Cessna killer caps, or not?

[Sam Rutherford]

I've been reading on US based forums about the 'extreme dangers' of the Cessna 172 and 182 (and perhaps others) recessed fuel caps allowing water to ingress whilst parked outside. The type where you flick up the little lever, and then turn-open the cap (similar to many Cirrus) - also known as 'lift and turn' I think. Cessna even produce an upgrade kit to save yourself from certain demise.

But, nothing at all here or anywhere else in the UK.

Now, given that rain is not unknown on this fair isle - what's the deal?

Fly safe! Sam.

[Genghis the Engineer]

The deal is that you do a fuel check first flight of the day and after refuelling, and during that make sure you've pulled off any water that got in.

Job done. I recall years ago doing a course in a C150 in Florida where we always had to draw quite a lot of water off each afternoon following the daily thunderstorms. No big deal, and the aeroplanes ran fine.

Aircraft fuel tanks are designed with a sump, which is at the lowest point in the tank and where the drain is, and a draw off that's around half a gallon above that, for exactly these reasons. Unuseable fuel is at the bottom and where the water should settle.

G

[justmaybe]

Same problem arises with the newer model Piper PA28s - the older fuel caps were much more effective at keeping rain water out. Regardless of what caps are fitted, the fuel drain check is a MUST.
Welcome back Genghis!http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/infopop/icons/icon7.gif

[kingmomo]

you make me not want to fly in the cessna 172 now *.* (extreme dangers)

[Tony Mabelis]

My personal experience is that it doesn't rain enough in Jordan to get frightened about.:)

Leaving a fuel cap off on a high wing Cessna, then going flying, can ruin your day just as well.
I've seen a 182 loose half a tank in about 20 minutes, creates a very impressive "contrail".
Tony

[dubbleyew eight]

one of the benefits of 100/130 avgas is that is does not mix with water.

I once took over half an hour to drain all the rainwater out of a Cessna 150's tanks. I took a bit of rocking to persuade the final bits of water into the sump but once done the engine ran just fine. we replaced the caps after that.

you will only ever have problems with fuel and water contamination if you are silly enough to use a fuel with alcohol in it.

[24Carrot]

The deal is that you do a fuel check first flight of the day and after refuelling, and during that make sure you've pulled off any water that got in.

How long after refuelling do you have to wait for the water to settle, so you can remove the water, or at least test for the presence of the first to settle out?

During my PPL I was told there was no point checking if you re-fuelled just before flying. But I have always wondered...

[Genghis the Engineer]

How long after refuelling do you have to wait for the water to settle, so you can remove the water, or at least test for the presence of the first to settle out?

During my PPL I was told there was no point checking if you re-fuelled just before flying. But I have always wondered...

I don't think that I've ever seen a definitive (=actually supported by some research) answer, but 20 minutes is often quoted.

G

[The500man]

I think Lycoming suggest you check the drain before fuelling and not after. It's much more likely that the water was in your tank before you fuelled.

[Cobalt]

It depends on where you re-fuel.

Any aviation refuelling station gets checked daily by drawing off some fuel, and also the tanks are checked after they are refilled from the truck, which in turn gets checked. Little chance of water there.

Hence the simple fact that pretty much nobody waits for 20 minutes and re-checks fuel, and still aircraft do not fall from the skies.

If you refuel from anything else (jerrycans, barrels etc.), or in rain, have a cup of tea before checking.

All the water-in-fuel related accident reports I remember reading were about either suspected ingress through the filler cap, or contamination in fuel provided from places other than aviation fuel stations or professional bowsers.

[hoodie]

"Killer caps"?

Well, are they regularly falling out of the sky due to water contamination?

(Hint: No)

[Big Pistons Forever]

Leaking fuel caps can be an issue on any plane, and there have certainly been many engine failure accidents caused by water in the fuel. While condensation can cause water to be present, a lot of water in a fuel sample is almost certainly due to a leak at either the cap itself or the fuel cap fitting.

