Vibration In Flight

[CJ Eliassen]

On July 28, 2004, at 1332 eastern daylight time, a Robinson R22 Alpha, N103MH, impacted the terrain while attempting to perform a forced landing at the Selfridge Air National Guard Base (MTC), Michigan. The accident occurred on the airport between taxiways Bravo and Delta. The commercial pilot was fatally injured and the helicopter was destroyed. The 14 CFR Part 91 flight was operating in visual meteorological conditions without a flight plan. The origin of the flight is unknown.

 

The pilot contacted the control tower at MTC stating he was nine miles south of MTC and he was transitioning through their airspace en route to the Ray Community Airport (57D), Ray, Michigan. The tower issued a squawk code to N103MH. The pilot then reported to the tower that he was experiencing some vibrations. The tower controller asked the pilot if he wanted to land at MTC and the pilot reported he was going to continue to 57D. Shortly thereafter the pilot contacted the tower stating he did not think he could make it to 57D and he wanted to turn around and land at MTC. The controller stated N103MH was two to three miles northwest of MTC at this time. The controller declared an emergency for N103MH and cleared him to land on the south side of the airport.

 

Witness stated they saw N103MH approaching the airport from the northwest. They stated the helicopter was approximately 200 - 300 feet above the ground, flying straight level, and fast. The nose of the helicopter then dropped approximately 60 degrees and the helicopter descended to impact with the terrain.

[Wally]

A change in the aircraft is always something to take seriously- vibrations and smoke are land at the first "survivable place" situations. Think about it- something dynamic on the helicopter has changed status. It won't get better with continued flight and could suddenly get much much worse.

 

It's always better to be on the ground wishing you were flying, than flying and wishing you were on the ground.

[RDRickster]

How many safety notices have we seen from RHC on this subject?  Yet, time after time, folks decide to push the envelope... for what?  Unless he was in moderate to severe turbulence that could explain the shakes, "increasing vibrations" spells "impending doom."

 

He should have landed to at least inspect the aircraft instead of passing the field like that.  That said, if I was only 2-3 miles from an airport, I would probably go for the field, too (unless vibrations continued to get progressively worse).

[CJ Eliassen]

I wouldn't.  I would land in the first field available.  2 to 3 miles is 3 to 4.5 minutes.  If the upper sheave bearing is shredding apart, it only needs a few seconds to do so.

[Bart]

It cpould have been engine trouble!

 

A couple weeks ago I was taking off from the GA ramp area at Sacramento Intl. when at about 100 ft. AGL and 300 yards from the ramp, my R22 started shaking like a wet dog.  I had no idea what was going on...my first thought was the rotor system.  I made a quick glance at the panel and saw my RRPM was still good, but my manifold pressure gauge was busting the red line by 1 or 2 inches.  After I saw that, I lowered coll but started dropping like a rock.  So I pulled it back up, and turned 180 degrees back toward the ramp, but I could only make it halfway there.  I landed in the weeds about 100 yards away from the tarmac.  I did a quick shutdown, and got out to inspect the rotor systems and found nothing out of the ordinary.  Luckily, the GA personel saw me sitting out in the field as he was getting in his car to go home (this was at 10:30 at night) and ran over to see if I was alright.  He asked what happened but I still didn't really know...so I was was gonna start it up and try to find the problem.  As soon as the engine started I heard a funny ticking noise and realized I wasn't going anywhere anytime soon!  Soo he let me back in the office, and I made some phone calls to the flight school GM.  He told me to find a hotel and he would send the mechanic up the next morning.

 

Anyway, 5 beers and 8 hours sleep later, I went back to the airport and met our mechanic.  He started checking things out, and about 5 minutes later found the culprit...The right-front cylinder had stuck a valve, the pushrod and guide were bent pretty good.  Then we spent the next three hours pushing the helicopter back to the ramp using our strong backs and some 4x8 sheets of plywood.  None of the airport personnel wanted to get their hands dirty over the whole ordeal.

