Upset Prevention and Recovery: Slow Flight

Slow flight is an important flight-training maneuver that helps pilots understand airplane handling characteristics at low airspeeds and high angles of attack (AOA). Practicing this maneuver develops the ability to recognize stall warnings, maintain coordinated flight, manage power and pitch, and respond appropriately to changing flight conditions. These skills help pilots maintain aircraft control during takeoff, approach, landing, and other situations involving reduced airspeed.

Slow Flight

Flying at reduced airspeeds is normal during the takeoff/departure and approach/landing phases of flight. Although pilots typically perform these operations at low airspeeds and close to the ground, they learn to maneuver an airplane in slow flight at a safe altitude.

During slow flight, any further increase in angle of attack, increase in load factor, or reduction in power will result in a stall warning (e.g., aircraft buffet, stall horn, etc.). Pilots should respond appropriately to and correct for any stall indication.

Note that stall training builds upon the knowledge and skills acquired during the slow flight maneuver. It encompasses the period from the stall warning (e.g., aircraft buffet, stall horn, etc.) to the stall.

The objective of maneuvering in slow flight is to develop the pilot’s ability to fly at low speeds and high AOAs. Through practice, the pilot becomes familiar with the feel, sound, and visual cues of flight in this regime, where the response to control inputs is reduced and maintaining a selected altitude is more difficult.

It is essential that pilots:

1. Understand the aerodynamics associated with slow flight in various aircraft configurations and attitudes.
2. Recognize airplane cues in these flight conditions.
3. Smoothly manage coordinated flight control inputs while maneuvering without a stall warning.
4. Make prompt, appropriate corrections should a stall warning occur.

For pilot training and testing purposes, slow flight includes two main elements:

• Slowing to, maneuvering at, and recovering from an airspeed at which the airplane is still capable of maintaining controlled flight without activating the stall warning. An airspeed 5 to 10 knots above the 1G stall speed is a good target.
• Performing slow flight in configurations appropriate for takeoffs, climbs, descents, approaches to landing, and go-arounds.

Slow flight should be introduced with the target airspeed sufficiently above the stall to permit safe maneuvering, but close enough to the stall warning for the pilot to experience the characteristics of flight at a low airspeed.

One way to determine the target airspeed is to slow the aircraft to the stall warning in the desired slow flight configuration. Then, pitch the nose down slightly to eliminate the stall warning and add power to maintain altitude. Note the resulting airspeed.

When practicing slow flight, a pilot learns to divide attention between aircraft control and other demands. The way the airplane feels at slower airspeeds demonstrates that control effectiveness decreases as airspeed decreases.

For instance, reducing airspeed from 30 knots to 20 knots above the stalling speed results in some loss of effectiveness of flight control inputs because of reduced airflow over the control surfaces.

As airspeed is further reduced, control effectiveness decreases even more. The reduced airflow over the control surfaces means that larger control movements are required to produce the same response. Pilots sometimes describe the feel of this reduced effectiveness as “sloppy” or “mushy” controls.

When flying above the minimum drag speed (L/DMAX), more power is required to fly faster. When flying at speeds below L/DMAX, more power is required to fly slower.

Since slow flight is performed well below L/DMAX, the pilot should be aware that large power inputs or a reduction in AOA may be required to prevent the aircraft from decelerating.

It is important to note that when flying below L/DMAX, or on the backside of the power curve, small changes in pitch control can result in disproportionately large changes in induced drag as the AOA increases toward the critical AOA and the airplane’s speed continues to decrease.

As a result, pitch becomes a more effective control of airspeed when flying below L/DMAX, while power is an effective control of the flightpath.

It is also important to note that an airplane flying below L/DMAX exhibits a characteristic known as “speed instability.” The airspeed will continue to decay without appropriate pilot action.

