Can You Afford a HUMS and HFDM System? 

By By Michael Hangge (mjhangge) | September 1, 2014
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Fully integrated flight data recording is now affordable for the light single and twin engine fleet. PHI is outfitting their Bell 407s with NORTH FDS HUMS/HFDM recorders. Photo courtesy PHI

Health and usage monitoring systems (HUMS) and helicopter flight data management (HFDM) systems are powerful aviation tools. Their capabilities will eventually make them mandatory and will prove indispensible to the future of helicopter maintenance, safety, and operations. But are the current systems worth the cost to install, monitor, and maintain? Have the systems matured to the level that now is the best time to invest? How will these systems increase the productivity and profit margin of investors today?

Those are just some of the questions each owner and operator must ask before investing valuable dollars. Therefore, it is incumbent upon the manufacturers and proponents of these systems to discuss and answer those very basic questions.


When combined, the goal of HUMS and HFDM is to predict failures before they occur. This prognostic approach focuses on monitoring usage to predict component failures in order to improve the helicopter’s reliability, productivity, and availability. The two systems attack these issues from different directions - HUMS monitors health status and trending data, while HFDM evaluates flight operational data and addresses crew habits. This combined data can then be compiled to determine how an aircraft was operated at any given point, and, compared with the health status signals, one can determine the root cause of equipment wear in relation to its flight regimes. While both can be considered separate systems and programs, many contend that they are simply different methods to achieve the same goal and that future HUMS will be incomplete without some level of HFDM interface.

A strong correlation exists between the cost advantages of these systems and the operator’s profit margin. Like anything in aviation, this equipment is not cheap to purchase, install, or maintain. The savings these systems offer, however, are dramatic and can quickly offset the entry and operating costs. The impact statements are difficult to dispute: improved operational reliability and predictability, reduced maintenance man-hours and early part replacements, proactive maintenance, intelligent parts management, and minimization of accidents caused by aircraft systems failures or avoidable pilot actions.

The U.S. Army, currently the world’s single largest user of HUMS, has proven its effectiveness on its vast fleet of helicopters. In a study that encompassed more than 500 aircraft and hundreds of thousands of flight hours, the Army demonstrated impressive parts savings and significant increased aircraft availability. To a civilian helicopter operator, these improvements would correlate directly into a higher, long-term profit margin and an improved reliability reputation.

In the past, these systems have only been cost effective in the most expensive helicopters. But due to the lower entry and operating costs of next generation systems, it is now becoming easier to justify the installation on light to medium helicopters. The technological advances have made them lighter, more functional, easier to operate, and less expensive.

Though rotor smoothing is often thought of as HUMS’ greatest attribute, the system has advantages beyond rotor track and balancing that offer impressive cost savings. Photo Courtesy of RMCI

Aircraft without HUMS, and even some legacy systems, avoided costly delays or mission cancellations by simply (and expensively) replacing parts on predetermined and artificial timelines. There is evidence that, on average, many helicopter components are being retired at between 25-40 percent of their designed fatigue lives. While this may seem like an unnecessary expenditure, there has traditionally been good reason to emplace those exorbitant time penalties.

The lack of accurate and predictive monitoring in helicopters has always necessitated this wastefulness to protect against the even more costly risk of an accident. As much as one quarter of helicopter accidents are attributable to some level of parts or systems failures, but there are many studies that suggest nearly half of those accidents could have been mitigated by the use of HUMS.

Improvements in safety records will also reduce potential liability, litigation, and damage costs. Ken Speaks, CEO of RMCI, said, “If an operator provides advanced safety features that are not mandated, such as HUMS and HFDM, the operator has an advantage should an unexpected event occur.”

Quantifying the costs of a major accident may be difficult, but insurance companies will soon help make those calculations and, as these systems become more widely used, insurance providers will increasingly recognize their benefits and offer discounts for usage.

The holy grail of HUMS has always been the possibility for maintenance credits. George Grove, vice president of Helitune, states that, “Because HUMS continuously monitors a component, the possibility exists to eliminate some periodic inspections. That would be an immense benefit and cost saver to an operator.” The principles of condition-based maintenance (CBM) would result in fewer time-based inspections and, in theory, extend the usable lifespan of many expensive parts, reducing operating costs by as much as 10 percent.

