Some Practical Hints on Preservation of Aircraft Engines Using a Rig from Corrosion Problems

Abstract

Aircrafts need to be grounded for want of routine scheduled maintenance and inspection after certain period of flying hours. During such maintenance practices, the turbo-propeller engines are kept dismantled, un- installed and non-operative conditions for a longer period even up to two years. During this non-operative period, the engines and components are susceptible to extensive chronic corrosion hazards. To prevent this hazard, the engines and components are required to be preserved both internally and externally from corrosion that is the engine components such as turbine, turbine blades, compressor, fuel nozzles, fuel system pipelines, diffuser, combustion cum mixing chamber, expansion nozzle and exhaust manifold. Over the long experience of operating the aircrafts, it has been observed that the appliance provided by the manufacturer is only meant for internal corrosion preservation purposes of the operative and installed engines and cannot be used for external corrosion preservation of non-operative and un installed engines which led to drastic reduction of engine lives and unsafe operating conditions to the aircrafts due to inherent materialistic corrosive effects. The material of the turbine blades could not able to withstand its designed high combustion temperature due to the corrosion problems, which leads to unsafe engine conditions. The problem was attributable to the design factor that the high pressure cock in the fuel supply system could open and allow the preservative oil to enter into the main fuel system only when sufficient oil pressure is built up in associative oil system, which needs rotating the engines at least in idling speeds. Simulating this mandatory condition is not possible for the non-operative uninstalled engines. To overcome the corrosion hazard problem of aircraft engines, a bogie hinge joint flushing device has been designed, fabricated and tested using the local resources after taking into consideration of this important engine external preservation requirements, layout of the turbo-propeller engine power plant and fuel supply systems. This innovative external preservation rig has got multiple options coupled with internal preservation for preserving the engine components such as turbine, turbine blades, compressor, fuel nozzles, fuel system pipelines, diffuser, combustion cum mixing chamber, expansion nozzle and exhaust manifold during the course of long maintenance period. The newly designed and developed external preservation rig has resulted in achieving the complete external preservation requirements of following categories of turbo-propeller engines. a) New/overhauled engines in storage and kept on expiry of preservation life b)Installed engine required to be removed for storage but cannot be cranked or rotated c) Installed engines that are not in running condition/installation-seized engines d) Uninstalled engine for defect investigations/defect rectifications e) Non operative unsafe engines