Servicing and installing fuel cells is a time-consuming job that takes patience and attention to detail. According to representatives at the factory, some installers aren’t following the maintenance manual guidance carefully, or they aren’t being thorough enough during the process.
The manual calls for a process where the bay is fully cleaned and all sharp edges and protrusions are rounded and taped. The fuel cell is then folded up, put in the bay, and fasteners are installed. It sounds straightforward, and it is, but as always the details matter. Aero Air Service Center Manager Andre Pridgen has dozens of tips to help make sure the process results in zero leaks for Aero Air or customer airplanes. He said he gets one or two calls a month from someone who has a fuel leak, and often those leaks begin soon after maintenance. Many of those issues may have been prevented with a proper leak check before the airplane left the shop. But some leaks are slower, and will only show up later.
The process begins with a clean bay. Because many cells are being installed after maintenance in the bay, Pridgen recommends taking the time to thoroughly clean the bay and make sure it is completely free of metal shavings, stray wires, and other objects. Then the prep work starts. Aero Air goes beyond the manual and adds a non-melting foam to the floor of the bay between the stringers to give the entire area a flat bottom. Then everything with a sharp edge, including all rivets, screws, and stringers gets fuel cell tape. He said the close-out panel is a common spot many technicians miss. He or another supervisor inspect each bay before the cell is installed.
Once the bay is prepared the bladder is ready to be installed. The factory cautions against using a knife or box cutter to open the shipping box. Although they ship the cells with a protective flap under the tape, some have come back with clean knife cuts that most likely came from opening the box.
Installing the bladder is pretty straightforward. Pridgen recommends leaving the new bladder folded. Then he rolls it up, puts it in the hole where, generally, it unrolls by itself to fill the space.
Next the transfer tubes must be connected. This is a tricky job and each technician has his or her own technique. Pridgen cautions using coat hangers or other “sticks” that could cause damage. “Poking holes is a bad idea,” he said. Instead, Pridgen said that Royco makes an acryloid synthetic assembly fluid and O-ring lubricant, part number HF-825, that will make the couplings slide together without effort.
To ensure things don’t leak, Aero Air adds an additional clamp at 90 degrees. They then go through and double check each clamp a few hours later after things have had a chance to settle. Once everything is closed up and ready to go, they top the wing with fuel and check for leaks. If you find a leak, and find the bottom of the bay is wet, you have to keep working outboard. Eventually you should come to a cell that is wet near the top, and that’s the culprit. This is especially true if the cell was punctured by a bent or damaged lacing hanger when it was being closed.
By double checking at various times in the process, following proper procedures, and employing a few tricks, fuel cell installs can be much more reliable.
