I knew it as soon as I saw the telltale stripes of blue dye on the metal fairing covering the gap between the bottom of the right wing and the fuselage. A leaking fuel bladder.
I recalled from my days as a tech rep that the most common failure of a light airplane fuel bladder is age-related deterioration of the top surface due to long-term exposure to heat. When I began to get a good whiff of fuel after filling the right main of 7 Lima Juliet, my 1966 Cessna 182J, I knew it was bladder time.
Some Cessna owners “solve” this tank porosity problem by never completely filling the tank, thereby eliminating the fuel smell. This not only renders the airplane officially unairworthy, it’s dangerous.
According to Bill Thompson, author of Cessna Wings for the World and longtime Cessna test pilot, Cessna chose bladder tanks over integral tanks to decrease the likelihood of fire in the event of a crash. Flying an aircraft with a weakened bladder negates this safety feature.
Prior to putting down my money on 7LJ, I contacted the FAA Registry office and asked for copies of the aircraft registration and aircraft maintenance records. Two CDs at a total cost of $10 arrived in a few days.
The registration records showed that 7LJ had been based in Albuquerque, N.M. for at least 20 years. That hot, dry climate went a long way in allaying my concerns about corrosion in the airframe.
Due to a spate of less-than-stellar logbook maintenance records that referred to the shop work order numbers in lieu of actually describing the work done, I wasn’t able to accurately determine the age or type of the installed bladders. But the right one was leaking and it did have to be changed.
Repair, send out, or replace
Theoretically, it’s physically and materially possible to field repair a bladder given enough time, diligence and discipline.
The early Cessna 100 series and 200 series service manuals do contain parts and procedure information for field repairing leaking fuel tanks. However, I’ve never seen this done nor was I able to find any information about the repair kits and adhesives referred to in the manuals.
If an owner came to me asking me to help him repair a bladder tank or approve a field repair of a bladder tank I’d say no because I don’t believe the parts are available nor is the data sufficient to ensure a safe field repair.
Before choosing the option to send out for repair or install new, the leaking bladder must be inspected to determine the best course of action. The first step is to know which bladder your aircraft uses. Cessna service manuals refer to BTC-39 cells by Goodyear and US-907, US-943 and US-932 bladders by U.S. Rubber.
The three biggest light aircraft fuel bladder companies today are Aero-Tech Services in Santa Fe Springs, Calif., Eagle Fuel Cells in Eagle River, Wis., and Floats & Fuel Cells (FFC) in Memphis, Tenn. Eagle Fuel Cells and Floats & Fuel Cells are CFA supporters. According to information on both Eagle’s and FFC’s websites, only the US-943 is a candidate for repair. The other two U.S. Rubber types aren’t mentioned. The BTC-39 bladder can’t be repaired and must be inspected every 100 hours for leakage in accordance with AD 78-05-06 until it’s removed from service.
After checking for the type of bladder in my airplane, I knew it wasn’t a candidate for repair, but repair can be an affordable option for some leaking bladders. All of the major bladder repair companies offer a “test and advise” option that clarifies the repair/new decision.
I spoke with Aaron McCloskey, the senior sales representative at FFC who said that the repair cost for most tanks is between $200 and $400. McCloskey said that repair is a good option since even the most extensive repair is less than half the cost of buying a new tank.
During repair new nipples are installed and repaired tanks are guaranteed for two years. If time is critical, providers offer repaired bladders on an exchange basis.
The bladder I purchased was a much smoother and a much more flexible tank than the removed tank, which was stiff and felt semi-rigid by comparison. Included with the new bladder was an installation kit that included all new clips, a roll of bay tape—applied inside the tank bay prior to tank installation to cushion any wear points—cork gaskets and nipple clamps. All of the providers include installation kits.
Tank removal and installation
After draining all the fuel from the right tank I started preparing the bladder for removal. Eagle Fuel Cells’ notes recommend grounding the airframe to lessen the possibility of generating a static electricity-generated fire.
I did have some difficulty loosening the nipples connecting the tank to the fuel outlet and the fuel cell vent. The Hints page of the Eagle Fuel Cells website suggests loosening all clamps and waiting to let the rubber relax. Then the rubber of each nipple can be softened by wrapping it in a towel or rag that’s been dipped in hot water.
Since I was installing a new bladder I cut one side of each nipple on the old bladder and shot a little bit of LPS-1 into the cut; that helped release the tubing. (Any penetrant type lubricant will do.)
After removing the screws holding the filler neck plate in place and setting it aside, I worked through the access hole to remove the fuel tank air vent valve. I also had to remove the tank sump quick drain fittings and the fuel quantity transmitter and float. Then I used a mirror and flashlight to make sure I had freed all the clips holding the top—and the bottom—corners of the tank in position before removing the bladder.
