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Wednesday, February 1, 2006

HUMS: Health And Usage Monitoring Systems

Health and usage monitoring systems (HUMS), initially developed for the larger twin-engine helicopters flown to offshore rigs in the North Sea, are becoming more affordable, more capable and more commonplace in the rotorcraft industry. These systems, which have been around for some 30 years, are being refined and offered at lower costs by non-traditional HUMS providers.

"Moving down the road I see these systems becoming standard in helicopters," said Matt Zuccaro, in an interview by Avionics Magazine. Zuccaro recently was named president of the Helicopter Association International, an association representing civil rotorcraft operators. HUMS "will be more of a requirement by the clients in a lot of segments in the industry--even to operate the aircraft more economically," he added.

Monitoring systems have been developed for fixed-wing aircraft, but the HUMS effort focuses on rotorcraft, which benefit from a system's ability to record engine and gearbox performance and provide rotor track and balance. HUMS may also monitor auxiliary power unit usage and exceedances, and include built-in test and flight data recording (FDR) functions. Overall, a full HUMS is expected to acquire, analyze, communicate and store data gathered from sensors and accelerometers that monitor the essential components for safe flight. The analyzed data allows operators to target pilot training and establish a flight operations and quality assurance (FOQA) program, in which they can determine trends in aircraft operations and component usage.

The widespread use of HUMS is expected to be a major contributor to the helicopter industry's goal of reducing the accident rate by 80 percent with 10 years. The goal was discussed at the International Helicopter Safety Symposium in September 2005 in Montreal.

The major HUMS manufacturers include Smiths Industries, which owns a division that was formed from the original North Sea HUMS manufacturer Stewart Hughes Ltd (SHL), and Goodrich, a long-time supplier of HUMS to the military and some civilian helicopters. Other companies, including airframe manufacturers, are moving into the HUMS arena. Some offer lower-cost systems that are bound to make the use of HUMS more widespread.

The benefits of HUMS have become more and more apparent over the years. During a Smiths Aerospace HUMS conference in 2003, a U.K. Civil Aviation Authority (CAA) presenter said that independent studies show that "HUMS was probably the most significant [stand alone] safety improvement of the last decade."

More statistical information was offered by Kenneth Pipe, principal consultant with Humaware and former director of Stewart Hughes. "North Sea experience documented by the CAA shows a 70 percent success rate in detecting defects." Eurocopter's Rotor Journal magazine cited statistics showing that the return on investment for HUMS includes the following:

�60 percent reduction in check flights,

�25 percent reduction in tests, and

�Unscheduled maintenance down by 20 percent.


But the benefits have come at a cost. "The big challenge is that most HUMS are expensive," said Douglas Thompson, general manager of engine-monitoring developer Altair Avionics. "It's almost cost-prohibitive in some cases."

Altair, owned by Pratt & Whitney Canada, along with Intelligent Automation Corp. (IAC), Bell Helicopter and Aeronautical Accessories Inc. (AAI), has developed a system that monitors helicopter engines and provides vibration-monitoring and other HUMS features. The IAC-Altair system is part of Bell Helicopter's new Helicopter Vibration Monitoring (HVM) system for Bell's model 412. "We've integrated [IAC's system] with our usage monitoring to create an integrated system," Thompson said.

The Altair portion of the system consists of the SmartCycle+, which monitors the gas generator, turbine speeds and temperature, rotor speed, and engine torque, plus altitude, airspeed, outside air temperature, and two additional channels. IAC's system adds vibration monitoring, rotor track and balance, and gear and bearing diagnostics.

"Both systems have their own database, so sharing data back and forth is not that big of a deal," said Thompson. "It's straightforward. We didn't make significant changes to SmartCycle." The HVM kits are available though AAI.

Bearing in mind the weight sensitivity of rotorcraft, Altair kept the SmartCycle+ processor unit down to 27 ounces, with total system weight of 11 pounds (not including the IAC portion). The SmartCycle+ has been installed on various helicopters, including the Bell 212 and 412, and the Agusta A109 and A119. Thompson added that Altair will work with other companies to integrate SmartCycle+ with vibration-monitoring systems.

