APR 2019 Chapter 95 Instrument System Page 95.9
95-23 Engine (N
2
) and Rotor Dual Tachometer (continued)
C. Installation
1. Turn battery switch off and pull out TACHS N
2
(2 amp) and R (2 amp) circuit
breakers on circuit breaker panel.
2. Install screws securing F792-1 dual tachometer to instrument face. Verify
security.
3. Plug in console harness connector to tachometer and install connector screws.
Verify security.
4. Install perimeter screws securing face to console. Verify security.
5. Perform accuracy check and needle synchronization per Part D.
D. Accuracy Check and Needle Synchronization
CAUTION
Inadvertent engine overspeed can occur if accuracy check is
not performed.
1. Perform PTG rigging check per § 76-22.
2. Install magnetic pickup (or photocell) portion of calibrated main rotor balancing
equipment per § 18-11.
3. Push in TACHS N
2
(2 amp) and R (2 amp) circuit breakers on circuit breaker panel.
Turn battery switch on, open throttle, and “beep” actuator to minimum (RPM)
setting. Close throttle and turn battery switch off.
4. a. Start engine and run-up helicopter per R66 Pilot’s Operating Handbook (POH)
Section 4, establish stable idle, and record dual tachometer’s % N
2
indication.
Also record RPM displayed on balancer.
b. Multiply dual tachometer’s % N
2
indication (use 0.69 for 69%, 0.70 for 70%,
etc.) by 408 RPM. Verify calculated RPM is within ± 8 RPM displayed on
balancer.
c. If calculated RPM is more than ± 8 RPM displayed on balancer, shut down
helicopter per POH Section 4. Do not proceed further; contact RHC Technical
Support.
5. Monitor RPM displayed on balancer and increase throttle to full open. Immediately
close throttle and shut down helicopter per POH Section 4 if balancer indication
exceeds 412 RPM.
6. Monitor RPM displayed on balancer and “beep” actuator until dual tachometer
indicates 100% N
2
. Verify RPM displayed on balancer is 408 ± 4 RPM; do not
exceed 412 RPM.
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