich: "light and stiff" yes; "ideal for point loads" no.

Failure condition categories (CS-25)

← Faites glisser le schéma →

Table of failure condition categories and associated probabilities

© ForAllPilots

The certification rules for transport aeroplanes (CS-25.1309 and its AMC) classify failure conditions according to their effect and impose a maximum probability per flight hour.

  • Minor: slight increase in flight crew workload, physical discomfort for passengers.
  • Major: significant increase in workload, discomfort; physical distress and possible injuries to passengers.
  • Hazardous: excessive workload, serious or fatal injuries to a small number of occupants.
  • Catastrophic: loss of the aeroplane, many fatalities. It must be extremely improbable.

Remember

Catastrophic < 10⁻⁹ / h; hazardous 10⁻⁷ to 10⁻⁹; major 10⁻⁵ to 10⁻⁷; minor 10⁻³ to 10⁻⁵.

Exam trap

The question bank says "rare" for major and "extremely rare" for hazardous; EASA texts say "remote" and "extremely remote". They are the same ranges.

The course goes on with chapter 2, « Flight controls ». It is read in the Course tab of the app with a ATPL subscription, and each chapter ends with the questions of the bank about it. See pricing

How ForAllPilots trains you

  • Series of 20 or 30 questions

    New questions, mistakes to review or a mix of both, with the answer and its explanation straight away.

  • Flashcards

    Question on the front, explained answer on the back, filtered by subject, to learn without a timer.

  • Timed mock exam

    100 questions in 150 minutes, drawn from the whole ATPL bank: a training format, not a copy of an official paper.

  • AI instructor, optional

    From €4.99 a month on top of the Private pilot or PRO offer: it quizzes you in writing and explains your mistakes. A beta tool, it does not replace an approved instructor.

ATPL access comes with the PRO offer (which also includes Private pilot): €19.99 a month, cancel anytime, or €129 once with the Exam Pass (18 months of access, nothing renews). Prices include all taxes.

The other ATPL courses

All about the ATPL exams: format, subjects and method