On the list of aircraft components that can ruin your day, flexible hoses rank pretty high.
Throughout the engine and airframe, these hoses carry hydraulic fluid, oil, fuel, and even air. They perform at pressures ranging from zero to over 2,000 psi (or more) at fluid temperatures that can vary from subzero at startup on the coldest winter day to over 200 degrees Fahrenheit on a hot summer climbout. And, they do all of this in an environment where they are subject to vibration and, in the case of brake hoses, constant flexing and motion.
Having seen many cases of failed hoses that grounded aircraft (or caused unplanned landings), I decided to embark on a complete brake and engine hose update on our Bonanza. Modern hoses have many options to choose from, so I took some time at EAA AirVenture Oshkosh in Wisconsin to meet with Randy Herber, president of Herber Aircraft Service. Herber Aircraft does much more than just aircraft hoses, but hoses are a core competency, and the company is the industry’s go-to for just about any hose question you could have.
There are two basic types of modern flexible hoses for GA aircraft: rubber and Teflon (for the sake of simplicity, we will use Eaton/Aeroquip model numbers, but other manufacturers are similar). Rubber hoses such as Eaton Aeroquip 303 have been around for ages and are the least expensive option. They are usually black with a rubber core, a carbon steel reinforcing braid, and a black nylon outer layer for chafe resistance. They are the least expensive hose option, and they are life limited because they degrade both internally and externally as a result of age and heat exposure. Rubber hoses should be replaced every five years and inspected carefully for signs of failure as they age.
Teflon hoses, on the other hand, are considered “lifetime hoses” because they are not expected to fail internally simply as a result of time in service (TIS). Teflon hoses such as 666 (medium pressure) or AE246 (high pressure) are composed of a blue Teflon inner hose, coated with a black lining to provide electrical conductivity between the end fittings. They are wrapped in stainless steel (versus carbon steel), and use stainless fittings as well. The durability of the Teflon, coupled with the corrosion resistance of the stainless wrap and stainless fittings, provides the “lifetime” of service that these hoses are known for. That said, the concept of “lifetime” is a bit of a misnomer because even Teflon hoses must be routinely inspected for damage caused by mishandling, wear, or other issues.
When using hoses in the engine compartment, it’s imperative to protect against fire in the case of a hose failure. This is where the “firesleeve” comes in. The FAA requires an additional layer of protection around hoses designed to contain flammable fluids in the event of a hose failure. The most common form of firesleeve is the orange sleeving that is commonly applied over hoses, using crimped steel bands at each end. Teflon hoses, on the other hand, offer an upgrade to molded-on integral silicone firesleeves that are attractive and easy to clean. They are available in brown or blue and really spruce up an engine.
Randy Herber knows hoses like no one else, so I asked him for a list of things that every owner should know:
Too many aircraft in the GA fleet are flying with decades-old brake, fuel, and oil hoses. It’s a recipe for disaster that’s easily remedied. If you’re curious about the age of your hoses, just check the tags. Every hose has a data tag that includes the part number, parts manufacturer approval information, and the date of manufacture. Just a few minutes of inspection will give you either piece of mind or a new project to tackle. If you have questions, contact a hose expert such as Herber Aircraft to get answers and make decisions that are right for you. Until next time, I hope you and your families remain safe and healthy, and I wish you blue skies.