Fuel boost pumps
Each fuel tank contains one Main and one Auxillary fuel boost pump which is located in the bottom of each hopper tank.
These pumps are used individually to supply fuel at low pressure to each engine under normal operations.
The main boost pump is selected on the boost pump switch for normal operations.
The auxillary boost pump is identical to the main boost pump and will perform exactly the same functions as the main boost pump whether selected manually by the pilot or automatically should the main boost pump fail.
As stated, the auxillary boost pump will switch on automatically should the main boost pump fail whilst the boost pump switches are selected to MAIN.
This automatic selection of the auxillary boost pump is achieved by a low pressure switch which allows the auxillary boost pump to assume the duties of the main boost pump.
|Failure of the Main boost pump can be confirmed by illumination of the L. / R. AUX BOOST ON light while the boost pump switch is selected to the MAIN position.|
The L. / R. AUX BOOST ON light will also illuminate when the boost pump switches are manually selected to the AUX position or the fuel tank selector is selected to a cross feed position.
|The L. / R. AUX BOOST ON light will illuminate if the boost pump switch is selected to the AUX position.|
|The L. / R. AUX BOOST ON light will also illuminate if the fuel Tank selector is selected to either CROSS FEED position.|
Failure of both the main and the auxillary boost pumps on the same side will significantly raise the unusable fuel in the fuel tank due to the lack of motive flow through the transfer ejector pumps, i.e. nothing will be filling the hopper tank.
If cross feeding to the tank from the operative side is required cross feed prior to reaching 150 lbs in level flight and 300 lbs in any other flight attitude.