Piper Comanche's can vent fuel and then ya lose both engines

[CobraDriver]

I was at 7000 ft going to Augusta, tanks were topped, more than enough for a 2 hr flight. Took off on the mains then went to switch to the outside tanks and the engine sputtered, so I put it back on main and figured still more than enough for my 2 hr flight. Well that was the beginning of my problems.

I was 14 miles out from destination on an IFR approach which quickly became a direct vector to the airport and little did I know I had been losing fuel the entire time. The left engine spit...then quit. I put the boost pumps on and restarted the engine....it did start. A few minutes later the right engine did the same and I repeated my procedure. From that point on it was left, quit, I restart...right, quit, I restart until I was on downwind and the right died but would not restart. I landed on the left engine and during taxi to parking that one quit too and would not start.

Being my lucky day, the FAA was there and met me at the plane ready to hang me for running out of fuel. With the speakerphone going I called the owner in the FAA's presence, he confirmed the airplane was topped when I left. That's when the FAA asks me then what happened...I said to him you're the FAA you tell me!

I mention the events to a buddy of mine at work, he flew over 100 aircraft and had 27,000+ hours. He says "ohhhh...you were venting" I said what do you mean? "when you switched from mains to tips then went back to mains....sometimes that plane will vent fuel overboard if the pressures aren't right" he continues "I was once sitting in the back as a passenger and the pilots did the same thing, I tapped one on the shoulder and said hey you're venting fuel off the wing...I can see it back here"

I asked him to call the FAA and the owner to tell them that and he did. I received my conclusion of the investigation from the FAA and all that remains is the entry in my logbook.

So....BEWARE....a PA-30 (corrected/Edit) can vent when you switch from mains, to tips and back to mains and then you'll have an interesting descent from 7000 ft and 14 miles away.

 

[WannFly]

Wow... thanks for sharing and glad everything worked out, this could have easily been a disaster if the airport was further ..... curious , do you have any kind of totalizer that would tell you the fuel burn? I guess that doesn’t help in this case, but you can probably come to a conclusion that if you are burning 12 gal/hr and the fuel indicator shows near zero, fuel is being dumped. I do not feel bad about putting a digital sender to figure out how much fuel there actually is anymore.

 

[CobraDriver]

do you have any kind of totalizer that would tell you the fuel burn?

It wasn't my plane, it was a lease by my organization and I don't rem it having one. I only flew this plane 3 times and this was the last time.

 

[Pilawt]

Your narrative sounds like a Twin Comanche (PA-30 or PA-39). Is the issue the same with the single-engine Comanche (PA-24)?

 

[Tantalum]

Wow man, epic write up, and glad you made it out of that one unharmed!

 

[CobraDriver]

Your narrative sounds like a Twin Comanche (PA-30 or PA-39). Is the issue the same with the single-engine Comanche (PA-24)?

You are correct Sir, it was a twin...that I rem...ohhh boy do I remember. The series I forgot

 

[GRG55]

So the questions remains...why does it vent under that switching sequence?

 

[hindsight2020]

i dont think "sequence" with the mains has anything to do with it. the second he selected the aux the engine sputtered. that means the auxes were siphoned the entire time, the engine pump cant overcome it. clogged vent tubes are not unheard of in these old birds with bladders. aux and main tank plumbing are not connected (other than presumably at the fuel selector, those are another doozy in the system and hard to procure). tips and auxes however are, via an electric solenoid that prioritizes either tank to use the aux fuel plumbing to the engine. bladders also dont help since theyre also prone to collapse like a juice pouch under vacuum.

additionally, in those aux plus tip STC equipped comanches, the solenoid that connects the tips to the aux piping in order to have the in cockpit selector switch between tip and aux, can leak. when that happens the tip transfers to the aux, and the aux ****es the whole tip quantity via the vent. this doesnt seem to be the OPs case however. what is interesting is to have both auxes have clogged vents. thats some extra special mx practices, though if the reason for clogging was corrosion or nature (bugs), then it stands to reason both sides were affected at the same time without mx attention to the problem. BL this doesnt happen overnight.

