HYD RAT PUMP FAIL
(Caution)

DAU 4 is reporting hydraulic system No. 3B pressure below 2400 psi when the RAT is deployed.

• ACPC (A54) Secondary Logic Card (SLC) 4
• Hydraulic System 3 Quantity Low
• Hydraulic System 3B Pressure Switch (S40)
• Data Acquisition Unit (DAU) 4 (A31)
• Hydraulic System 3 Accumulator Pressure Circuit
• Hydraulic System 3 has high internal leakage
• Ram Air Turbine (RAT)

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

1. Carry out a quantity check of the hydraulic system.
   NOTE: Low accumulator service pressure at RAT extension can cause a RAT pump start-up failure.
2. Pressurize the No. 3 hydraulic system with the ACMP 3B.
3. Verify the pressure of the No. 3 hydraulic system.
4. If the pressure is below 2400 psi, replace the valve manifold.
5. If the pressure is above 2400 psi and the message HYD PUMP 3B FAIL message is not shown, go to step 7.
6. If the pressure is above 2400 psi and the message HYD PUMP 3B FAIL message is shown, disconnect the hydraulic system 3B pressure switch connector S40P1.

   • If there is continuity, install a jumper between S40P1- A and S40P1-B.
   • If the message goes away, replace the hydraulic system 3B pressure switch (S40).
   • If the message is still shown, swap DAU 4 with DAU 3.
   • If the message goes away, swap back the DAUs and replace DAU 4.
   • If message is still present, swap back the DAUs and do a wiring check between pressure switch S40 and DAU 4.
   • If the wiring is good, continue with next step.

7. Do a functional test of the No. 3 hydraulic system accumulator pressure circuit as follows:

   1. In the flight compartment, on the HYDRAULIC control panel, set the selection of the ACMP 3B switch to OFF.
   2. In the No. 3 hydraulic service compartment, do a check of the pressure gauge on the accumulator.
   3. Record the time (in seconds) for the accumulator pressure indication to reach the service pressure.
      NOTE: The time for the pressure to decrease must be 43 seconds or more.

8. If the bleed down time is less than 43 seconds, replace the valve manifold and do the functional test of the No. 3 hydraulic system accumulator pressure circuit as follows:

   1. In the flight compartment, on the HYDRAULIC control panel, set the selection of the ACMP 3B switch to OFF.
   2. In the No. 3 hydraulic service compartment, do a check of the pressure gauge on the accumulator.
   3. Record the time (in seconds) for the accumulator pressure indication to reach the service pressure.
   4. If the bleed down time is more than 43 seconds, do close out.
   5. If the time for the pressure to decrease is 43 seconds or less, carry out the No. 3 hydraulic system (internal leakage check).
   NOTE: Too much internal leakage can cause the hydraulic output pressure from the RAT to be low.
   6. If the internal leakage of the No. 3 hydraulic system is satisfactory, replace the RAT.

9. Do close out.