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Switching to fullest tank on landing


ragedracer1977

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Do you do this everytime?  It's on the checklist, but sometimes I wonder.

If I take off with full tanks and fly for an hour, when I come in to land, does it really make sense to switch tanks right as I'm getting low?  I know I have 2.5 hours of fuel in each wing.  I have 1.5 hours left, roughly in the tank selected.  It's been running great for an hour.  I don't really *know* what's going on in the other tank.  

Is it always wise to switch tanks on landing or is it prudent to stick to the one you're on when you have plenty of fuel in it?

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It really makes sense when the tanks are less than half full.  As fuel can easily slosh away from the pick-up when you most need it...

Not so critical when both tanks are at the same level, or have a lot in them.

PP Thinking only, not a CFI.

Best regards,

-a-

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If I'm landing with around 10 gallons in the tank I'm currently flying on I won't switch for many of the reasons you cited. There's also the "what if the selector gets stuck"  that I have heard of. I still check the well that the selector is in before every flight for small rocks or debris after reading of that happening and jamming the switch. 

However, changing routines is a great way to get in trouble. So I plan before the flight which tank I will be on for each leg of the flight. When going through my GUMPS I verbalize which tank I'm on and how much I expect is in the tank and reach down to physically check that I am on the tank I want even if I'm not switching. I don't want to sometimes skip it and then find I skipped it when I shouldn't have. 

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I think generally under the scenario you've described (you still have 1.5 hours remaining in the lowest tank) there's no harm in not switching tanks.  

However, these procedures are written with less rosey scenarios in mind.  Low fuel levels and an unplanned diversion, for example, where in the heat of battle one might become task-saturated and forget to switch tanks until it's too late.  As humans the best line of defense against that trap is adherence to consistent procedures, and muscle memory.   So we do things the same way every time.   It sounds mindless but it's actually proactive.  If you're worried about an interruption in fuel flow from switching tanks (I don't know what the chance of that happening is, but it seems low) then you could switch tanks at the top of your descent while there's still plenty of altitude to switch back if there's a problem.

 

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1 minute ago, Aviationinfo said:

If you're worried about an interruption in fuel flow from switching tanks (I don't know what the chance of that happening is, but it seems low) then you could switch tanks at the top of your descent while there's still plenty of altitude to switch back if there's a problem.

 

This is a great point. When I am switching tanks prior to landing I do it before beginning my descent. I was taught that you want to switch while flying straight and level so that's what I do. Maybe that's just an OWT, I I don't know. 

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There's been many times I haven't switched.  I fly from DVT-FFZ now and then.  It's a 12 minute flight.  However, I do run through the checklist and when I get to "Switch to fullest" I touch the selector and check the fuel gauge.  

I'm trying to ingrain at least the concept of always looking/checking whether I switch or not. 

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I just want a tank selected that has at least 8 gallons.  If I'm planning on landing with 10-12 total, I'll manage my tanks so that I have 10 in one tank when I arrive at the field and switch to that tank approaching the pattern.

If I have plenty of fuel in both tanks, I'll just leave it on the current tank.

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If its local I rarely bother.  On longer trips I try to remember to do it, just in case there's too little fuel and it starts sloshing.  I actually do the thing of burning on the left for an hours dn then the right unit it runs out, except I haven't gone long enough to burn through the right.  Probably wouldn't, I'm too chicken shit to run a tank dry.

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I manage fuel such that I have at least 10 gallons minimum in at least one tank prior to beginning descent.  If a switch is required then I do that just before beginning descent.  If I have over 10 gallons in both tanks then I do not switch.  I never switch tanks in the pattern, just bad JuJu to tempt fate in the pattern.  Nor do I switch tanks from the time I turn the key at startup to the time I level off at cruise altitude.

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I have a 30 minute reminder set in one of my GPS's.  It is automated from lift-off, no need to manually start.  Every 30 minutes I get a message.  That generally keeps me in the loop and tends to keep tanks even.  For landing, it really depends on when I last switched, what I am flying over and how much are in the tanks.  As I get toward the 1/4 tank point, or under 10 gallons, I am much more careful to be on the fuller tank for landing. At a minimum, like Skates, I try to make an informed decision on which tank to land on.    

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4 hours ago, steingar said:

If its local I rarely bother.  On longer trips I try to remember to do it, just in case there's too little fuel and it starts sloshing.  I actually do the thing of burning on the left for an hours dn then the right unit it runs out, except I haven't gone long enough to burn through the right.  Probably wouldn't, I'm too chicken shit to run a tank dry.

I've run mine dry on purpose twice.  Non event.  Of course, that's only because the engine restarted.  :huh:

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I manage fuel very deliberately, not by check list or muscle memory, and almost never change tanks in the pattern. If we're out formation flying, there will be enough fuel in both tanks to ensure landing on either tank won't matter and so no need to switch. If i'm on a cross country, I'll have planned to arrive in the pattern with at least 10 gal minimum and all of it in a single tank. So again, no need to switch tanks in the pattern.

My deliberate fuel management includes minimizing tank switching. Most cross countries only involve two tank switches. Start on Left and burn 15 or 20 gal, switch to Right and spend the rest of the trip there until it runs dry or we are descending to our destination, switch back to Left with 15 or 20 gal left for approach, pattern, landing.

I try to minimize the before landing checklist to just the most important and critical items. I've eliminated any and all items that aren't critical, required, or those that often get skipped anyway. Changing tanks is one item that has been eliminated. 

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20 minutes ago, gsxrpilot said:

I manage fuel very deliberately, not by check list or muscle memory, and almost never change tanks in the pattern. If we're out formation flying, there will be enough fuel in both tanks to ensure landing on either tank won't matter and so no need to switch. If i'm on a cross country, I'll have planned to arrive in the pattern with at least 10 gal minimum and all of it in a single tank. So again, no need to switch tanks in the pattern.

