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From Justhelicopters.com

 

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Subject: Re: Astar AS350 starflex failures

 

 

After having a starflex arm failure occur on start-up on an starflex with less than 100hrs on it and new shock struts and heel springs on the helicopter I am looking for any information anyone may have concerning starflex failures. THIS WAS NOT GROUND RESONANCE. We were lucky in that the starflex failed prior to reaching groung idle. The aircraft was about to depart from a rig in the GOM and could have been catastrophic. Eurocopter claims a 15 MPH wind with an corrisponding 15 mph updraft probably caused the failure. If thats the case EVERY flight in the GOM off a rig would be susceptible to these types of failures. Any help with info and details would be appriciated, Thanks.....

 

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On February 2, 2004 our AS-350B experienced a failure of a new “0

time” Starflex part number 350A31-1916-00 during a post installation

run up.

 

The pilot was slowly advancing the fuel flow lever to the flight detent

position. Just prior to the flight rpm, a main rotor blade was observed

to go out of track and the aircraft began to bounce violently. The fuel

flow lever was immediately retarded as the aircraft continued to

bounce and rotate to the right. The aircraft ultimately rotated 270

degrees to the right and sustained substantial damage to the tail

boom, I beams, cabin area, and aft fuselage.

 

The aircraft had been positioned in its normal parking spot on dry level

asphalt.

 

During two post accident inspections by American Eurocopter technical

experts, no installation or maintenance errors were noted that could

explain this failure.

 

AEC has suggested that this failure of the starflex was the result of

ground resonance, although the Chief Pilot and two senior A&P

mechanics present at the time of the accident observed nothing that

resembled ground resonance. Subsequent checks of landing gear and

other components associated with ground resonance found all items

meeting Eurocopter parameters.

 

After some research and discussions with other operators we have

learned that this is not an isolated incident. There have been two

similar incidents in Southern California, and another in Northern

California.

 

Other strikingly similar failures have been reported in Texas, Louisiana,

Washington, Canada, and Australia. These incidents have occurred at

both a hover and on the ground.

 

Representatives of American Eurocopter have attributed most of these

starflex failures to ground resonance and pilot mishandling.

Contributing to the confusion is the fact that the starflex is made of

composite materials that are not easily analyzed for failure.

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my question to them, since nobody eluded to it, was how do they tie them down in these high winds? Are they tying them down properly? During constant high winds, guys might get the impression you tie them down tight, really tight. You don't. And overall was there a preflight done? They're lucky they didn't just clear the deck when it happened.

Regardless of new springs on the skids, they don't do a **** if they're not touching the ground. If i recall, alot of rig decks are covered in a net, can they prove the spirings were in contact with the ground, or can we assume they may have been elevated off the ground because of the net.

Yes there may have been a defect internally, but that would mean it got by several non detructive steps without detection. Highly unlikely in my opinion.

Starflex's by nature are very tough, I've seen a broken one from a canadian operator who kept flying even though the vibration was getting worse, it fell apart on the ramp as soon as he rolled the throttle off. I've seen them after a rollover with barely a mark on them and have seen them splintered beyond recognition too.

These guys are looking to blame someone but the whole story isn't available to us.

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Having flown in the GOM I know how windy it can get sitting on the deck, have I seen all three blades tied down thats a good question. I know when I flew A-star's we were told to alway tie the blades down to eliminate the blades flapping in the wind thus possibly leading to premature cracking in the star.

Fly often but fly safe

SOB

ps Saturn Five rocket from Appollo 19 that never went into orbit. Man do I feel small

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Of the 10 or so cracked starflexes I have had to deal with all were fixed by filing to the limit specified in the MM. They would last about 400-500 hrs after the initial crack filing before the crack elongated beyond limits. Most of the time the cracks were on the top side and about 4 inchs outboard of the curved areas. The main reason for cracking was the failure of the crew to tie the blades down in windy situations. I once was sent to Nordegg to replace a starflex that had cracked overnight after a storm. The storm was severe enough to break all three tie downs. A 204 at the same job had the blade come down and dent the T/R driveshaft cover. The Star flex didn't look the one in the picture it was less severe. I think someone didn't tie the blades down and then started in some very heavy winds.

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I would also like to add that I have changed a tx'd starflex that once removed reveiled 3 layers on corrosion washer on top of the mast attachment flange. This condition can prevent proper torquing of the attachment bolts and possibly lead to some damaging head walking.

I believe one operator in Canada had one of these incidents and it negatively affected the aircrafts flight characteristics.

We have many -1916 and -1917 starflex's installed in our fleet and most of them have made it to their retirement life. We did have one -1916 starflex debond a coupling last year. Was noticed during maintenance and it didn't move anywhere thanks to the white plug.

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"I know when I flew A-star's we were told to alway tie the blades down to eliminate the blades flapping in the wind thus possibly leading to premature cracking in the star"

 

 

Yes, you want to restrain your blades from excess flapping but you also do not want to flex them to their lower limit and stress them. The Starflex in that area is made to flex up and down, yet it's main strength is fore and aft. If you notice the curvature of the arms, they are on an upwards angle because for coning. to pull the blade down and leave a force on the starflex after excessive tie down force is applied, you'd just be asking for trouble. I think they found it.

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The blades of any 3 + bladed helicopter should be tied down taking the slack snuggly and tied to the helicopter. If the helicopter should bounce, the blades will bounce with it.

 

The blades of a two bladed system should both be tied down as in the above fashion, except at 90 degrees to the helicopter, to prevent flapping of the one blade and causing rocking of the helicopter.

 

This is assuming high winds on the flight deck.

 

Tie the blades to the helicopter and the helicopter to the flight deck.

 

Cheers, Don

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