One fact that seems to frequently missed at flight schools is the importance of the aircraft attitude when taking a fuel sample from pre 1996 high wing Cessna's.

The fuel drain point will only be the lowest point of the tank if the aircraft is wings level and has a nose up attitude. If it is parked on a slope it may be impossible to properly drain the tank. I highly recommend moving the aircraft to a spot that will cause it to be laterally level anf holding the tail down while sampling the fuel for any plane that has been left outside in the rain.

I once watch a student (not mine) sample the fuel on an airplane parked on a downslope. The sample was clear fuel. However when I held the tail down we got a full sample tube of pure water. :ooh:

[irish seaplane]

Monarch Fuel Caps are an excellent solution to the problem. I think even recessed caps with perfect seals are an imperfect job. The Cessna retrofit kit is good too. Take your pick.

[ericferret]

Genghis

Many light Cessna aircraft e.g 150/152 do not have a sump which always at the low point in the tank . Cessna introduced a mod probably over 20 years ago to increace the number of tank drain points to give a better chance of draining all the water. Few aircraft actually had it embodied.
Strangely the low point on the fuel system on some aircraft has a blanking cap and cannot be sampled from.

Checking the tank cap seals regularly and daily water drains is a must.

Commercial aircraft do not check the tanks for water after every refuel although helicopter pilots when refuelling at an offshore installation are usually shown a fuel sample by the refuelling crew. There have been several incidents where offshore fuel has been found to be contaminated.

For those lucky enough to be operating a gas turbine, Jet fuel also abscorbs water, hence the use of water detecting capsules as well as visual inspection of the drain fuel.

[IFMU]

I have never seen a cessna without a sump, including the older 120/140 series.
Bryan

[Pilot DAR]

As mentioned, the "killer caps" (which is a wholly silly term) are those with the fold down tab. They were the factory arrangement on some Cessnas of 177 and higher numbers, not a 172 or 150/2 that I have ever seen.

There are two short comings of these caps, compared to other simpler ones: There are two O rings which must be maintained. Well meaning maintainers replace the larger outer one, but can miss the inner one. Water will fill the pocket for the folding tab, and run down the tab's shaft into the tank. The other problem can be that a careless fueller can engage only two of the three locking tabs, and the cap does not seal. Though the cap is "on", you can loose 30+ gallons of fuel from the wings of a 177RG in 20 minutes - ask me how I know!

If these caps are well maintained, and properly used, they are perfectly fine. They are the common cap for many larger aircraft, and not subject to ridicule in those installations - probably because of more careful maintenance and use.

As said, if you suspect water in your tanks, drain the sumps (ALL certified aircraft have tank sumps which can be drained) before you move or fuel the aircraft. If you think you need to check for water after you fuel, I would not put that fuel in the plane at all! If you think you need to check for water because you fuelled, you have now missed your opportunity for some time, while the water separates back out of the fuel again. I'd wait half an hour.

I have owned my 150M for 26 years. Never ever have I drained more that about a CC of water from a tank sump. I have drained more from the belly low point, which as mentioned, comes capped, and must have a drain installed - I did. That said, the "gascolator" is down stream of that sump, and should catch water before it goes up to the engine. Of course, drain it preflight.

Know that water in the tanks can also come from condensation inside the tank, and thus have nothing to do with the caps. Leaving the tanks full will prevent this (and is good for bladder tanks).

On the other hand, a 182 I used to fly a lot always drained some water from the tank sumps, so I always checked it.

[ericferret]

I concede on the sump issue I suppose it depends on your definition of sump. I regard a sump as a significant low point in to which all loose water will drain. Cessna having to add 3 extra drain points to their tanks says to me that the "sump" ain't up to much.
I have ammended my post to try and make it read a little better.

Criticism always welcome.

[subsonicsubic]

I rent my aircraft wet. The rubbers on the wing tops are often perished and water / condensation is often present. I pull through until all drain points provide me with pure sweet 100LL. Like I said, I rent wet.

