The “Collective Cue” Misnomer
In the MH-60T helicopter, one of the methods used to fly an instrument approach to the water harnesses flight director cues. Because the flight controls cannot be coupled to the flight director, pilots hand fly the approach using cues. The vertical flight director cue is named the “collective cue.” If airspeed is constant, the name “collective cue” is accurate. For example, if pilots are flying an ILS at a consistent 90 KIAS and are above glidepath with a “down arrow” on the “collective cue,” to descend onto glidepath the collective must be lowered to increase rate of descent while maintaining airspeed.
However, during a descending and decelerating instrument approach to a hover on the backside of the power curve, the term “collective cue” is a misnomer. For example, if pilots are slightly high on the computer-generated glide path, prompting a down arrow on the “collective cue,” the correct response is not to lower the collective. Repeating myself intentionally from the previous post… If pilots are flying a well stabilized approach that is slightly high, instead of lowering the collective to increase rate of descent, the pilots need to simply continue to bleed off airspeed. As airspeed decreases on the backside of the power curve, rate of descent increases. As the helicopter slows, without adjusting collective, the collective cue will go from a down arrow to a diamond (appropriate rate of descent to remain on glidepath), at which point the pilot can resume increasing the appropriate amount of power at the appropriate rate. If the pilot continues to decrease airspeed without adjusting collective, the “collective cue” will turn to an up arrow as rate of descent increases and the helicopter “sinks” below glidepath.
Ideally, power application is smooth throughout the approach to a hover. However, during a stabilized hand flown approach, in reality, power is applied, held steady, then applied again in small, short increments as the helicopter slows at the beginning of the approach. When the helicopter slows toward a hover, the rate of application increases exponentially to a smooth power application, peaking just above the power required to hover, to stop the descent.
