Should "Check fuel tank breathers are free of obstruction" be part of every daily"?

[ForkTailedDrKiller]

I am posting this in the hope that it might help someone else avoid a potentially dangerous situation.

I had a fuel starvation event in the Bonanza on Monday (don't tell Wally!). As it turned out, it was not a big deal - but it could have been!

I was in cruise at FL150 at the time and just happened to be watching the fuel flow guages when the digital fuel flow numbers started to wind down and the needle on the analogue guage headed north. I barely had time to think "What the @#$%", when the engine died.

I had changed tanks about a minute earlier, but that is just a co-incidence and not relevant to subsequent events - but my hand was already headed for the tank selector when the engine died. A change of fuel tank immediately restored power. I had drained 1.5 hrs of fuel from that tank in 30 min blocks, alternating with the other tank.

My first thought was that I had missed the detent when changing tanks, but I have done 1000+ tank changes in that aeroplane with no problems. My next thought was that I had a leaking fuel tank and had vented fuel overboard leaving an empty tank - but the fuel guages didn't support that. As it was I did drain another 30 min out of the tank which was enough to get me home without having to divert.

As indicated by the title of this thread, the problem was a blocked fuel tank vent. On landing I extracted insectoid material from the vent outlet for that tank with a length of lock wire. I flew the Bo again yesterday and drained 2.5 hrs continuous from that tank with no problems.

I have read about this occuring, but in 30 yrs and 3000+ hrs I have never experienced it before. The fuel being pumped out of a sealed rubber bladder had collapsed the bladder and obstructed the fuel outlet.

I had a hint the previous evening that something was amiss but I didn't pick up on it! When I removed the cap from that tank to refuel after a long flight, air was sucked into the tank! That should have alterted me to the problem.

I religously put the cover on the pitot to keep bugs out but have never paid much attention to the fuel breathers. It is not easy to cover or block off the breathers on the Bo while on the ground.

I now have an additional item for my daily pre-flight inspection.

Dr :8

[goin'flyin]

They are included on our preflight checklist. 'Fuel Tank Vents - CLEAR of OBSTRUCTIONS'
It doesn't take long to have a quick look and keep walking.
And it's much better than giving yourself a heart attack when the engine coughs.

I bet you'll check them from now on after that little scare.

Maybe an additional checklist item should be "Change of Jocks - Onboard":uhoh:

[QSK?]

Thanks Doc for bringing that to my attention.

About 6 months ago, I removed one of the fuel (aux) caps off the Baron and got a a big whoosh of air. At the time I thought 'why did it do that?" and then did not give it another thought. Your article has now alerted me to the potential problem and I will certainly be more vigilent in the future.

[Wanderin_dave]

Had it happen in a Tiger Moth, the non-return breather on top of the tank has corroded closed. Impossible to detect from the outside - short of sticking the gob on it and giving it a blow.

After an engineers inspection it was assumed the engine failure was due to carby ice, i agreed, given the conditions on the day were perfect for it. Of course she started up beautifully after we had opened the tank a few times! Thankfully the owner of the field was nice enough to let us slash a strip and out I flew.........5 mins later........ I learnt a lesson that day :ugh:

The second farmer was just as nice, though she got trucked home.... I walked.

Ironic really, the Tiger's the only aircraft i've flown where checking the breather isn't part of my Pre-Flight, mainly because of accessibility.......it is now.

[rioncentu]

Yes a good lesson.

My vents get mud wasp nests in them but fortunately have an tiny hole further down the line to act as a secondary vent should the main vent be obstructed.

Little bits of fly wire cable tied over the ends of the vents have hopefully solved the problem.

With wet wings I imagine the fuel flow would stop a lot sooner with a blackage than than with the bladders.

[load it, launch it]

Doc,
When i was flying them on charter, the operator i worked for was paranoid about that very incident and included a piece of hose which fitted over the breathers to check the flow by blowing through them and some wire to clean the inevitable build up out.
Glad it all went well
Load it

[Jabawocky]

Fly screen mesh rolled and inserted in the end gives the bugglies nowhere to live and breathes well still.

J:ok:

[VH-XXX]

Similarly, heard recently about a composite aircraft owner had his tanks sealed at the vents by a similar event. Supposedly due to the internal de-pressurisation the tanks delaminated from the external skin. Both of them. Ouch.

[Peter Fanelli]

Fly screen mesh rolled and inserted in the end gives the bugglies nowhere to live and breathes well still.


You got a STC and associated flight manual amendment for that?

I'm from the govt and I'm here to help you.

:=

[Milt]

Fuel Tank Vent Problems

Way back when airliners had props a DC4 Skymaster overnighted at Perth Down Under. Tanks were topped up. Next day was hot and the fuel started dripping out of the wings' integral tank vents. Some non thinking idiot put some bungs in the vents.
Yes - it took to the air with the bungs in place. Result - wing surfaces sucked in and ruined. Powerful suckers are those fuel booster pumps.

