ENSTROM 280FX OPERATOR’S MANUAL
3-21
FAA Approved: Nov 26/13
Rev. 9
Report No. 28-AC-020
Nov 5/13
FLIGHT CONTROLS
3-20. Abnormal Vibrations
Vibrations in this helicopter can usually be classified as
either low frequency or high frequency. Low frequency
vibrations are generally caused by the main rotor system
while the high frequency vibrations usually originate from
the engine, drive system, or tail rotor. Any abnormal
vibrations are an indication that something is not correct
and should be referred to a mechanic before further flight. If
a vibration suddenly appears during a flight, it is an
indication that something has suddenly changed. The
helicopter should be landed as soon as practical and
inspected to find the cause of the vibration. After the cause
of the vibration has been identified, the pilot and the
mechanic can determine whether the helicopter can be
safely flown or should be repaired before further flight. An
abnormal vibration is reason to get the aircraft down as
soon as possible, but the pilot must also use caution and
select the safest possible landing site, working around
wires, people, and other obstructions.
3-21. Cyclic Trim Failure
Failure of the cyclic trim control system will result in either
inoperative trim or a trim runaway in one of the four
primary directions (forward, aft, left or right). If the trim
circuit breaker trips, it should be left out for the remainder
of the flight. Depending upon the failure mode and the flight
condition at the time of failure, the cyclic forces may be
relatively light or they may be excessive. The pilot should
evaluate the situation and determine if a precautionary
landing is indicated or if the flight should be completed as
planned. The pilot should be aware that the cyclic forces
will change between cruise flight and approach and landing.
If the trim stops operating when the switch is engaged, the
trim does not stop when the switch is released, or if the
circuit breaker trips, the operator should:
1. Immediately stop using the trim and pull the TRIM
circuit breaker to deactivate the circuit. Leave the circuit
breaker out for the remainder of the flight.
This electronic document is not linked to a subscription for revision control or distribution. Refer to theTechnical
Publications Status link under the Technical Support Page of the Enstrom Helicopter website for the current revision
level of the 280FX Rotorcraft Flight Manual.
UNCONTROLLED COPY WHEN DOWNLOADED OR PRINTED
