Principles of Flight

Exceeding the critical angle of attack. A stall can occur at different airspeeds and attitudes; airspeed alone does not define it.

Flaps generally increase wing camber and maximum lift coefficient, allowing lower flight speeds. They also increase drag; the balance depends on design and setting.

When an aircraft banks, its lift vector tilts. If total lift were left unchanged, its vertical component would become smaller than the aircraft’s weight and the aircraft would descend.

In a steady, coordinated and level turn:

$L \cos \phi = W$

Therefore:

$L = \frac{W}{\cos \phi}$

where:

• $L$ is total lift,
• $W$ is weight,
• $\phi$ is the bank angle.

Total lift must therefore be greater than weight. At a given airspeed, the pilot increases the angle of attack to generate the additional lift required to keep the vertical component equal to the weight.

The higher lift coefficient and load factor increase induced drag, so additional thrust is normally required to prevent the airspeed from decreasing.

The load factor in a coordinated level turn is:

$n = \frac{1}{\cos \phi}$

This is also why stall speed increases as the bank angle increases during a level turn.

Vectors are shown for explanation and are not necessarily to scale.

Reference: FAA Airplane Flying Handbook — turns and load factor.

Critical Mach number (Mcrit) is the lowest freestream Mach number at which airflow anywhere on the aircraft first reaches Mach 1. Above it, local supersonic regions and associated shocks can develop.

MMO is the certified maximum operating Mach number. It is an operating limit; Mcrit describes an aerodynamic condition that varies with configuration and flight condition.

Mcrit is not necessarily below MMO in every case. Follow the approved MMO and other speed limits; do not treat Mcrit as a universal maximum permitted operating speed.

References: FAA Pilot Handbook chapters 5 to 8 and 10 to 12.

The two primary types of aerodynamic drag acting on an aircraft are:

• Parasite drag: Caused by the aircraft moving through the air. It includes form drag, skin friction, and interference drag. Parasite drag increases with the square of airspeed.
• Induced drag: Also called lift-induced drag, it results from the generation of lift. It is highest at low speeds and decreases as speed increases.

Total drag is the sum of both:
Total Drag = Parasite Drag + Induced Drag

In a conventional light propeller aircraft, approach trim may already produce a strong nose-up tendency when power is increased. Increased propeller slipstream over the tail can amplify the pitch change. If the pilot does not maintain positive pitch control, the nose may rise above the intended climb attitude and the aircraft can approach a stall despite the added power. The FAA calls this an elevator-trim stall. Appropriate control pressure and timely retrimming follow the aircraft’s published go-around technique.

Scope: Conventional light propeller aircraft; not an Airbus automatic-trim description.

Sources

• FAA Airplane Flying Handbook, FAA-H-8083-3C, Chapter 5 — pp. 5-20–5-21, “Elevator Trim Stall”. Accessed 2026-10-03.

A helicopter’s rotor produces lift and an energetic wake. Close to the surface in a hover, downwash spreads outward after striking the ground. In forward flight, departing or landing helicopters can leave strong trailing vortices, so the hazard is not confined to visible dust directly beneath the rotor. The FAA calls for caution behind and across helicopter flight paths. Fixed-wing pilots should account for helicopter wake during taxi, departure and arrival rather than assuming only large airliners create a meaningful threat.

Scope: Fixed-wing awareness of helicopter wake; follow local separation and helicopter operating guidance.

Sources

• FAA Aeronautical Information Manual, Chapter 7 Section 4 — Wake Turbulence — AIM 7-4-7, Helicopters. Accessed 2026-10-03.

Reducing angle of attack can break the first stall before the aircraft has recovered enough energy for an abrupt pull-up. If the pilot then demands too much lift too quickly, the critical angle of attack can be exceeded again, producing a secondary stall. The urge to regain lost height can make this especially tempting near the ground. Recovery must rebuild a safe flight path without recreating excessive angle of attack, using the aircraft’s approved procedure and smooth, coordinated inputs.

Scope: Conventional aeroplane stall-recovery principles; aircraft-specific procedures apply.

