Switch Tanks Before Takeoff

[midlifeflyer]

Almost 200 posts. I haven’t been paying attention. Is this a big deal?

I never worried about it much. Started, taxied, ran up, and took off on one. Switched in a safe place. Figured the airplane had been flying and, in the case of rentals, no squawks about it. Maybe I was being naive  

Then I joined a flying club which had an SOP to start on one tank, then switch to the other for the runup on the theory that both would be operating long enough to act as an operational check. Beats me if it’s effective but the extra second it takes to switch at the beginning of the runup is no big deal to me, and I started doing it as my own SOP.

I guess I should go through the thread to see if any mechanics have weighed in. 

[A64Pilot]

I’m an A&P/IA and don’t think it’s a big deal largely because mechanical things that break do so with little warning meaning just because it worked on run up doesn’t mean the next time it will.

We used to do “Stand to” in the Army where we would go out first thing in the morning and run everything up, creating a whole lot of unnecessary work for me, because lots of especially electronics would fail when first powered up.

We tracked everything by computer even back then, there was no decrease in failure rates after a couple of days of Stand to so it didn’t decrease failure rates.

Over the years it became obvious that usually instructors who always had zero mechanical training would come up with what they thought were good ideas and incorporate them into training.

Latest thing that annoys me is the puppy mill flight schools in Fl are apparently teaching teardrop traffic pattern entries.

Had one of them do a 180 on downwind the other day executing his “teardrop”. When did teardrop traffic pattern entries come into existence? What happened to mid field downwind?

But back to the tank selector if it makes you feel good do it, however as someone who’s disassembled a few I can’t imagine the failure mode where the selector could click into the next position and not still flow fuel, and wonder are you really performing an “MOC” maintenance operational check on a fuel valve by requiring less than full fuel flow through it?

I don’t know about you, but on run up my fuel flow isn’t close to the 19 GPH I burn on takeoff. So did you induce a partial failure by mucking with the thing on run-up and you going to find that out on takeoff?

My only issue I’ve ever had with one was I had the handle come off on me I think in the C-210, it didn’t but it could have come off in off or partially to selected tank, luckily it came off after the tank was selected.

Now I don’t muck with the thing until I’m in cruise, select fullest tank at the beginning of let down if tanks are way out of balance.

The whole tank selector thing has me a little baffled to be honest, why do we even have the things? Did it come from the Military where you could be shot in one tank and wanted to keep all of the fuel running out of that tank?

The Thrush crop duster has been built since 1965, it has no fuel selector, just on and off and that’s worked well for 60 years? 

[Pinecone]

18 hours ago, wombat said:

Please don't take any of this too seriously, but....       I already know both tanks worked before taking off, because they worked last flight.   What happened while the plane was on the ground that would have caused it to work the previous time but not this time?   If the answer is 'nothing' then you gain nothing.    If the answer is 'something',  then... What the heck are you doing to your plane?

Based on that logic, why do a preflight or runup???  Everything was fine on the last flight......

Let's see, one scenario is that the set screw for the selector handle is loose.  Just loose enough that you were able to select fullest tank for landing, but the next time you try to turn it, the handle comes off.

Or, your less than stellar landing jars something loose in the less full tank and it covers the pickup.

The things that can go wrong do not only include the selector.

[Schllc]

My takeaway from this discussion is that there are good arguments for moth methods, and it comes down to personal risk management. 
I prefer to not touch the fuel selectors prior to takeoff, but I understand why some believe this induces more risk, I just happen to disagree.  Not to the point I care to debate, it’s just my personal opinion. 
To each their own. 
Merry Christmas and  Happy Hanukkah 

[A64Pilot]

36 minutes ago, Pinecone said:

Based on that logic, why do a preflight or runup???  Everything was fine on the last flight......

Let's see, one scenario is that the set screw for the selector handle is loose.  Just loose enough that you were able to select fullest tank for landing, but the next time you try to turn it, the handle comes off.

Or, your less than stellar landing jars something loose in the less full tank and it covers the pickup.

The things that can go wrong do not only include the selector.

Now I’m not beating on you if moving the selector during before or after runup gives you comfort then by all means go ahead.

I’ll tell you what I used to tell my Commanders that going through a full pre-flight and run-up every day at the crack of dawn trying to ensure readiness is as logical as turning on a light every hour to ensure the thing didn’t burn out while it was turned off.

Of course we check free and clear of all flight controls, but most don’t include flaps and maybe that is where the operate the fuel selector comes from.

‘On the 210, there was no looseness or anything else that gave warning the lever was going to fall off, just one day it did.

Arguably if the screw was checked frequently for tightness that would have prevented my failure, so maybe we should be putting a screwdriver on it every run-up or pre flight?

You can’t reduce risks to zero and there is some point to where it becomes silly, or we would be depanneling the aircraft on every pre flight checking every flight control.

