Component maintenance manuals help eliminate downtime
By Eric Blickley
Strict maintenance of the engine and its components is required to maximize engine performance for a variety of flight conditions. In time these components, as well as the engine, require overhaul. Whether removed for scheduled or unscheduled
maintenance, it is critical to follow the information in the component maintenance manual (CMM) and the Material Safety Data Sheets (MSDS).
Engine flight-hours are the primary reason to remove the engine or engine component. The time between overhauls (TBO) can be found in the engine maintenance manual and in the CMM for the individual components. Many original equipment manufacturers (OEMs) post this information on their web site. Woodward's recommended TBO periods for their propeller governors, pumps, auto feather valves, speed signal generators, and Type I synchronizer components can be found at www.woodward.com/AES/customer/glservbul.cfm .
Surges and fluctuations in engine and/or propeller speeds are often attributed to problems with the control accessories. However, this is not always the case. Internal leakage, rigging, or problems with the propeller may cause these symptoms. Improperly adjusting the settings on propeller controls can also cause overspeed or fluctuations. To save downtime and cost of repairs confirm the cause of engine symptoms before removing any component by following the aircraft troubleshooting recommendations.
Common causes of unscheduled removals for propeller controls include:
- sudden stoppage
- oil contamination
- lightning strike incidents
If the propeller makes contact with any object, it can cause sudden stoppage, which causes stress in the rotating components. The propeller does not have to come to a complete stop. Bird and deer strikes and "gear -up" landings are known causes for sudden stoppage.
Oil contamination can also cause excessive wear on the component and reduces the TBO. Lightning strikes can cause serious damage to the components by arcing the bearings and magnetizing the metal.
Common causes for unscheduled removal of fuel controls include:
- Overboard drain leakage
- Slow start
Overboard drain leakage is due to failure of a carbon-faced seal. This is most likely caused by engine vibrations. Slow starts are generally caused by low flow at given gas generator speeds. This condition requires removal and repair at a certified repair station. The fuel control and propeller governor interact to control the propeller speeds. Therefore, improper field adjustment of the propeller governor control can cause surging.
After identifying and confirming the cause for removal, the first step is to properly remove the accessory to minimize downtime and the overall cost to repair the engine accessory.
Removing the accessory from the engine must be complete - no hardware should be attached. Common items attached to the controls include push/pull levers, linkage, and drive pads. Generally, repair stations certified to remove fuel components are not certified for airframe related materials. Your component will be returned with the extra items unattached and will require some additional assembly.
If you exchange the accessory, rigging hardware or fittings will not be included. You must either wait for the return of the extra parts or find replacements.
"If you are getting an exchange, it is best to wait until you receive the replacement unit before sending in the core," advises Duane Bourgeois, customer service representative at Woodward. "Waiting for the replacement ensures you don't send airframe or linkage parts that aren't part of the governor."
After removing the component from the engine, it is vital to purge the system of all fluids. Many fluids are hazardous and will stop the shipment or require additional documentation. Even when the fluids are not hazardous, if leaks occur during shipping, the package will be delayed. For fuel and propeller controls, the hazardous materials include Jet A and a variety of oils.
Check the MSDS
According to the Material Safety Data Sheet (MSDS), Jet A fuel is a mixture of petroleum, aliphatic, and aromatic hydrocarbons, which is considered a class 2 health hazard and a class 2 fire hazard. Avoid contact with skin and clothing. Inhaling the vapors can cause irritation to the nose, throat, and respiratory tract. High vapor concentrations may result in central nervous system depression, which causes giddiness, headaches, dizziness, and nausea.
Both natural hydrocarbon oils and synthetic oils may be found in propeller controls. An MSDS should be available at all locations where the material is found. If you are using a new fluid, and do not have an MSDS sheet, the product manufacturer can provide one. An MSDS includes the product description and ingredients that may pose hazards. Physical data, fire and flammability data, health hazard data, reactivity, spill or leak procedures, and special handling precautions are also provided.
After the item is properly removed and purged of all liquids, the orifices should be secured to prevent any FOD (foreign object damage). The component should be sealed in plastic and placed in a durable, appropriate container.
"Proper packaging is essential. If the operator or maintenance company does not properly purge and package the item, it will be delayed," states Mark Munger, customer service representative at Woodward. "The shipper may repackage the item to meet its requirements. We've seen fuel controls put in small barrels by the shipper. While this keeps fluids from spilling during shipment, it does not secure the control and protect it from damage."
is also very important. A piece of note paper with the essential information is adequate if placed inside the box," says Bourgeois. "This includes the reason for repair, time since new, time since overhaul, and complete contact information including name, full address, and telephone number. This will expedite the repair process."
To ensure you receive the best possible service, stipulate in the documentation your preference for upgrading to the latest configuration. In general, most OEMs automatically upgrade the component to the most recent configuration unless otherwise requested. Upgrades and modifications will enhance the component's performance and alleviate performance issues experienced in the field.
Engine components require servicing for both time-based scheduled removals and unscheduled removals. Following the CMM requirements and the MSDS sheets is vital for proper removal. Appropriate shipping and documentation will ensure your components reach their destination safely and are serviced quickly by the repair station.
Practicing appropriate and professional techniques for component repair and overhaul will ensure rapid turnaround of your parts and keep your aircraft in the air, operating at top performance. If you have any doubts about what to ship with your component and how to package it for shipment, contact the repair station. It is much easier to assist you in advance than to spend time later helping locate lost or delayed components.
International Air Transport Association:
The Hazardous Materials Advisory Council:
Dangerous Goods International:
The Bureau of Dangerous Goods, Ltd.:
The Environmental Resource Center: