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Fly 'Em BetterIFR Maneuvering: A Chance to Catch Up! by Jim Irwin, Vice President, Products Airplanes maneuver around the three axes of roll, pitch and yaw. During autopilot controlled maneuvers, the commands are typically limited to roll and pitch with yaw commands being a reaction to yaw upsets requiring damping, normally through a yaw damper. Commands through the roll and pitch axis are made to accomplish a specific objective, i.e. to turn or not turn and to climb or descend or to hold an altitude. In instrument flight, maneuvering standards are taught. A standard rate turn, a specific bank angle for normal maneuvering, a specific intercept angle for certain course offsets, a 500 FPM climb or descent for short climbs or descents or when nearing the desired altitude. These standards create a maneuvering, rate and position judgment capability the pilot uses to unconsciously judge where he is, or where he will be. This is based upon the pilot's intuitive judgment of the elapsed time and the rate of movement provided by these standards. This, in turn, provides the pilot with a degree of instrument scan flexibility - if he has 1000 ft to lose at 500 FPM he has two minutes he can use to concentrate on some other requirement. This use of time and rate is one of the techniques available in instrument flying to increase precision and situational awareness and allow time for housekeeping. S-TEC rate autopilots lend themselves to this capability, not only by handling many of the flying duties, but also by providing predictable maneuvering rates in both turn and climb or descent maneuvering. To maneuver in the pitch axis, S-TEC full function autopilots use vertical speed (Vs) as the command reference. Our autopilots use either a time based modifier switch that modifies the Vs reference at a specific rate (Systems 60-2, 60PSS, & 65) or a digital Vs selector (System 55 & Altitude Selector/Alerter). New owners and operators of S-TEC System 60-2, 60PSS, or 65 Autopilots often hold the modifier switch for up or down until the aircraft attitude has changed to the attitude that they believe will produce the desired climb or descent. However, since the device is time related, this procedure will produce a larger attitude change than desired. The correct method is much faster, easier and less obtrusive, especially during instrument maneuvering flight when you must divide your attention between so many activities. The up or down modifiers revise the reference Vs at the rate of 160 FPM per second of activation. Therefore, to initiate a standard rate descent or climb (500 FPM) it is only necessary to select Vs mode and then push the desired modifier and hold it for about 3 seconds. During this period the aircraft will begin a very smooth pitch change in the direction commanded, verifying the command. At the end of the 3 seconds input, the Vs will be at approximately one half the desired rate. Releasing the modifier button the pilot can resume the instrument scan or direct his attention to other duties. Thus, a turn or intercept can be accomplished while the autopilot is completing the Vs command. On the next scan cycle the pilot can verify proper operation and see how close the command came to 500 FPM. For a shallow descent, such as that from a procedure turn altitude to a lower intermediate segment altitude, a 200 FPM descent rate requires only slightly more than a one second activation before you can return to your scan and other approach chores. Push the modifier for the required period, then get on with other duty items while the maneuver is initiated and developed. For significant changes in vertical speed, such as 1000 FPM or more, input a 3-second, 500 FPM, command to get things started, then go to the next step in the maneuver such as initiating a turn. Finally, return to add the additional Vs command. This management technique allows you to get the course and altitude changes started immediately, which is often appreciated by ATC, while not spending an excessive amount of time on any one chore. While proper use of the time based modifiers is both easy and fast, the use of the optional S-TEC Altitude Selector/Alerter is even faster, particularly if you need a large Vs change. With this system installed, the pilot simply dials in the desired up or down Vs on the selector. Next, he selects the autopilot Vs mode, observes the initial pitch over, and then goes on with the instrument scan. Returning to verify the desired result on the next scan is the last step. To increase or decrease the original Vs selection, it is only necessary to rotate the Vs selector knob to the new Vs command value. If you have chosen, or been assigned an altitude, you can input that altitude to automatically level off there. An altitude alert chime advises you of the approaching altitude. Beginning to make IFR maneuvering pretty easy, isn't it? The S-TEC System 55 has a digital vertical speed selector built in. As with the optional Selector/Alerter added to Systems 60-2, 60PSS, or 65, you can input the desired Vs and then select the autopilot Vs mode, observe the initial pitch change and resume your scanning or housekeeping. Once again, the last step is returning on the next scan or two to verify the vertical speed. There are times, in IMC, when you must maneuver the aircraft in response to ATC commands while simultaneously familiarizing yourself with new and unexpected approach or navigation problems. It is during these busy times in the cockpit that understanding the maneuvering rate and time relationship will be very helpful. You won't have to feel panicked by changes and clearance amendments - simply dial in the initial requirements, heading and Vs, and use the maneuvering period to catch up with your other duties. Try it, it works. |