TM 1-1520-240-10
9-1-6
9-1-10. Dual Engine Failure.
CAUTION
Jettison external cargo as soon as possible
after engine failure. This will help to prevent
damage to the helicopter during touchdown
and will reduce weight and drag, thereby
improving autorotational performance.
a. Low Altitude / Low Airspeed. When both engines
fail at low altitude and low airspeed, sufficient altitude is
not available to increase RRPM. Establish the best
autorotational airspeed, jettison external cargo (if
applicable), and decelerate effectively prior to
touchdown. Initial thrust reduction will vary from no
reduction at zero airspeed below 20 feet to full reduction
at higher airspeeds and altitudes. Attempt to maintain at
least 96 percent.
b. Cruise. c. In cruise flights up to Vne, reduce
thrust immediately to full down position to regain RRPM.
Adjust cyclic pressure as necessary to maintain the re-
quired airspeed. The Autorotation Approach Corridor,
figure 9-1-8, presents those combinations of airspeeds
and wheel heights from which a safe autorotatiive landing
may be made following a second engine failure. Autorotative
approaches are recommended in the caution area. At high
gross weights, the rotor may tend to overspeed and may
require thrust application to maintain RPM below the upper
limit. Thrust should never be applied to reduce RPM for
extending glide distance because this reduces RPM avail-
able for use during touchdown. When both engines fail at
cruise, proceed as follows:
CAUTION
The helicopter must be maneuvered into
the autorotation approach corridor prior
to landing to assure a safe outcome of the
maneuver.
1. AUTOROTATE.
2. External cargo — Jettison.
3. ALT switch — Disengage.
9-1-11. Single Engine Failure.
The action taken after one engine fails will depend on
altitude, airspeed, phase of flight, areas available for
landing, and S/E capability of the helicopter. Immediately
after any engine malfunction, the flight engineer should
check the engine for the possibility of fire. If required,
external cargo should be jettisoned as soon as possible
after engine failure. This will help to prevent damage to
the helicopter during touchdown and will reduce weight
and drag, thereby improving S/E performance.
Thrust control adjustments will depend on altitude at the
time of engine failure. For example, at (HIGE) below 20
feet, maintain thrust control position as the operative
engine beep trim is increased. At a hover above 20 feet,
thrust should be lowered slightly to maintain at least 96
percent RRPM. If altitude permits, thrust may be lowered
sufficiently to maintain normal RRPM.
Cyclic inputs will depend on altitude and airspeed. At a
(HIGE), the helicopter should be maintained in a hover-
ing attitude. in forward flight, at low altitude (below 50
feet), when S/E flight is not possible a decelerating atti-
tude should be assumed to dissipate airspeed and aid in
cushioning the helicopter. If airspeed is slow and altitude
permits, the helicopter should be placed in an accelerat-
ing attitude of up to 30_ nose-low to gain airspeed as the
operative engine beep trim is increased. This nose-low
attitude should not be used at extremely low alttiude
because of reduced reaction time, R/D, and the response
of the helicopter. Any time the helicopter assumes a de-
celerating attitude in close proximity to the ground, avoid
rotating the aft gear into the ground at touchdown.
