Recent Topics - Rotate.Aero Mon, 17 Feb 2020 11:10:36 +0000 MYOB en-gb ATA 28-25, APU Fuel Valve - by: Mark D Francis

This warning is shown when the commanded position of the fuel shutoff valve does not match the actual valve position. There would be similar warnings for the APU Fuel Isolation Valve also.

The valve is located in the left forward wing root.

9.9 times out of 10...... the valve is going to be the faulty component, but just to make sure I checked for coil voltage at relay K192 and jumped the relay control wires at the actuator plug.

No voltage at relay and the jumper caused the fault to clear...... obvious bad valve (either the internal switch was failed or the valve was not actually moving. In this case, the valve was stuck open.)

Valve removed.

Two drawings of system indication. A explanation of internal actuator switch functions can be found here.

767-300 SSM 28-25-01]]>
ATA 28 Fuel Systems Tue, 04 Feb 2020 13:55:50 +0000
ATA 24-30, DC Tie Bus Control - by: Mark D Francis
The system uses a DC Tie Control Unit that senses a lack of 28VDC on either the left or right DC bus. The unit will wait 12 seconds before closing the tie relay.

The control unit is located on the P6 panel (forward section).

A simple test after replacement is to pull a T/R breaker and monitor the DC EICAS screen to verify both sides still have power.

A simple depiction of the system.

ATA 24 Electrical Power Wed, 15 Jan 2020 19:17:45 +0000