With the helicopter positioned above the intended landing area, and aligned parallel to the slope, the pilot should descend by lowering collective. When the uphill skid contacts the slope, pause, and add just a little cyclic into the hill. This will help to lock in the landing gear. Both the front and rear (toe and heel) of the gear should be in contact with the ground. If not, the helicopter will tend to yaw around the single pivot point in contact with the slope. If the slope and the skid are not at the same angle, the helicopter can be pivoted slightly using pedal to find an angle where the skid will be alighned with the slope. Care must be taken not to swing the tail rotor into the hillside. The landing can be done with only a single contact point on the uphill skid, but it will be much harder. The pilot should first see if there isn't another section of slope that will allow the skid to be properly planted.
Once the skid is planted, the pilot lowers the downhill skid toward the ground by lowering collective. Rather than a continuous rolling motion, an iterative process of lowering the skid a few inches then pausing before lowering it some more prevents too much of a rolling momentum from building up. This is important if the slope turns out to be too steep to land on.
As the downhill skid is lowered, the cyclic needs to be deflected into the hillside in order to keep the rotor disk horizontal. Since the swashplate is connected to the fuselage, failure to displace the cyclic into the hillside will cause the rotor to tilt toward the downhill side, and the usual result will be skidding the helicopter sideways down the hill (not such a great idea!). Cyclic inputs should be coordinated with fuselage roll, not with collective pitch motions.
After the downhill skid makes contact, the pilot should continue to use caution lowering the collective in case there is any tendency for the helicopter to tilt toward the downhill side. Some people recommend centering the cyclic after the collective reaches flat pitch, other people recommend keeping it displaced into the hillside for the entire duration of the slope landing (including shutdown if the helicopter is to be parked on the slope).
Pilots who fly helicopters with twin, cross feeding fuel tanks mounted high on the fuselage (like the Bell 47) need to consider the fact that while parked on the hill the fuel will cross feed from the upper tank to the lower tank, and the CG shift may be severe enough to roll the helicopter over while it is parked, or to prevent a safe liftoff later on.
Similarly, if tail rotor translating tendency requires left cyclic to counter, less left cyclic authority will be available. Thus landing on a slope right skid upslope may allow a steeper slope landing. Manufacturers tend to tilt the masts to counter translating tendency, so this guideline may be more or less true given different makes and models of helicopters.
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