STUDENT GUIDE FOR T-1A AIRCRAFT SYSTEMS
504. HYDRAULIC PACKAGE
An air-over-oil type hydraulic reservoir uses filtered regulated engine bleed air to maintain
hydraulic pressure and prevent foaming of the hydraulic fluid in the reservoir. Each hydraulic
reservoir has a capacity of 1.1 gallons and air pressure is regulated to 15 psi.
The hydraulic system normally stabilizes at 1500 psi as indicated on the HYD PRESS indicator.
If the pressure exceeds 1500 psi, a relief valve opens at approximately 1650 psi, relieving the
overpressure condition. If the relief valve fails to relieve the overpressure condition, opening the
bypass valve returns the hydraulic fluid to the reservoir. Failure of the relief valve to relieve
pressure at 1650 psi is indicated by the flight deck HYD PRESS indicator display approaching
505. HYDRAULIC SYSTEM CONTROLS AND INDICATORS
Hydraulic Pressure Bypass Switch
The switch is placarded HYD PRESS NORM - REL and is located adjacent to the HYD PRESS
indicator on the lower part of the P's instrument panel. When the guard is raised and the switch
is placed in the REL position, the bypass valve opens directing the hydraulic fluid back to the
Hydraulic Valve Position Switchlights
The switchlights are used to open or close, and indicate the position of the respective hydraulic
and fuel shutoff valves. Normally the top white half, placarded OPEN is illuminated. When the
guard is raised and the switch is pressed, the hydraulic and/or fuel shutoff valves will close and
the lower amber half, placarded CLOSE, will illuminate.
Hydraulic Pressure Indicator
The hydraulic pressure indicator placarded HYD PRESS (located on the lower portion of the P's
instrument panel) indicates hydraulic fluid pressure in psi.
Hydraulic Pressure Annunciators
These annunciators illuminate when system pressure falls below 750 psi.
Hydraulic Fluid Level Annunciator
This annunciator illuminates when the fluid level in the reservoir falls below 0.6 gallon.
506. HYDRAULIC SYSTEM LIMITATIONS
Refer to Instrument Markings, Section V, T.O. 1T-1A-1, for specific hydraulic system limits.
HYDRAULIC POWER SUPPLY & SYSTEMS