The Rotax Line Maintenance manual dated 09-20-12, Section 05-10-00, paragraph 2.1 and subject head “Time limit for rubber parts” is the section we will be addressing in this article. There are two important issues here to cover. First is the issue with hose time limits and how long will a rubber hose last? The second and possibly more important is hose selection and the right way to install a hose which is covered in part 2 of this article.
Many of the machines we use now days in a high risk environment have some type of maintenance program the manufacturer wants followed and some are mandatory. Even our automobiles have a recommended hose, serpentine belts and V-belt replacement program. Some owners are good about following these practices and of course we see some autos stranded on the side of the road or even a damaged plane in an off field landing and these folks may not have been as good about their maintenance practices. Even with a good maintenance program mechanical parts and hose can and do fail. The whole idea is to put the odds in our favor and not test the limits.If we are in our auto and have a hose failure we can pull over and call for assistance. If we are flying in our aircraft then a hose failure is probably going to bring you and possibly a loved one down in the worst possible area. Do aircraft hoses fail before their time? Yes they do and have caused many an aircraft emergency. With that in mind many aircraft engine and aircraft manufactures in general have recommended time tables to which they recommend a hose maintenance program which is usually backed up by 20-60 years worth of data and failures not to mention the recommendation right from the hose manufacturer themselves. The bottom line is Rotax and others are trying to error on the side of safety and not test the limits of each hose within the hostile environment in the engine compartment as you are flying over the Grand Canyon. If you are one that says don’t fix it until it breaks then you may be willing to switch sides as you glide down into the Grand Canyon that has no landing areas and a has the fast running Colorado river.
Many aircraft manufacturers now recommend that you follow the Rotax 5 year rubber replacement program. So how long is oil, fuel and coolant hose good for? The answer is, who knows for sure. Could it last only one year before a failure, yes. Could it last ten years before a failure, yes. No one can ever tell you exactly when a hose may fail so we use decades of observance and factor in some safety and make our best guess for you to get to that point and not have an issue. Over the last several years we are seeing a huge increase in owner compliance with the hose replacement program and that’s good news, but too many have had hose particles reaching the carbs and causing a power reduction.
The immediate response has been that it must be bad hose, but in 98% of the cases it has been mechanical damage from poor installation practices and possibly poor hose choices. There have been a few pieces of bad hose and Rotax issued a Service Bulletin for the fuel pump hose because of that very issue, but that is usually very rare compared to the amount of hose actually sold and used. Let’s look at the hose time table for replacement. Many want it to be a condition inspection replacement item. Okay so what are your replacement limits? Is it when the hose gets hard? That’s too late in the game. What about the fuel and oil hose in the fire sleeve? Do you dismantle all that hose and pull it all out of the fire sleeve to inspect it? I know of no one that does that. While you are looking at the outside what about the inside that begins to flake or degrade from time? How do you inspect that? How do you inspect the hose for cracking and separation under the hose clamp at the edge of the fitting on the inside and outside of the hose? (This is the most common problem area.) How many of you have been trained by a hose manufacturer to know even what to look for or were you just taking someone else’s word for your education?
So looking at it from a safety stand point, none of us are hose experts or have all the data the engine and hose manufacturer have so it just makes good common sense to error on the safe and practical side for you and your passenger’s safety. I would like to mention one other item here and look at it from a legal burden which none of us hopes to have to encounter. If you have someone in the plane with you and go down because of a hose failure and it is past the aircraft and engine manufacturers recommend rubber replacement time and the other person or other person’s family member takes you to court I would hope that you can back up all the good solid reasons that you didn’t do the recommended maintenance because it will be brought up and your hose expertisewill come to the forefront. Family members and their lawyers are not very forgiving. That alone is enough to scare me because I have been to those types of court cases for over 30 years. If you error on the right and safe side it is much easier to defend from a legal standpoint.