Sources

• FAA Airplane Flying Handbook, FAA-H-8083-3C, Chapter 5 — pp. 5-18–5-19, “Secondary Stall”. Accessed 2026-10-03.

Excessive rudder can make the turn skid while the pilot applies opposite aileron to restrain bank. Pulling back to keep the nose up then raises angle of attack in an uncoordinated condition. If the aircraft stalls, it may roll rapidly into a spin, with very little height available for recovery. The FAA identifies this as a classic cross-control stall scenario. An overshoot is a reason to reassess and go around, rather than force alignment with the runway.

Scope: Conventional light-aircraft traffic-pattern operations.

Sources

• FAA Airplane Flying Handbook, FAA-H-8083-3C, Chapter 5 — p. 5-20, “Cross-Control Stall”. Accessed 2026-10-03.

A developed spin involves stalled wings and autorotation. A spiral dive is a steep descending turn in which the wing is no longer stalled; airspeed and load factor can rise quickly. Similar-looking rotation can therefore conceal very different states. Treating both as the same problem risks an inappropriate response, especially an abrupt pull during a fast spiral. Recognition must combine attitude, speed trends and the aircraft’s behavior, followed by the manufacturer’s approved recovery procedure and the pilot’s upset training.

Scope: Conventional aeroplane upset recognition; recovery procedures are aircraft-specific.

Sources

• FAA Airplane Flying Handbook, FAA-H-8083-3C, Chapter 5 — pp. 5-22–5-26, Spin Awareness, Developed Phase, Spiral Dive. Accessed 2026-10-03.

The critical angle of attack is the angle above which aerodynamic stall occurs. At this point, the airflow can no longer remain attached to the upper surface of the wing, leading to a rapid loss of lift.

At the critical angle, the lift coefficient ($C_{L}$) reaches its maximum. Beyond this point, even if the angle of attack increases, the wing can no longer generate sufficient lift to sustain flight.

Note:
- Every aircraft stalls at a specific angle of attack for a given configuration — not at a specific airspeed or attitude.
- The critical angle of attack decreases at high altitude and high Mach numbers due to compressibility effects and aerodynamic limits.
- Airframe icing can also lower the critical angle of attack significantly.
- Wing configuration affects it as well:
- Leading-edge slats and flaps, when extended, tend to increase the critical angle of attack.
- Trailing-edge flaps, on the other hand, generally reduce it.
- For this reason, in most jet aircraft, leading-edge devices extend automatically when trailing-edge flaps are deployed.

Coffin corner, also called Q-corner, describes the high-altitude region in which the usable speed margin between the low-speed buffet boundary and the high-speed Mach-buffet or MMO boundary becomes very small.

• If speed decreases, the angle of attack must increase to maintain lift. This can lead to low-speed buffet and eventually a stall.
• If speed increases, the Mach number approaches its upper limit. Further acceleration may result in an MMO exceedance; shock-wave-induced flow separation can cause Mach buffet and reduced control effectiveness.

It is therefore inaccurate to describe the upper boundary simply as a “high-speed stall.”

At the theoretical aerodynamic ceiling, the low-speed and high-speed boundaries meet. The AFM maximum operating altitude is below this point, and the selected cruising altitude must retain an adequate buffet and manoeuvre margin.

Higher aircraft mass, increased load factor, bank angle, gusts or turbulence can further reduce this margin. Flight crews must therefore respect the aircraft’s buffet limits, maximum operating altitude and procedures.

Conceptual diagram: exact boundaries depend on aircraft type, mass, load factor and configuration.

Reference: FAA AC 61-107B — high-altitude operations and coffin corner.

In a coordinated level turn at a given bank angle, turn radius is proportional to the square of true airspeed. A faster aircraft therefore travels around a wider circle, while its rate of turn decreases. Maintaining the same radius requires more bank and therefore a different load factor. This is an air-relative relationship: wind separately changes the ground track. It explains why a familiar bank angle is not a guarantee of the same turning space in every flight condition.

Scope: Coordinated, level, still-air turn geometry; wind changes the path over the ground.

Sources

• FAA Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25C, Chapter 5 — pp. 5-38–5-40, Rate of Turn and Radius of Turn. Accessed 2026-10-03.