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Hydraulic System
All 3 hydraulic systems use skydrol hydraulic fluid, and operate at 3000psi. System logic for Elec Pumps 1, 2, 3B, and the PTU is implemented in the SPDAs. If the respective SPDA goes off-line, the pumps can be manually selected on. Hydraulic fluid overheat may be caused by failure of a pump compensator.
System 1
- 1 engine driven pump
- 1 AC electric pump
- 1 reservoir
Located in the left centre fuselage bay.
System 2
- 1 engine driven pump
- 1 AC electric pump
- 1 reservoir
Located in the right centre fuselage bay.
System 3
- 2 electric pumps, ACMP 3A (main, on AC ESS Bus) and ACMP 3B (backup)
- 1 reservoir
- pump unloader valve
- flow limiter valve
Located in the aft fuselage.
PTU (power transfer unit)
Installed between system 1 and 2 to transfer power between the 2 without mixing fluid. Used for landing gear extension and retraction when engine driven pump 2 is unavailable.
Control panel
| Pump | Selection | Operation |
| Elec Pump 1/2 | AUTO | activates during an engine failure (loss of EDP 1/2) and during takeoff (thrust TO/GA or groundspeed >50kts) and landing (until 1 minute after groundspeed <50kts) and flaps >0° |
| Elec Pump 2 | AUTO | with engine 1 started and the park brake released pump is activated (allows single engine taxi) |
| Elec Pump 3A | ON | select ON after start |
| Elec Pump 3B | AUTO | activates only when Elec Pump 3A is lost |
| PTU | AUTO | activates when engine 2 or EDP 2 fails during takeoff or landing with flaps not 0° |
Schematic
