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Lost art of H-60 inspection proves useful after lightning strike
Story by Joseph Mendiola on 08/08/2019
REDSTONE ARSENAL, Ala. (Aug. 8, 2019) A lost art of inspecting helicopters is coming back to the forefront due to a liaison engineer’s presentation at the Vertical Flight Society’s 75th Annual Forum in Philadelphia in May.
Travis Massa, a U.S. Army Combat Capabilities Development Command Aviation & Missile Center Aviation Engineering Directorate liaison engineer, discussed his technical paper on using a magnetometer to inspect aircraft after a lightning strike.
The technical paper is based on an event from March 9, 2017. That evening, a storm capable of producing EF-2 tornadoes ripped through southern Missouri and into western Tennessee. In its path was Fort Campbell, Kentucky, located on the Kentucky-Tennessee border. Maintainers inspecting a MH-60M Black Hawk a few days later noticed the helicopter had some unusual damage. They called Massa, the AvMC AED liaison engineer supporting the 160th Special Operations Aviation Regiment there.
Massa walked out to the flight line and saw the maintainers scratching their heads. “After a little bit of discussion, we realized this is probably a lightning strike,” he said. “So they pulled the aircraft into the hangar and consulted the maintenance manual for the aircraft.”
The manual details certain areas of the Black Hawk for the Soldiers to inspect, starting with the highest point: the rotor and tail rotor blades. However, the manual only contains guidance for visual or obvious damage.
That’s where the magnetometer, or magnetic field indicator, came in.
While discussing issues with Clark Lemons, another AvMC AED liaison engineer supporting the 101st Airborne Division, Lemons told Massa he picked up an inspection technique for lightning strikes over his 34-year career. Lemons provided engineering support at Corpus Christi Army Depot in Corpus Christi, Texas, before transferring to Fort Campbell in 1993.
“If you have a part that is made of a type of material that can be magnetized (and) if a large electrical direct current is applied, the flow will magnetize those parts and leave a residual magnetism,” Lemons said.
Residual magnetism occurs when lightning flows through the aircraft and magnetizes metal parts made of nickel, cobalt, or iron elements. While a large part of the Black Hawk is made up of aluminum and nonmetallic parts to make it light enough to fly, smaller parts like bearings, bushings, screws and rod ends for flight controls contain some of these elements. Those smaller parts run the risk of becoming magnetized and can pass inspection if there’s little to no visible damage.
Lemons met with Massa and demonstrated the process. When a magnetometer is placed near the aircraft part, it detects strength of a part’s magnetic field. Any high readings on the indicator show which parts were magnetized by lightning.
“You can trace the direction of the lightning bolt through the airframe,” said Lemons.
“Knowing those (lightning) paths allowed us to clearly and intentionally look at all the components in the aircraft along that path,” said Massa. Visual damage and inspection with a magnetometer told them the lightning path passed through the tail rotor.
As a result, Massa recommended the Soldiers replace additional tail rotor components beyond what was required in the aircraft maintenance manual. “We felt it very prudent, from a safety standpoint and an airworthiness standpoint, to go ahead and replace those parts. There could be damage on the inside that we can’t see,” said Massa. “The bearings in the gearbox could have had the same kind of arcing marks we saw on the exterior components. Obviously that damage was not major but, over time, that damage could cause a premature failure.”
Lemons said he sees this as affecting readiness and safety. “I have had aircraft in the past that were struck by lightning and the division expected to have to load that aircraft on to a flat bed or lowboy trailer and truck it all the way down to have Corpus Christi Army Depot run it through their overall program,” he said.
Instead of packing the aircraft up and shipping it to CCAD, the technique helped Lemons find parts to demagnetize on site. He got the aircraft back into service in just under a month, saving time and money and eliminating questions about the aircraft.
Massa said the important thing is to spread the word on the magnetometer technique, which is not in any current aircraft maintenance manuals. He discovered the technique in maintenance manuals for Bell helicopters, like the Huey and the Cobra, both of which have been out of service for nearly 15 years.
“In the post-lightning strike section task in those particular manuals for those aircraft, I think the verbiage (was) Check for residual magnetism with a magnetometer’ and that was it,” said Massa. “There was no How do you actually accomplish that?’, What are you looking for?’, What do you do about it when you find magnetism?'”
His research on the topic led his supervisor to nominate him to write a white paper, which was ultimately presented at the VFS symposium.
“Right now, it’s about educating the engineers that are in the field supporting the aviation customers,” he said. “If they come across an instance of a lightning strike, and if they are pretty certain it was a lightning strike, they can use this technique to supplement the task that’s already in the technical manuals.”
The CCDC Aviation & Missile Center, formerly known as the Aviation & Missile Research, Development and Engineering Center (AMRDEC), is part of the U.S. Army Combat Capabilities Development Command, which conducts responsive research, development and life cycle engineering to deliver the aviation and missile capabilities the Army depends on to ensure victory on the battlefield today and tomorrow. Through collaboration across the command’s core technical competencies, CCDC leads in the discovery, development and delivery of the technology-based capabilities required to make Soldiers more lethal to win our Nation’s wars and come home safely. CCDC is a major subordinate command of the U.S. Army Futures Command.