 

[EdFred]

What solenoid?

There's no solenoid in the system from Osborne. (At least on the singles) It's just an octopus at the fuel selector.

 

[Chip Sylverne]

Go over to the Airworthy Comanche board on Delphi and post your experience. Lots of twin experience over there to sort this out.

I have heard of bladders collapsing due to clogged vents. I've never heard of fuel venting overboard due to them, but I have a single without tips.

 

[bflynn]

Ok, so if it's pressure related...

How do you fix it?

 

[dtuuri]

What solenoid?

There's no solenoid in the system from Osborne. (At least on the singles) It's just an octopus at the fuel selector.

My Twin Comanche had electric switches that flipped solenoids mounted to the spar in the cabin. It flipped the plumbing to the fuel selector from Aux to Tip. Never heard of this kind of "venting" problem and can't see how. The thermos-style fuel caps, yes. If you leave the tip switch on while on mains, I can see fuel running downhill through the solenoid and into the aux tank and overboard, but you'd still have a full aux tank when the tip drained.

A problem I found with mine was a bad ground from the solenoid to the spar which then didn't open as it should causing perplexing fuel balance and tank level indications.

Also, there is a fuel line purging step during preflight that makes sure you have no air in the line from the tips, in case the previous flyer ran them dry. If you don't do it, the engine quits when you switch to tips (for a few seconds). Sounds to me like that's what happened to the OP. Going back to mains should still leave most of 60 gallons of fuel. If he ran out, maybe the bladders were both collapsed? More enlightenment on the cause would be appreciated.

 

[dtuuri]

i dont think "sequence" with the mains has anything to do with it. the second he selected the aux the engine sputtered. that means the auxes were siphoned the entire time, the engine pump cant overcome it. clogged vent tubes are not unheard of in these old birds with bladders.

He said he switched to the "outside tanks". That would be "tips", IME. To do what you say, wouldn't both the vent have to be clogged and the fuel cap on top of the tank siphoning fuel? That doesn't fit with Occam's Razor does it?

...what is interesting is to have both auxes have clogged vents.

Oh, Occam!

 

[unsafervguy]

The only time I ever had it happen in the 15 years I had mine was when I had a bad cap that was not seated well on the aux (no tips on mine) it was at night so I did not see it but I saw it in the morning when the top of the wing was blue.

 

[Chip Sylverne]

He said he switched to the "outside tanks". That would be "tips", IME. To do what you say, wouldn't both the vent have to be clogged and the fuel cap on top of the tank siphoning fuel? That doesn't fit with Occam's Razor does it?


Oh, Occam!

The 90gallon Comanche, post 1960 I think, has 4 tanks standard. The two inboard are the mains 30gallon each, the two outboards are the aux 15gallons each. All of those tanks have bladders, and are vented out the front/lower of the wing. The vents icing over was a problem in the early models, so the vent design was changed.

Then there are the tips which are aftermarket, without bladders.

 

[dtuuri]

The 90gallon Comanche, post 1960 I think, has 4 tanks standard. The two inboard are the mains 30gallon each, the two outboards are the aux 15gallons each. All of those tanks have bladders, and are vented out the front/lower of the wing. The vents icing over was a problem in the early models, so the vent design was changed.

All very nice, but he also said, "So....BEWARE....a PA-30 (corrected/Edit) can vent when you switch from mains, to tips and back to mains and then you'll have an interesting descent from 7000 ft and 14 miles away."

 

[Chip Sylverne]

The quote was "he switched to outside tanks, that would be aux in my experience". In my experience, flying my buddy's 260B with tips, aux tanks are the 15 gallon. Tips are the tens and referred to as such.
So a semantic difference.

However, I still fail to see how this could be, without it being common knowledge among Comanche owners. I just messaged my friend with a single with tips. Never heard of it happening that way, and he switches from tips to mains all the time. You can can't set it back down with full tips due to the weight of the fuel.

Not saying it didn't, just trying to understand it.

 

[hindsight2020]

He said he switched to the "outside tanks". That would be "tips", IME. To do what you say, wouldn't both the vent have to be clogged and the fuel cap on top of the tank siphoning fuel? That doesn't fit with Occam's Razor does it?


