This maneuver is used to transition from forward flight to a hover or
a landing. A JPEG and
GIF sequence of photographs of a
normal approach are available.
We usually consider a normal approach to be a 10 degree approach. More
than 10 degrees is considered to be a "steep" approach, and less than that
is considered to be "shallow". For reference, 10 degrees is about what you
get in a Cessna 172 with engine at idle and 40 degrees of flaps hung out.
We initiate the maneuver by intercepting the 10 degree approach angle.
Normally a collective pitch adjustment will be required to start the
helicopter descending on the 10 degree angle. The exact power setting
will depend on things such as wind, density altitude, and helicopter
The way that a helicopter pilot judges whether he is maintaining
the desired angle is similar to what an airplane pilot does. There
are multiple cues which will tell you whether you are changing approach
angle. These include:
- Shape of the landing area changes on different angles (shapes
get distorted by perspective more at lower approach angles).
- Position of the landing zone in the windshield. The LZ will be
lower in the windshield on a steep aproach, higher on a shallow
Unlike an airplane, helicopters do not fly constant airspeed approaches.
That's partly because they don't have to. If an airplane attempts to
decelerate too much on approach, it stalls. A helicopter doesn't have that
problem. Normally, inside of a mile of the landing zone the helicopter is
decelerating at the same rate it is losing altitude so that by the time
the altitude of the helicopter approaches zero, the ground speed will also
be approaching zero. One way for helicopter pilots to judge this is to
look at apparent ground speed. From high up, the ground seems to be going
by very slowly. As we descend, the ground appears to speed up. Helicopter
pilots simply hold the apparent ground speed to approximately a jogging
pace, and that will insure that as they approach the ground they will be
moving forward at a jogging pace. The last few knots of ground speed can
be killed as the helicopter transitions into a hover.
During the deceleration from approach speed to minimum sink airspeed,
less power is required as the helicopter slows. This will require the
helicopter pilot to be decreasing collective initially. However, from
minimum sink airspeed until reaching the LZ, the power required will be
going up, because the helicopter is on the back side of the power curve.
During the last portion of the approach, typically begining around 40
knots of airspeed, the helicopter is on the part of the power required
curve where power requirements are going up very quickly. The pilot will
normally notice a sudden tendency for the helicopter to sink below the
approach angle. The pilot will have to increase collective substantially
to maintain angle.
Because the helicopter is in a slightly flared attitude, this increase in
thrust will increase the deceleration force (because the rearward component
of thrust will be increased). If the pilot does not push forward on the
cyclic at this time, the helicopter will generally come to a stop well
short of the LZ, typically at a height of 25-35 feet. By adding forward
cyclic, the pilot will keep the helicopter moving forward at a slowly
declerating rate, losing altitude at the same time, until the helicopter
reaches the LZ at the desired hover height.
The maneuver can terminate either in a hover, which is the usual case, or
can be flown right to the surface. Approaches to the surface are typically
used when the pilot wants to minimize downwash, or does not want to hover
for one reason or another (poor visibility is one reason that comes to
mind). The pilot will find that a large amount of left pedal is required
to maintain skid alignment as the helicopter decelerates through
Whether the maneuver is going to terminate in a hover or to the ground,
the pilot should align the skids with the ground track at approximately
100' AGL. This prevents a rollover accident should the skids touch down
with forward speed.
Failure to maintain approach angle
Until the pilot can judge approach angle accurately, he may deviate from
approach angle and not realize it. While overshooting onto steeper angles
certainly occurs, the more common problem is failure to increase power
to account for the back side of the power curve. Especially below 40 knot,
the power required increases quickly, and the pilot may simply not raise
collective fast enough.
Failure to decelerate properly
Airplane pilots who solo in helicopters are famous for flying very
fast approaches (because of their trained in behavior to avoid low
airspeed which can stall an airplane). Even non-pilots have this problem,
though. Maintaining too high an airspeed until on short final causes a
couple problems. Usually a flare is required to decrease ground speed,
and if this is done too low a tail rotor strike is possible. Another
problem is the pilot who flares and reduces his airspeed while keeping a
high descent rate may encounter
settling with power.
Failure to reach the LZ
As described above, on short final the power increase required will cause
the helicopter to stop short of the LZ unless the pilot adds forward cyclic
at the same time. Indeed, it's not unusual for student pilots to come to
a hover well short of the LZ at about 35 feet, and then begin spinning
around because as translational lift is lost the tail rotor loses substantial
thrust, and a large increase in left pedal is normally required to counter
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