By Donna Doleman, Engine Air Magazine

Service costs related to helicopter engine platforms are a significant part of an owner/operator’s bottom line. They may comprise as much as half of   total maintenance, repair, and overhaul (MRO) costs. Yet based on discussions with industry specialists on the costs of maintaining helicopter engines in the field today, it appears that the relative advantages of one engine over another in terms of MRO costs are difficult to quantify, primarily due to the broad range of helicopter usage. Of course, there are some measurable differences between similarly rated engines.

Some engine manufacturers offer longer warranty periods or a longer interval before overhauls are required. Newer engine models may have more auxiliary products, such as accessory gearboxes that may be “oncondition” maintenance items, as opposed to being scheduled for maintenance at fixedhour intervals.

However, engine manufacturers are also proposing very similar new engine technologies these days. Borrowing from successes on large commercial aircraft and engines, helicopter engine manufacturers have been working toward “smarter” engines and systems. Improvements include dual channel FADEC control and engine monitoring systems (EMS) as part of an aircraft’s overall health and usage monitoring systems (HUMS).

We queried repair specialists about a specific group of engines: the GE CT7/T700, the Honeywell T53, the Rolls-Royce 250, Pratt & Whitney Canada’s PT6 and PWC200 series, and the Turbomeca Arriel. Although these models vary in performance characteristics and ratings, factors other than the name on the engine were more often cited as the primary cost drivers or maintenance issues by the FAA-approved repair facilities interviewed.


The FAA issues separate Type Certificates (TCs) for helicopter aircraft and engines. As part of the certification process, every engine manufacturer must prepare a model-specific operation and maintenance manual. This manual specifies heavy and line maintenance requirements and time before overhaul (TBO) for the engine, under an array of functional and operating conditions.  The savings associated with longer intervals between TBOs can be significant. Turbomeca once postulated that a 500-hour increase in the TBO could save operators as much as 17 percent in engine costs.

According to Walter Given, Director of Technical Services at JSSI, headquartered in Chicago, Illinois, which services the Pratt & Whitney Canada PT6 and PW200, the Rolls-Royce 250, and the Turbomeca Arriel, the times between maintenance checks or overhauls, in actual practice, are seen as “basically the same.” Many service providers interviewed felt the same way. That being the case, what really drives significant cost differences in engine MRO on the turboshaft engines examined?


Although TBO intervals vary depending upon the engine employed, they vary to an even greater extent as a result of the helicopter’s usage. The PT6, T53, and other turboshafts investigated, for example, generally have TBOs ranging from 3,500 to 5,000 hours, but for a helicopter engine used in heavy logging work, the TBO may be as low as 1,000 hours. That is a huge difference in the time and money spent for overhauls. “Engine overhaul costs are a function of usage, maintenance plan, operating environment, and many other factors,” explains Les Dorr, FAA spokesperson. “All engines are certified with a Recommended Overhaul Period, per Appendix A of Part 33. In Part 91 operation, these are only recommendations.

In Part 121 and 135 operation, these are mandatory, unless the operator has an approved inspection program.”  Dorr continues, “When the mission and operating environment are known, and the type of maintenance plan is factored in (i.e. fixed overhaul limit in hours, or on-condition maintenance), costs are more predictable. However, cost will vary given the initial condition of the engine (i.e. new versus previously overhauled, time on Life Limited Parts, and so on).

An engine operated in a benign mission, rather than an aggressive mission, will likely have lower overhaul costs, as engine wear/distress will likely be lower.” Claus Eisenschmid, Director of Operations at ACROHELIPRO Global Services, Inc., a subsidiary of Vector Corporation, has nearly a quarter century of experience in engine design and maintenance. He sums up the sentiments of a number of MRO specialists: “In my experience, reliability is more dependent on the type of operation and the quality of maintenance than on ‘design.’ It is a natural trend in the market that cost per hour is very similar across the products I am familiar with.”

Those products include the Pratt & Whitney Canada PT-6 Twin Pac, the Rolls-Royce 250, the Turbomeca Arriel 1, and the General Electric CT/T58, CT7/T700 series, and T64 series, all serviced by ACROHELIPRO. It is the very nature of helicopter usage that makes predictability extremely difficult. Empirical data shows that environmental conditions such as the presence of sand, humidity, salt, or even volcanic ash, such as that found in Hawaii, can affect engine component erosion, corrosion, and wear.  High temperatures and the high thermal cycle counts that result from numerous starts and stops are tough on engines, too, because the greatest strain on a helicopter’s engine occurs during landings and takeoffs.

