Transfer hydraulic fluid from A > B or B > A to equalize reservoir levels. 737-ALL

When its necessary to equalize the fluid levels between the A and B hydraulic reservoirs , you can use the procedures below.

Make sure the total quantity displayed on the gauge is approx 2/3 between refill and FULL (classic) , or approx 92% on the DU (NG). This is to prevent overfilling and fumes in the airco system , see maintenance tip  737-MT-12-002.


Hydraulic fluid transfer:

A > B

1.    A pump                ON

2.    Park brake           ON

3.    B pump                ON

4.    A pump                OFF

5.    Depress A sys (continiously moving the aileron wheel is a good option)

6.    Park brake           OFF

7.    A pump                ON

8.    B pump                OFF

9.    Depress B sys

10.  Repeat step 2 to 8 as required

(can be 10 to 15 times)


B > A

1.    Alt flap switch        ON

2.    Reverse #1            DEPLOY

3.    Alt flap switch        OFF

4.    A pump                  ON

5.    Reverse #1            STOW

6.    A pump                  OFF

7.    Depress A syst.

8.    Repeat step 1 to 7 as required (1 to 3 times)

Make sure the REV light on the P5 OVHD panel extinguishes after T/R stow, else reset.

Another easy method is almost similar, but transfers the fluid in small steps from B to A:

In both cases A pump must be ON.

From A > B: 1-apply brakes, 2-b pump on, 3-release brakes, 4-b pump off, repeat as required.

From B>A:  1-b pump on, 2-apply brakes, 3-b pump off, 4-release brakes, repeat as required. When switching b pump, wait a moment (approx 2 sec.) with the next step, so the system can switch from alt to norm or from norm to alt. This can be felt/heard as a click on the brake pedals. Thanks to Virgil.

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