As airplanes and engines attain age, there appears to be a need to reemphasize the inspection or replacement of engine hoses or lines carrying fuel, oil, or hydraulic fluid. The hose manufacturers definitely recommend regular inspection and replacement of all such hoses at engine overhaul even though they look good.
Age limit of rubber-steel or fiber banded hose has generally been established at four years. This limit of four years is generally considered to be "shelf" life. All hose manufactured for aircraft use is marked indicating the quarter year in which it was manufactured. The listing "4Q92" means the hose was manufactured in the fourth quarter of 1992. Maintenance personnel should not use hoses with a high "shelf" life age.
To eliminate relatively short "shelf" life limits, Textron Lycoming has phased in Teflon hoses with silicone coated fire sleeves. These are the only hoses which are available for field replacement, and they will be found on engines shipped from the factory
Service Instruction No. 1274 lists the fuel and oil hoses used by Textron Lycoming. It also explains how the numbering system defines hose size. This instruction should be used as a reference anytime hoses are to be replaced.
Textron Lycoming Service Bulletin No. 509 must also be complied with if rubber hose is used to carry low-lead aviation gasoline. Aeroquip, the manufacturer of hose used by Textron Lycoming, has recorded several failures of 601-type rubber hose. Although it is satisfactory for other purposes, this hose appears to be adversely affected by low-lead aviation gasoline. 601-type rubber hose used for low-lead aviation gasoline is to be replaced after no more than two years of use. Aeroquip and Textron Lycoming recommend that rubber hose be replaced with Teflon hose. Teflon hose is normally unaffected by many of the operating variables that contribute to rubber hose degradation.