Oh, Occam!

no not tips, aux, as i said. theres plenty on ICS regarding bad caps and bad vents siphoning auxes and collapsing bladders. also a well established scenario where the tips flow overboard thru the auxes when the solenoid leaks, for those airplanes so equipped. i merely mentioned it appeared to me to be a case of the former not the latter.

As to occam, haha let it go brother, it's just the internet. my opinion on the king air crash is just that.

 

[schmookeeg]

Glad I never experienced that in our PA30. That sounds like a shedload of work on an approach to boot. I'm not sure I could've managed that all in IMC, that's hairy.

If the FAA inspectors did anything but offer to build a statue to your airmanship with public funds, F those guys. I assume you opened up the fuel caps and gave them a "voila" so they could put their nooses away.

The owner may be receiving an unamused letter soon, and possibly his mechanic.

 

[dtuuri]

The quote was "he switched to outside tanks, that would be aux in my experience". In my experience, flying my buddy's 260B with tips, aux tanks are the 15 gallon. Tips are the tens and referred to as such.
So a semantic difference.

Actually a punctuation difference. Allow me to correct: "The quote was 'he switched to outside tanks,' that would be aux in my experience".

As to occam, haha let it go brother, it's just the internet. my opinion on the king air crash is just that.

Heh, heh, take no offense. The irony of you casting poor Occam in the dumpster to make a point simply poised itself over the net for someone to slam dunk it. Sometimes I just have no impulse control.

 

[dtuuri]

no not tips, aux, as i said. theres plenty on ICS regarding bad caps and bad vents siphoning auxes and collapsing bladders. also a well established scenario where the tips flow overboard thru the auxes when the solenoid leaks, for those airplanes so equipped. i merely mentioned it appeared to me to be a case of the former not the latter.

Well, the OP never went to AUX at all, so that can't be it. [EDIT: The handle would be in AUX, but the tip switch would draw from the tip tank.] As to the ICS, it's like shopping at TJ-Max. Some articles have value and others are pure garbage depending on who submitted it. Automotive bucket seats and vacuum cleaner parts for your fuel pumps seem to come to mind.

 

[CobraDriver]

Glad I never experienced that in our PA30. That sounds like a shedload of work on an approach to boot. I'm not sure I could've managed that all in IMC, that's hairy.

If the FAA inspectors did anything but offer to build a statue to your airmanship with public funds, F those guys. I assume you opened up the fuel caps and gave them a "voila" so they could put their nooses away.

The owner may be receiving an unamused letter soon, and possibly his mechanic.

I wasn't wearing a scarf with my hands on hips and chest into the wind that day For a few minutes I thought it was over...if you look at the chart I posted from the flight my airspeed went from 240 to 96 and everywhere in between during the ordeal. I had my hands full and ATC wanted to put me on an approach in the opposite direction from the airport. I requested a direct vector and Prayed to God that I would punch thru the clouds and see the airport. Around 1500 ft and about 2 miles away I saw the runway popping thru and I was on a left downwind at that point.I nosed it over and dove into my base leg...on final I lowered the gear, got it dirty and got it down on the runway.

There are many details I have left out but only because my point was to advise of what can happen and to be aware. I had prolly 30 hrs in that type aircraft. I have around 1200 in an Aztec but always flew that with a crew of 2 in the northeast doing cargo runs and check runs to the Fed Deposit in Utica then on to Teterboro for 800 lbs of newspapers I delivered to Buffalo. This flight I was alone, in the soup and not very happy to be there but extremely happy when it was over.

And yes the FAA was worthless with all this. When the refueler was out there I asked him to be exact in his numbers. He said I had 1.6 gallons in 1 tank and 1.4 in the other. The FAA was standing right there for all of this and had nothing to say or help me with any of this.

