The technique for straight descents varies according to the airspeed on entry and whether a constant airspeed or constant rate descent is made.
A descent may be performed at any normal airspeed the helicopter can attain, but the airspeed must be determined prior to entry.
The application of both constant speed and constant rate descents are quite similar. While the aim in constant rate of descent is maintaining the target descent rate, which is usually 500 fpm or 1000 fpm, it is maintaining the target airspeed in constant airspeed descent.
Even with high performance helicopters, descent rates of more than 1000 fpm are not common practice due to the high rate of pressure changes in a pressurized cabin and some aerodynamic concerns.
For constant airspeed descent:
For a level off at descending airspeed, the lead should be approximately 10 percent of the vertical speed.
To level off at an airspeed higher than descending airspeed, increase the power approximately 100 to 150 feet prior to reaching the desired altitude
This type of descent is generally used for training purposes. It is also used when a specific amount of descent is required in a specific amount of time.
For constant rate descent:
The level off from a constant rate descent should be accomplished in the same manner as the level off from a constant airspeed descent.
Helicopter is in straight-and-level flight at 2000'.
Objecive: Descend to 1500' at 60 knots with 500 fpm rate
Simultaneously decrease power to the descent power setting and adjust pitch attitude to the approximate descent attitude.
When the helicopter stabilizes at a target airspeed and vertical speed, continue cross-checking other pitch instruments and adjust the power and pitch as necessary.
Initiate level-off at 1650' by applying level flight power and forward cycling as necessary. Hold the vertical speed constant until 1550'.
Establish straight-and-level flight by adjusting power and pitch as necessary.