Flying Instruments on the Back Side of the Power Curve

In weather flying posts #1-#5, we talked about flying in rapidly deteriorating conditions that result in lost visual cues, forcing a transition to instruments. However, mission demands often require Coast Guard crews to launch on cases in which they commit to flying on instruments from the onset. They are typically over water missions (e.g., MEDEVAC or a boat taking on water), and away from IFR infrastructure, where we provide our own obstacle and terrain clearance. Many times on these cases, we fly what our Coast Guard helicopter community refers to as an instrument approach to the water, a descending, decelerating approach to a hover. For the purposes of general discussion, I will refer to this procedure as an instrument approach to a hover.  

When I began flying in the Coast Guard we did not have flight director cues. Instead, we relied on the attitude, airspeed and vertical speed indicators combined with the radar altimeter, and some rudimentary doppler hover bars to fly an instrument approach to a hover. The maneuver, when practiced diligently, improves the whole spectrum of a pilot’s instrument air work. Throughout a 20+ year career flying in various weather conditions, I have often relied on this foundational air work at night, with low visibility and little to no visual cues. As referenced in weather flying post #3, because of the capability and safety margins this foundational air work has afforded our crews, I regularly fly instrument approaches to high hovers, over water, during the day, with autopilot/AFCS off, using a vision limiting device (maintaining ample altitude for flyout, in the event of a power loss).

Despite avionics upgrades (EGIs and flight director cues), that have changed how we establish an instrument hover, the fundamental tenets of flying a stabilized instrument approach to a hover remain the same. During an ideal instrument approach to a hover, once the descent is established after approach initiation, power is not reduced again until the descent is stopped, and a hover is achieved. To maintain a constant glidepath, power must continually increase as the relative wind/airspeed decreases.  

Understanding that the rate of power application is commensurate with the relative wind/airspeed, is crucial to flying consistent stabilized instrument approaches to a hover. In the next post, I will further explore this important concept.