Common ways slow flight can go wrong and how to fix them.
Slow Flight trains pilots to recognize and handle situations in which the airplane is flying at or near its minimum controllable airspeed with the wing flying at high angles of attack (AOA). It is a vital step on the road to becoming a proficient pilot. It’s also one of those maneuvers that seems simple to perform but can be difficult to perform well. Here is a compilation of slow flight common errors, and what to do about them.
Omitting Clearing Turns
Before any maneuver, you must clear the area by turning to scan for traffic all around you. Your school or instructor may have their own clearing procedure, but a commonly accepted standard is to complete either a single 180° turn or a 90° turn in one direction followed by a 90° turn back to the original heading.
Failure to Establish Specified Configuration
Slow flight is most often done in the landing configuration (gear down, full flaps), but can be done in other configurations specified by the Instructor/evaluator. Before the maneuver, brief what the desired configuration will be. Be sure to slow below the maximum allowable airspeed before extending the landing gear or flaps.
Improper Entry Technique
Slow flight is entered with a slow deceleration to the desired airspeed while establishing the desired configuration. Ensure use of carburetor heat in accordance with manufacturer instructions. The pace of the entry to slow flight is controlled by the throttle setting. Too much power and the aircraft may never slow to the specified airspeed. Too little power and the pilot may have difficulty maintaining altitude as the airplane decelerates, or may slow below the desired speed before the aircraft can be fully configured for the maneuver.
Failure to Establish and Maintain the Specified Airspeed
During training your instructor may have you fly slow flight at minimum controllable airspeed (MCA) at which the stall warning system will be active throughout the maneuver. This was once the standard for both training and checkride purposes, but in 2016 the FAA revised the evaluation criteria for slow flight and now stipulates a higher airspeed with no stall warning activation. That’s how you’ll be expected to perform the maneuver on your checkride.
In that case your target airspeed will be just above the speed at which the stall warning system activates. The FAA Airplane Flying Handbook allows the target airspeed to be found by slowing until the stall warning system first activates and then accelerating to slightly above that airspeed. Once the target airspeed is reached, hold that pitch attitude and add sufficient power to prevent the aircraft from slowing further or descending. Don’t go below that airspeed or more than 10 knots above it. Private Pilot ACS Tolerance is +10 knots/-0.
Excessive Altitude Deviations
Maintaining altitude while slowing to and maintaining the target airspeed is a central theme of this maneuver. In general maintaining altitude is a function of power, but pitch control also plays an integral role. Here I’ll describe controlling pitch by varying the amount of “backpressure” – the pressure applied to pull back on the control wheel or stick. This more accurately describes the control inputs than moving the controls a certain amount. Let’s look at common pitfalls specific to each stage of the maneuver:
During entry to the maneuver, three common culprits cause most altitude deviations:
- Too little elevator backpressure as airspeed slows – this is the most common case. As the airplane slows, you will need to increase the pitch of the airplane to keep it from descending. Once a descent begins it can be difficult to arrest. Watch for this error and correct for it early.
- Too much backpressure as airspeed slows – this is a common error when attempting to avoid making the first error described above. If you begin to climb during deceleration, either slightly decrease backpressure or hold it steady for a moment. As the aircraft continues to slow the pitch will reduce and the airplane will descend again.
- Not Anticipating angle of attack changes during flap extension – Extending flaps changes the angle of attack and camber of the wings which allows them to produce more lift for any given airspeed. As you extend flaps the pitch attitude of the airplane will change and you must compensate to keep the aircraft on altitude.
Once established in the maneuver, altitude deviations generally result from improper power settings for the present conditions. It’s not uncommon for pilots to continuously vary their pitch throughout the maneuver, but leave the power set and not adjust it until a major change is needed. Instead, actively adjust power throughout the maneuver. As you make changes in pitch, anticipate any corresponding changes needed in power. Actively manage both.
During a turn in slow flight the aircraft will have a tendency to descend. In a turn, maintain the pitch attitude with a slight increase in elevator backpressure and add sufficient power to keep the aircraft from descending. As stall speed increases in turns, your airspeed during a slow flight turn should also increase slightly. The more bank used, the more difficult the turn can be. The AFH recommends banks of “approximately 20 degrees.” Whatever the desired bank angle, you will be expected to maintain it during turns to ±10°
Improper Rudder Coordination
Slow flight is a maneuver that trains pilots to control the aircraft when it is flying at high angles of attack, near the stall regime. Since inadvertent stalls and improper rudder inputs are ingredients of stall-spin accidents, proper rudder coordination should be a central theme of the maneuver. A common error in slow flight is insufficient correction of the engine left turning tendencies at high angles of attack. The combination of low airspeed and high power settings will result in pronounced left turning tendencies from the engine and propeller.
The ball inclinometer provides a good reference for overall coordination, and with practice you will begin to develop a seat-of-the-pants feel for how well the aircraft is coordinated. Another valuable tool in straight (non-turning) flight can be using a distant external reference point. Keeping the wings level with the ailerons, use the rudder to prevent any yaw by holding the reference point steady in your field of view. If the wings are level and there is no yaw, you are coordinated.
Fixation on Flight Instruments
Like any other visual maneuver, the primary reference for attitude control during slow flight should be looking outside the airplane. The position of the nose with respect to the horizon provides the primary pitch reference. Roll orientation is ascertained by comparison to the horizon as well. Heading, yaw control, and general orientation can be provided by referencing roads and ground landmarks. Briefly reference your instruments, note any deviation and trend toward or away from your intended airspeed and altitude, and then look to your outside references to adjust pitch, power, roll, and yaw inputs as needed.
Improper Trim Technique
Use elevator trim to help you maintain the appropriate airspeed during slow flight. Be aware that this amount of nose-up trim is likely to produce a natural tendency to pitch up once power is applied for recovery from the maneuver. If you find yourself holding a strenuous amount of backpressure to maintain the desired pitch attitude, adjust the trim.
Inappropriate reaction to stall warning or stalls
Another central tenant of slow flight is being able to operate the aircraft at high angles of attack without stalling the wings. Once established at the target airspeed stall warning activation is undesirable and should be avoided. For a momentary stall warning (e.g. a chirp of the stall horn) reduce pitch to reduce angle of attack and add power as needed then continue the maneuver. Prolonged stall warning activation or warnings progressing to a full stall require a complete stall recovery.
Inappropriate Removal Of Hand From Throttle(s)
The most common hand placement error I have seen is when a pilot takes his/her hand off the throttle to grasp the yoke with both hands. This is neither necessary nor desirable. If the control forces are too much for one hand, adjust the elevator trim. Keep one hand on the throttle, ready to adjust it as needed. Make trim adjustments or perform any other actions necessary with this hand, but in the end return it to the throttle.
Slow flight teaches important skills necessary to become a competent pilot. Hopefully you found some useful information on common errors pilots make during slow flight. You can read more about this and other maneuvers in the FAA’s Airplane Flying Handbook (AFH). What lessons have you learned during slow flight? Share your stories in the comments below.
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