Maximum performance takeoff procedures used when departing a confined area, high/hot operations, rapid thermodynamic cycling during fast takeoffs, and partial cycles resulting from some descent procedures further contribute to unpredictability.  These variations affect MRO costs to such an extent that engine OEMs may offer differing fixed maintenance costs per hour, depending on the nature of the buyer’s typical flight profile. And it is this broad range of uses and operational parameters that can drive maintenance costs up for many owner/operators. The mission must be accomplished, but the costs are high in terms of more frequent and costly MRO needs.  Is there any way those owner/operators can reduce their expenses? Perhaps so.


The majority of owner/operators choose to do line maintenance “in-house.” Most keep degreed engineers on staff to manage those required annual and hourly checks, such as servicing the engine (oil, fuel, and air system maintenance) and preventive maintenance procedures (compressor and turbine washes, testing and cleaning the fuel nozzles, checking the chip detector, and a variety of maintenance manual engine repairs within the scope of their FAA certification approval level).

When Mr. Eisenschmid mentions the “quality of maintenance,” he refers to maintenance details that save owner/operators money in the long run. This means not just changing the oil, but choosing the right type and quality of oil, even though several may be acceptable. Service leaders learn from experience which choices are the right ones in the long run, even if it costs more today. These service specialists offer the benefit of that experience – which, like using a better oil, can sometimes be incorporated into line maintenance procedures – to their customers.

When it comes to heavy maintenance and overhauls, however, for most owner/operators, the cost of maintaining the experienced personnel, tooling, and test equipment necessary in order to obtain and hold the appropriate FAA class ratings is too costly. For these requirements, owner/operators often turn to the OEM Type Certificate holder or their licensees, to FAA-approved independent repair and overhaul stations, or to other FAA-approved owner/operators who not only manage this work on their own fleet, but also perform third-party work.

The work most likely to be outsourced to an approved repair station includes procedures that require engine disassembly, such as hot section inspection and refurbishment, engine overhaul (OH), and any engine repairs not covered in the maintenance manual. Owner/operators would be well-advised to shop around for the support company that best suits their needs, as there are many maintenance programs available and a broad variety of services from which to choose. In addition, a number of service providers have been able to develop new, cost-saving FAA-approved repairs that are not described in the OEMs’ manuals.


The first support option to consider is that offered by the OEM, as engine manufacturers generally offer comprehensive service programs and staffed personnel who have learned from a wide range of applications and service experiences. In one example, according to a U.S. Navy report, the General Electric T700 Team worked with NAVAIR to improve readiness in desert conditions.

Low power in the two GET700-GE-401C engines was the main cause for Navy H-60 engine removal. Operating in desert environments allowed too much debris to enter the compressor. These particles eroded compressor blades and coated hot section parts, plugging cooling air holes and decreasing the life and efficiency of hot section components.  NAVAIR and the T700 engine team developed a hot-section wash-sprayer nozzle and a related procedure to perform hot-section cleaning.

NAVAIR made it a requirement to perform the hot-section wash in desert environments to preserve the fleet’s T700 engine life and improve readiness; as a result, the Navy saw fewer engines removed for low power, compared to previous years. The T700 design has since been improved on other GE- derivative, and new engines, such as the CT7-8. The OEMs do not have all the valuable experience, though. Independent and licensed repair facilities may work on a variety of engine types, or they may specialize in a single type. Customers can benefit from new repair procedures they develop, from their often-lower overhead rates and from the customized programs they have time to create, especially for smaller operators.

As Given of JSSI says, “Our hourly cost maintenance programs help manage the costs of engine, airframe, and APU maintenance for jets, turbo-props, and helicopters. With JSSI, customers pay monthly, based on hours flown, and can choose the level of coverage their flight department requires, based on variables such as contract term-length, scheduled versus unscheduled maintenance costs, and engine-only or complete airframe coverage. JSSI offers a flat-line budget solution to the often unpredictable costs of scheduled and unscheduled maintenance.”

Some independents, such as Standard Aero Limited, headquartered in Winnipeg, Canada, are clearly focused on reducing their customers’ Direct Operating Costs (DOC).  According to Brian Hughes, Director of Marketing and Business Development, Helicopter Programs, Standard Aero is the largest Rolls-Royce Model 250 shop in the world, servicing some 2,000 customers globally.  The company offers comprehensive support with six overhaul facilities equipped to custom build engines that produce more power and meet customer-required specifications. Among the Standard Aero costsaving targets are unscheduled removals of customers’ engines.

