ENSTROM 280FX OPERATOR’S MANUAL
7-17
Rev.
11
Report No. 28-AC-020
Sep 20/17
7-17. Rotor RPM Warning System
The Rotor RPM Warning System uses a magnetic pick-up in
the main rotor transmission to measure rotor RPM. A control
unit activates a light and a warning horn when the main rotor
RPM is below 334. This system is armed by the same switch
that operates the clutch disengaged warning light. Neither the
low rotor RPM light nor the warning horn will operate when
the clutch is disengaged. A switch installed on the collective
torque tube disarms the warning horn so that the light will
operate, but the horn will not operate when the collective is on
the down stop.
On aircraft S/N 2136 and subsequent, the Hi/Low Rotor RPM
Warning System provides a visual and audio indication of low
and high rotor RPMs. This system is essentially identical to the
low rotor RPM warning system except it also indicates when
the rotor RPM exceeds the upper limit. The activation points
on this system are fixed and cannot be adjusted in the field.
As with the low rotor RPM system, the horn is silenced when
the collective is fully down. Thus, the horn will not sound if
the RPM limit is exceeded during an autorotation with the
collective fully down; the light will still illuminate.
Some earlier S/N aircraft may have been modified with the
Hi/Low Rotor RPM Warning System.
7-18. Annunciator Panel
All of the warning and caution lights are contained in an
annunciator panel, which is located at the top of the
instrument panel. On early production helicopters, the
warning lights include LOW ROTOR RPM, CLUTCH ENGAGE,
and LOW FUEL PRESS; the caution lights include
OVERBOOST, MRGB CHIP, and TRGB CHIP. On later
production helicopters, STARTER RELAY is added to the
warning lights and LOW VOLTAGE is added to the caution
lights. Further information about these lights is contained
elsewhere in this section and in Section 3, “Emergency and
Malfunction Procedures”.
For aircraft equipped with the Hi/Low Rotor RPM Warning
System, ROTOR RPM replaces LOW ROTOR RPM in the
annunciator panel.
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