The next step for Altair is to obtain a supplemental type certificate for its digital monitoring system, ADAS+, in the Agusta A109 and A119. This digital monitoring system weighs 5 pounds installed and is the company's first Arinc 429 bus-capable system. With connection to the Arinc 429 bus, the Altair system can gather more data. "It opens us up not just to engine information, but airframe as well," Thompson explained.

Altair's SmartCycle+ and ADAS are JAR OPS 3-compliant. Thompson believes a market will continue for both small and large HUMS. "We will continue to have full-up HUMS and a subset, which is vibration monitoring and usage monitoring separately [mini-HUMS]."


As the supplier for the first U.S. helicopter--the Sikorsky S-92--to incorporate HUMS as standard equipment, Goodrich has already delivered more than 100 health and usage monitoring systems to commercial and military customers. HUMS development at Goodrich is in the third or fourth generation, according to Kip Freeman, business director, government systems for Goodrich Aerospace's Fuel and Utility Systems Division.

Diagnostic information from the Goodrich HUMS ranges from which gears in the transmission or which specific bearings have a problem to water penetration in composite rotor blades and mis-shimming in the drive train. To obtain precise results, the HUMS uses a greater number of highly sensitive sensors, but also combines the sensor readings with other measurements, according to Freeman.

"We synthesize the data with other aircraft parameters," he explained. This allows the Goodrich system to deliver early indicators of potential problems. "That's the whole idea," he added, "identify a flaw starting to develop months before it causes a problem." At that point, the operator can choose either to fix the defect or use the information to plan for maintenance. "If you have this flaw starting to develop and know it's going down for maintenance in 30 days, you can fix it then. I can plan, versus a surprise maintenance event."

The Goodrich HUMS also provides trackless rotor balance, designed to give maintenance technicians precise adjustment information, with no need to attach a rotor tracking system and run repeated tests. "We acquire data every time [aircraft] fly," said Freeman. If the pilot feels abnormal vibrations, the tech makes the adjustments according to the HUMS and, he added, "there are no test flights. There's an immediate benefit. Our algorithms show you can bring it just about `dead nuts' with one adjustment."

Goodrich's HUMS, certified to the DO-178B Level B, the RTCA-created criteria for software certification in aircraft, is an open-architecture design, which means that third parties can design systems to hook into the HUMS. For example, a satcom link can transmit HUMS data to the ground in real-time. Or a third party's troubleshooting diagnostics system can narrow down possible causes of the identified problem to assist maintainers in making quicker repairs.

In addition to the civil S-92, Goodrich HUMS also are installed in new military helicopters and retrofitted into existing military fleets. The newest Sikorsky H-60 Black Hawk, the Army UH-60M, and the Navy's MH-60R, will incorporate Goodrich's latest, fourth-generation HUMS system with a built-in digital flight data recorder.

Smiths Industries

Stewart Hughes achieved the first certification of a commercial HUMS, in 1991, working with Teledyne Controls, and was subsequently purchased by Smiths Industries. Now Smiths' HUMS are installed on the U.K. Royal Air Force Chinook, Canadian Forces Bell 412, Eurocopter Super Puma, Sikorsky S-61 and Turbomeca Arriel-powered S-76, EH-101, and the Bell-Agusta 609 tiltrotor, in development. More than 250 Stewart Hughes/Smiths HUMS are in service and have gathered more than 500,000 flight hours worth of data.

A company white paper, titled Helicopter HUM/FDR: Benefits and Developments, noted that the U.K. CAA studied 63 "airworthiness-related arisings [defined as] an event which has led to significant maintenance action," and found that "HUMS successfully detected approximately 70 percent of these arisings." Six of these were potentially catastrophic and the CAA estimated that one or two could have resulted in an accident.


Shadin offers the Engine Trend Monitor (ETM) for helicopters and fixed-wing turbine-powered airplanes. The 10-pound (installed weight) system is designed for operators that can't afford a full HUMS but want many of the benefits. "The reason for HUMS is to increase safety and reduce costs," said Shadin's executive director of operations, Allan Kramer.

The ETM does not measure vibration. It could be combined with a vibration analysis system, according to Kramer, though Shadin has yet to do this.

