Firesleeve is cut too short Firesleeve needs to be cut longer than the hose. The longer the hose, or the tighter the firesleeve, the longer it needs to be. Firesleeve cut too short will pull back from the fitting when the hose is bent. This exposes the fitting. In a fire the fitting is the weak point and needs to be fully protected. Such a hose no longer meets its fire rating and should be fixed or removed from the aircraft. Nut and nipple assembly not fully screwed into socket If you don't have the correct tools, it can be hard to get the nut and nipple screwed together to the correct gap - especially if you stop turning halfway on. If you leave too much gap the fitting doesn't fully grip the hose. Either get the correct tools or have someone who does fabricate your hoses. If you inspect hoses and you see one with excessive gap, then red tag the hose - it's not airworthy. Rubber flap cut into hose inner tube The hose nipple is larger than the hose inner tube. As you screw the nipple into the hose a bulge is formed in front of the nipple. The mandrel is used to compress the bulge. The two critical elements are the mandrel diameter and the speed at which you turn the nipple, as the bulge must move forward in front of the nipple. Hand mandrels are undersized and therefore tend to cut flaps. A proper sized mandrel is only 1 to 2 thousands smaller than the inside diameter of a new nipple. Hand mandrels are usually 10 to 15 thousands smaller. You must be able to inspect the inside of the hose - either by sighting down the hose or dropping a sized ball through the hose. Socket backed out of hose during nipple-nut assembly When screwing the socket onto 303 or Mil-H-8794 hose, you must stop immediately when the socket bottoms out on the end of the hose. If you keep turning the threads, the socket pressed into the hose cover is stripped. This is the most common reason for this type of hose blowing the fitting off the end of the hose. This is common if you turn the socket with a wrench or a machine where you can't feel the hose bottoming in the socket. Not pressure testing hose after assembly Hoses do fail the pressure test occasionally. If you don't pressure test them on the bench, then the first pressure test is during use. On an aircraft this is the first take-off. Socket turned too far during installation Socket turns on hose when screwing nut-nipple assembly The hose is ruined if the socket turns or even starts to turn when screwing the nut-nipple assembly onto the hose. During a pressure test the fitting will blow off the end of the hose at a low pressure rating. You can't save it - start over. Collapsed inner tube from improper assembly Excessive friction between the hose nipple and hose inner-liner has torn the inner-liner loose from the hose. This can be caused from using an undersized mandrel. An undersized mandrel doesn't compress the hose ID sufficiently, creating excessive friction between the nipple and inner-liner. If you hear crackling noise as you screw the hose together, then you are ripping the inner-liner away from the hose and the hose is ruined.

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We highly recommend having an FAA approved hose shop fabricate all hose assemblies. When you receive a completed hose from and authorized fabricator, the hose has been through all of the pertinent inspections, tests and all proper assembly tooling was utilized in the fabrication process. This is the best way of determining you have an airworthy hose assembly and it will be tagged as such. This also transfers the liability of the hose assembly from the owner/mechanic to the hose manufacturer. If you decide to assemble your own hoses or have them assembled by a mechanic, the following are guidelines for common mistakes to avoid.