 

So I went to the RHC Safety course the next week and told Tim Tucker about my incident, he said knew of a pilot that experienced the same thing but at 200 ft. agl...she entered into an auto, crashed and killed herself and her passenger.  He told me I made the right decision, and I totally agree

  .  Then, on the flight portion of the class, the instructor, after telling him my story said, " yeah, I've had that happen to me a couple of times too!"  Sheesh, I had never heard of this before!  Oh, well...I guess I can't be too surprised, I'm still pretty green at 130 hours.

 

Anyway I learned a great deal from that experience and I'm glad my instincts didn't tell me to enter an auto!  

 

Aaron

[MidwestHelicopter]

That reminds me of the story they told out at safety school of the student (or low time PPL) that had a low oil pressure indication and light come on in flight.  He landed, checked the oil.  It showed 6 quarts.  He took off and the engine seized up about 4-5 minutes later.  I can't remember if it was a fatal accident.

 

Valve sticking is quite common in R22s--it appears more when people aren't doing proper warm up and cool downs.  Usually its the exhaust valve sticking after cool down and then runs like crap when you start it up.  We'll usually ream the exhaust guide valves when a R22 hits 300-400 hours TT as per Lycoming.  Its about a 3-4 hour job.  Most of that time is spent fishing the valve out of the cylinder and back into the guide.

 

Good job on getting it back on the ground!

 

-Jonathan

[Wally]

Yuh done real good, Bart. It couldn't have been more intelligently handled had you thousands of hours.

When in doubt, chicken out! And fly the aircraft...

[CJ Eliassen]

Midwest,

 

Tie some fishing like around the valve before you drop it into the cylinder.  When you are done reaming the valves, put a vaccuum up to the valve guide, or you can aldo use compressed air in the spark plug hole if the other spark plug hole and valve guide are not open.  Use very thin line that flows easy.

[Lu Zuckerman]

If the vibration develops over time notify your maintenance mechanic.  Work with him telling him under what conditions the vibration manifested itself and hopefully he can rectify the problem.  If the vibration manifests itself in a short period of time get on the ground and if something hasn’t failed on the way down tell the maintenance mechanic after you have landed.

 

Many years ago I flew in a Los Angeles Airways S-61 from Orange County to LAX.  It was an extremely rough ride and you had to keep your jaw clenched to keep from chipping your teeth.  It was obvious looking at the tip path that one of the blades was really out of track.  When I got off at LAX I told one of the ground crew about the out of track blade and he said they would correct the problem at the next maintenance cycle.  Several days later that same ship experienced a rotorhead failure killing all aboard.  A short time later their other S-61 experienced a rotorhead failure killing all aboard including the grandson of the airline owner.  Shortly after that they went out of business.

 

If you are interested in what caused the failures let me know.

 

 

:unclesam:  ::whisper:: This is Pierre.  He is the blue one.  After telling his girl friend of his dilemma she told him to piss off.

[Lu Zuckerman]

To: yzchopper

 

I'm curious to know what caused the rotor failures on those helicopters you mentioned in your post. If you could fill me in as to what happened that would be appreciated.

Thanks

 

Both rotorheads were returned to Sikorsky for overhaul however there was no overhaul manual for the rotorheads.  What they did was to strip the rotorheads and among other things they ground the chrome plate off of the spindles.  The only reference they had were the design drawings for the spindles.  After grinding the chrome off to the parent metal they re-plated the spindles and reground them down to the specified diameter as indicated on the design drawings.

 

What they did not do was to shot peen the spindles prior to re-plating.  This removed the residual stress in the spindle and in essence turned it into a brand new part.  The spindles were reinstalled after the overhaul and they had all of the high stress concentrations still in them.  Upon entering service the spindles were exposed to high vibration levels such as those mentioned in my post and as a result they fractured.

 

 

:unclesam:  ::pray:: This is Pierre.  He is praying to get back with his girlfriend.

[yzchopper]

To: Lu

 

 Thanks for the info, much appreciated. ::thanks::

 

 Steve ::rotorhead::