Hydraulics

Electrical

Engine

OBOGS

Fuel

Pressurization

The hydraulic system on the T-6A aircraft is a closed-loop system that is pressurized by the engine-driven pump in the engine accessory compartment. The pump will maintain the pressure of both the normal and emergency systems to 3000 +/- 120 psi. The system contains a pressure relief valve (3250-3500 psi) to prevent damage to the aircraft. Components that are powered by the normal system are the flaps, landing gear, main gear doors, speed brake, and nosewheel steering. When the pressure drops below 1800 psi, a HYDR FL LO annunciator will illuminate on the CWS.

The emergency system is available only if the normal system pressurized the emergency accumulator. The emergency landing gear extension handle in the front cockpit activates the system. A check valve is built into the emergency hydraulic system which will prevent fluid from flowing back into the normal system.

NOTE: Both inboard main landing gear doors must extend past 70% to allow either main landing gear to extend. During the exterior check, make sure to inspect the bell crank and connecting rod to the interior doors.

Numbers to know:

Quantity: 1.25 Gallons (includes 0.6 gallon power package reservoir
Closed Loop system
3000 (+/- 120) psi system pressure
Normal operation of landing gear, main gear doors (inboard), flaps, speed brake, and nose wheel steering
No pilot servicing capability

Emergencies/Abnormal Ops:

With the HYDR FL LO annunicator illuminated the following systems should be considered inoperative: (assuming no pressure) normal landing gear extension, normal flap extension, speed brake, and nose wheel steering.
With the EHYD PX LO annunicator illuminated, the emergency landing gear and emergency flap extension should be considered inoperative.
Low Emergency Accumulator Hydraulic Pressure (EHYD PX LO)-annunciator will illuminate whenever the pressure in the emergency accumulator drops below 2400 psi.

NOTE: Loss of pressure may indicate a fluid leak in the emergency hydraulic system. If the leak is of small enough flow rate (less than.25 gpm) that it does not activate the hydraulic fuse, all fluid could leak out of both systems and a gear up landing would be required. Unless fuel range is a factor, lower the gear (and flaps if desired) prior to depletion of hydraulic fluid.

Follow the check list (Check hydraulic pressure, configure with gear and flaps as required), and land as soon as practical. Add 20% drag index with gear extended and 80% with gear extended and landing flaps.
Low Hydraulic Fluid Quantity (HYDR FL LO)-annunciator will illuminate whenever the fluid level in the reservoir drops below approximately one quart.

NOTE: Flap extension may require use of the emergency landing gear and flap extension system if the normal hydraulic system pressure has dropped below usable levels. If the emergency gear handle has not been pulled previously to lower the landing gear, it will have to be pulled in order to emergency extend the flaps. Landing gear and flap retraction is not possible once extended using emergency landing gear extension system.

Follow the check list (Check hydraulic pressure, configure with gear (flaps as required), and land as soon as practical. Add 20% drag index with gear extended and 80% with gear extended and landing flaps.

Annunciators and their meanings:

HYDR FL LO (amber)-Hydraulic reservoir fluid level below 55 cubic inches (1 qt)

EHYD PX LO (amber)-Emergency hydraulic pressure at or below 2400 psi