2. INTRODUCTION
Helicopters are quite reliable for flight. But it is
always important to know and understand
emergency procedures. Discussing and
practicing these procedures is important.
Helicopter Flying Handbook 2012

3. AUTOROTATION
“In a helicopter, an autorotative descent is a
power-off maneuver in which the engine is
disengaged from the main rotor system and the
rotor blades are driven solely by the upward flow
of air through the rotor.”
Helicopter Flying Handbook 2012

4. AUTOROTATION
Is the action taken when engine failure occurs or the
initiated action of a complete tail rotor failure (refer
to the individual helicopters RFM)
The freewheeling unit automatically disengages the
engine from the main rotor
This allows the main rotor to rotate freely
When revolutions per minute are less than the rotor
rpm, the freewheeling unit will disengage
Helicopter Flying Handbook 2012

5. AUTOROTATION
Once an engine failure happens the pilot
must lower the collective pitch which lift
and drag will be reduced. This will cause
the helicopter to descend to produce an
upward flow of air. Having upward flow of
air will allow for enough air to provide
thrust to maintain rotor rpm during descent.
The antitorque pedals need to maintain
heading control like in normal flight.
Helicopter Flying Handbook 2012

6. AUTOROTATION
Kinetic energy and Potential energy are used by the
rotor blades to arrest the descent rate and ensure a
soft landing, when landing from an autorotation.
“Autorotative descents at very low or very high
airspeeds are more critical than those performed at
the minimum rate of descent airspeed.”
For particular helicopter specific autorotation
airspeeds, refer to the Federal Aviation
Administration (FAA) and the approved rotorcraft
flight manual (RFM).
Helicopter Flying Handbook 2012

7. RETREATING BLADE STALL
“In forward flight, the relative airflow through the main
rotor disk is different on the advancing and retreating
blades.”
“Retreating blade stall is a major factor in limiting a
helicopter’s never-exceed speed (Vne) and its
development can be felt by a low frequency
vibration, pitching up of the nose, and a roll in the
direction of the retreating blade.”
Helicopter Flying Handbook 2012

8. GROUND RESONANCE
“Helicopters with articulating rotors (usually designs
with three or more main rotor blades) are subject to
ground resonance, a destructive vibration
phenomenon that occurs at certain rotor speeds
when the helicopter is on the ground.”
A rotor that is out-of-balance can be intensified when a
mechanical design issue from the helicopter’s
airframe having natural frequency is ground
resonance.
Increase in vibrations can cause the helicopter to self-
destruct in a matter of seconds.
Helicopter Flying Handbook 2012

9. DYNAMIC ROLLOVER
Dynamic rollover is when a helicopter is
susceptible to a lateral rolling tendency.
Caused when the helicopter pivots or rolls
around a skid or landing gear wheel until the
rollover angle is reached.
Beyond a certain point of roll over recovery is
impossible.
To stop a dynamic rollover, quickly reduce
collective pitch. (this is the most effective way)
Helicopter Flying Handbook 2012

10. LOW-G CONDITIONS AND MAST BUMPING
Low-G conditions is the imbalance of force, not the
loss of thrust. Such as excessive forward cyclic
pitching causing a feeling of weightlessness in your
body.
Mast bumping is when the rotor blade exceeds
flapping limits which then the rotor hub bumps into
the rotor mast.
Helicopter Flying Handbook 2012

11. LOW ROTOR RPM AND BLADE STALL
During an autorotation with low rotor rpm can result in
a less successful maneuver but if rotor rpm decays
and all rotor blades stall, the results are fatal.
 Decrease in rotor rpm= blades produce less lift making it
necessary to increase collective pitch.
 Pitch increased + drag increases= more power to keep
the blades turning at the proper rpm.
 When power is not available to maintain rpm= helicopter
will begin to descend which changes the relative wind
causing the blades to stall unless rpm is restored.
Helicopter Flying Handbook 2012

12. RECOVERY FROM LOW ROTOR RPM
Simultaneously applying additional throttle (if
available) when low rotor rpm is detected and
lower the collective based on altitude.
“Rotor rpm is life!”
Helicopter Flying Handbook 2012

13. ADDITIONAL INFORMATION
For additional information and more in depth
explanations please ask your instructor, visit the
Federal Aviation Administration (FAA)
documents, manuals and books and the
approved rotorcraft flight manual (RFM).