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Running one tank dry. How?

Well I did inspect my fuel bladders and they are so clean that I just can’t imagine there to be so much dirt.

Anyhow, this is only of any importance if you really plan on using up the fuel for longer flights.


RobertL18C wrote:

Conversely bladder tanks may carry a few gallons more than stated capacity

Mine don’t. It is exactly the amount indicated. However I heard that older bladders could shrink or partly collapse.

RobertL18C wrote:

To clarify my earlier point about bladder tanks, as they age they can develop wrinkles where sediment and water build up

Mi bladders are 51 years old. No sediment. No water build up. But of course it may be, so tanks should be inspected.


Surely the nature of aircraft movement from normal flight even with minimal turbulence will mean as soon as the tanks are below 1/2 capacity, the fuel will slosh around enough to agitate and thus draw most contaminants into the fuel and either be burned or caught in a filer somewhere.
Anything more resistant to that process will be unlikely to ever depart the tank even at low fuel.
If the take-off-point it very low, it would pull contaminants all the time, if the take-off-point leaves unusable fuel then to simultaneously agitate something which rarely is an issue to then suddenly be an issue is unlikely IMHO.

In boating this issue sometimes occurs when a river loving owner of many years, sells a boat to someone who ventures out to the wavey bits, and stirrs up years of sludge and debris.

United Kingdom

UdoR wrote:

You know that you would actually SEE 2 Gallons (regardless whether U.S. or imperial) of mud in a fuel tank?

Experience varies: on my two wet-wing cessna’s, after four decades since mfr only some minor lint, a couple of paint flakes, and a lot of good clean aluminum walls and PR1440 sealant on corners and fasteners…Opening up the tanks is a typical 1000hr task on wet-wing Cessna’s for good reason.

I would clean any fuel tanks with such an amount of debris as reported by @UdoR before further flight.

Last Edited by Antonio at 04 May 12:11
LESB, Spain

On fuel impurities, it would be interesting to know how many EFATOs due to fuel contamination vs engine quit on taxi & checks, it seems there is more in the former case, maybe as water/dirt gets mixed up with mouvement or fuel in the lines gets consumed, but could be that load of engines do stop on the ground just not that much reporting is going on?

I had one in motor-glider while on taxi at Glocs, I pushed TMG out of the line resampled fuel near holding point and spent 20min at high power with fuel pump ON/OFF before deciding that I am brave to go for a takeoff, initially I suspected it was the engine driven fuel pump that went bust (taxi is done with electric OFF) but my guess it was vapour lock after a long taxi in hot day at idle all the way to runway 09, the flight was uneventful

A friend on mine had EFATO at 200ft and walked away landing ahead, the investigation revealed the cause to be water in the tanks (very specific problem in vintage Mooneys), he spent 15min on ground before takeoff and had sampled fuel before departure, the aircraft was parked outside for 2months

Last Edited by Ibra at 04 May 12:31
Paris/Essex, United Kingdom

UdoR wrote:

The Rotax will stop in-flight. But with proper conditions restored (e.g. fuel available) it will restart with ease

Not the 912s in the Tecnam twin (P2006T) I fly. These ones cannot be restarted by airflow. They simply stop, no windmilling. That’s why the airplane has a secondary battery that serves one purpose and one purpose only: to air-start the engine(s).

One important thing to be aware of if restarting engine in flight using the starter motor: the starter puts huge transients on the supply bus, which can blow up avionics.

That is why one turns OFF the avionics master during starting. And why the TB GT have a relay which breaks the avionics bus supply when the key is in the Start position (in case you forgot the avionics master switch).

I reckon, most people would forget this when air starting, due to the urgency.

Shoreham EGKA, United Kingdom

Peter wrote:

most people would forget this when air starting

Also it may take an (eternal) while to get the GPS back online if switched off in flight, so one may consider his options and bets based on the particular scenario…

Also, in my experience, 28V systems are less tough than 14V systems on avionics with start-up transients. This is possibly because 28V avionics will typically continue working with 50% voltage drop in the bus whereas 12V systems will in that case turn your avionics on and off several times while cranking, risking more damage.

All G1000 aircraft I have seen start the engines with G1000 on (although maybe on a different diode- or relay-separated battery?)

LESB, Spain

Antonio wrote:

All G1000 aircraft I have seen start the engines with G1000 on (although maybe on a different diode- or relay-separated battery?)

Yes! In the G1000 aircraft I fly, at least (a C172S), the G1000 runs off the standby battery when you start the engine. Indeed the POH has a caution note that the avionics masters must be off for engine start or the avionics may be damaged.

ESKC (Uppsala/Sundbro), Sweden

“As a rule, all the fuel you use is drawn from the bottom of the tank (save for the unuseable which still puzzles me as to why anyone would build such a fuel tank). If it were not so your unuseable would be as much as is left in the tank after the outlet port is exposed to air due to (eg) running down to half tank…”

That “unuseable fuel” seems to confuse pretty many. The definition is something like “not useable in ALL normal angles of attack” or such. Usually you can use all fuel in level flight. Like someone mentioned, the fuel line sucks from the bottom of the tank. In level flight all fuel is “useable”.
But when you fly nose up at low approach speed (or any not level position), some fuel will be in the rear of the tank (or front) and as the fuel line usually starts from the middle, there will be some liters which do not come to the line in that position. The company does not promise you to get the last liters in these nose up/nose down angles and that amount is called as “unuseable”, which is not dirtier than the rest.

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