The following is a common method of fuel management (quoted from
the Grumman-Gang list mailer):
Regardless of when I depart, I
try to switch tanks on the hour and on the half hour. The rationale
being that it is very unlikely that I will have BOTH feeds fail,
but If I have a problem with ONE of the feeds, I will learn about it
while I still have a comfortable amount of fuel in the remaining tank.
There's an inherent gottcha in systematically switching
tanks, whether to prevent a wing from becoming too heavy or, as expressed
above, to have an out if the switch-to tank won't feed. I became aware of this
gottcha when flying cross country in Nevada
and Utah. I had planned a comfortable reserve of 1 hr and switched tanks
every half-hour as always. I then found myself
having to divert around some rather nasty thunderstorms which ate
into my reserve by about 30 minutes. Continuing to switch tanks,
I proceeded to my destination uneventfully, but upon approaching
the airport I realized that I couldn't reliably ascertain which was
fuller (the gauges are useless, of course).
To add to the pucker factor, I couldn't be absolutely
certain that I had 5 gallons remaining. If I had timed the switching
perfectly, and calculated the fuel burn perfectly, I had a maximum
of 2.5 gallons in each tank. There might, however, be 2 gallons in
one tank and .5 in the other--with no way of knowing which was
What I wouldn't have given to know that all my remaining fuel was
in one tank--and which tank it was in!
I reasoned it to be near suicidal to fly a normal approach to land--to
do so would be to risk unporting the fuel line while banking in the
pattern. I flipped a mental coin, selected a tank, maintained
altitude until overhead the airport, throttled back completely, and
performed an "engine-out" landing on the longest runway.
My engine died on the ramp while taxiing to fuel.
The FBO had been monitoring UNICOMM and sent the fuel truck. I had
3+ gallons in the unselected tank.
Now, I can hear the tongues clucking about the things I did
wrong, but the fact is...I didn't do anything wrong. The build-ups
that caused the diversions were not forecasted, and there was no
airport nearer than my destination. Once I realized my predicament,
I throttled back for best economy. The morals of this story are: (a)
situations can arise that will stretch any fuel reserve, and (b) know where your fuel is.
Since this experience, I've changed my fuel management technique. I
take off and fly for 1.5 hrs on one tank. I then run the other tank
dry (more on that in a moment). I am therefore guaranteed to arrive
at my destination with all my fuel in one tank. Rear-seat passengers
become ballast against the heavy wing (I've also got a wing-
leveler). I plan for a 45-minute fuel reserve, even in VFR.
Now, about running a tank dry. In my '79 Tiger I've experimentally
determined that the fuel pressure gauge begins to fluctuate about 15-20
seconds before it drops to zero. It then takes another ten seconds
for the engine to stop. (BTW, it doesn't sputter--it just goes
bang-dead quiet and keeps wind-milling at several hundred RPM.)
During cross-country trips, I turn on my electric pump about 30
minutes before the tank is due to run dry. If I have a
passenger, I ask him to watch the fuel pressure gauge; if not, I
keep my eye on it closely. I continue to scan for traffic; if I get
a traffic call from ATC, I switch back to the fuller tank while I
resolve the situation. I then switch back to the "dry" tank.
At the first sign of fuel-pressure fluctuation, I switch tanks. I've done
this dozens of times without once letting the engine go quiet. Since
this incident, I've also added a fuel-flow monitor to my Tiger, which
enables me to calculate to an accuracy of a couple of minutes when the tank
will be empty. I've also added a fuel-pressure warning LED that blinks
when the pressure drops. In truth, however, if I'm solo or with an
experienced pilot, I don't pay much attention and just let the engine run
the tank dry. It's really a non-event.
Note: if you have first-hand knowledge or documentary proof of
an engine failing to start on its own when switched from a dry to a
wet tank, please with the details.
N4524P (Hayward, CA)
P.S. For a similar article, read the
esteemed John Deakin's
Run That Fuel Tank
Dry! article from his "Pelican Perch" column at AvWeb. John
systematically dismisses every objection to this practice either as bad
reasoning or deriving from a old wives tale.