On May 12, 7:28 am, Angelo Campanella wrote:
Mxsmanic wrote:
When do you use boost pumps on small GA aircraft?

The purpose of a fuel boost pump is to assure adequate fuel flow in all
flight conditions, especially in a nose high attitude when the tanks are
nearly empty; where the height difference between the fuel level and the
engine pump is considerable. Another vulnerability is on hot days when
vapor lock in hot spots nearer the engine is possible. It probably is
discovered by the test pilot in the ceritifcation process that fuel
starvation occurred in some situations. Thereafter, the manufacturer of
that aircraft is obliged to install one in the aircraft, likely in a low
and cold spot such as under the cabin, then certify that it solves these
problems, then tell in the flight manual how and when to apply it.

The pilot is obliged to comply. The most applicable condition is that
it should be used on every takeoff until flight climb is stabilized....

Angelo campanella

Boost pumps are often used even on high-wing airplanes if the
engine also has a mechanical fuel pump. Some systems don't have enough
flow capacity via gravity alone and need the pump, and any pump needs
a backup. Low-wing airplanes having fuel in the wings need a pump, of
course, to lift the fuel, and that's where vapor-lock becomes a
hazard, when the fuel is being pulled from the engine end of the
system. A good boost pump system there has the boost in the tank
itself, so the fuel is pushed all the way. Pressure on the fuel raises
its boiling point and vapor lock disappears.

Dan