Sometimes things happen! It’s not very profound, but it is very true. Engines suffer through prop strikes, wire strikes, hot starts and hard landings. Frequently, post incident inspections reveal minor damage and the engines are repaired and returned to service promptly. Recently, engines have been brought to Covington for investigation because “things” have happened to them. One was a reported incident of a starter/generator arcing. The starter/generator malfunctioned and was replaced. While the maintenance appears to have been performed properly, “things” still happen. Here is what we found upon disassembly:
An indication of electrical discharge was noted from the starter gear and all through the accessory gearbox. The #1 bearing failed, which in turn allowed the compressor to shift causing a severe rub of the compressor components and the compressor turbine blades. Another engine suffered from oil starvation:
Another engine suffered from oil starvation:
And a third engine had a failure in the turbine area:
Even though the engines pictured here suffered from in-flight shutdowns, all of the aircraft were able to land safely and all pilots walked away.
A photo posted by Covington Aircraft (@covingtonaircraft) on
Although we understand that “things” happen, we don’t want them to happen to you. If they do, we will work with you no matter where your previous maintenance was done, to ensure that you have a rental/replacement engine as quickly as possible to keep you flying. Remember to be aware of changes in your engine or events that could cause damage. Pay attention to the way it sounds (blade rubbing), looks (metal or debris in oil), smells (oil burning) and feels (vibrations) along with watching the gages. You may be able to detect a problem before some ”thing” happens to your engine.
Need to have a certified expert look at your PT6A engine? Founded in 1972, Covington Aircraft is a world-leading aircraft engine maintenance, repair and overhaul facility specializing in the PT6A turbine engine and R-985 and R-1340 radial engines. We are a Pratt & Whitney Canada certified Distributor and Designated Overhaul Facility (DDOF), and provide world-class corporate and agricultural aircraft service.
Recently added to the ESP™ plan, our (Pratt & Whitney Canada’s) Oil Analysis Technology is a powerful diagnostic and prognostic tool that helps customers avoid unscheduled events. We outline some key benefits below.
1. A SIMPLE, USER-FRIENDLY SAMPLING PROCEDURE
Taking routine oil samples from your engine and sending them for analysis is a fast, simple process that gives detailed insights into engine health that wouldn’t otherwise be possible.
This technology enables operators like Germany’s Arcus Air, an airline that offers chartered cargo and corporate flights, to plan maintenance in advance, thereby minimizing the risk of unscheduled events and maximizing engine availability.
Pratt & Whitney’s Oil Analysis Technology is a powerful tool that helps us better understand the health of our engines. We receive clear and concise data that allow for a quick overview but also for deep insights. Daniel Bürcky, Chief of Maintenance, Arcus Air
The sampling procedure is designed to be as user-friendly as possible. We provide customers with a kit that contains everything they need, from a syringe and tube or O-rings for collecting the oil to a pre-paid envelope with all the necessary paperwork for sending the sample to the lab in Canada.
Customers simply need to collect a sample during scheduled engine maintenance, then have the package picked up by FedEx. In return, they’ll receive a report outlining the results, along with recommended follow-up actions.
The sampling interval is typically from 200 to 300 hours, meaning that for a typical business jet or general aviation operator, samples only need to be taken once or twice a year, notes Frédérique Richard, Senior Manager, Oil Analysis Technology.
2. EXPERT INSIGHTS THAT ENHANCE OPERATIONAL CONFIDENCE
Oil analysis technology is used to monitor trace particles in oil-wetted components such as carbon seals, gears and bearings. It compares their current condition with the signature of other healthy engines in the fleet. Once a component deteriorates past a certain threshold, our team will provide specific maintenance recommendations.
It’s like going to the doctor to have a blood sample taken, explains Frédérique. If the doctor analyzes your blood and sees that you have a health issue, like slightly high cholesterol, she’ll suggest doing something like changing your diet or exercising more. Our Oil Analysis Technology works in a similar way.
We look at the data and if anything needs to be done, we help customers figure out the right next steps. We give them a tailored ‘prescription’ – a specific maintenance recommendation to address the matter before it becomes an issue. Frédérique Richard, Senior Manager, Oil Analysis Technology
The insights gained from this technology therefore give customers greater operational confidence by letting them know when they should keep a closer eye on specific components or take action to repair or replace them.
One example is carbon seals. If these components are left to deteriorate, it could eventually lead to unplanned maintenance events, which may entail unexpected costs like hangar rental, spare engine shipment or cancelled revenue flights.
