Student having issues holding altitude in IMC?

[FlyingArgentine]

I have seen more often than not a student struggle with altitude hold in simulated or actual IMC. The reason for this issue is simply that the students want to use the altimeter to hold altitude. Logically it seems like a sound idea, altimeter measures altitude, so to hold altitude the altimeter is needed. Not bad reasoning really, but incomplete. The FAA states that the altimeter is the primary instrument to use to hold altitude, however, it also states that: "the concept of primary and supporting instruments does not devalue any particular flight instrument, when available" (Instrument Flying Handbook, FAA-H-8083-15A, pg4-10). That is exactly what students tend to do, without realizing the value of other instruments to hold altitude.

Imagine flying in IMC and taking a snapshot of the instruments, now ask the question, which instruments provide information on what the aircraft is doing? Since it is just a snapshot, the altimeter is useless, since there is no movement shown. The VSI and Attitude Indicator, however, give a direct indication of whether the aircraft is climbing, descending, or level. Why is this information important? Well, during the scan needed to fly the aircraft in IMC a pilot needs to just glance at the instruments, staring at an instrument for too long is considered an error in scanning, fixation. To gain an appropriate idea of how fast an aircraft is climbing or descending using the altimeter requires more time than is advisable to spend on one given instrument.

The Attitude Indicator has a great value when wanting to hold a specific pitch attitude, however it is important to specify that the particular pitch attitude to hold level flight changes depending on many factors, following are just a few: How high the student sits on the seat (instrument parallax), how high or low the miniature aircraft is placed on the instrument, and the airspeed of the aircraft (controlled by the power setting). Considering these factors, there is a need to use another instrument to verify which specific pitch attitude holds altitude. The best instrument for that action is the VSI.

The VSI provides two pieces of information: rate of climb or descent and trend of climb and descent. The rate is the direct indication of the value indicated by the needle on the instrument in thousands of feet per minute. The major drawback to the rate information is the lag inherently present due to the nature of the instrument (the calibrated leak on the aneroid wafer or capsule in the casing). The trend information displayed on the other hand is instant. The difference between rate and trend is as simple as the difference between the position of the needle and the movement of the needle. The difference is extremely important in terms of control. When making a control change using the VSI the rate should be ignored and a change of trend should be the goal. If the needle of the VSI shows an upward movement, then a pitch down correction is needed, the correction though should be just enough to reverse the trend of the needle (form an upward trend to a downward trend) not to get the rate to show 0. Once the trend has been controlled and the rate has stabilized at 0, then note should be taken of the attitude shown on the AI, that is the level position for the aircraft taking into account power setting. A further step that I normally encourage is to have the student change the position of the miniature aircraft so the nose of the aircraft shows level with horizon.

Now, you ask, how can I practically use this information to get my student to quit simulating a roller-coaster while in IMC? Force the student to use the VSI and the AI indicator while in flight to maintain altitude. How do we force them? Easy, cover the altimeter. Once the student reaches a given altitude, cover the Altimeter and have said student use the VSI trends to find a level flight attitude, once that is done, have the student set the miniature aircraft on the AI and use both instruments from then on to hold altitude. At first there might be some over controlling since the student will most likely try to control the rate and not the trend displayed on the VSI. Once the level pitch attitude is dialed in, a good trim setting will assure that the aircraft will maintain altitude almost perfectly.

This method works great on most students as long as they understand the difference between rate and trend, a small demonstration in VFR conditions normally get the job done. As you control the aircraft up and down, they get to see the relationship between the position of the needle, the trend, the horizon, and when is the nose of the aircraft level with the horizon. I have found that the most important time to use this method is when a student is trying to maintain MDA. Since the PTS standards are so strict for this portion of the approach (-0/+100ft) the student tends to over control while fixating on the altimeter.

This is a method that works great for me and my students, I would love to hear what your methods are to teach holding altitude, enjoy!