Then there was the time we flight testers wanted to force fuel out of a repositioned fuel vent back in the tail of a Canberra to prevent any vented fuel going anywhere near the horizontal stab trim motor. A USAF TP on exchange to the RAAF launched the Canberra out of Darwin for the venting trials not knowing that the convoluted tubing to the new vent was kinked enough to be blocked. To force fuel venting fuel transfer was commenced from the wing integral tanks into the full bladder fuel tank sitting on top of the weapon bay and the control rods to the tail. The bladder fuselage tank became pressurised enough to deform its floor and Jam the rudder and elevator controls.
Ejection was an option but brute strength was just enough to permit a hairy landing and earn a USAF TP a British/Australian Air Force Cross.

[lazysundays]

On a slight side note, plugging up the vents after ditching could help buy you some time - a partially full tank can make a nice pontoon once its sealed up.

[Jabawocky]

PF.... in my case...YES! :p

In yours probably not!

Get some big red pipe cleaners from the local Kindy..... shove them in and remove before flight along with everything else. If you forget them it wont kill you wither!

happy now PF?..... You can shove them up ya nose too!!! :}

J:ok:

Friendly banter PF :ok:

[chimbu warrior]

A known problem with single-engine Cessnas is misalignment of the fuel vents. Location is quite critical, and the tolerance is only about 8mm.

If not installed/aligned correctly, fuel venting can easily occur.

[Tmbstory]

In the 1960's I was returning to base in a C172 when the engine started to splutter. In my quick look around I noticed the left fuel tank drain in the lower surface of the wing going up into the recess. I opened the window and pressed the drain up which let air into the tank, the engine ran and we landed ok. There was quite some distortion in the tank. In those days we used to do aerial photography and so had disconnected the window hinge which allowed the window to float up towards the bottom of the wing, which helped me get to the drain plug.

Regards

Tmb

[RadioSaigon]

Damn fine point FTDK. :ok: Thanks for posting. I've read/heard of similar events in the past.

If memory serves, not all aircraft types have an "external" tank vent. Some (similar with cars, trucks etc.) have vented fuel-caps. A similar situation can arise if those vents should become blocked for any reason or the caps unwittingly be replaced with non-vented caps. Your AFM should have the good oil on that, or have a yarn with your LAME if in doubt.

[PA39]

:\:\We learn by experience (if we live to tell the story). Yes, I too have been guilty of not checking fuel vents on a Rockwell Commander.....same result FTDK. Fuel starvation enroute Canberra to Port Macquarie (during winter). My guardian angel got me into Scone where i found.....yep you guessed it, mud from a wasp nest. From that day after I check vents methodically on the daily. Sometimes the older and more experienced we get the more complacent we become. The coughing and spluttering soon had me dropping the coffee and grabbing switches.

[Aerodynamisist]

FTDK, sir you might want to check your bladders as well, I had a 182 on line that went for a lap with the fuel cap off, which apart from sucking the fuel out - deformed the bladder, thought nothing of it bought a new fuel cap and off we go again for another 100 or so hours, the bladder then fretted against the interior of the wing and had to be replaced. (not a cheep exercise).

[Unhinged]

Should "Check fuel tank breathers are free of obstruction" be part of every daily"?

Interestingly enough ... CAO 20.2 Section 5.3: "The operator and pilot in command must ensure that, before the commencement of each day’s flying, all external fuel tank vents are inspected for freedom from obstruction."

[BULLDOG 248]

AERO's right...Had the same problem with a C206 bladder came unclipped from the top of the wing and in doing so broke the clips off all together. Sure was an expensive exercise...From then on, all fleet had fuel vent covers to go with the pitot covers.

chimbu warrior is also right about the alignment of fuel vents...Can also be the major cause of fuel tanks not feeding evenly to the engine of C150 thru to C182's

[Jabawocky]

Half a chance Forkie still owns some new bladders somewhere:}

[ForkTailedDrKiller]

Have you had the deformed bladder checked?

Yes, my pit crew were doing that today!

Dr :8

[Jabawocky]

Mate you have the slowest Pit crew in Aust..........

Let me see how they compare to mine........................What do you reckon boys??? :ok:

http://file047b.bebo.com/11/large/2009/07/23/12/4525920200a11283359091l.jpg

[BULLDOG 248]

Jabawocky......PAN....F@#K....MAYDAY....your pitcrew look nothing like my set of gorillas??? Trying to post an image but it's all to hard and not worth the quality????? Trust me!!!!:{

[BEACH KING]

I thought you would would have known about the hornets nest in the breather trick Forkie.
I had it drummed into me as part of the preflight during my Bonanza endorsement 17 :( years ago. It's generally the inboard vent (foward facing near the underside wing root) that are the most vunerable to mud wasps and hornets. The phillips screwdriver part of your fuel drain tool fits neatly into the hole to check for obstructions. Out here in the Summer you often find it blocked.