Heck it seems it’s mags that almost fall off that cause 1000 times more forced landings than fuel selectors, yet I’ve rarely if ever heard of anyone that checks them for condition and security, especially the dual mag as we only have one.

[PT20J]

At two Part 135 operators I flew for, our FAA-approved checklist called for a run up on the first flight of the day only and we never checked the fuel selector.

[EricJ]

There may be less risk in waiting until you're at cruise and ready to switch tanks for balance rather than switching it before you take off.     If switching tanks creates a problem at cruise due to some issue, like water, whatever, you can switch back to the other tank and then figure out how to handle it.    If you switch sometime during ground ops and it has a problem during or shortly after takeoff, that's much less desirable.   For this reason I find it preferable to just wait until established airborne to switch tanks.

[cliffy]

There is some truth to maintenance and/or operational induced failures.

The more you use it the more it wears out and/or possibility of improper reassembly

[PeteMc]

1 hour ago, Pinecone said:

Based on that logic, why do a preflight or runup???  Everything was fine on the last flight......

I went on the Cayman Caravan years ago and one of the organizer had a great talk/roleplay that he would do.  "Brother Jimmy" would tell you to check everything and the buffoon pilot would respond every time with something along the lines of "But Brother Jimmy I checked those fuel tanks a week ago.  I'm sure none of the rain we've had has gotten in there."  Bird nests in the tail was another one.

It was a good little talk that made the point of why we do a Pre-Flight.

[A64Pilot]

2 hours ago, cliffy said:

There is some truth to maintenance and/or operational induced failures.

The more you use it the more it wears out and/or possibility of improper reassembly

However over and over it’s always been the aircraft that fly the most that seem to break the least, seems they just like to fly?

Military we didn’t do Annuals, we did phases, on the AH-64 they were every 250 hours regardless of calendar time, on average I’d say an aircraft went through a phase every 24 months.

As I said everything was on computer and therefore it was easy to build stats if you wanted, one of those was the most trouble free hours were the last 50 before phase and the worst were the first 50 out of phase.

Now it’s likely but unproven that may have been because the most often an aircraft flew was just before phase as phases were scheduled and you needed to burn the time off to make the schedule, and it had sat often for a month during phase of course not flying. But maybe it was because a whole lot of stuff had been taken apart and it took awhile to work the bugs out, plus of course often parts were robbed from the phase bird to keep the rest of the fleet flying, furthering the amount of disassembly that was done.

So yes there were things broken in phase but actual “maintenance induced failures were very rare”

I have never had one in a GA airplane, sure I’ve had the occasional leak or something like right now I’m changing the motor mounts on my C-140 and noticed the alternator that I installed last year had a slight oil leak on its gasket, was that maintenance induced? Or just one of those things that happens every so often? I have no idea. 

I used to tell people if you came into the hangar at night when no one was there that if you listened carefully you could hear them breaking. Joking of course but I swear the more they flew the more reliable they were and the very early Apaches were terrible, we would crank five and cross our fingers that four would make the mission. 90% of the time they broke before they broke ground, if they flew away it was very uncommon for one to break in flight.

[midlifeflyer]

4 hours ago, A64Pilot said:

Had one of them do a 180 on downwind the other day executing his “teardrop”. When did teardrop traffic pattern entries come into existence? What happened to mid field downwind?

Thank you for the comments on switching tanks.

But wow! This is what I call thread creep! But you have the history backwards.

The "teardrop" is supposedly the shorthand term for the FAA's long-preferred entry from the upwind side of the pattern - cross above the pattern, head away 2-3 miles, descend to pattern altitude, and return for a 45° to downwind.  That favored maneuver never had a name, and recently picked up the generic (not official) name "teardrop." 

The "teardrop", not the cross mid-field at pattern altitude to downwind entry, has been the FAA's favored child for scores of years. In fact, if I recall correctly, it wasn't until sometime after 2015 that the FAA would even recognize the midfield-to-downwind as a legit entry in the AIM, the Airplane Flying Handbook, or any guidance material. Even now, the FAA refers to it as the "alternate midfield entry." 

I said "supposedly" for a reason.  "Teardrop" makes me cringe and I don't use the term. In the FAA version of the entry you remain above pattern altitude until well clear of the pattern on the downwind side. Then you descend to pattern altitude. Then you turn to enter on a 45.  The problem with the term "teardrop" is that pilots (and sadly some instructors) end of thinking of it as a teardrop that ends on downwind. The result is that it's done way too close to the pattern. Combine that with Cessna 152s flying 737 patterns and I'm flabbergasted there aren't more mid-airs.

 

[PeteMc]

1 hour ago, midlifeflyer said:

The problem with the term "teardrop" is that pilots (and sadly some instructors) end of thinking of it as a teardrop that ends on downwind.

