Q: Switches and buttons? A: Back up pump switch, tail rotor servo switch, trim, SAS/BOOST, 1st and 2nd primary servo off switch, hydraulic leak test, weight on wheels switch.
Q: Pump modules? A: Three identical pumps. The #1 and #2 pumps are driven by the accessory gearbox; the backup pump is electrically driven. Each pump has two filters: return and output, both with impending bypass indicators. The input filter has a bypass valve. The pumps also have a fluid level sight window, temp sensing labels, res low sensor, a pressure relief valve and an external pressure connection (for maintenance).
Q: Function of the transfer modules? A: These control distribution. Spool valves at the input side determine the source of pressure (backup or the respective #1 or #2 sides).
Q: #1 transfer module shutoff valves? A: The #1 transfer module includes the shutoff valves for the #1 primary servo (pilot activated) and the #1 tail rotor servo.
Q: #2 transfer module shutoff valves? A: #2 primary servo (pilot activated) and the pilot assist servos.
Q: Function of the utility module? A: Provides the backup pump with distribution to the #1 and #2 transfer modules, the #2 tail rotor servo as well as the accumulator and rescue hoist. A pressure sensor in the module illuminates the BACKUP PUMP ON advisory.
Q: Function of the pilot assist module? A: This provides distribution and control for the various pilot assist valves (trim, SAS/BOOST). The trim button controls pressure to the pitch and roll trim servos. The SAS/BOOST button controls two valves: one to the SAS actuators and pitch boost, and one to the yaw and collective boost (if you want to secure SAS separately, you need to turn the SAS buttons off). LDI shutoff occurs in the #2 transfer module.
Q: 2nd stage tail servo shutoff valve? A: Down stream from the utility module, this valve controls pressure to the 2nd stage tail servo and is controlled by the LDI or the tail rotor switch on the MISC control panel.
Q: Function of the hydraulic leak test? A: This is a ground test to check the operation of valves and warnings/cautions. In this test, the 1st tail rotor shutoff valve and pilot assist valves close, the back up pump turns on, and the 2nd stage tail rotor servo valve opens. The three res low lights illuminate, and all the associated caution and advisories come on as well as the master caution and the AFCS degraded (because the pilot assist servos aren’tgetting pressure). To accomplish the test, you need AC power, back up pump in auto, full reservoirs and WOW (note – the hyd pump cautions do not come on).
Q: Interlock function? A: The primary servo interlock prevents the pilots from securing both primary servos at the same time. It also prevents securing the “good” servo when the other has low pressure. Lastly, it restores operation of a servo that has been turned off if the operational servo has a malfunction. The interlock operates using a series of pressure switches.
Q: PRI SERVO PRESS caution? A: All three servos in each stage have a pressure switch, a loss of pressure at any one of the servos (forward, aft or lateral) will result in the warning light.
Q: When does the LDI turn on the back up pump? A: #1 RES LOW, loss of pressure from the #1 or #2 hydraulic pumps, loss of pressure in the #1 tail rotor servo.
Q: When does the LDI operates shutoff valves? A: #1 RES LOW (closes the #1 T/R servo shutoff and opens the #2 T/R shutoff), #2 RES LOW (closes the pilot assist shutoff). #1 or #2 complete loss (opens the shutoff to the #1 T/R, closes the shutoff to the #2 T/R servo, opens the shutoff to the pilot assist servos).
Q: Spool valve function? A: Spool valves allow the back up pump to power the #1 or #2 system following a pump failure (the LDI turns the backup pump on).
Q: WOW interaction with the back up pump switch? A: On deck the back up pump must be set to auto for the LDI to work. Weight off wheels, the switch can be in any position and LDI will still work (pilot proof).
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