As the title says, what are the consequences of low levels of fuel – besides running out obviously, and having to land somewhere not of your choice? What I am trying to get at is whether climbing or banking or even choice of tanks is of any significance.
Also, does anyone run ‘dry’ on one tank, and then switch so that they know really what they have left? I have seen it done on a friends YouTube video, but he was at a decent altitude anyhow, and there was only a slight cough, then he changed tanks, and all was fine. Personally, this looks scary to me !
The other day I found myself in an uncomforable situation where I was low on fuel, and according to the PA28 fuel gauges (which are analogue, rather than digitial in terms of presentation), indicated 2 – 3 gallons either side upon landing (45 minutes flight perhaps). What led to this was over optimism on my side that I didnt need to fuel up for two legs of a journey that were due to take about 1 hour each in the air, and considering that the ~24 gallons I had would be more than sufficient. Due to choice, leg 1 was slightly extended to take in some scenery, and leg 2 didnt result in a piece of CAS transit I was hoping to achieve. Also, in reality, we werent operating at best economy, more like best cruise. So, lessons learnt, and next time (like most times) I will fill up before I go and depart with full tanks, or land en-route for more fuel if I think we need it.
It dawned on me that if I had 2 tanks with low levels of fuel, what would happen if I climbed? What would happen if I was on the left hand tank, and then I banked left in the circuit, and the fuel sloshed to the outer end of the tank, and was effectively ‘dry’? Is there any protection for this kind of event – I assume so but for how long? Obviously with analogue fuel gauges I wont get into this situation again, but it has prompted some questions I hadnt considered before, and technically I do not know the answer too.
I already had an incident in this atmosphere: took off from a rather empty tank, and got some air trapped in the header tank at the first turn. The header tank is not vented, so the air could not get out, and there was enough of it to activate my “fuel low” alarm. I should have been reassured by the continued fuel flow but wasn’t, and made a straight in at my home way against the active direction – after giving ample warning on the radio, and getting a much appreciated reply that there was no other traffic around. Luckily it was only a 15 minutes flight, otherwise I’d certainly have returned to the departure field.
What I am trying to get at is whether climbing or banking or even choice of tanks is of any significance.
This is totally dependent on the fuel system of your aeroplane. On some types, the POH will tell you what to expect with low fuel levels (like “avoid high pitch angles” or “avoid yaw”), others let you completely alone. Ideally, unaccellerated level flight should result in a maximum amount of useable fuel.
Also, does anyone run ‘dry’ on one tank, and then switch so that they know really what they have left?
When you are really tight on fuel, this is your only choice. Fly one tank dry and then forget about it and focus on what you have left in your other tank. That’s better than having two tanks with unknown quantities remaining. Like this, you know that switching tanks will have no effect and you better spend every remaining second on planning your forced landing… On some twins that I flew (especially the C340 with six tanks) running the tanks dry was the only way to get the full range out of it. If you need to do that, better warn your passengers before so they will not get scared. If you turn on the fuel pump when the fuel gets really low and switch tanks upon the first signs of the engine missing beats, they might not even notice.
…and the fuel sloshed to the outer end of the tank, and was effectively ‘dry’? Is there any protection for this kind of event – I assume so but for how long?
Some tanks have “anti slosh baffles” installed to prevent the fuel moving away from the drain even when the aircraft moves, others have “bladder” tanks that slightly change their shape and keep the fuel close to the drain. Other tanks again have several drains with floats that are supposed to close the dry ones and prevent air from getting sucked into the fuel lines. And others again have no protection at all. I must confess I don’t know about the Pa28 even if I instruct on this type… It might also depend on model and year of manufacture.
I would also add that in a balanced turn (ball bang in the middle) the fuel doesn’t slosh to one side.
Last year (or was it the year before) I’d occasion to want to run a tank dry. This was on a PA28
Around the time that I was expecting it to run out, it started to surge. It wan’t anything dramatic, and maybe not noticable unless you were waiting for it. It wasn’t massive power changes or anything.
After a few second it went away and was ok for another few minutes, then it happened again. Ok for another minute, and then started again.
It didn’t get much worse, but was now noticable. It felt like maybe 3-5% power change; nothing dramatic but noticable. I could see the effect on the fuel flow meter.
I waited for about two minute with my hand on the tank selector, before I lost my nerve and changed thanks 
It didn’t actually stop, and the surging never got dramatic, and there was never a cough. I don’t know how much longer it would have run, but I doubt more than 2 minutes. This was all in level flight.
What I found interesting, is that there was plenty of warning of what was going to happen, if you knew the signs to recognise. Having seen it before, I’m sure that I’d be quick to recognise it in the future. If I’d never seen it before, I’m not sure how quick I would have recognised it, and how quick to diagnose.
It doesn’t answer your question about turns/climbs/descents, but dpes at least suggest that you’ll get some warning in your PA28.
Thanks, all for the replies, that helps me with my understanding. As I did a brief climb near home, there was a slight ‘cough’ as I pitched up, hence I wondered about the configuration of tanks. I will see if I can find out something specific about the PA28 anyhow, but in the absence of more knowledge, and a fuel totalizer I will just make sure I have plenty of fuel and don’t need to concern myself about it.
Yesterday I performed a ground run after two days of work on the aircraft for the ARC. Engine started normally and ran fine, I tried all sorts of different power settings, the magnetos, prop governor etc and then the idle run. All was fine until suddenly the idle run become rough. Trying to find out what was wrong I kept changing settings when the engine died in slow and stuttering idle — because I played with the mixture at too low rpm with too little inertia I thought. Trying to start the engine again was not successful but that is well within the expected results as starting and engine that just ran can be difficult at times.
Only when I was pondering about which maintenance could have an effect on idle RPM and idle mixture, my mechanic asked me why I was doing the ground run with the fuel selector shut!
I am still amazed for how long the engine ran with the fuel selector shut. My plane does not have a header tank, there is just an aluminum tube from the fuel selector to the carburetor so all I had was the fuel in the carburetor (the fuel selector is lower than the carburetor so the fuel in that line could not have been drawn). If I did not perform a warmup and runup and there was no extensive taxi involved, I could theoretically take off in that timeframe. Such accidents have happened but usually in aircraft with header tanks where there is several minutes of fuel.
Only when I was pondering about which maintenance could have an effect on idle RPM and idle mixture, my mechanic asked me why I was doing the ground run with the fuel selector shut!
Yes, that happened to me when I was a passenger in a plane someone hired, and the previous occupier in the PA28 turned the fuel off (no one does this as far as I know in a PA28), and the plane was started, taxied for some time, commenced power checks and then died. It scared the pilot, and while it didn’t take long to figure out why, I am glad it didn’t occur in the take off run – though not that it should as one changes tanks as part of the power checks anyhow.
Quotethough not that it should as one changes tanks as part of the power checks anyhow.
I no longer change tanks immediately before take-off – because, IF there was a blockage, the engine would stop after lift-off. I’d rather have that happen when I change tanks at about 1000’. (I’ve had a partial finger-filter blockage, in the rear tank which is not used at take-off.)
I think the TB checklists tell you to switch tanks very early after starting the engine and before taxi to give you enough time to detect a potential blockage.
As a high wing gravity fed airplane pilot, I usually pay very little attention to fuel selectors and when flying other aircraft (like the TB10 this week), I always have to take precaution. The early TB10 are even worse than the PA28: they hide the fuel selector behind the yoke whereas in the PA28 you obscure it with your legs. At least in the PA28 it is very big and red whereas. In the TB, it’s small and has a meaningless pictogram. Two idiotic designs