Another hint that you might have a partially blocked vent problem, is to see if the fuel bladder has risen up towards the fuel cap opening, when you refuel. There won't be a big rush of air in when you remove the cap, but the lower part of the fuel bladder will have risen up a bit from the floor where it usually sits.
(I hope that makes sense)
I hope that you don't end up getting a green/blue stain happening on the underside of the wing in the near future. That's often what happens after a scenario like yours.... the bladder starts leaking.

Another place to check for obstructions is in the nose gear well. The exhaust for the Vac pump (it's a pressure system on the Bonanza) exits out here, and if blocked... the pneumatic instruments won't work! It mimics a vac pump failure.. and took us a whole week and 2 new vac pumps to get to the bottom of it!! It turned out that it was simply blocked by a Hornets nest.

[BEACH KING]

Let me see how they compare to mine........................What do you reckon boys??? http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif

http://file047b.bebo.com/11/large/2009/07/23/12/4525920200a11283359091l.jpg
http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/statusicon/user_offline.gif http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/report.gif (http://www.pprune.org/report.php?p=5078359)


So that was why it took you so long to get airborne the other day Jaba.
You need a pit crew to program your Garmin 530 for you.

[Jabawocky]

Don't start me....... they could do better in the intuitive department like they do with other products! :rolleyes:

Lucky I have a Manual on board, apart from the paper one, where you can word search really quickly! :ok:

[Unusual-Attitude]

Little bastards those mud wasps eh! They seem to love the vents on my van for some peculiar reason. I know of at least one case where the wing has 'imploded'...in the states i believe.

He got down ok...but costly!:ooh:

[BEACH KING]

There are a couple of stories in assorted "crash comics", where blocked fuel tank vents have scrunched up the fuel bladder and pulled the metal fuel drain cock out of the bladder on Bonanzas. The fuel drain cock snares on the wing skin.

This instantly fixes the vent problem, but then lets all the fuel out under the wing, where you don't notice it escaping.

Pretty sure it did not end well on a couple of occassions.

[flog]

I blow air into each vent on the Yak every pre-flight.

[sockedunnecessarily]

Just a few points:

1. The blockage should have been removed by an engineer. Removal a fuel vent system blockage does not fall under schedule 8.

2. Any engineer worth 2c would have then done a lot of checks a pilot can't do. This would include checking the bladder for distortion or damage, checking the fuel quantity system and conducting a fuel calibration, draining fuel and checking for contamination in case some of the foreign material entered the fuel before the complete blockage occurred, cleaning the fuel screens/filters and injectors. I can recall at least one PA31 accident where a blocked vent caused bladder deformation and as a result the float fuel quantity system indicated an empty tank to be full. Fuel starvation and fatalities resulted.

3. Composite aircraft with wet wings are another level again. One Australian operator I know of has been cost hundreds of thousands of dollars due to delaminated wings caused by wasp nests in fuel vents.

4. Anyone on here suggesting jamming things in there to stop nests forming is crazy. An engineering order or STC (often a lengthy process) would be required to make it legal. It leaves you in a compromised position if something were to go wrong, not only legally but also with insurance.

5. I also wouldn't go blowing on them. Might end up with a mouthful of fuel for your trouble, or blow contaminants back into the fuel tank. If in doubt, ask a LAME to check it for you.

[ForkTailedDrKiller]

1. The blockage should have been removed by an engineer. Removal a fuel vent system blockage does not fall under schedule 8.

However, in carrying out the requirement of CAO 20.2 Section 5.3 "The operator and pilot in command must ensure that, before the commencement of each day’s flying, all external fuel tank vents are inspected for freedom from obstruction." you are likely to remove the blockage anyway!

2. Any engineer worth 2c would have then done a lot of checks a pilot can't do. This would include checking the bladder for distortion or damage, checking the fuel quantity system and conducting a fuel calibration, draining fuel and checking for contamination in case some of the foreign material entered the fuel before the complete blockage occurred, cleaning the fuel screens/filters and injectors.

In this case - Done! Vents cleaned, bladders checked etc etc. On further reflection, it is unlikely that the bladder was distorted in this case as fuel quantity indications remained normal at all times. More a case of the mechanical fuel pump being unable to pump any more fuel from the "unvented" tank.

5. I also wouldn't go blowing on them. Might end up with a mouthful of fuel for your trouble, or blow contaminants back into the fuel tank. If in doubt, ask a LAME to check it for you.

No - blowing into fuel tank vents does not seem a good idea to me - and difficult to achieve on a Bonanza.

Dr :8