I have seen there are many experts on here, and I mean that sincerely, that have a hellll of alot more answers to this issue than I have ever heard before. My buddy with 27,000 hrs was very casual about the whole thing but then again he was flying Israeli aircraft as a Warrant Officer back in the day whilst he was in the US Army. Now explain that one to me

Take Care and be safe

 

[hindsight2020]

I wasn't wearing a scarf with my hands on hips and chest into the wind that day For a few minutes I thought it was over...if you look at the chart I posted from the flight my airspeed went from 240 to 96 and everywhere in between during the ordeal. I had my hands full and ATC wanted to put me on an approach in the opposite direction from the airport. I requested a direct vector and Prayed to God that I would punch thru the clouds and see the airport. Around 1500 ft and about 2 miles away I saw the runway popping thru and I was on a left downwind at that point.I nosed it over and dove into my base leg...on final I lowered the gear, got it dirty and got it down on the runway.

There are many details I have left out but only because my point was to advise of what can happen and to be aware. I had prolly 30 hrs in that type aircraft. I have around 1200 in an Aztec but always flew that with a crew of 2 in the northeast doing cargo runs and check runs to the Fed Deposit in Utica then on to Teterboro for 800 lbs of newspapers I delivered to Buffalo. This flight I was alone, in the soup and not very happy to be there but extremely happy when it was over.

And yes the FAA was worthless with all this. When the refueler was out there I asked him to be exact in his numbers. He said I had 1.6 gallons in 1 tank and 1.4 in the other. The FAA was standing right there for all of this and had nothing to say or help me with any of this.

I have seen there are many experts on here, and I mean that sincerely, that have a hellll of alot more answers to this issue than I have ever heard before. My buddy with 27,000 hrs was very casual about the whole thing but then again he was flying Israeli aircraft as a Warrant Officer back in the day whilst he was in the US Army. Now explain that one to me

Take Care and be safe

I think maybe jest doesn't come across clearly in written form so forgive me if I'm misunderstanding your position, but I don't get why you seem puzzled about the whole thing. It's not complicated. Your auxes siphoned overboard, and tank switching to the mains had nothing to do with it. As the auxes vented off the airplane, you never had the benefit of their use and your range was significantly reduced. You had to run on the main tanks' existing capacity only and as you point out, you almost didn't make it on such reduced fuel load. Kudos on keeping your cool, but you got lucky wrt making it to the runway before the engines didn't re-catch anymore.

As to being aloof of the fuel loss, that's the real lesson learned, and what will ruffle feathers around here. Again, that's a function of the craptastic fuel indicator setups some of these ancient contraptions have. In the stock comanche's case, you have to select the tank in order for the analog indicator on the panel to give you a reading. Good bad or indifferent, that creates a scenario where these multiple tank setups without dedicated indicators being out of sight out of mind, can siphon off without nary a peep from the aloof pilot.

Of course, these days people who are that upset about the inconvenience go on to slap those CGR units or whatever they're called, and now have full time indicators. Which presumably would have alerted to the fact you were p!ssing your auxes overboard, making you land immediately upon recognition of the leak, instead of attempting to complete a flight and wondering why you're coughing engines on final.

That airplane had crappy mx. Two plugged tanks and/or caps is indicative of economics-driven pencil whipping, which comanches (and twincos to boot) are certainly not immune from (and I'm being euphemistic).

 

[CobraDriver]

I think maybe jest doesn't come across clearly in written form so forgive me if I'm misunderstanding your position, but I don't get why you seem puzzled about the whole thing. It's not complicated. Your auxes siphoned overboard, and tank switching to the mains had nothing to do with it.

Ok see, this whole time WE ALL thought the entire system was venting fuel....you are saying it was just the AUX and I still had fuel and was flying off my mains!

Got it and thank you for that. I will share that point with other folks that would be interested in knowing that around here.

 

[hindsight2020]

Ok see, this whole time WE ALL thought the entire system was venting fuel....you are saying it was just the AUX and I still had fuel and was flying off my mains!

Got it and thank you for that. I will share that point with other folks that would be interested in knowing that around here.

Well you were flying, not me. I'm saying that based on your anecdote.