Wow, that's pretty bad.  ALL of the docs and pics I've seen clearly show the tear...  er...  roundish turn thingy ending on a 45dgr entry TO the DW.  Personally, I'd stick with "Teardrop" as it basically is just like a Hold entry Teardrop.  But maybe the FAA needs to do what of their Hot Topic things in the CFI(I) refreshers to make sure people get that it's a Teardrop to the 45. 

(Sorry....  And the thread creep continues.)

 

[Pinecone]

One BIG thing is, NO ONE is saying to switch tanks just before take off.

I start and taxi on the lowest tank.  Then switch tanks BEFORE the run up.

[Gone]

3 hours ago, Pinecone said:

One BIG thing is, NO ONE is saying to switch tanks just before take off.

I start and taxi on the lowest tank.  Then switch tanks BEFORE the run up.

+1

[PT20J]

From the Airplane Flying Handbook

[DCarlton]

52 minutes ago, PT20J said:

From the Airplane Flying Handbook

How much above pattern altitude should you cross mid field before descending ?  1000 feet ?  

[PeteMc]

56 minutes ago, DCarlton said:

How much above pattern altitude should you cross mid field before descending ?  1000 feet ?  

On the diagram you copied it shows +500 if you're doing the teardrop into the Downwind.  AT Pattern Altitude if you're doing the direct turn into the DW.

 

[midlifeflyer]

6 hours ago, DCarlton said:

How much above pattern altitude should you cross mid field before descending ?  1000 feet ?  

500 feet above the traffic pattern. That means it’s variable to some degree. The standard traffic pattern is 1000 AGL. But jets fly it at 1500 AGL so it depends a bit on the mix at your airport.

 

[Pinecone]

On BIG mistake people do with that entry is the diagram states "Descend to Pattern Altitude then Turn."

TWO steps.  Descend THEN turn.  It is NOT a descending turn to the 45.

[midlifeflyer]

16 minutes ago, Pinecone said:

On BIG mistake people do with that entry is the diagram states "Descend to Pattern Altitude then Turn."

TWO steps.  Descend THEN turn.  It is NOT a descending turn to the 45.

Exactly the problem, especially when combined with pilots flying wide downwinds.  I'm at least 3 miles from the pattern before I even begin the straight ahead descent.  I'm convinced the use of the term "teardrop" is a contributing factor to what amounts to descending 215° turns within the bounds of a typical nontowered traffic pattern. I avoid the unofficial term entirely..  When I announce one, it's "crossing midfield [direction] at [altitude] to return on the 45.." 

I went to a Wings seminar on traffic patterns about 10 years ago where the speaker was talking about the maneuver as the most dangerous pattern entry of all. Set up a simple 3 airplane scenario, apparently from an old accident report. I couldn't help pointing out that he was challenging the FAA's preferred entry from the upwind side of the pattern, although I agreed wit him completely.

[cliffy]

Everything is spelled out in the newest release of AC 90-66C below-

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_90-66C.pdf

[Jetpilot86]

On 12/9/2023 at 1:34 PM, jlunseth said:

I follow my checklist. (I wrote it.) My checklist says to switch to the fullest tank for start up and the part of the checklist that I do on the ramp, then switch to the other tank for taxi and run-up, then switch back to the fullest tank for takeoff. Now, in addition to having sumped the tanks, I have verified that there is good fuel in both tanks. That way not only do I insure I have good fuel for takeoff, but I have also insured that I don’t get down range somewhere and over the middle of nowhere, and then change to an untested tank. I used the basic format for checklists that the school where I got my PPL uses for its Pipers, Warriors, Archers and Arrows and modified it for my 231.

My Bravo’s POH mandates the switch. I start fullest, swap, then return to fullest for Takeoff. 

[Fly Boomer]

22 hours ago, A64Pilot said:

As I said everything was on computer and therefore it was easy to build stats if you wanted, one of those was the most trouble free hours were the last 50 before phase and the worst were the first 50 out of phase.

Somewhere, Mike Busch has a graph of failures vs time that looks like an inverted bell curve.  Infant mortality on one end, and old age on the other.

[DCarlton]

11 hours ago, PeteMc said:

On the diagram you copied it shows +500 if you're doing the teardrop into the Downwind.  AT Pattern Altitude if you're doing the direct turn into the DW.

 

Crap I see it now.  And I looked for it more than once.  500 feet would make me pretty uncomfortable at an uncontrolled airport.  I've always circled well clear of an airport in this scenario and entered on the 45.  I might try this though with a little more altitude.   [yes I know this is major thread creep]. 

[Schllc]

It doesn't really matter what the FAR says about uncontrolled fields.  No on there will pay attention to this, and they will continue to do whatever they want.

i was practicing landings at an uncontrolled field and i had two people in the pattern with radios not talking at all, one guy calling a straight in from 20 miles out not answering anyone, one guy doing a run up on the runway on the tailwind side, one guy lined up and waiting  on the correct runway, and another guy taking off with an intersection departure, also not talking.

good luck with "rules" there!