TM 55-1520-228-10
Change 14 8-11
SECTION III. INSTRUMENT FLIGHT
8-26. INSTRUMENT FLIGHT – GENERAL.
This aircraft is restricted to visual flight conditions. Flight
into instrument meteorological conditions will be con-
ducted on an emergency basis only. Flight handling,
stability characteristics, and range are the same during
instrument flight as for visual flight. Navigation and com-
munication equipment are adequate for instrument
flight.
SECTION IV. FLIGHT CHARACTERISTICS
8-27. OPERATING CHARACTERISTICS.
a. The flight characteristics of this helicopter, in
general, are similar to other single-rotor helicopters.
b. N2 droop may occur during a normal flight ma-
neuver requiring a rapid increase in power (i.e., rapid
collective and/or tail rotor inputs, high-G maneuvers). If
N2 droop occurs, but low RPM warning is not activated
and N2 recovers to 100 percent within 5 seconds, and
further droop is not experienced, this is considered a
normal flight characteristic.
8-28. MAST BUMPING.
Mast bumping (flapping-stop contact) is the main yoke
contacting the mast and may result in a fractured mast
and rotor separation. It may occur during slope landings,
rotor startup/coastdown, or when the flight envelope is
exceeded. If bumping occurs during a slope landing,
reposition the cyclic to stop the bumping, reestablish a
hover, and land on less sloping ground. If bumping oc-
curs during startup or shutdown, move cyclic to mini-
mize or eliminate bumping. If the flight envelope is
inadvertently exceeded, causing a low “G” condition and
right roll, move cyclic aft to return rotor to a positive
thrust condition, then roll level, continuing flight if mast
bumping has not occurred. As collective pitch is reduced
after engine failure or loss of tail rotor thrust, cyclic must
be positioned to maintain positive “G” forces during au-
torotation. Touchdown should be accomplished prior to
excessive rotor RPM decay. After landing, an entry in
DA Form 2408-13-1 is required for appropriate mainte-
nance inspection.
8-29. SPIKE KNOCK.
a. Spike knock occurs when the round pin in the
drag-pin fitting contacts the side of the square hole of the
pylon stop, which is mounted to the roof. It creates a loud
noise and will occur during a rocking of the pylon. The
following factors can cause spike knock
: low rotor RPM,
extreme asymmetric loading, poor execution of an auto-
rotational landing and low G maneuvers below +0.5 Gs.
b. Spike knock will be more prevalent during zero
ground run autorotational landings than for sliding auto-
rotational landings and running landings.
c. Spike knock in itself is not hazardous but is an
indicator of a condition that could be hazardous. If spike
knock is encountered, an entry must be made on DA
Form 2408-13-1, to include the flight conditions under
which the spike knock occurred. An inspection will be
performed by maintenance personnel before continu-
ing.
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