For example, if turbulence disturbs the airplane and the airspeed decreases, the airspeed may continue to decrease unless the pilot takes appropriate action, such as reducing the AOA or adding power. [Figure 1]

Performing the Slow Flight Maneuver

Slow flight training includes:

• Slowing the airplane smoothly and promptly from cruising speed to approach speeds without changes in altitude or heading, while increasing the angle of attack and setting the required power and trim.
• Making configuration changes, such as extending the landing gear and adding flaps, while maintaining heading and altitude.
• Turning while maintaining altitude.
• Performing straight-ahead climbs and climbing medium-banked turns (approximately 20 degrees), as well as straight-ahead power-off gliding descents and descending turns, which represent the takeoff and landing phases of flight.

Slow flight in a single-engine airplane should be conducted so that the maneuver can be completed no lower than 1,500 feet AGL (3,000 feet for multiengine airplanes), or higher if recommended by the manufacturer.

In all cases, slow flight practice should be conducted at an adequate height above the ground to allow recovery if the airplane inadvertently stalls.

To begin the slow flight maneuver, the pilot should clear the area and gradually reduce thrust from cruise power. The pilot should adjust the pitch to allow the airspeed to decrease while maintaining altitude.

As the speed of the airplane decreases, the sound of the airflow changes. As the airplane approaches the target slow flight speed—an airspeed just above the stall warning in the desired configuration, approximately 5–10 knots above the stall speed for that flight condition—additional power will be needed to maintain altitude.

During these changing flight conditions, the pilot should trim the airplane to compensate for changes in control pressures. If the airplane remains trimmed for the pre-maneuver cruising speed, strong aft (back) control pressure will be needed on the elevator, making precise control difficult.

Slow flight is typically performed and evaluated in the landing configuration. Therefore, both the landing gear and the flaps should be extended to the landing position, as applicable.

It is recommended that the prescribed before-landing checks be completed to configure the airplane. The landing gear and flaps are typically extended after cruise power has been reduced and at appropriate airspeeds to ensure that their operating limitations are not exceeded.

Practicing this maneuver in other configurations, such as a clean or takeoff configuration, is also good training and may be evaluated on the practical test.

With an AOA just below the angle that may cause an aerodynamic buffet or stall warning, the flight controls are less effective. [Figure 2]

The elevator control is less responsive, and larger control movements are necessary to retain control of the airplane.

In propeller-driven airplanes, torque, slipstream effect, and P-factor may produce a strong left yaw, requiring right rudder input to maintain coordinated flight. The closer the airplane is to the 1G stall, the greater the amount of right rudder pressure required.

Maneuvering in Slow Flight

When the desired pitch attitude and airspeed have been established in straight-and-level slow flight, the pilot needs to maintain awareness of outside references and continually cross-check the airplane’s instruments to maintain control.

The pilot should note the feel of the flight controls, especially the airspeed changes caused by small pitch adjustments and the altitude changes caused by power changes.

The pilot should practice turns to determine the airplane’s controllability characteristics at this low speed. During turns, it will be necessary to increase power to maintain altitude.

Abrupt or rough control movements during slow flight may result in a stall. For instance, abruptly raising the flaps while in slow flight can cause the airplane to stall.

The pilot should also practice climbs and descents by adjusting the power after stabilizing in straight-and-level slow flight. The pilot should note the increased yawing tendency at high power settings and counter it with rudder input as needed.

To exit the slow flight maneuver, add power. As airspeed and lift increase, apply forward control pressure to reduce the AOA and maintain altitude.

Maintain coordinated flight, level the wings as necessary, and return to the desired flightpath. As airspeed increases, clean up the airplane by retracting the flaps and landing gear, if they were extended, and adjust the trim as needed.

A pilot should anticipate changes in AOA as the landing gear and flaps are retracted to avoid a stall.

Common Errors

Common errors in the performance of slow flight include:

1. Failure to adequately clear the area.
2. Inadequate back-elevator pressure as power is reduced, resulting in altitude loss.
3. Excessive back-elevator pressure as power is reduced, resulting in a climb followed by a rapid reduction in airspeed.
4. Insufficient right rudder to compensate for left yaw.
5. Fixation on the flight instruments.
6. Failure to anticipate changes in AOA as flaps are extended or retracted.
7. Inadequate power management.
8. Inability to adequately divide attention between airplane control and orientation.
9. Failure to properly trim the airplane.
10. Failure to respond to a stall warning.