Refueling Part 2

Arhur asked,

Helmis, This happen in Pucallpa, Peru, during a Boeing 737-200 refueling, as you explain, the aircraft system controls the max. level in the tanks, but there must be a pressure sensor as a safety device (pressure set a little more than 50 psi???) that delivers flow over the wing, when the tank is full…..is that right?? If the refueler delivers fuel at 50 psi, the aircraft system must stop the flow when it sense an excessive pressure in the line or when the tanks are full….the option to deliver excess flow overwing is a risk condition...probably on these old airplanes...or the new generation units have other system to avoid fuel spills in this cases?? Thank you, for your answer.

Flighteng replied,

Aircraft system only control the quantity, there is no control for pressure as far as aircraft system is concern. Take a loook at the refueling panel, there is a warning of maximum pressure allowed during refueling which is 55 psi, this have to be taken care by engineers who doing the refueling plus the bowser operator as well.

From 737-200 to classic and NG, the refueling system is almost the same, only improved instrumentation plus in NG you can set how much fuel in KG or LBs which it will automactically stop when it reach that level.

Fuel Control In Refueling

Arthur asked...

Hi Helmis, could you give us some information about the fuel controls needed in refueling operations. In one opportunity I saw how fuel start droping overwing during a pressure refueling...how it happens??....probably instruments misfunction on the plane…or human error by plane crew???.....does each tank have a safety pressure device that allows fuel exhaust when the tank is overfilled...or when the tank is completelly fueled the systems cut the inlet fuel from the refueler.

Engineer Helmi replied..
Arthur, where did u saw it happen? I just had an experience last week in Al Ain.

The fuel can overflow if automatic cut of function of fuel system failed to activate during refueling. It can be the maximum level sensor or fuel quantity processor failed to send a signal to refueling sitch to close the fuel valve.

Normally if it overflow, it is airplane system, it can be a human error if someone manually override the system and continually fill the tank which rarely happen. The refueler only pump the fuel to aircraft but the aircraft system that will stop the fuel flow when maximum or desired selected fuel quantity obtained.

Best regards