Fuel Pump - why turn off at low altitude?

[kaz3g]

It only happens if the tank the fuel is returning to is full or nearly so.It's part of your fuel management. Know your aeroplane. Nev

Yes Nev ...and both have good checklists and use them.

 

The AUSTER W&B requires me to empty the belly tank first and, if I switch to it soon after take off, the main is still nearly full and...blue streaks on the white paintwork don't look good but the cause is immediately discernable.

 

In a low wing it's not so easy to see fuel loss occurring.

 

Kaz

 

 

[Oscar]

Whatever strategy you use, it seems to me that consistency in practice is very necessary.

 

Without having the experience necessary to make any significant contribution to this debate, some thoughts occur:

 

Fuel delivery is supposed to be a redundant system, with primary fuel delivery coming from a purely mechanical pump that will continue to function in the event of total electrical power failure.. Whether that redundancy is supplied by a secondary electric pump or by gravity, is necessitated by the configuration of the fuel system. Wing tanks that deliver to a low-mounted sump (a la Jabiru), do not provide gravity feed redundancy.

 

Mechanical pumps will not overcome fuel vapourisation - that is ONE function supplied by the electric 'boost' pump. Another, is ensuring that there is positive pressure in the entire fuel delivery circuit, so that a collapsing fuel filter membrane or a mis-routed fuel line that constricts under negative pressure does not shut off fuel delivery ( e.g. as for that Jab. that landed on the beach in N.Z. and then was destroyed by a mug's attempt at take0off).

 

BOTH the primary - mechanical - pump and the 'secondary' - electric boost pump / gravity feed - need to be able to provide the necessary fuel flow to the engine for a full-power application, for at least sufficient time to climb-out to a safe height.

 

If you habitually run the boost pump full-time, then you will not know it if the mechanical pump has failed / you are operating for whatever reason (ambient temperature / fuel quality) in conditions where fuel vapourisation may occur. Now, IF you normally do NOT run the boost pump full time, then it is quite possible that on your downwind check you will turn OFF the boost pump in an instinctive reaction to move the fuel pump switch - and if the mechanical pump has failed /fuel vapourisation happens, if you need to go around, you are in deep trouble.

 

I know of a case where a highly-experienced pilot selected a full tank for take-off when taxying out for a dawn take-off, decided the sun was in his eyes on the selected runway, back-tracked to take off in the opposite direction and while dutifully doing his pre-take-off checks again, then selected the empty tank.. one written-off expensive Twin.

 

 

[facthunter]

Replace the diaphragms in your fuel pumps regularly . Don't wait till they fail. With mechanical pumps a'la Auster you can end up with a heap of fuel in the engine oil. Nev

 

 

[Geoff13]

I remember reading an article about a fuel pump being left on, caught fire during a cross country flight, the cabin filled with smoke, and the pilot had to make an emergency landing around Gympie last year. I can't remember if it was supposed to be left on through out the flight.But to address the original post, I guess it greatly depends on the plane, what do their procedures and checklist say?

In fact the fuel pump in that instance had not been left on during flight, it had been turned on to switch tanks as per the poh and then turned off again. It was some short time after turning off the pump that the cabin filled with smoke.

 

I have an electronic aux fuel pump. I turn it on during startup. I turn it off again immediatly after startup. In fact my hand goes from the starter button to the fuel pump switch as I check for oil pressure, which is first thing I do after startup.

 

The next time I turn it on is the next time I start the motor.