 

[dtuuri]

Well, if you followed tank switching protocol you turned the handle to Aux then hit the switch to Tip in order to empty the tips first. You said you went back to mains because the engine quit and then you ran out of gas on the mains. Am I correct? If so, the status of the Auxes is moot, other than that you could have used the fuel in them and the tips once the air bled out of the lines which happened because you forgot to purge them on preflight, right?

Even if the auxes and tips all ran dry — you said you only had a two hour flight. That's only about 30 gallons worth. You would have another 30 left as reserve in the mains even if you stayed on mains for the whole trip. So, did you have full or a substantial amount of fuel in the auxes and tips after landing? If yes, you could have burned it. If no, due to a venting problem, it wouldn't affect the fuel delivery from the main tanks anyway even if it all blew overboard on both wings (not very likely, see Occam).

What did a mechanic do to correct the problem?

 

[dtuuri]

Here's the schematic:

 

[Brad Smith]

My instructor used to say, “Never trust a fuel gage, but always monitor it.” Sage advise for those that follow it.

 

[Kristin]

It is hard to say what the cause was with any certainty from the description of what happened. I haven't a clue as to what the OP's friend meant by "venting". I would need more of an explanation of what that person thought was happening. Having a passing acquaintanceship with the Twin Comanches, I have never heard anything like this. I would seriously have to wonder if the aux tanks really had any fuel in them to start with. I have had the experience of asking the FBO to top all tanks and come out to find that some were missed entirely. I learned to supervise personally from that. That airplane merits some troubleshooting by someone who knows something about Twin Comanches.

All that being said, good job in handling the situation and landing safely.

 

[dtuuri]

Ok see, this whole time WE ALL thought the entire system was venting fuel....you are saying it was just the AUX and I still had fuel and was flying off my mains!

Here's what I think (sorry you had to use your superior skill to overcome lack of knowledge of the system, if I'm correct ):

1. You leveled off at 7,000' and turned to Aux and switched to Tips (as you should).
2. The engine quit because you didn't purge air from the line during preflight (as you should have done).
3. You unswitched from the Tip position to keep the engine(s) running (good move).
4. But you left the lever(s) in Aux (15 gallons each capacity) rather than turn to Main (30 gallons each capacity).
5. After about two hours at about 15 gph, the engines started to die as you burned off the last of the fuel in the Aux tanks, but with you thinking you were back on Mains.
6. The reason the engines kept dying and restarting is due to the descent attitude — aux tanks are only to be used in level flight, not climbs or descents.
​

If this is correct, then now you know more about the system. If not, then please post what the mechanic found and did to correct the problem. Many here, me included, have a fondness for Twinkies and need to learn more about what actually happened to you that day.

 

[Chip Sylverne]

All that tells me is the OP would have missed the most basic engine out procedure...switch tanks. Visually confirming the fuel selector would tell him if he were on aux or main. That also should be on the pre-landing checklist. (Not that running that would have been foremost in his mind at the time.)

If the 1.4 and 1.6 were all that was remaining in 2 hours out of 6 full, and that was in the mains, and the caps were on and tight, this is a mystery indeed. Should be a lot of blue staining somewhere.

 

[CobraDriver]

All that tells me is the OP would have missed the most basic engine out procedure...switch tanks. Visually confirming the fuel selector would tell him if he were on aux or main. That also should be on the pre-landing checklist. (Not that running that would have been foremost in his mind at the time.)

If the 1.4 and 1.6 were all that was remaining in 2 hours out of 6 full, and that was in the mains, and the caps were on and tight, this is a mystery indeed. Should be a lot of blue staining somewhere.

I could not have switched tanks sine the outboard were the ones causing problems and I ran out on the mains. And yes a mystery indeed.

My reason for posting this IS the mystery. I had no confirmation from the FAA, from the owner or from other sites I posted on.

As a matter of fact, a couple months ago there was an accident that involved with that type airplane, I called the local FSDO off the news reports I saw and shared my story, told them to call the guy that did my investigation and I never heard anything back from those guys either.

My whole point to this post was simple, be careful what happens when you go from mains to tips in a twin Comanche. That flight right there was the last time I flew THAT plane and ANY Comanche. I will never fly another again, and I love PIPER aircraft. It's what I grew up in.

