Hydraulic Leak in Aircraft System

Aircraft hydraulic is a very complicated system with a lengthy plumbings, joints, connections, valves, pumps and so on. As the aircraft aging, especially on component where the seals start to deteriorate, leaks can occur. This is most common findings during routine inspection on aircraft especially in the wheel well area.

Any leakage found should be treated promptly however it is not economical to keep changing any component that have started to leaks. There is an allowable limit set by the manufacturer which allows aircraft that have leakage on its component to be release for flight after details of the leakage been recorded.

In the maintenance manual, the allowable limit basically is how many drop per minute. It further will be specified static or dynamic which is with component is off condition or operational. Aircraft engineers will switched on the relevant aircraft hydraulic system and observed the leaks to find whether it is within limit or not. If out of limit then the component must be changed before next flight.
Not all leakage is allowable, on plumbing connection for example leakage is not allowed at all. With 3000 psi pressure (that is normal operating pressure for most aircraft) any leakage can drain whole system fluid, the good news is that normally there is 2 or 3 independant hydraulic system available on an aircraft so if one system is down, there is still a backup.

All pics sample of leakage is from the aircraft wheel well.

Hydraulic System Transfer

Hydraulic system on B 737 divided into 3 system which is A, B & Standby however only A & B system quantity shown in the system page on lower display unit. Standby system reservoir is connected to system B.

It can happen that few amount of hydraulic fluid did transfered to one another during flight even though theoretically it's not posible. It can happen through movement of shuttle valve that connect both system together when it supplied as back-up such as alternate brake. To normalise it back basically we need to drain it and replenish another system system with new fluid.

Experienced 737 engineer know the trick to transfer it with-out to drain and topping-up. Here i would like to share you the trick. From the photo we can see system B is higher, now to transfer from B to A.

1. Turn on B emdp pump.
2. Set park brake.
3. Turn on A emdp pump.
4. Turn off system B pressure by operate the flight control
5. Release park brake.
6. Turn off system A emdp pump.

After few repetition we can see the fluid transfered to another.

* This is just for information sharing and not to replace the aircraft maintenance manual procedure.

Hydraulic Pressure Module Leakage

I was in Kuwait for 2 days trip, after landed and parked infront of VIP terminal in Kuwait Airport, i've noticed hydraulic fluid accumulated below system B hydraulic pressure module, from my observation i suspect it is from System B Hydraulic Electrical Pump pressure transmitter however it cannot be confirmed even with pump turned on , I've cleaned the area and wipe it dry, ready to be verified on next flight.

The next day after flight back to base, confirmed the leakage was from the transmitter base, as per IPC (Illustrated part catalog) there is a seal inbetween. Ordered and replaced the seal, ground check no leak as well on subsequent flight... problem solved...