Cushioning the edges of the access hole with tape lessens the chances of damaging the bladder during removal (and installation) and reduces the amount of skin rubbed raw while working through the hole.
After all the nipples were free and all the hangar clips were removed, I rolled the tank into a tube and slid it out the hole in the top of the wing. Prior to installing the new tank I spent quite a bit of time cleaning the bay to remove any fuel stains and dirt. Then I renewed the bay tape where necessary.
Installation of the tank was pretty easy. The only real glitch involved sliding the vent tube onto its nipple. Next time, I’ll polish the outside surface of each tube with a scouring pad and lube the tube with a little light oil to lessen friction.
I used a small block of wood as a pusher to get enough push to drive home one of the snaps located at the end of my reach. Long, strong arms are required.
The fuel vent valve must be reinstalled with the hinge line up. These vents have “top” etched into the valve body.
The Eagle website contains a long list of hints to make installation and removal easier, and I can tell you that making the bladder more flexible by heating it is a help. Flipping the bladder to expose the top and bottom surfaces while it’s spread out in sunlight on the top of the wing is an easy, safe, no-cost—and “green”—heating method.
McCloskey said that some installers tape a pad onto the end of a broomstick or dowel and use it to push the bladder into position in the corners of the tank bay.
The torque specs for the 10-32 and ¼-28 screws and bolts used to complete the installation were printed on the bladder and are on the suppliers’ websites.
Collapsed fuel bladders
Collapsed fuel bladders have caused many incidents and a few accidents due to restricted fuel flow or to fuel exhaustion because a partially collapsed tank appears from the filler opening and on the gauge to be full of fuel, but in reality contains much less.
Tanks collapse because the air vent valve tubes and vents get plugged by insects or dirt and dust. This stops the flow of air into the tanks that’s needed to offset the vacuum created as fuel flows out of the tank during flight. Put your ear down by the filler cap and open it. If you hear an inrush of air it’s a signal that the vent system is blocked. Don’t fly again until the blockage is opened.
When vents are blocked it’s not unusual for the floor of the bladder to be pulled up. If the pulled up section is near the wing root the float part of the fuel level sensor will also be pulled up, and the fuel gauge readings will be wrong.
One simple tool that every Cessna owner should use before every flight is a fuel quantity dipstick—it’s a surefire way to determine if the floor of the bladder is out of position and to determine the actual fuel level in bladder tanks. When fuel starvation shuts down an engine, the silence is mighty loud. Using a fuel level dipstick will lessen the possibility of ever hearing that silence.
Cool bladder tanks live longer
The keys to getting great bladder service life start with the installation. Experienced and diligent first time installers must strive to achieve a tank installation where the tank bay is clean and prepped to provide an abrasion-free home for the bladder; where steps are taken to insure that any wrinkles in the bladder’s bottom surface are minimized and where the nipples aren’t pulled out of position or stretched during installation.
After the bladder is in and is deemed ready, I like to fill the tank in five-gallon steps—with the airplane on level ground and the landing gear struts and tires at normal inflation—for two reasons. This is the perfect time to make up a fuel tank quantity dipstick (I know I sound like a dipstick salesman, but they work and they are a simple safety tool) and to make sure you know exactly how much fuel your new bladder holds. It’s not unusual for the actual fuel capacity of a bladder and the capacity written in the owner’s manual or the aircraft flight manual (AFM) to differ.
A new bladder should provide good service for at least 20 years and much longer if you take steps to keep the top surface of the bladder cool. Shade the top surface of the wings whenever possible and strive to top off the fuel tanks after each flight since the fuel will moderate bladder surface temperatures by acting as a heat sink. Hangaring an aircraft is the most effective method for preserving its fuel bladders.
When you smell fuel outside the airplane for an hour or two after topping off the fuel but not when the fuel level is down, the most likely cause is age-related deterioration of the top of your bladder. If replacing the gaskets on the filler plate and quantity transmitter don’t solve the problem, it’s bladder time.
New bladders cost between $800 and $1,000 apiece; refurbishing costs one-quarter to half as much as new. Removal and replacement labor usually runs between 10 and 12 hours.
Removing and replacing a bladder is not a difficult process. It can be a way to cut back on labor costs if an owner/pilot is comfortable in their technical abilities and savvy about working on one of the most important systems on their Cessna. Check with your mechanic to see if he or she is willing to supervise as you take on the through-the-hole job of bladder R&R.
Steve Ells has been an A&P/IA for 39 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation and lives in Paso Robles, Calif. with his wife Audrey. Send questions and comments to .
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