North FDS provides affordable, fully integrated voice, video, and flight data recorders to the light single and twin-engine helicopter community with Flight Analysis and Animation software. Photo courtesy of North FDS

While this is certainly a worthy goal, the FAA is still working to develop a solid plan for these credits. That doesn’t mean the goals of CBM or the installation of HUMS should be abandoned, though. Just their intermediate benefits alone should still make the installation a fiscally responsible idea. Tom Hart, vice president of Honeywell Aerospace, states that they have “customers realizing returns on their investments in only one to two years based solely on maintenance cost savings.”

Much of that savings is due to HUMS’ ability to minimize the damaging effects of vibrations. The capacity exists to collect continuous vibration baselines on the entire aircraft and, specifically, the rotor systems, which are the largest cause of vibratory damage. With this ability, small track and balance adjustments could be made without verification by a maintenance flight.

Not only would this limit the unprofitable flight hours on the airframe, it would also result in a continuously smoother helicopter, and significantly increase rotor component lives. This also provides maintenance personnel with the unique ability to view vibratory data as it is trending, allowing earlier detection of deterioration and advanced warning of issues.

Any scheduling manager can attest to the frustrations and costs of unplanned asset down time. The scramble for parts and spare aircraft can whiten any operator’s hair, not to mention the actual expense of positioning the parts and conducting the maintenance while all potential revenue is being lost. By better predicting issues, the aircraft can be removed from the flight schedule for repairs at more logical times and locations. In companies with larger fleets of similar aircraft, the benefits may be even larger, since what can be detected on one aircraft can be used to comprehensively analyze an entire fleet.” All of this results in fewer expensive and frustrating mission aborts due to maintenance, while allowing smarter scheduling of the helicopter.

OEMs have already begun working with HUMS providers and, as these systems continue to mature, more collaboration will be seen. Chris Carella, manager of HUMS strategic planning at UTAS, states, “These kinds of partnerships will automate or even eliminate some maintenance checks while making the aircraft safer, more reliable, and mission ready.” One of the issues, according to Carella, is that as more data is captured from a growing list of parts on several platforms, the challenge shifts from successfully measuring high quality data, to efficiently managing and utilizing the data to drive changes in regulated maintenance practices. Equipment such as UTAS’ pulse ground station software, which is compatible with current Microsoft Windows operating systems, will assist by making the data easier to collect and use.

XRDS is RMCI’s cutting-edge HUMS solution for civil helicopters; its unique combination of low cost, light weight, and tremendous capability provides unparalleled benefits for operators who want to save money and increase safety. Photo courtesy of RMCI

The safety of a helicopter is obviously critical for many reasons, but it cannot be the exclusive consideration irrespective of the costs involved to attain it. Safety cannot be in conflict with the needs to operate efficiently and cost-effectively, or it will put operators into a position of having to choose between chance and profit. It is difficult to balance the cost of these systems against the imagined cost of just one preventable accident, but the costs of replacing the aircraft, crew, passengers, and business reputation must be considered worthy of calculation.

While the immediate cost benefits of these systems can be seen in the operational and maintenance savings, the cost advantages of safety may be more difficult to envision and quantify. Though aviation accidents are relatively uncommon, they tend to get more attention because of their dramatic nature. This is the type of attention that can destroy a company’s reputation, and possibly even the company itself. The U.K.’s Civil Aviation Authority (CAA) estimates that 80 percent of helicopter mechanical defects are detectable, and HUMS has the ability to identify many of those. In the relatively few years that the Army has been using HUMS, the systems are already being credited with the prevention of three Class A mishaps, and are predicted to prevent one more each year.

While the safety features of HUMS are easy to explain, the advantages of HFDM are more elusive, yet no less significant. Information attained by HFDM in a “just culture” is uniquely objective, as it offers a more well-rounded description of what is actually occurring in flight. With a combination of the data acquired by both systems, an investigation team can better determine the cause of an accident, which may shift some of the burden from the easy-to-blame crew and onto the mechanical and environmental causes which create their own share of issues. This is not to say that any one cause is better than another in the aftermath of an accident, but these systems may find more truth to the root causes.

Bristow Helicopters has chosen to equip their fleet of S-76 helicopters with the UTC Aerospace Systems (UTAS) HUMS/HFDM system. Photo by John S Goulet,

As Jeff Warner, president of North Flight Data Systems, stated, “With the advent of some innovative technologies, we will be able to combine our exhaustive flight and airframe data to deliver economical solutions, which include communication and analytic tools that deliver actionable data to operators of any size. We film, wire up, and measure professional athletes to get every extra advantage. Our industry’s professional pilots deserve that same focus to help improve their skills and training to get every bit of additional performance available.”

