Elevator Trim Stall
The elevator trim stall demonstration shows what can happen when the pilot applies full power for a go-around without maintaining positive control of the airplane. [Figure 4-10] This is a demonstration-only maneuver; only flight instructor applicants may be required to perform it on a practical test. However, all pilots should be familiar with the situations that can cause an elevator trim stall, how to recognize it, and the appropriate recovery action should one occur.
This situation may occur during a go-around procedure from a normal landing approach or a simulated, forced-landing approach, or immediately after a takeoff, with the trim set for a normal landing approach glide at idle power. The objective of the demonstration is to show the importance of making smooth power applications, overcoming strong trim forces, maintaining positive control of the airplane to hold safe flight attitudes, and using proper and timely trim techniques. It also develops the pilot’s ability to avoid actions that could result in this stall, to recognize when an elevator trim stall is approaching, and to take prompt and correct action to prevent a full stall condition. It is imperative to avoid the occurrence of an elevator trim stall during an actual go-around from an approach to landing.
At a safe altitude and after ensuring that the area is clear of other air traffic, the pilot should slowly retard the throttle and extend the landing gear (if the airplane is equipped with retractable gear). The next step is to extend the flaps to the one-half or full position, close the throttle, and maintain altitude until the airspeed approaches the normal glide speed.
When the normal glide is established, the pilot should trim the airplane nose-up for the normal landing approach glide. During this simulated final approach glide, the throttle is then advanced smoothly to maximum allowable power, just as it would be adjusted to perform a go-around.
The combined effects of increased propwash over the tail and elevator trim tend to make the nose rise sharply and turn to the left. With the throttle fully advanced, the pitch attitude increases above the normal climbing attitude. When it is apparent the airplane is approaching a stall, the pilot must apply sufficient forward elevator pressure to reduce the AOA and eliminate the stall warning before returning the airplane to the normal climbing attitude. The pilot will need to adjust trim to relieve the heavy control pressures and then complete the normal goaround procedures and return to the desired flightpath. If taken to the full stall, recovery will require a significant nose-down attitude to reduce the AOA below its critical AOA, along with a corresponding significant loss of altitude.
Common errors in the performance of intentional stalls are:
- Failure to adequately clear the area
- Over-reliance on the airspeed indicator and slip-skid indicator while excluding other cues
- Inadvertent accelerated stall by pulling too fast on the controls during a power-off or power on stall entry
- Inability to recognize an impending stall condition
- Failure to take timely action to prevent a full stall during the conduct of impending stalls
- Failure to maintain a constant bank angle during turning stalls
- Failure to maintain proper coordination with the rudder throughout the stall and recovery
- Recovering before reaching the critical AOA when practicing the full stall maneuver
- Not disconnecting the wing leveler or autopilot, if equipped, prior to reducing AOA
- Recovery is attempted without recognizing the importance of pitch control and AOA
- Not maintaining a nose down control input until the stall warning is eliminated
- Pilot attempts to level the wings before reducing AOA
- Pilot attempts to recover with power before reducing AOA
- Failure to roll wings level after AOA reduction and stall warning is eliminated
- Inadvertent secondary stall during recovery
- Excessive forward-elevator pressure during recovery resulting in low or negative G load
- Excessive airspeed buildup during recovery
- Losing situational awareness and failing to return to desired flightpath or follow ATC instructions after recovery.