Best,

SSS

PS C152 / 172's :)

[Sigurd]

It's the combination of the leaking caps and wrinkles in the bottom of the bladder tanks that lead to the term "killer caps".
You can check at the sump for contamination all you like, but if there is water trapped at the bottom of the tank by a wrinkle, it is not going to come out...until (e.g.) rotation!

Please see below, an extract of a letter from Cessna Pilots Association. It's specific to c182 but I would assume relevant to all aircraft with bladders prone to wrinkling and leaking fuel caps.


FUEL BLADDERS AND FUEL CAPS
If you fly a 1956 182 thru a 1978 182Q, your airplane uses rubber bladder tanks in each wing. These bladders have a tendency to develop wrinkles along the bottom. The wrinkles act as little dams that can prevent water from moving to the sump drain. You can sump the tanks at pre-flight and see no water, yet water could still be present in your fuel tanks.
To make matters worse, Cessna originally installed flush-style fuel caps on these aircraft. The caps can leak if the aircraft is exposed to moisture. If your fuel caps have a small hinged pull-up handle that fits into a recess in the cap, you have the dangerous fuel caps. At CPA, we call them "killer caps."
There have been a number of engine failures immediately after take-off even though the pilot sumped the tanks thoroughly during pre-flight. Some of these incidents have been fatal. The FAA issued Airworthiness Directive AD 84-10-01 to deal with the problem. It requires inspection of the bladders for wrinkles, and suggests changing the flush-style fuel caps to umbrella-style caps.
If you fly a bladder-equipped 182 that still has flush-style fuel caps, the Cessna Pilots Association strongly urges you to change immediately to either the Cessna umbrella cap (kit SK-182-85 available through any Cessna service center) or the Monarch Development cap sold by Hartwig Aircraft Fuel Cell Repair (phone 800/843-8033 US or 800/665-0236 CAN).
I beg you not to overlook this fuel cap situation on your 182. Accident statistics show that the 182 Skylane has one of the highest rates of accidents caused by fuel contamination and the flush style fuel caps coupled with the bladder fuel tanks are the main cause.

[Sam Rutherford]

I have read that same article - and it's the combination of cap and wrinkles that made me post.

Does sound, though, as if checking the TWO o-rings (and renewing regularly) solves the big problem (water being held by a wrinkle before the drain point).

Fly safe, Sam.

[gasax]

I was going to mention the rubber bladder things but got beaten to it!

As far as separation is concerned however I can add something. In oil and gas processing the rule of thumb to separate oil from water is a residence time of 2 to 3 minutes. Given that we are talking about petrol and water (so less vicous and less dense than crude oil) the separation time will be less than a minute. So as soon as you have put the filling hose away you can use the drain cocks.

A bigger issue than time, is however getting the water to the drain cocks. With wide flat tanks using a natural slope is the obvious solution - but it does mean the aircraft has to be turned around.

[slacktide]

More information on the alleged "killer caps." Also used on Cessna 310, several Beechcraft models, and later Grummans.

CSOBeech - Beechcraft Fuel Caps (http://www.csobeech.com/fuel-caps.html)

[Machinbird]

I would like to commend the points made by Pilot DAR and Sigurd in their prior postings. These are the key issues with water in the fuel that I've experienced while owning two Cessna 210s (1960 and 1970 models).

That small o-ring surrounding the connecting 'bolt' below the flip-up lever has got to be a big part of the problem. Since it is not visible just looking at the cap, it is easily missed.

My second 210 showed me that water in the fuel can be a particular hazard when it gets well below freezing. I had left the fuel valve open intending to help the water get to the low point, for easy sumping. What happened instead is that the electric fuel boost pump was damaged from ice expansion and I lost one tank of fuel!

Fuel systems really are not intended to hold significant water. Boost pump replacement is expensive. Fuel is expensive. Do not let the water get into the system in the first place. Buy the upgrade caps!

[Monocock]

You could always get these little tinkers to hop up and check them for you.:}

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