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How the heck does that happen?!

 

The aircraft we fly are subject to the imperfections of human endeavor. No matter what we do, we must remember, it’s just a piece of machinery and we’re only human. It could come down to a single part that we have no control over. Some minute detail, gone unnoticed, that escaped the manufacturing and testing process. This reminds me of the Bell 222 in-flight break-up in Texas.

 

The main transmission remained connected with the main fuselage and was covered with soot. The transmission outer case exhibited several holes in it, consistent with impact fractures. The right aft transmission mount was fractured, but the other three mounts were intact. Free rotation was observed through the intact tail rotor gearbox assembly.

 

The main rotor was found approximately 220 feet northeast from the fuselage. The main rotor mast was fractured and separated near the top of the mast and just above the transmission top case. The appearance of the fractured surface at the top of the mast was consistent with a hard contact with the main rotor yoke. The main rotor system was found mostly intact.

 

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

 

The fracture of a swashplate drive pin as a result of “hydrogen embrittlement” due to an unknown source, which resulted in an in-flight breakup of the main rotor system during cruise flight.

 

Hydrogen embrittlement is the process by which metals such as steel become brittle and fracture due to the introduction and subsequent diffusion of hydrogen into the metal. This is often a result of accidental introduction of hydrogen during forming and finishing operations. This phenomenon was first described in 1875.

 

REF: Aircraft: BELL 222, registration: N515MK - Accident occurred June 2010 in Midlothian, TX

 

Hydrogen Embrittlement of Metals
Edited by iChris
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That's from the accident helicopter iChris mentioned???

 

The way I interpreted the excerpt he post, it seemed like there should be more of the mast attached to the... well... the mast...

Edited by ridethisbike
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That's from the accident helicopter iChris mentioned???

 

The way I interpreted the excerpt he post, it seemed like there should be more of the mast attached to the... well... the mast...

 

The failure of the A-Side Drive Pin led to the in-flight breakup of this Bell 222 rotor system.

 

The rotating blades of a helicopter produce high centripetal loads on the rotor head and the blade attachment assemblies. centripetal loads may be from 6 to 12 tons at the blade root of small to medium helicopters. Larger helicopters may develop up to 40 tons of Centripetal load on each blade root.

 

As long as the rotor head, blades, and blade attachments remain intact and operational, the forces produced about this rotating mass will remain in balance and restrained. However, if any part of this rotating mass of hardware fails, the imbalance of these forces will cause the rotor system to self-destruct in a matter of seconds.

 

Centripetal force is the dominant force affecting the rotor system; all other forces act to modify this force. Centripetal force keeps an object a certain radius from the axis of rotation. It’s the force that makes a body follow a curved path. Centrifugal force is the apparent counteracting (equal and opposite) force that tends to make rotating bodies move away from the center of rotation.

 

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The main rotor mast was fractured and separated near the top of the mast and just above the transmission top case.

 

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Edited by iChris
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Centripetal force is the dominant force affecting the rotor system; all other forces act to modify this force. Centripetal force keeps an object a certain radius from the axis of rotation. It’s the force that makes a body follow a curved path. Centrifugal force is the apparent counteracting (equal and opposite) force that tends to make rotating bodies move away from the center of rotation.

 

I love you

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  • 3 weeks later...
Airbus Helicopter Crash Probe Narrows In on Component Failure
Norwegian investigators probing the crash of an Airbus Group SE helicopter off the west coast of Norway in April are focusing on possible failures of some components linked to the rotor system.
The Accident Investigation Board Norway, or AIBN, on Friday said failure of the housing of the main gearbox, a gear called the epicyclic module and a suspension bar that helps hold the rotor in place are being considered as possible causes for the April 29 crash of the Airbus EC225, also called the Super Puma.
Airbus late Friday said only the failure of the suspension bar seemed a probable scenario given current evidence. However, the helicopter maker added that it was still unknown what might have caused such a failure. The chopper flown by CHC Helicopter Services crashed en route to Norway’s Bergen Airport from Statoil AS A’s Gullfaks B oil field, killing all 13 people onboard.
Data from the helicopter’s so called black box showed everything normal during the flight until a catastrophic failure occurred within 1 second to 2 seconds, causing the rotor to detach.The French air-accident office, the BEA, which is aiding the probe was able to extract additional information from another memory unit to glean further data, the AIBN said, and this is now being analyzed.
Some of the wreckage that has been collected is being subjected to detailed metallurgical assessment, the AIBN said, adding those efforts are at an early stage. “So far, these examinations have not identified a conclusive primary cause of the accident.”
Norwegian and British air-safety regulators imposed a ban on all EC225 passenger flights, though Airbus said it saw no reason to ground the model. Airbus and the European Aviation Safety Agency have since called for emergency inspections of EC225 helicopters.
Airbus EC225s have been involved in previous incidents linked to problems with the main gearbox. However, Airbus said early evidence suggest last month’s accident had a different cause, based on its investigators’ findings.
CHC Group, which was financially struggling already before the crash, on May 5 filed for chapter 11 bankruptcy protection.
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REF: Airbus Helicopter Crash Probe Narrows In on Component Failure

Edited by iChris
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I flew Twinstars (AS355F & F1) at my previous employer, 11 years and 6000 hours. At that time the "suspension bars" were stainless steel tubes compressed/flattened around the bearing itself, through-bolted to the deck fitting and upper transmission. I had 2 separate events where the bearing shifted in the tube: once on the lower end; and once at both ends on the same bar. A solid metallic thunk and slight change in aircraft pitch attitude announced each event, followed by a precautionary landing.

Maintenance personnel couldn't identify the issue with the first single bearing dislocation as it set back into normal position when I landed.... With the second event, the bearings were still displaced when roving maintenance started inspecting. I guess I was luckier than I thought.

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I had an R22 CFI if flew with for like 5 years and then in 1990 he took a job flying a 500E overseas. He was actually the first pilot I paid to fly a helicopter I owned. Some other pilot grounded the 500E but this other guy thought he could fly it back to maintenance. Big mistake. I heard a rotorblade separated from the fuselage and items were found 2 miles apart. Don't know what altitude he was at. Apparently, it was relayed to me that another pilot had grounded that aircraft so it's more understandable to me. If you are just flying along something lets go I don't know how to process that. Think I'd rather be in one of my cars so that if something fails you are at one altitude. Now if you hit something remember that we all have in cars those airbags that have shrapnel in them and the manufacturer can't replace them all quickly enough. Think I'll just sit here at the computer.

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