by Harold Green, CFII
Published in Midwest Flyer – February/March 2019 issue
Ever notice how some pilots hold exact altitude with no apparent effort? Wonder how they do it? The key is knowledge and practice. Knowledge can be used to minimize the required practice time. Practice simply requires time and attention. Hopefully the following information will aid you in acquiring this skill with a minimum amount of practice time.
One of the first skills to master is reading flight instruments with little or no effort. Only when establishing or changing flight conditions as you reach your target altitude, is it necessary to actually read the numbers on the flight instruments. Once established and in stable flight, there is no need to actually read the numbers on the dials with any frequency. It is only necessary to note the pattern of needle excursion from the original readings.
Scanning the instruments becomes akin to speed reading. Of course, not only is the actual excursion important, the rate of excursion is also important. If the altimeter is moving slowly, and the Vertical Speed Indicator (VSI) is off center only a little, a gradual corrective control input is desired. If the vertical speed indicator indicates a rapid change of altitude, then more immediate control input is needed. The goal here is to stop the VSI movement. Then you can move the altimeter needle back to its original position with appropriate pitch or power corrections.
The speed of correction is also very important. Suddenly you notice you are 100 feet off your target altitude, probably because your attention was diverted. The usual reaction is to correct the situation instantaneously, but sudden changes are not necessary, and can startle passengers. Indeed, with a gradual return to altitude, maybe no one except you even noticed. Another very important factor is the pilot’s goal to hold altitude with zero deviation.
As the final altitude is approached, level flight is achieved by changing pitch and power to hold the altitude. Appropriate power and pitch are adjusted to achieve level flight. During the transition to level flight and a stable airspeed, it may be desirable to adjust the trim to ease the force. However, recognize that final trim will not be achieved until the airspeed is steady.
It is necessary to fine trim the airplane by adjusting the trim to remove the control wheel force while holding airspeed steady. General aviation aircraft, when properly trimmed, fly for long periods of time in smooth air with no pitch correction from the pilot, providing power input remains constant.
Having trimmed your aircraft, it is time to look at reasons why your aircraft can deviate from level flight, and what can be done to overcome this. The principal factors are: pilot generated control input, turbulence, and center of gravity (CG) excursions.
Probably the most prevalent cause of unintended altitude excursion is “pilot induced.” Typically, this is caused by unintended control input. The two most prevalent causes of such inputs are muscular reaction while reaching for something in the cockpit, and what can be described as attempting to “drive” the airplane.
Consider the “reaching” effect. When the pilot reaches for something in the cockpit, such as a radio control, an approach plate, or aeronautical chart, both arms tend to become involved because of the way our arms and torso are connected. The further the reach and the further to the side, the greater the impact. This results in changing force on the control wheel. The result is a change in roll and/or pitch, and usually both. Once the pilot becomes aware of this, the cure seems to follow automatically. It just requires awareness on the part of the pilot.
When “driving” the airplane, the pilot is constantly moving the controls, usually the pitch and roll, regardless of need for control input. That is opposed to simply using the controls to correct any excursions from steady flight by the airplane. The individual seems to be seeking confirmation of control by moving the controls and sensing a response from the airplane. The result is that precise and smooth control of the airplane is very difficult. It is usually very difficult to correct this problem as the pilot is so used to such actions and is subconsciously doing it. It takes dedicated attention on the part of the pilot to correct this habit and often requires someone pointing out the practice as it occurs.
Much of the turbulence encountered results in merely bumps in the road with little or no altitude change. However, it is not uncommon for pilots to react to the abruptness of the turbulence, rather than the actual altitude effect. The result is sporadic control input with pilot induced altitude excursions. To prevent this the pilot should react to the effect on the airplane altitude or attitude and ignore the abruptness of the bumps. Initially, this can take considerable mental discipline, but it rapidly becomes second nature.
At the next higher stage, turbulence can cause altitude excursions requiring correction. In this case corrections should be applied as early and gradually as possible. This minimizes the stress on both airplane and passengers. However, there are times when turbulence is a significant factor in altitude excursions.
The most extreme of these are the conditions found in a thunderstorm. In this case you are advised to forget altitude and maintain airspeed and heading. However, there are other atmospheric conditions which prevent holding altitude.
One example of this is the waves encountered at times over mountains. While often accompanied by turbulence, these waves at times can be quite peaceful. If you are on a wave downslope, you can find yourself applying full power, holding Vy and still descending while in apparently smooth air. (Vy is the indicated airspeed for best RATE of climb. Vx is the indicated airspeed for best ANGLE of climb.) In this case, all you can do is ride it out, and perhaps turn to minimize the exposure time. On the upslope you may be pitched down approaching Vne (never exceed speed) with power removed and still climbing. If you are IFR, this is a perfect time to request “block altitude.” Obviously holding altitude in these conditions is secondary to maintaining airspeed, just as in a thunderstorm.
Center of gravity (CG) shifts can also cause altitude deviations. CG shifts can be caused by someone including the pilot, leaning forward or backward while in level flight. Should this occur, it is necessary only to re-establish altitude. No pitch or power adjustments need to be made unless the altitude excursion is excessive and there is need for immediate altitude corrections, rather than a gradual change. In some airplanes, particularly some twins, it is possible for the CG to shift as fuel is consumed. In these cases, trim must be adjusted to ensure altitude hold. Fuel shift is gradual and can be compensated for with small trim adjustments as the flight progresses.
In summary, attention to the gauges, acceptance of high standards, and proper trimming and smoothness of control, coupled with attention to these details whenever flying, will result in better altitude control with an overall improvement in flying.
EDITOR’S NOTE: Harold Green is an Instrument and Multi-Engine Instrument Instructor (CFII, MEII) at Morey Airplane Company in Middleton, Wisconsin (C29). A flight instructor since 1976, Green was named “Flight Instructor of the Year” by the Federal Aviation Administration in 2011 and is a recipient of the “Wright Brothers Master Pilot Award.” Questions, comments and suggestions for future topics are welcomed via email at email@example.com, or by telephone at 608-836-1711 (www.MoreyAirport.com).
DISCLAIMER: The information contained in this column is the expressed opinion of the author only, and readers are advised to seek the advice of their personal flight instructor and others, and refer to the Federal Aviation Regulations, FAA Aeronautical Information Manual and instructional materials before attempting any procedures discussed herein.