Bell 525 Bell Helicopter Textron
The Bell 525’s vehicle condition-monitoring system was engineered into the new helicopter’s design. Its data will be communicated to the pilot and show the detailed health of core components such as the gearboxes, driveshafts, engines, transmissions and other dynamic parts.

Digital Helicopter Condition-Monitoring On Increase

Helicopter health-monitoring systems increase digital data acquisition and provide upgraded examinations

More helicopter operators soon may realize greater maintenance benefits and safety enhancements as OEMs make further inroads into digital data acquisition and a new generation of health- and usage-monitoring systems (HUMS).

Using multiple sensors, HUMS check health and performance through continuous monitoring of such critical components as engines, tail rotors, transmissions and main gearboxes. Any generated actionable information will be the basis for making informed maintenance decisions and enabling condition-based service. 

Josh Melin, Honeywell Aerospace’s senior product line manager for HUMS, explains that the market for line fit and retrofit has two segments.

“The first includes the more sophisticated helicopter operators who demand increased capability and functionality, allowing more complex measurements to be carried out at greater frequency and at increasingly complex algorithms,” Melin says. “These operators are mainly our military customers who already have a lot of experience with HUMS.”

The second market for HUMS, he says, is “cost-sensitive customers,” who are mostly civil helicopter operators.


On the S-92, Sikorsky developed a methodology to adjust component retirement times using HUMS-collected data, with DAL Level B software. The result is that main rotor life limits have been increased by as much as 40%.

“This group has not enjoyed the advantages of an onboard health- and usage-monitoring system but now desires the critical-component monitoring, which is core HUMS functionality,” Melin explains. At the same time, the cost-sensitive market also has requested such capabilities as flight data-monitoring, streamlined wireless data movement with more cloud/server integration, along with simple, intuitive user interfaces, notes Melin.

He stresses that to meet the needs of this market, it will be necessary to develop lighter-weight, smaller systems that will cost less than the typical HUMS solutions now available. 

For now, Honeywell is serving much of the cost-sensitive market with portable, carry-on systems that provide select monitoring of the track and balance of the main and tail rotors. Essentially a flight-line test system, the carry-on requires no modification to the aircraft or STC. However, Melin predicts, the market ultimately will favor onboard HUMS. “Onboard HUMS provides continuous monitoring of all the critical systems, at a given rate and structures the data in real time while doing a data analysis,” he points out. Portable systems provide snapshots, or measurements, of what is happening at a given time, rather than analyses of the data generated.

HUMS has substantially reduced the time involved with main rotor track and balance for one operator, according to Robert Roedts, director of engineering at Columbia Helicopters, a Portland, Oregon-headquartered provider of global helicopter services. 

“Our primary focus with HUMS has been on main rotor track and balance monitoring. Prior to HUMS, it would literally take several weeks of flight testing, because we had no hard data to go on. With HUMS, we can normally determine correct track and balance with just one or two test flights,” explains Roedts. “It has taken the guesswork out of the maintenance action we need to perform.”

That outcome is based on seven years of experience, starting in 2010 with the installation of a Honeywell VXP HUMS on a Columbia Model 107. Since then, an additional three Model 107s have been equipped. The operator also has certified a Honeywell MSPU (modern signal-processing unit) HUMS on its Boeing CH-47Ds, with three equipped to date.

Roedts reports that within a few years, the plan is to transition to real-time monitoring of the entire aircraft for predictive maintenance. “To do that, we are looking at new-generation packages, along with people who know the aircraft and can interpret the data to determine if it is actual or an anomaly.”

Jim Cycon, director of aircraft health management systems for Sikorsky Aircraft, says that while the primary focus of HUMS has been vibration monitoring, the trend during the past 10 years has been to combine that function with avionics diagnostics data and information from flight data recorders. At the same time, HUMS equipage has been reduced in size and weight.

“In 2004, when we first installed HUMS on the [Sikorsky] S-92 helicopter, there were four avionics boxes performing diagnostics/HUMS functions,” Cycon notes. “But by the time we applied it to the UH-60M Black Hawk product line, all of the diagnostics/HUMS functions resided within a single box, which has been considerably reduced in size and cost from the ones originally installed on the S-92.”

With the introduction of the S-92A, Cycon reports, the OEM further enhanced HUMS, enabling a larger amount of data collection from within a single place. That, he points out, opened new methods of component inspection  and predictive maintenance, with the goal of preventing removals prior to an unscheduled maintenance event. 

Bell Helicopter Textron

The Bell 525’s vehicle condition-monitoring system was engineered into the new helicopter’s design. Its data will be communicated to the pilot and show the detailed health of core components such as the gearboxes, driveshafts, engines, transmissions and other dynamic parts.

For example, Cycon notes that in 2014, the FAA approved a new process Sikorsky proposed to adjust the retirement of the S-92A’s main rotor hub, which had a mandatory 4,900-flight-hour life limit.

