The birth of the T53 Turboshaft Engine began in 1951 with Avco Lycoming in Stratford, CT. It was developed under a joint U.S. Air Force/Army contract. The first experimental engine went in test in 1953, at a design rating of 447 kW (600 shp). In 1956, it was picked to power the Bell XH-40 prototype which became the famed “Huey” helicopter. About 19,000 versions later, and more than 50 million hours in service on a variety of airframes, the T53 program has never looked back. Today through a variety of mergers and acquisitions, the T53 engine is manufactured and supported by the Aerospace Division of Honeywell International Inc.
The engine is a free power turbine engine that employs a five-stage axial and single-stage centrifugal compressor driven by a two-stage gas producer turbine. What is a free power turbine engine? It is an engine that is made up of two rotating assemblies that are mechanically free of each other. What are the advantages of a free power turbine engine? It eliminates the use of heavy clutches and prevents rpm control problems that would exist if the engine engaged the transmission directly.
The two rotating assemblies are known as the gas producer, sometimes referred to as the n1 or first stage, and the power turbine n2 or second stage. The symbol “n” refers to rotation (rpm) of the two independent stages. Actually, the n1 and n2 components rotate in opposite directions and at different rpms. What is the purpose of the gas producer? It produces all the gases that atomize the fuel for the engine operation. The power turbine n2 is driven by the hot gases produced by the n1 assembly and combustion, which supplies the power to drive the transmission, which in turn drives the main rotor and tail rotor. The engine output varies with different models but is between 1,250 and 1,500 shp. (By the way, the T in T53 stands for turbine engine, and the number 53 indicates the number given to the engine by the military.)
There are only three Honeywell-authorized T53 service centers in North America and only one of them, Airborne Engines Ltd. (AEL), is in Canada.
In 1991, AEL first opened its doors in a small leased warehouse unit located in Richmond, British Columbia (BC), Canada, where it began providing the aviation industry with gas turbine repair and overhaul services, while focusing on the Rolls-Royce M250 series engines.
In 1995, it became apparent that the services supplied for the Rolls-Royce M250 was also required for the Honeywell T53 series engines. With that, AEL began to focus on a controlled expansion within the gas turbine repair and overhaul industry. The shop doubled its size in 1995 with the lease of an adjoining unit, which also increased manpower to 10 people. Over time, expansion continued as did the workload. The latest expansion occcurred in 2009, and the shop moved to its current 32,000-square-foot home in Delta, BC, just outside of Vancouver.
AEL is a member of M International Inc. and as such, is partners with Mint Turbines, Keystone Turbine Services and Southwest Fuel Systems. AEL is a Transport Canada-approved repair and overhaul facility, a member of the Joint Aviation Authority JAR 145 Repair Organization, and a member of the European Aviation Safety Agency (EASA).
I recently visited AEL and discussed the T53 engine with them.
HeliMx– Approximately how many T53 engines do you repair or overhaul yearly?
AEL– Eighty to 120 engines with varying degrees of work to be accomplished.
HeliMx– What are some of the more common maintenance issues you see when the engines come into your shop?
AEL– Foreign object damage (FOD). This is a major factor in unscheduled engine maintenance. FOD in North America alone exceeds $13 billion dollars yearly in direct and indirect costs. Engine inlet barrier filters would be a highly-recommended upgrade to any operator. Aside from helping to minimize FOD, the filters also help to keep out dust and dirt that erodes engine gas path components and has a negative effect on engine performance.
Incorrectly performed compressor washes. Occasionally mechanics completing a compressor wash neglect to perform a proper fresh water rinse and dry, causing more harm than good. By not properly rinsing and running the engine, to allow the solution to dry, the chemical deposits left behind will over time cause corrosion of vulnerable magnesium casings resulting in costly future repairs.
Burnt combustion liners. This is generally caused by streaking and/or spitting fuel nozzles that are not delivering properly atomized fuel, and will degrade the engines available power output.
Carbon ball erosion. This is caused by inefficient atomization of fuel in the combustion liner, which results in build up of carbon deposits around the fuel nozzles in the swirl domes of the combustion liner. During engine operations, these carbon deposits break off and impact the gas producer nozzle vanes and leading edge of the first-stage gas producer turbine rotor blades. This erosion is actually carbon particle blasting and causes degradation of the gas producer gas path parts, resulting in increased operating temperatures, increased inefficiency and low-power conditions. A contributing factor to this condition is the use of dirty fuel.
HeliMx – Do you have recommendations as to upgrades, and why?
AEL– Upgrade from T5313B/T53L13B to the T5317B/ T53L703 engine. The 17B/703 engines use a measured gas temperature (MGT) indicating system located in the gas path which results in less thermo-shock instances of turbine parts as opposed to the 13B/L13B exhaust gas temperature (EGT) indicating system located in the exhaust section of the engine. The 17B/703 models have numerous internal design improvements that provide greater internal cooling of gas path components which allows higher internal operating temperatures. With these upgrades and better cooling, the 17B/703 series engines are very well suited to hot and high operating environments with an increased 1,800 thermodynamic horsepower as compared to the 1,400 thermodynamic hp of the 13B/L13B models. The 17B/L703 series also are favorable due to a much better availability of spare parts support.
HeliMx– What suggestions do you have for prolonging engine life?
AEL– Perform regularly-scheduled clean and flow checks of the main fuel manifolds and start fuel nozzles. This helps prevent burning of internal engine parts caused by coking fuel nozzles that result in streaking/splitting fuel delivery into the gas path.
HeliMx– Run us through a typical repair/overhaul cycle, from the time an engine comes in your door until you ship it back to the customer.
AEL– The paper trail starts when the customer has informed us that they have sent an engine to us for repair or overhaul. Based on the information they provide, we start a file on the engine. The file will contain many different forms that will be filled out as the work on the engine progresses. The incoming form has the customer’s contact information, shipping information, engine serial number, type of helicopter and work being requested. If the customer is requesting some special work to be done, that is also put in the file at this time.
The customer is notified as soon as the unit arrives at our facility, and a visual inspection is performed on the shipping container and contents for any sign of visual damage. When the engine does come into the shop, we perform a receiving evaluation, identify customer reported discrepancies and review engine log book/technical records. We also record the engine’s times and cycles at the time of the removal.
We now open a work order that specifies the scope of the work to be performed, keeping the customer informed of our progress as each step in the process is completed. Now the engine can be prepared for an incoming engine test cell performance evaluation. This is then compared to any performance discrepancies reported by the customer. The engine is then routed to the disassembly area.
Here the engine is torn down per the work order. Then the components are sent to be cleaned and inspected. If required, some parts will be sent for nondestructive testing (NDT). After NDT, all the engine parts are returned to the engine line for additional inspection.
When all this has been done, the work order is sent to sales and marketing so they can prepare a cost quote. Once the quote has been prepared, it is sent to the sales director for review and approval. Once approved, the quote is presented to the customer, along with the detailed engine tear down report. Our customer support team is always available to answer any questions or concerns the customer may have.
When the customer has approved the quote, we review the new part requirements and stock levels, submit required reworks to the machine shop, pick parts and order parts that are not in stock.
With all parts in and rework completed, assembly begins. This entails performing engine sub-assembly builds, final engine assembly, route the engine to the test cell and provide the customer with the new performance figures. The engine is then routed for post-test service and final inspection. Successfully completing final inspection, and ensuring that all log book entries and required paperwork is signed off, the engine is now ready to be preserved, installed back in its shipping container and returned to the customer per their instructions.
With more than 30 years and 50 million hours of service, Airborne Engines Ltd. is working to keep the T53 legacy going strong.