 

[hindsight2020]

For clarity, let's make sure we are making a distinction between tip tanks and auxiliary tanks. They're not the same. Not all comanches have been outfitted with tip tanks, but all post (61?) comanches 250 and higher have 4 internal tanks, called mains and aux, for a total usable capacity of 86 gallons. "Outboard" is a common term people use for the auxes, but "tips" and "auxes" are specifically different tanks wrt comanches.

From my read of your anecdote, seems you attempted to feed from the AUXES and couldn't because they were plugged and venting overboard. So you flew the rest of the trip on mains only (28 usable per side) and ran out of gas pretty much on final. I see no mention of tip tanks being a relevant issue here, nor do I really understand from your anecdote if the twinco in question even had tip tanks installed in the first place, considering the loose/alternating use of the term tips, outboard, and aux on here.

There is a plumbing interaction between aux and tip tanks; they share a manifold to the fuel selector. Mains do not interact with the plumbing of the auxes and tip tanks. To be clear, main tanks can suffer the same venting problem as auxes, it's just that auxes are typically underutilized/frequently flown empty and they crud up the flexible vent attachments, or caps rust out. Mains generally exhibit more resiliency by virtue of common use and fuel saturation.

 

[CobraDriver]

For clarity, let's make sure we are making a distinction between tip tanks and auxiliary tanks. They're not the same. Not all comanches have been outfitted with tip tanks, but all post (61?) comanches 250 and higher have 4 internal tanks, called mains and aux, for a total usable capacity of 86 gallons. "Outboard" is a common term people use for the auxes, but "tips" and "auxes" are specifically different tanks wrt comanches.

From my read of your anecdote, seems you attempted to feed from the AUXES and couldn't because they were plugged and venting overboard. So you flew the rest of the trip on mains only (28 usable per side) and ran out of gas pretty much on final. I see no mention of tip tanks being a relevant issue here, nor do I really understand from your anecdote if the twinco in question even had tip tanks installed in the first place, considering the loose/alternating use of the term tips, outboard, and aux on here.

There is a plumbing interaction between aux and tip tanks; they share a manifold to the fuel selector. Mains do not interact with the plumbing of the auxes and tip tanks. To be clear, main tanks can suffer the same venting problem as auxes, it's just that auxes are typically underutilized/frequently flown empty and they crud up the flexible vent attachments, or caps rust out. Mains generally exhibit more resiliency by virtue of common use and fuel saturation.

They were aux tanks if I rem correctly yes. The tips make "an extension " to the entire wing system and this aircraft did not have that

 

[EdFred]

So you wont even fly a Comanche with manual fuel selectors ?

Let me find the knife for your nose...

 

[CobraDriver]

So you wont even fly a Comanche with manual fuel selectors ?

Let me find the knife for your nose...

I'll stick to my lil 172 and BlackHawks and Lakotas...I'm fine right there

 

[EdFred]

I'll stick to my lil 172 and BlackHawks and Lakotas...I'm fine right there

You know that 172's vent fuel too, right?

 

[CobraDriver]

You know that 172's vent fuel too, right?

PU-Lease don't tell me that one!! LOL So far I have nothing but pleasure and amazing flights from my lil D model I flew 0.7 the other day and burned 3.7 gallons and the oil was exactly the same so I am very happy with this lil thing

 

[EdFred]

Any fuel tank is capable of venting/leaking. Usually, easily determined by looking at the wing or the fuel gauges. The Comanche will lose 13gallons from the mains in one trip around the pattern if the fuel door is shut, but the fuel cap is left off. (That's what happens when it is very windy when you are fueling, the fuel cap gets blown off the wing, and the door blows shut.)

 

[Chip Sylverne]

Any fuel tank is capable of venting/leaking. Usually, easily determined by looking at the wing or the fuel gauges. The Comanche will lose 13gallons from the mains in one trip around the pattern if the fuel door is shut, but the fuel cap is left off. (That's what happens when it is very windy when you are fueling, the fuel cap gets blown off the wing, and the door blows shut.)

Pretty good wind if it can blow the door shut and turn the locking tab too.