All of that could be avoided with our Oil Analysis Technology.
“In some cases, we can tell hundreds of flight hours in advance if a carbon seal is deteriorating,” says Frédérique. “Once we see that, we’ll issue a recommendation to monitor its condition more frequently. When action is required, we’ll advise the operator to proactively remove the engine at the next scheduled maintenance and send it to the shop for replacement.”
Thanks to this technology, we’ve been able to identify early deterioration patterns and recommend proactive maintenance on a number of engines. These customers were able to schedule maintenance and avoid the disruption of situations such as cabin air contamination and metal in oil. Frédérique Richard, Senior Manager, Oil Analysis Technology
3. A CONTINUOUSLY EVOLVING TECHNOLOGY
To date, with the help of customers around the world who want to go beyond basic engine maintenance and are embracing early detection, we have collected tens of thousands of oil samples.
The more data there is to work with, the more detailed and accurate our Oil Analysis Technology becomes, because it’s not static. It continues to evolve, as the new data helps us to refine engine oil signatures and fine-tune our algorithms.
“It’s an ongoing journey,” says Frédérique. “We keep investing in the technology and working to improve it.”
The advanced analytics that we use allow us to go deeper than human analysis alone could accomplish. This enables us to identify engines at risk of a particular issue, prioritize maintenance work, and ultimately drive operational improvements, cost savings and greater engine availability Frédérique Richard, Senior Manager, Oil Analysis
technology combined with other technologies such as our FAST™ solution, it enables customers to understand their engine inside out and fly with peace of mind. If our Oil Analysis Technology is like a blood test, FAST is like an MRI. These prognostic and diagnostic tools complement each other, contributing to a more holistic view of engine health.
Oil Analysis Technology is one of several recent additions to our ESP™ maintenance program. Learn more here.
In an aircraft engine, oil is much more than just a lubricant. It plays a number of other important roles, including cooling, cleaning and noise reduction. It’s therefore vital to monitor and analyze oil to ensure it’s doing its job properly.
WHEN AND WHAT TO ANALYZE
Engine oil sampling and analysis are recommended if a visual inspection reveals that the oil is very dark, has an unusual odor or exhibits other abnormal properties. You don’t necessarily have to change the oil, but at the very least, it should be analyzed to determine its total acid number (TAN) and water content.
Typically, the water concentration in brand-new oil varies between 0.02% and 0.04%, or 200 and 400 parts per million (ppm). However, water can enter the engine’s oil system due either to accidental contamination during compressor wash or normal condensation. Since aircraft engine oils easily absorb water and moisture from the air, their water content will rise over time. If it exceeds 1000 ppm, the TAN may rise as well, eventually leading to engine component corrosion.
HOW TO SAMPLE AIRCRAFT ENGINE OIL
When you take an oil sample, identify it with the brand name, engine serial number, total run time (oil life) and engine time since new (TSN) or time since overhaul (TSO). Have the sample analyzed for its TAN and water content by an approved laboratory. If necessary, ask the lab to analyze the oil viscosity and additives as well.
If a parameter exceeds the established limit, it’s recommended that you: 1) drain and discard the oil from the tank; 2) check the condition of the oil filter and, if needed, replace it with a new one; 3) refill the tank with fresh oil.
If you have access to the right kits, you could also perform the analysis yourself. Use a Titra-Lube TAN Test Kit to analyze the oil’s TAN and a HydroScout Analyzer kit for the water content.
Every time you add oil into your engine, write down the amount so that you can calculate the average consumption. Check this figure against the limits indicated in the maintenance manual. If the engine is using more oil than it should, there may be a part that needs maintenance. For example, a damaged O-ring could be causing a leak, or something may be happening in the engine that’s burning up extra oil.
A BRIEF HISTORY OF AVIATION GAS TURBINE ENGINE LUBRICANTS
The earliest aviation piston engines were lubricated with natural oils such as castor oil and refined mineral oils. However, they lacked the thermal-oxidative stability needed for high-temperature mechanical systems and would form deposits like gum and lacquer on metal surfaces.
In the 1950s, following research efforts aimed at improving thermal-oxidative stability, synthetic polyester-based lubricants became the base stock of choice for aviation gas turbine engine oils. Thanks to their chemical properties, these lubricants are effective over a wide temperature range, from -65oF to 425oF. They possess good thermal-oxidative stability, high lubricating film strength, good surface wetting, and low friction and wear rates, making them ideal for aircraft engines.
Aircraft engine overhauls are all about flying like new and they require careful planning. It all takes time and a maintenance scheduling. Imagine replacing your engine with one that has already been overhauled, all at a guaranteed price?
