Research continues to advance helicopter maintenance

LONDON (March 3, 2011) -- A deadly civilian helicopter crash in the North Sea on Nov. 6, 1986, led the British Civil Aviation Authority to invest more into vibration health monitoring systems used to detect maintenance issues and prevent accidents.

Twenty-five years later, improvements on installed systems are still being developed to provide flight and maintenance crew's earlier detection and lower false alarms.

"We want to reduce the maintenance burden and remain operationally flexible, while assuring continued airworthiness," said Dr. John Berry, chief of Aviation and Missile Technologies at the U.S. Army International Technology Center - Atlantic, USAITC-A.

Through a cooperation made possible by the USAITC-A, an organization under the Research, Development and Engineering Command's Forward Element Command-Atlantic, research to improve the software behind the Health and Usage Monitoring System, or HUMS technology is ongoing.

Also known by the military community as a Digital Source Collector, this technology is already installed on many U.S. Army helicopters.

Much of the initial research began under the British Ministry of Defense, and collaborative efforts between both countries advanced the systems over the years.

"About 80 percent of this technology is from MOD work completed over 30 years ago," said Ken Pipe, a British engineer and long-time researcher within the field.

Pipe has worked multiple times on both sides of the Atlantic on Health and Usage Monitoring Systems projects benefiting the entire aviation community. More than 20 years ago, he was part of a Stewart-Hughes team that was handed the Cockpit Voice Recorder data from the 1986 Boeing 234LR crash.

The Air Accident Investigation Board gave multiple companies the CVR data for analysis because the pilot had reported an odd noise, and had no indication of what it meant. The team discovered the location and type of defect that caused the accident through analysis of the tapes using its HUMS technology, proving that such vibration- monitoring technology could be used to assure airworthiness.

"The key is that you can perform a reliable diagnostic with a prognostic that ensures you determine the need for maintenances well before the helicopter's airworthiness is compromised," Pipe said.

It is important to both diagnose a fault within an aircraft and have the information to know what to do about it and when. Just because a part is worn does not necessarily mean it needs to be replaced; however, just because the schedule gives a part more time does not mean it is safe to fly.

But finding the fault is like trying to find the one out-of-tune instrument in the whole orchestra, during the concert, and you do not know which piece of music the orchestra is playing, Pipe said.

This technology ties to a larger concept known as condition-based maintenance, or CBM, which is a model that has fascinated both the civil and military communities for decades.

"The Office of the Secretary of Defense has mandated an advanced form of this maintenance strategy," said Berry.

The CBM model asks a simple question with an incredibly complicated answer: can we determine when the condition of the part requires maintenance action in sufficient time to safely and efficiently supply the part and schedule the action'

To bring this example closer to home, one might ask if car repairs are made only at the scheduled maintenance dates or when an expert mechanic identifies those parts truly need replacing' And how does that information impact decisions about money and crew safety'

Each helicopter design is different, each having different parts with varying vibration signatures. Collaborative efforts like those made by USAITC-A and various research groups can advance these systems in order to reach the broader aviation community faster.

HUMS technology may reduce corporate helicopter insurance costs and is CAA mandated on certain helicopters operating in the UK.

Both Pipe and Berry hope that the research will provide improvements that will quickly make its way into the military inventory, but an exact time cannot be estimated.

Improving systems that save lives, instill more confidence in pilots, reduce the maintenance burden and reduce costs. All appear attainable, long-term goals of this research partnership, they said.