ENSTROM F-28F/280F SERIES MAINTENANCE MANUAL SUPPLEMENT
Rev.
4
MM-21-3
Jun
21/12
A.
Lamp Replacement – Annunciator Panel
Each indicator light contains two lamps. These lamps can be replaced as follows:
(1)
Press inward on the right edge of the indicator until indicator opens.
(2)
Swing indicator fully open.
(3)
Grasp base of lamp firmly and pull lamp out of socket.
(4)
Insert replacement lamp and push into place.
(5)
Swing indicator closed.
(6)
Push on left side of indicator to close.
B.
Clutch Disengagement Warning Circuit
The clutch disengagement warning circuit consists of a microswitch on the clutch plate
which operates a red warning light in the annunciator panel. This switch is normally closed
and completes a circuit to ground when the clutch is disengaged. When the clutch snaps
overcenter into the engaged position, an arm on the actuating mechanism opens the
switch, which turns out the light. The “normally open” side of this switch arms the rotor rpm
circuit.
If the clutch disengagement light does not go out when the clutch is engaged, or if the light
comes on in flight, this indicates that the clutch is misrigged or the clutch actuator cable
needs servicing. The problem must be found and corrected before the aircraft is returned to
service. Press to test warning indicator on F-28F.
C.
Low Fuel Pressure Warning Circuit
The low fuel pressure warning circuit comprises a pressure switch in the fuel line between
the electric boost pump and the engine-driven fuel pump which activates a red light in the
annunciator panel. If the pressure in this fuel line drops below 15 psi, the switch will turn on
the red light. This circuit provides the pilot with a warning if the electric boost pump should
fail. This light does not indicate the condition of the engine-driven fuel pump. Press to test
warning indicator on F-28F.
D.
Low Rotor RPM Circuit
The low rotor rpm circuit comprises a magnetic sensor in the main rotor transmission, a
signal conditioning unit behind the passenger’s seat, an amber light in the annunciator
panel, and a warning horn. The magnetic sensor is located in the forward portion of the
main rotor transmission housing. It is positioned to sense the passage of the ring gear
teeth. The signal is sent to a small unit located in the backrest of the passenger’s seat. The
unit reads the signal from the magnetic sensor and activates the light and the warning horn.
UNCONTROLLED COPY WHEN DOWNLOADED OR PRINTED
Visit www.enstromhelicopter.com for instructions to order an original manual and to register for email notification of updates.