“On the S-92, Sikorsky developed a methodology to safely adjust component retirement times using HUMS collected data,” he explains. “One of the key factors in getting FAA approval of our component-retirement adjustment methodology was the fact that the S-92’s HUMS software is Development Assurance Level (DAL) Level B, while the software used by most other HUMS is DAL Level D. Using HUMS data to adjust a component retirement, and keep it on an aircraft longer, has the dual benefit of reducing both maintenance and operational cost.”

Since the FAA approval, Sikorsky has seen retirement-time increases as high as 40% on some S-92A’s main rotor hubs, Cycon reports.

He also stresses that HUMS has “a lot of untapped potential in helicopter maintenance and safety, citing tail-rotor torque-monitoring.

“Today, we really do not have good data on the amount of torque going to the tail rotor. If we had that information, we could do more predictive maintenance there,” Cycon says. 

Helicopter operators stress that a one-size-fits-all approach to HUMS is no longer viable. To meet that concern, UTC Aerospace Systems’ Pulse is now in field-level evaluation by representatives of helicopter and fixed-wing OEMs and operators, with certification slated for mid-2018. 

“Pulse is lightweight, incorporating a 1-lb. [line-replaceable unit]. However, its main advantage is its distributed architecture, which is designed to enable adding additional modular application layers to the core operating software,” explains Kevin Hawko, UTC Aerospace Systems’ vehicle health business development manager.  “Those layers can be added over time to serve individual customer needs, such as vibration monitoring with a mechanical diagnostic function, or strain-monitoring, and electrical-current monitoring.”

Hawko says adding modules would not require significant software development, thus minimizing work and impact on the certification process.

UTC Aerospace Systems

UTC Aerospace Systems’ Pulse is now in field-level evaluation by representatives of helicopter and fixed-wing OEMs and operators, with certification slated for mid-2018.

Helicopter engine health-monitoring is also on the fast track. In late 2015, Pratt & Whitney Canada certified its Flight Acquisition, Storage and Transmission (FAST) monitoring system on its PT6C-67C, which powers the Leonardo AW139. It was the first application of FAST to a helicopter, according to Bjorn Stickling, the Montreal-based OEM’s manager of diagnostics, prognostics and engine health management.

“FAST is a compact total ecosystem. Its core function is to automatically capture and compact all aircraft and engine data and transmit it securely. Working in tandem with the aircraft’s main data bus, it is totally integrated, with full wireless connection to a Wi-Fi or cellular ground-based system,” Stickling points out. “It is a turnkey solution that does not require the user to set up a separate IT platform to receive the data, which is transmitted to an OEM engine data analysis center. Because of its rich data-mining capability, FAST is also a very significant compliance tool.”

He adds that FAST has been designed to solve key pilot workload issues, such as automatically calculating the engine’s operational margins.

FAST, notes Stickling, has been applied to more than 1,200 Pratt & Whitney Canada engines, and of that number, more than 50 have been selected by AW139 operators. Other helicopter programs for FAST are under study.

At Bell Helicopter Textron, “integrated vehicle health-monitoring” is integral to the design of the new Bell 525, a fly-by-wire, medium-size, 20-place, multi-mission civil helicopter slated for year-end 2018 certification.

“Integrated vehicle health-monitoring has been designed into the DNA of the aircraft,” says Glenn Isbell, Bell’s executive vice president for customer support and services. “We have integrated all of the helicopter’s systems with ground station support services, so that the aircraft mechanics and pilots can review the same information.” 

To accomplish that, Bell “designed and focused the technology of the Bell 525 on an integrated glass cockpit,” incorporating interfaces with the signals and diagnostics built into the software of all the systems being monitored,” Isbell notes. “The intelligence generated by the system, and fed into a central computer on the aircraft, will be accessible by the pilot and maintenance staff—in real time.” 

While predictability and optimization of maintenance events were the major drivers behind the development of the Bell 525’s vehicle condition-monitoring system, safety also was stressed, Isbell points out. “The aircraft will know, at all times, the status of its health,” he says. “The data, which will be more robust, will be communicated to the pilot—even in flight—showing the detailed health of core components such as the gearboxes, driveshafts, engines, transmissions and other dynamic components, as well as historical trends. That is its most significant advantage. Previously, pilots and mechanics could only determine the helicopter’s health status after landing the aircraft and downloading the information.”

As with all in-production Bell Helicopter Textron products offering integrated health-monitoring technologies, operators of the Bell 525, once registered with the OEM, will be able to access data on any mobile device, using MissionLink, a dashboard with an easy-to-use data-landing page available on the customer’s mobile device. “It allows our customers’ aircraft to communicate how it is performing, historical trends/analysis and detailed health on core components,” Isbell adds.

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