Lesson 2.3 - Stalls, Critical Angle of Attack, & Spin Awareness

Stalls, Critical Angle of Attack, & Spin Awareness

In the previous lessons we learned that the wings generate lift and that angle of attack is the key factor controlling that lift. In this lesson we examine what happens when the wing exceeds its critical angle of attack — the stall — and the related subject of spin awareness.

Reference:FAA Pilot’s Handbook of Aeronautical Knowledge (PHAK), Chapter 5 – Aerodynamics of Flight

https://www.faa.gov/sites/faa.gov/files/07_phak_ch5_0.pdf

What a Stall Is (and What It Is Not)

A stall is an aerodynamic condition in which the wing exceeds its critical angle of attack and the smooth airflow over the top of the wing separates. When this happens, lift decreases sharply and drag increases.

What a Stall is NOT:

Caused by insufficient airspeed alone
Caused by a particular aircraft attitude
Something that only happens at low altitudes

Core Lesson: A stall is strictly caused by exceeding the critical angle of attack, regardless of airspeed, attitude, or power setting.

Critical Angle of Attack

Every wing has a specific critical angle of attack (typically 16°–20° for most light training airplanes). When this angle is reached or exceeded, the wing stalls — regardless of your current airspeed, attitude, weight, or power configuration. This is why an airplane can be stalled at any airspeed and in any flight attitude.

Factors That Affect Stall Speed

While the critical angle of attack remains a fixed constant, the indicated airspeed at which the wing reaches that angle changes based on flight conditions. Stall speed increases with:

Higher weight
Higher load factor (steep turns or pulling G-loads)
Forward center of gravity (CG)
Flaps up (in most training airplanes)

Recognizing a Stall

Common indications of an approaching or full aerodynamic stall include:

Buffeting: Shaking or aerodynamic trembling of the airplane as separated air hits the tail surface.
Control Ineffectiveness: A noticeable decrease in control surface responsiveness as airspeed decays.
High Nose Attitude: Observed in many common training scenarios (though not a requirement).
Stall Warning Device: An activated warning horn or light.
Inability to Maintain Altitude: The aircraft sinks despite applying increased back-elevator pressure.

Check-ride Notebook: The stall warning horn is required to activate 5 to 10 knots before the actual aerodynamic stall begins, giving the pilot a clear buffer to recover before the wing lets go. Classic older aircraft often do not have a stall warning horn.

Keep the turn coordinator ball in the center using your rudder pedals. "step on the ball"

Stall Recovery (Basic Principles)

The primary goal of stall recovery is to immediately reduce the angle of attack. Typical recovery steps taught in light training airplanes:

Reduce Angle of Attack: Relax back-elevator pressure and move the control yoke forward as needed to break the stall.
Add Power: Apply maximum available power as appropriate to minimize altitude loss.
Level the Wings: Coordinate rudder and aileron inputs to bring the wings level.
Return to Normal Flight: Smoothly pull out of the dive and return to straight-and-level flight.

Always follow the specific Pilot’s Operating Handbook (POH) recovery procedure for the exact airplane you are flying.

Practical Stall Examples

Departure Stall (Power-On): Occurs shortly after takeoff or during a go-around when the pilot raises the nose too high while the airplane is accelerating at high power settings.
Arrival / Approach Stall (Power-Off): Occurs on final approach when a pilot attempts to "stretch a glide" or hold the aircraft off the runway without sufficient airspeed. This is especially dangerous due to its close proximity to the ground.
Accelerated Stall: Occurs in a steep turn or abrupt pull-up when the load factor is increased. The wing reaches its critical angle of attack at a significantly higher indicated airspeed than it does in unaccelerated, straight-and-level flight.
Cross-Controlled Stall: Occurs when the aircraft is stalled while in uncoordinated flight (slipping or skidding). This is highly dangerous because it can lead directly into an inadvertent spin. A common hazard location is a poorly executed base-to-final turn.
Stall from an Excessive Climb Attitude: Occurs when a pilot attempts to climb too steeply without maintaining sufficient airspeed to clear obstacles or terrain.

Spin Awareness

A spin is an aggravated stall that results in the airplane descending in a helical (corkscrew) flight path. For a spin to develop, two distinct conditions are always required simultaneously:

The airplane must be stalled.
There must be a yawing moment (uncoordinated flight).

Spin Recovery Procedure (PARE)

P - Power: Immediately reduce throttle to idle.
A - Ailerons: Neutralize the ailerons (keep wings level; attempting to roll out can worsen the spin).
R - Rudder: Apply full opposite rudder against the direction of the rotation.
E - Elevator: Briskly move the elevator forward to the neutral position (or slightly beyond) to break the stall.

Once the rotation stops, neutralize the rudder and recover from the dive with smooth back-elevator pressure. Avoid pulling back too abruptly, which can cause a critical secondary stall.

Private Pilot Expectation: Full spin entries and recoveries are not required for the Private Pilot practical test. However, spin awareness and prevention are heavily tested. Staying coordinated, especially when flying near the critical angle of attack, is your absolute best defense.