However, Shadin's system does log a rotor overspeed, using a blind ETM recorder with no panel display. "We have had instances," Kramer said, "where the pilot has oversped the rotors and not logged it as they should. When the recorded data gets analyzed, whoops, we have a problem. There's one example where it cost a quarter million dollars to change a rotor assembly due to a 20 percent overspeed."

Shadin's ETM also automatically counts engine component cycles and can share its digital data with Pratt & Whitney Canada's engine condition trend monitoring software. In a Eurocopter BK-117 installation, the Shadin ETM counts cycles on the engine according to a scheme outlined in a Lycoming engine service bulletin. The bulletin specifies when a cycle is actually counted, based on applicable maximum temperatures. "It's a complete paper trail, [working] almost like an accountant," said Rasheed Reda, Shadin's founder and director of new business development and technology.

Shadin's ETM also captures data to validate the engine's operating conditions. "From an engine manufacturer's or maintenance provider's standpoint," Kramer explained, "if you provide an engine warranty, you want to know exactly what the health of the engine is and [any] abuse. And you can write your contracts [such that] if it is an honest failure, the contract pays for the maintenance. [The ETM] limits exposure."

"Also, if trends are starting to show that the engine is using more fuel or running hotter, [the engine overhauler] can call that engine in," Kramer added. He cited as an example a pilot of a tuna-spotting helicopter who noticed that his Hughes 500's Rolls-Royce engine was burning more and more fuel each day. On the 10th day, the chip light for the tail rotor lit up, signaling an imminent failure in the tail rotor gearbox.

Shadin is evaluating data link technology for real-time transmission of ETM data, according to Kramer. In this case the ETM would be coupled with a communications systems such as airborne communications addressing and reporting system (ACARS). In the current system, technicians can download data using a special data key, which plugs into a box that hooks up to a personal computer. Data link transmission would "speed up analysis, [so] the operator immediately knows if he has a problem." And, with that information, operators may be able to apply for extended times between overhauls (TBOs), he said, as the U.S. Army has done with Shadin-equipped C-12 King Airs.


In early 2005 Sikorsky Aircraft selected Honeywell's VXP on board HUMS as an option on newly manufactured S-76C+ civil helicopters and for retrofit on fielded S-76s. The VXP HUMS, currently supplemental type certificated (STC'd) on a variety of Bell, Eurocopter and Sikorsky rotorcraft, includes on board sensors and a data processor, called the acquisition unit, which uses proprietary algorithms to calculate specific maintenance solutions such as rotor track and balance.

"We feel that we have the industry leading software algorithm for quickly and accurately performing rotor track and balance on both single and twin engine helicopters," said Tim Brand, PhD, international marketing director for Honeywell's Defense and Space Helicopter Team. "Most of our competitors' HUMS require six to 10 test flights [to balance a rotor system]. With our HUMS, it takes only one to three flights... resulting in tremendous savings across a fleet."

Instead of just spewing raw data that must be analyzed on the ground, Honeywell's VPX HUMS also provides the operator with already analyzed data in the form of Smart Charts for rotor track and balance, and Vibe Reviews for vibration analysis. The Smart Charts, for example, allow the user to determine whether the main rotor system is unbalanced and provides solutions to place the system in balance. Users can still download the raw data to a ground station for manipulation or fleet-wide analysis.

Offered in both on board and "carry on" versions, the VPX features open architecture that allows third parties to provide options for communicating HUMS data to the ground. However, look for Honeywell to offer combined HUMS/data recorder and communication packages in the future.

"Honeywell is a world leader in the production of cockpit voice and data flight recorders," Brand said. "Where we're going now in the field of HUMS is to combine features of the vibration monitoring and rotor track and balance with cockpit voice and flight data recorders. One of our new developments is to integrate the two features [HUMS and CVR/FDR] into a single box. The future for HUMS, especially in the military arena, is to have your on board HUMS continually monitoring systems, store the data in the HUMS box, then automatically transmit the data to the ground station for analysis while the helicopter is still en route."

Brand says the integrated HUMS/communications systems will be available in the next five years, and that the next generation of HUMS will also include engine exceedence data.

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