Training Scars from Boost Servo Off Training
Boost may be lost for a variety of reasons. The only scenario where aircrews might have some control over when boost is lost is during a tail rotor pedal restriction or drive malfunction. Other cases—such as a #2 HYD PUMP failure without the BACKUP PUMP ON, #2 RSVR LOW, Boost Servo Malfunction, or BOOST SERVO OFF—are hydraulic failures that can result in an unexpected loss of boost at any time.
Despite the unpredictable nature of these malfunctions, the CG H-60 community typically introduces the malfunction during cruise flight (e.g., on downwind), even though the more demanding profiles for boost-off flight are takeoff, hover, and decelerating final approaches. As with all training malfunctions, safety margins must be maintained through sufficient altitude and control guarding, and if the benefit of practicing any emergency does not outweigh the risk, the simulator is a more appropriate training environment. However, with proper aircraft commander control measures in place, pilots should train for boost loss in a variety of flight regimes.
For example, when discussing a boost loss while in a hover during a hoist, most pilots focus on the uncontrolled left yaw as the primary hazard. While uncontrolled left yaw is a valid concern, an even greater risk may come from the abrupt collective movement which could lead to an unplanned descent into obstacles—or, conversely, a climb while the rescuer or device is still on deck and attached to the hoist hook. The heavier the aircraft, or the higher the power demand, the more pronounced the collective drop as the system seeks a mid-collective position. In contrast, a light aircraft in high winds, where power demand is low, may experience an uncommanded climb.
Another common training scar is the tendency to land boost-off with excessive rate of descent and forward drift. In a flat, prepared surface environments, this may be acceptable, but in real-world scenarios—such as landing on a gravel beach, rocky riverbed, or snow-covered field—this approach could damage the helicopter or cause a rollover. For instance, the #2 HYD PUMP WITHOUT BACKUP PUMP ON procedure ends with “land as soon as possible,” which may require landing on unprepared terrain. If pilots cannot land smoothly, with minimal yaw and drift, they risk aircraft damage and crew injury.
As aircrew proficiency increases, pilots should aim to land under full control, with a descent rate appropriate for a flat, off-field site. Similar to the training progression used for autorotations—starting with a straight-in auto—aircrews might begin with a boost-off landing to a flat, paved surface. Once that is mastered, the next progression could be a controlled landing at a moderate descent rate, simulating arrival to an unprepared surface.
Finally, aircrews must be prepared to wave off a boost-off landing if the selected landing zone (LZ) is deemed unsuitable during the approach. Practicing these go-arounds in a controlled environment builds confidence and enables sound aeronautical decision-making when the risk of continuing the approach outweighs the risk of continued flight.