Standard Aero believes data is their specialty, and they collect and analyze it in order to develop preventive measures to reduce costs caused by unscheduled removals and other emergency maintenance. As Mr. Hughes says, “DOC management is focused on the total long-term cost, rather than comparing individual transaction costs. An offering like our Power Assurance Software is one of the tools our customers use to trend their performance data while the engine is in service.

This allows them to immediately identify any significant changes in their engine’s operation and get to maintenance issues before they cause more costly damage. Keeping engines installed and increasing mean time between removals (MTBR) is ultimately the goal for a DOC reduction program to be effective.”

Dallas Airmotive is OEM-authorized for repair and overhaul on a number of helicopter engines, including Pratt & Whitney Canada’s PT6T at its Dallas location, and the RollsRoyce 250 at its Premier Turbines division and at its H&S Aviation affiliate in the United Kingdom. H&S also is OEM-authorized on the GE CT7-2 and -8.

“The use of serviceable parts has become increasingly desirable, as operators search for ways to lower the cost of overhauls without sacrificing quality,” says Chris Pratt, Director of Marketing. “We have a facility in Lafayette, Louisiana, that is dedicated to component repair on the RR250. From there, we support all of our RR250 shops. This facility is expanding and will be adding components for other engine lines in 2007.”

Similarly, ACROHELIPRO sees its strengths in its platform support, capability list, and huge product portfolio, which includes P&WC, GE, Turbomeca, and Rolls-Royce engine types.  Eisenschmid notes that his company has solid relationships with all the OEMs it supports, offering the services of a competent team with a wide range of experience, and is dedicated to customer support.

ACROHELIPRO holds numerous commercial and military approvals and performs maintenance and repair services at their over 158,000-square-foot facility in Vancouver, Canada, and at five additional MRO facilities throughout Canada and the United States. CHC Helicopter Corporation is a giant in global commercial helicopter operations.

Their service arm, Heli-One in Richmond, Canada, is the world’s largest independent commercial helicopter support company, other than the original manufacturers. Heli-One supports the entire 250-helicopter CHC fleet, plus aircraft operated by third-party customers, and the company has been providing helicopter services for more than 50 years.

According to Chris Flanagan, “About 35 percent of the work we perform on engines is third-party maintenance and overhaul, and we bring know-how gathered from CHC real-life experience in providing helicopter services to offshore oil and gas companies around the world.” Heli-One offers a broad range of services, including integrated logistics support, aircraft leasing services, repair and overhaul, heavy maintenance, design and engineering, helicopter parts inventory management, safety and survival equipment.

Some providers focus on other niches. One example is Magellan Aerotech, located in Abbotsford, Canada. As Joe Braz, Technical Sales Manager, says, “We’re a small shop and as such, can provide our customers, who would otherwise be lost in the shuffle of a larger repair shop, with more personalized service. Also, because of our location, smaller operators, who are often more price-sensitive, benefit from our lower overhead, which translates into lower engine repair costs.” Magellan Aerotech provides complete repair and overhaul services for commercial, military, and industrial gas turbines.


Many in the industry are closely monitoring developments in “smart” systems, and there is the hope that virtually all helicopter maintenance and overhaul will someday be “on-condition.” This paradigm shift is already happening, explains FAA spokesperson Dorr. “Modern helicopter engines are capable of being operated in either a fixed overhaul limit or ‘on-condition’ maintenance. The appropriate maintenance program is determined by aircraft equipage (engine condition monitoring equipment, engine health monitoring packages, engine vibration measuring equipment, etc.), the approved maintenance plan of the given operation, and the opera ting rules under which the aircraft is operated (i.e., Part 91, Part 121, Part 135, Restricted Category).

“Engines intended for use in Part 121 or Part 135 operation usually have an engine inspection program (an ‘on-condition’ maintenance program) provided by the manufacturer as part of the Instructions for Continued Airworthiness that, if approved by the FSDO, can be used in lieu of the manufacturer recommended overhaul period. Or, the operator can develop and utilize his own inspection program for the engine, if approved by the overseeing FSDO.” It appears helicopter engine on-condition maintenance programs on new engines will replace many fixed overhaul limit programs, paralleling the successes of large commercial airframe engines.

Even so, many in the industry, like Eisenschmid, predict that operating conditions will continue to strongly affect the frequency and extent of engine MRO. Owner/operators will still need to depend upon service centers they trust, in order to perform the necessary on-condition maintenance, to service parts from unscheduled removals, and possibly to assist in managing and interpreting their engine performance and condition data, as a number of providers expand their capabilities in that area.  The good news for maintenance providers is that helicopter owner/operators will require excellent, customized maintenance and overhaul support for many years to come.