Peter wrote:
Regarding MarkW’s post, which is about an SR22, does the SR22 POH say anything about this?
The POH states “Selecting BOOST energizes the fuel pump in low speed mode regardless of oil pressure to deliver a continuous 4-6psi boost to the fuel flow for vapor supression in a hot fuel condition.”
The placard next to the Boost/Prime rocker switch in the aircraft states something along the lines of “Use for takeoff, climb, maneuvering, landing and switching tanks”. There is no mention of the hot fuel condition.
For many Cirrus pilots flying in Arizona, Spain and the like where such conditions are the norm, use of the BOOST pump in all stages of the flight would have been a natural choice in the weather I had on Sunday. I posted in the ILAFFT section not because there is a suggestion of aircraft error, but rather pilot error.
The Q is really whether these cases are
The 1st one is obviously possible on any plane. Look at the “hot start”, or better still “warm start” fun with fuel injected engines…
The 2nd one is much more dangerous. But I don’t believe the SR22 has such a huge design defect in this department. It would have come to light by now. This is after all not some sort of air intake icing at FL230 which almost nobody will see even if it happened on 100% of planes. This is a really common situation in Europe in the summer.
“Use for takeoff, climb, maneuvering, landing and switching tanks”
That is fairly normal for electric pump use, but there are few if any reports of engine stoppages if one forgets. Perhaps the SR22 really does need it?
If one is happy to change his electric fuel pump very often, they can leave it ON for whole flight? I understand you only need switch electric OFF on taxi to test that the mechanical pump is ON and you need the electric ON anytime a failure of the mechanical one would be fatal
But I would argue that an engine blurp at FL80 on high power setting does not warrant leaving the electric ON all time and it is worth saving the hours on the device when it is really needed (low altitude and changing tanks in the middle of the sea) or one will have to conduct regular check on the health of the mechanical pump, on most SEPs one should not go for forced landing if all electrics goes off…
T28 wrote:
The european mountain roads are litterally littered with stranded cars – in winter because they do not have chains, in summer because vapour lock.
This was ironic, right?
Only half of it.
Many SR22 pilots (Turbo, especially), as a consequence of vapour lock occurences, keep the boost pump on at all times. I have long stopped reading COPA, so I don’t know what the current consensus is (if there is any) on whether the additional wear on the pump is “acceptable” or not, but I remember from years past that lots of pilots keep it running in cruise as well.
It’s also highly airframe SN / installation specific. My SR22 doesn’t need it; it has never made a single burp in 15 years and 1400 hours. I don’t even activate the pump when switching tanks. On for starting, takeoff and landing.
One of my club’s Rotax powered planes had a forced landing after the engine had failed shortly after takeoff. It was on a 35°C day during last year’s summer heat wave. Since then we avoid flying it on extremely hot days.
What fuel was that on?
As I wrote above, I am sure that potentially any fuel system, unless it runs downhill monotonically (no kinks), could get a bubble form, and such a bubble can take a while to clear. It isn’t going to want to be pushed downhill. It will likely clear in small bits, or possibly never other than by slow dissolution.
I think this is one reason why the electric pump is recommended for takeoffs. The other is that an engine stoppage is less convenient when close to the ground 
But why this should be highly installation/airframe dependent? Probably this is due to flexible fuel hoses having been installed like this
which is roughly 50% guaranteed to be the case because a flexible hose has to be longer than needed 
There must be a kink, and that kink must be above or below the “horizontal”, and the former case will give you trouble.
Google on e.g. io540 fuel hose and you will find lots of pics of installations where the pipework is guaranteed to produce bubbles which will be hard to shift. Especially ones in the engine compartment like this, where the heat will be guaranteed to vapourise the fuel
Also, the above is after the fuel servo, so whether the electric pump is on or not is not going to make any difference.