Certain equipment is essential for keeping a PT6A engine running smoothly. Here are four tools and parts that either the aircraft owner or the operator needs to have when doing routine maintenance work.
1. FUEL NOZZLE FLOW CHECK AND PRESSURE CHECK FIXTURES
Typically, ultrasonic fuel nozzle cleaning should be carried out every 200 to 400 hours(1) of flying time, to make sure the nozzle is performing properly and there are no problems such as blockages. “Whenever you clean your fuel nozzle, you should also check it for leaks and flow irregularities like drooling, spitting, streaking or other patterns that could damage the hot section,” explains Yves Houde, PT6A Customer Manager at Pratt & Whitney Canada.
Checking for irregularities of the fuel nozzle requires the use of both a flow check fixture and a pressure check fixture. These are fitted over the nozzle to help identify tips that need to be cleaned or replaced and verify the presence of any leaks before the aircraft is returned to service. Learn more about what to check for in our article on fuel nozzle maintenance.
2. BORESCOPE KIT
Whenever undertaking fuel nozzle maintenance, make sure to perform a borescope inspection at the same time. To do this, you will need a borescope kit, including a guide tube for accessing hard-to-reach areas of the engine. Using a borescope is much easier than the old-fashioned method, which involves opening up the engine.
A borescope allows for assessment of hot section components for wear or damage that may not be evident from a regular ground power check or flight data collection. For instance, on a single power turbine engine, inserting a borescope through the exhaust duct port and power turbine stage may reveal trailing edge cracks on compressor turbine blades.
“It’s the number-one equipment you need to have for line maintenance,” says Yves. “The time when fuel nozzle cleaning is performed is an ideal moment for operators to assess the hot section’s condition with a borescope. We also advise using it to check the first-stage compressor for foreign object damage every year.”
Borescope kits are made by a number of companies. PT6A owners can check their engine’s maintenance manual for the recommended product’s part number and order it from a designated supplier.
It’s hard to generalize about PT6A engines, but there’s some equipment you can’t do without. It’s the core of the line maintenance you need to perform.
3. OIL FILTER PULLER/PUSHER TOOL
Oil filter maintenance is recommended every 100 hours or so. When doing this procedure, use a puller/pusher to open and close the filter’s check valve. While the oil filter can be popped out by hand, it’s not a good idea to do so, since it could damage the oil filter check valve seal, which in turn could lead to static oil leak when the engine is not running.
4. TURBINE RINSE TUBE AND COMPRESSOR WASH RIG
PT6A engines may need to be washed periodically to remove salt and other impurities; how often depends on the operating environment. Whenever it’s time to clean the engine, a compressor wash rig and turbine rinse tube are essential.
Unlike other engines, most PT6A engines already have a wash ring installed around the air intake, so all you need to do is connect the compressor wash rig and insert the water. After the compressor wash, use the turbine rinse tube to clean the turbine as well.
You don’t need any special cleaning solution for a desalination wash—pure, ionized water will do. “But it’s always a good idea to test the water quality first to make sure it’s suitable for cleaning,” adds Yves. “If you use the wrong water, washing may end up causing more problems than it solves.” Have a look at our article on desalination washes for more tips on keeping your engine free of contaminants.
(1) Refer to your Engine Maintenance Manual (EMM), Periodic Inspection Fuel Nozzle Cleaning interval for the interval that applies to your engine model.
When it comes to special mission aircraft, Textron Aviation has a deep lineup of airplanes suited to the task, ranging from the single-engine piston Cessna 172 to its most sophisticated Citation jets. But its most popular mission-oriented aircraft come in two turboprop types, the Caravan single-engine and the twin-engine King Air series. Both product lines are prime examples of dual-purposing, with a large following in the civil market for everything from owner-flown transport to commercial charter and business aviation flight departments. But these aircraft, when equipped for specific non-commercial or military operations, show their true mettle.
Climbing over the narrow, wing-root walkway and stepping on to the cushioned seat of the tandem, two-place, blue and yellow fabric-covered open-cockpit Boeing PT-17 Stearman registered N55171 in Stow, Massachusetts, I lowered myself into position with the aid of the two upper wing trailing edge hand grips and fastened the olive-green waist and shoulder harnesses. Donning era-prerequisite goggles and helmet, I surveyed the fully duplicated instrumentation before me and prepared myself both for an aerial sightseeing fight of Massachusetts and a brief, although temporary, return to World War II primary flight training skies.