Recently, HUMS and HFDM have become popular buzzwords. As a result, many companies have begun using them in their marketing strategies but have been less willing to define what services they offer. Because of the wide range of products and capabilities that fall beneath the HUMS umbrella, there is a lot of ambiguity in the market. This results in confusion for the operators, manufacturers, and even helicopter OEMs.

Though ISO Standard 13372:2012 addresses vocabulary in the “Condition Monitoring and Diagnostics of Machines,” much work is still needed to ensure that operators find the right products and services to make their aircraft safer and more efficient. Industry-leading companies such as Helitune, RMCI, and UTAS have all commented on this issue.

Helitune pointed out that “there are various standards and guidelines in existence for both terms – HUMS or HFDM – but they are still interpreted differently by different OEMs, manufacturers and operators.” RMCI defines HUMS to mean, “at a minimum, a data acquisition system that gathers vibration signals and provides monitoring of flight parameters and the algorithms necessary to make accurate determinations of components’ conditions.”

The green line at the top of this chart depicts the data from the Vertical Speed Indicator (VSI) and illustrates the sort of clear visual representation of the relevant flight data that a good HFDM can provide. Even a novice can easily see the progression of the severity of the event from low (Yellow) to medium (Orange) to high (Red). There were other less severe “events” also detected at the same time that are noted in the pitch rate (violet line) and the roll rate (blue line).  The bottom line depicts the Radar Altimeter data and the dotted line represents 500 ft. AGL, which is one of the parameter conditions defining the “event.” The dialog box at the top gives you the specific values of all the graphed data at that particular point.

UTAS reiterates the importance of collecting high-resolution data while the aircraft is in specific conditions. These three companies, and many others, offer excellent HUMS products, but each approach is so dramatically different that operators must thoroughly research the products to find the path which best suits their needs.

This issue, among many others, has not been ignored by the FAA. It has written legislation to improve and implement the Light-Weight Aircraft Recording Systems (LARS) into air ambulance helicopters. As of April 22, this new legislation has begun to take effect regarding these systems, which record flight performance and operational data. While this is a significant step forward, it is a difficult road to walk.

Helitune’s on-board systems provide solutions for Transmission Vibration Monitoring, Structural Vibration Monitoring, Structural Usage Monitoring and Rotor Track & Balance. Photo courtesy of Helitune.

Many small helicopters and operations cannot bear the additional weight or expense of some of the more extensive systems, but the lesser systems may not be effective enough to accomplish the FAA’s goals. Many of the LARS systems are not crashworthy, nor do they provide the same valuable information as cockpit voice recorders (CVR) or flight data recorders (FDR).

Warner very accurately commented that, “If you want to truly do FDM, you have to reach out to touch the aircraft’s systems. If you simply install cameras and collect geospatial data, you may think the legislative box will be checked, but it won’t tell you much more than ‘you were flying… then you weren’t.’”

This doesn’t mean that the FAA isn’t doing the right thing. Their rule focuses on FDM, and it just means that this is an issue much more complicated than simply writing legislation. As always, the devil is in the details. Thankfully, the FAA has issued a comprehensive advisory circular to spell out what is actually needed.

Until regulatory standards are set for these systems, the only true solution is for operators to become better educated on the differences. Operators should begin with the Health and Usage Monitoring Systems Toolkit and the Helicopter Flight Data Monitoring Toolkit provided by the International Helicopter Safety Team (IHST). Also, CAA’s CAP 753 is a good source for HUMS standards in use around the globe, and ADS-79D-HDBK is the U.S. Army’s handbook for CBM. These are all invaluable sources of information for any company considering the implementation of a HUMS, HFDM, or CBM program.

Companies should consider buying these systems now because they can’t afford not to. The systems will quickly pay for themselves, and will continue to provide benefits and cost savings long after that. Whether from the perspective of safety, maintenance, operations, or reputation, these systems are a reasonable and necessary means of company improvement. They provide the insight to know how the helicopters are being used and what is happening inside them. In the end, you can’t fix what you don’t know is broken, but you’d be surprised by what you don’t know!

In the November issue, Rotor & Wing’s HUMS capstone article will cover the improvements currently on the horizon for these systems, and explain what the perfect HUMS and HFDM system will look like in the future.

Related: Maintenance News

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