Stall speed is the minimum speed an aircraft must maintain to stay airborne. Below this speed, the wings can no longer produce enough lift to support the airplane’s weight, and it begins to lose altitude regardless of engine power. For a common training aircraft like the Cessna 172, stall speed is around 48 knots (55 mph) in cruise configuration and drops to about 40 knots (46 mph) with flaps extended for landing.
Why Planes Stall
A wing generates lift by forcing air to flow faster over its curved upper surface than its flat lower surface. The angle between the wing and the oncoming air is called the angle of attack. As a pilot pulls the nose up or the airplane slows down, this angle increases, and up to a point, lift increases too.
But there’s a limit. When the angle of attack gets too steep, the smooth airflow over the top of the wing breaks away from the surface. This is called flow separation. Instead of clinging to the wing’s curve and creating lift, the air becomes turbulent and chaotic. Lift drops sharply and drag spikes. That sudden loss of lift is the stall, and the speed at which it happens in straight, level flight is the stall speed.
The stall doesn’t happen because the engine quit or because the plane ran out of power. It happens because the wing exceeded its ability to bend airflow. A plane can stall at any speed and any altitude if the angle of attack is pushed too far, which is why understanding stall speed as a baseline matters so much.
What Determines Stall Speed
Four main factors set an airplane’s stall speed: weight, air density, wing area, and how much lift the wing shape can generate at its maximum angle of attack. Heavier planes need more lift to stay airborne, so they stall at higher speeds. Thinner air at higher altitudes provides less lift per square foot of wing, which also raises the stall speed. A larger wing or a wing designed to produce a higher peak lift coefficient brings the stall speed down.
This is why the same airplane has different published stall speeds depending on its configuration. With flaps extended, the wing’s shape changes to produce more lift at lower speeds, reducing the stall speed. The FAA defines two key numbers: Vso, the stall speed in landing configuration (flaps down, gear down), and Vs1, the stall speed in a clean configuration (flaps up). On that Cessna 172, the 8-knot gap between those two numbers (40 vs. 48 knots) is entirely due to the flaps reshaping the wing.
How Stall Speed Changes in Turns
Stall speed isn’t fixed during flight. It climbs any time the airplane experiences more than one “G” of force, which happens most commonly in turns. When you bank an airplane, part of the lift that was holding it up is now being used to turn it sideways. To maintain altitude, the wing has to produce more total lift, and that raises the effective stall speed.
The numbers get dramatic quickly. Using a baseline stall speed of 50 knots in level flight:
- 45-degree bank: stall speed increases 20%, to about 60 knots
- 60-degree bank: stall speed increases 40%, to about 70 knots
- 75-degree bank: stall speed doubles, reaching 100 knots
This is why steep turns close to the ground are so dangerous. A pilot flying at a speed that feels perfectly safe in straight flight can suddenly be below stall speed in a sharp turn. The wing stalls, lift disappears, and there may not be enough altitude to recover.
Warning Signs Before a Stall
Stalls don’t happen without warning. As an airplane approaches its stall speed, a predictable sequence plays out. First, the airspeed drops noticeably. Then the flight controls start to feel soft and unresponsive, requiring larger inputs to get the same result. The nose may need to be held increasingly high to maintain altitude, requiring more and more back pressure on the control column.
Most modern aircraft also have a mechanical stall warning system, typically a horn or a light, that activates a few knots above the actual stall speed. But pilots are trained not to rely solely on this device since it can malfunction. The final physical warning is a buffet, a vibration felt through the airframe caused by turbulent airflow from the separated wing striking the tail. That buffet is the airplane telling you the stall is imminent.
How Pilots Recover From a Stall
The single most important action in stall recovery is reducing the angle of attack. That means pushing the nose down. This feels counterintuitive, especially close to the ground, because the airplane is already losing altitude. But no amount of engine power will fix a stalled wing. The airflow over the wing has to reattach first, and that only happens when the angle of attack decreases.
The FAA’s recommended recovery sequence starts with disconnecting the autopilot, then immediately lowering the nose to reduce the angle of attack. Once the stall indications stop (the buffet fades, airspeed builds, controls firm up), the pilot levels the wings to point all available lift straight up, then adds power as appropriate to climb back to a safe altitude. The key training emphasis is that reducing the angle of attack comes before everything else, including leveling the wings or adding thrust.
Different Types of Stalls
Not all stalls feel the same. The way a wing stalls depends on its shape and thickness. Thicker, more curved wings tend to experience trailing-edge stalls, where the airflow separates gradually from the back of the wing and creeps forward. These are relatively gentle and give the pilot more time to react.
Thinner wings with sharper leading edges can experience more abrupt stalls. A small bubble of separated air forms near the front of the wing and suddenly bursts, causing a rapid and dramatic loss of lift. This type is harder to anticipate because it transitions quickly from normal flight to a full stall with little progressive warning. Aircraft designers account for these characteristics when choosing wing shapes, often prioritizing more forgiving stall behavior in training and general aviation aircraft.