My deliberate fuel management includes minimizing tank switching. Most cross countries only involve two tank switches. Start on Left and burn 15 or 20 gal, switch to Right and spend the rest of the trip there until it runs dry or we are descending to our destination, switch back to Left with 15 or 20 gal left for approach, pattern, landing.

I try to minimize the before landing checklist to just the most important and critical items. I've eliminated any and all items that aren't critical, required, or those that often get skipped anyway. Changing tanks is one item that has been eliminated. 

Saves me a speech. I only switch tanks prior to landing if there is less than 15 gallons in one and a lot more in the other. Otherwise it's a bad practice because it will make it harder to tell how much is in which tank later when you might really care.

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I only switch tanks when I am in gliding range of an airport as it approaches me.  Then I have all that time to fly on the new tank before I am out of gliding range on the other side.  

I also found that switching tanks as soon as I touch down on a touch and go makes me a better pilot.  

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19 hours ago, Bob - S50 said:

I just want a tank selected that has at least 8 gallons.  If I'm planning on landing with 10-12 total, I'll manage my tanks so that I have 10 in one tank when I arrive at the field and switch to that tank approaching the pattern.

If I'm expecting to be low on arrival, I'll switch at the top of descent. Messing with the tanks in the pattern is a half-step from switching tanks at the hold short line . . . IMHO.

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2 hours ago, Hank said:

If I'm expecting to be low on arrival, I'll switch at the top of descent. Messing with the tanks in the pattern is a half-step from switching tanks at the hold short line . . . IMHO.

Maybe.  But for me, I switch tanks enroute to keep my tanks within 5 gallons of each other.  Burn 5 from one, then 10 from the other, then 10, then 10, etc until I get one tank down to 10 gallons.  I then run the other tank until I'm approaching the pattern and switch to the tank with 10 gallons.  By that time I have thoroughly tested the ability of each tank to supply fuel.

I agree about the hold short line comment though.  I start on one tank, get all my avionics set up (a couple minutes) then switch to the other tank for taxi and run up before I go.

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Common sense should prevail here. If you have plenty left in the tank (>48lb), even the other tank is fuller, there is really no point of switching especially if you had been managing the fuel appropriately. ie. the difference between tanks shouldn't be much to start with.

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I carry 32 gallons on each side (really, closer to 33-34 when I've run a tank dry). I used to run 3 hours on the tank that I took off with and then switch to the other side. Rarely would it start to sputter by then. My rationale was that if something was drastically wrong with fuel flow, that the tank I climbed out on would burn a lot more than the other side and if I could get 3 hours of that side that the other would be good for three hours.

Now that I have a fuel totalizer, I'm more confident in my fuel consumption. I also have wing mounted gauges that appear to be pretty accurate in flight above 10 gallons. Now, with the fuel totalizer, when starting with full tanks, I burn 16 gallons on one side, 32 on the other, and then switch back to the side that I started with. If I'm down to less than, say 10, on that full tank, I'll switch it back to the tank with 16 gallons as I start my descent or approach -- especially if I'm in IMC, I want to minimize things to worry about when under heavy workload. A lot of pilots talk about switching every 10 gallons or every hour. I don't like the idea of having reserve fuel split between tanks. If you're to go every 10 gallons, it seems to be the same effect to go 10 gallons for the first switch, and then every 20 gallons to keep the balance within 10. 

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56 minutes ago, Bob - S50 said:

Maybe.  But for me, I switch tanks enroute to keep my tanks within 5 gallons of each other.  Burn 5 from one, then 10 from the other, then 10, then 10, etc until I get one tank down to 10 gallons.  I then run the other tank until I'm approaching the pattern and switch to the tank with 10 gallons.  By that time I have thoroughly tested the ability of each tank to supply fuel.

Interesting... this seems like a lot of opportunity to lose track, mess up the sequence, mis-calculate, along with a lot of work on the tank selector.  

I'm carrying 35 gal per side and only ever switch tanks twice, if that much. 

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Interesting... this seems like a lot of opportunity to lose track, mess up the sequence, mis-calculate, along with a lot of work on the tank selector.  
I'm carrying 35 gal per side and only ever switch tanks twice, if that much. 

I agree, not to mention breaking the selector valve. And I only change when either an airport is in range or at least good emergency landing area. Changing that frequently would likely force me to break that rule.
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Without a fuel totalizer... I used to....

1) use one tank for all the inaccurate estimate of fuel usage.  Start-up, taxi, climb and descent

2) Use the other tank for cruise. 

This helped me get the best handle on what my fuel flow was each time I landed and refilled....  leaning an old M20C without an engine monitor or FF gauge tests an engineer's inner compass...

 

Without an AP... I used to switch tanks often.

1) Hand flying and providing constant force to lift the heavy wing can get tiring...

2) In smooth air above the cloud level, it is really easy to sense the imbalance of forces, and make an adjustment...

 

With an AP, and FT, and 100+ gallons of fuel...

1) I switched Top of climb...

2) then every other hour...

3) Top of descent and gumps check, gets an extra review of what the levels look like.

4) My main fuel level indicators are marked in gallons 0, 11, 22, 33, F.  The wing gauges are marked in 5gal increments...

5) After a 5+ hour flight I actually saw the fuel level light come on the annunciator panel. Haven't seen that in years...

6) I also logged the tank switches and other notes during the flight... in case I forgot some detail along the way. 

7) briefly... I am highly unlikely to be changing tanks during the gumps check...

 

Pp thoughts on what I did and why I did it only, not a CFI...

Best regards,

-a-

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