The Four Phases of a Spin

Every spin progresses through four distinct chronological phases. Your students will face written and oral exam questions on these exact terms:

1. Entry Phase: The pilot stalls the aircraft while failing to keep the ball centered. As one wing drops more than the other, an uncoordinated yawing moment is introduced, initiating the rotation.
2. Incipient Phase: The period from the initial stall until the aerodynamic and inertial forces fully balance out. This typically lasts the first 2 to 4 turns. Airspeed is relatively low but unstable, and the turn coordinator ball will be pegged to the outside of the rotation.
3. Developed Phase: The aerodynamic and inertial forces achieve perfect equilibrium. The aircraft's rotation rate, pitch attitude, and vertical descent speed fully stabilize into a constant, predictable corkscrew down.
4. Recovery Phase: The pilot applies specific, immediate anti-spin inputs (PARE) to disrupt the balance of forces, stop the rotation, and break the core aerodynamic stall.

⚠️ Life-Saving Recovery Watchouts

The Secondary Stall Risk: Once the spin rotation officially stops, the aircraft will be in a steep, nose-down dive with rapidly increasing airspeed. If a panicked pilot pulls back on the control yoke too abruptly to recover from the dive, the wing will instantly exceed its critical angle of attack a second time. This snaps the aircraft right back into a highly dangerous secondary stall or an inverted secondary spin. Pull out smoothly!
Keep Your Feet Alive: During stall recovery, never look at the horizon or guess which way you are turning. Keep your eyes on the turn coordinator instrument and step on the ball. If the ball is kicked out to the left, step hard on the left rudder pedal to coordinate the airframe. Total coordination is your single greatest insurance policy against an inadvertent spin entry close to the ground.

The turn coordinator, shown at the upper part of the page, does 2 separate things:

1. The airplane part of the turn coordinator is driven by a gyro, and, if you bank until the little airplane's wing touches the lower left or right line, you are doing a standard rate turn. 2 minute turn, they are sometimes called. So, you will complete a 360 degree turn in 2 minutes if you bank left or right and keep the airplane in the coordinator touching the white line.
The turn coordinator differs from the traditional turn-and-slip indicator. The turn and slip indicator senses only the rate of turn.
The turn coordinator is designed to give pilots a quicker heads-up during a rapid roll entry.
Sensing Roll Rate: When you first push the control yoke to bank the wings, the canted gyro within the turn coordinator instantly senses that initial rate of roll. This causes the miniature airplane on your instrument dial to deflect immediately, even before the aircraft's nose actually starts swinging through the horizon.

Transitioning to Turn Rate: Once you stop rolling and establish your bank angle, the roll rate drops back to zero. At that exact point, the gyroscope transitions entirely to measuring the established rate of turn (yaw rate).

So, while the miniature airplane indicates both roll and turn rate sequentially, its fundamental mechanical advantage over the old turn-and-slip needle is its ability to sense that initial roll rate. That is exactly why the FAA loves to test students on this specific design difference!

2. The important feature in avoiding spins is the ball. It sits in a glass tube filled with a fluid. The tube is slightly curved. So, the ball settles to the center of the tube. It does not use power of any kind. The ball is present in both the turn and slip indicator, as well as the turn coordinator.

On the ground it just sits in the center, unless you have a flat tire.

In the air it tells you if you are in coordinated flight. This means each wing is generating equal lift. You will not spin if you keep it this way. To do this, you step on the ball using your rudder pedals. Have no fear...stalls are easy, spins are easy if you are in the correct aircraft. Some aircraft are not approved for spins and you should practice with an instructor.

According to the FAA Airplane Flying Handbook (FAA-H-8083-3C), the inclinometer ball is completely unreliable during a spin because the centrifugal and inertial forces acting on it vary wildly and can cause it to peg unpredictably.

The FAA Rule: To determine the direction of a spin when visual references are lost, the pilot must look at the miniature airplane (or turn needle) of the turn coordinator, which will clearly deflect in the direction of rotation. Rudder must be applied opposite the miniature airplane's deflection, regardless of what the ball is doing.
The Fix: "Step on the ball" is the perfect rule for preventing a spin (keeping it coordinated in the turn), but once you are in a spin, you apply rudder opposite the miniature aircraft's wing deflection.

A common source of accidents due to spins is when the pilot is turning from "base" to "final" on an approach to land.

The pilot will be slowing to approach speed at low altitude. Rather than flying a coordinated turn to final, the pilot chooses to "skid" the aircraft from base to final approach.

Typically this turn is a left turn.

The pilot, using left rudder to "skid" around the turn, at a low airspeed, loses lift on the left wing. As the left wing pivots aft, the right wing pivots forward. This causes the left wing to lose substantial lift, possibly stalling. The right wing gains lift. The aircraft enters a spin 400 above the trees. The surprised pilot is unprepared to react. The aircraft may also be incapable of recovering in time.

Keep the ball centered. Step on the ball.

In this image, the left wing has a lower angle of attack. The right wing, a larger angle of attack. The lift vectors differ (on wing tips). The slow wing is the right wing. The left wing lifts the aircraft into a spin.