Tail blade fail on Kompress CH-7 please help

[czheliman]

Halo heli-pilots,
sat news from Czech republic. One of our friend was involved in fatal accident (http://aviation-safety.net/wikibase/wiki.php?id=80752). Is already proved, that the reason of fatal accident was the broken tail blade. It become apart during flight, made the CH-7 uncontrollable. We have already information from UK pilots-owner of CH-7 already reported detection of macroscopic cracks found in materials of tail blades during first 100 hour inspection!

The aviation laboratory reported skin cracks. The problem is even worse! Immediately after the crash, the investigators found, that there was same problem on two previous cases and the blades has been changed just last minute before catastrophe. Third case caused death. You can read the unbelievable official report here (http://www.laacr.cz/pdf/bulletiny/OMEZENI_LETOVEHO_PROVOZU_ULH_CH7_15-11.pdf)

Most important part is:
V provozu byly v minulosti při předletových prohlídkách zjištěny na dvou jiných ULH stejného typu trhliny na listech ocasní vrtulky, a to ve stejném místě, kde při výše uvedené nehodě došlo s velkou pravděpodobností k oddělení listu od tělesa vrtulky. V těchto případech nebyl let proveden a listy vrtulky byly vyměněny bez dalších následků.

Briefly translation (or use google translator to read all) is: There was two cases before, but the blades was changed in last minute...

More pictures here (http://zpravy.idnes.cz/pilot-neprezil-zriceni-maleho-vrtulniku-na-olomoucku-ppi-/krimi.asp?c=A101114_134315_olomouc-zpravy_mad) :rolleyes:

http://media.novinky.cz/129/241296-top_foto1-dfkv8.jpg

[piggybank]

The Puma SA330J had problems with cracking on its tail rotor blades in the 90's to the point we were certified to do eddy current inspections of the blade skins. Maybe the pieces left of the tail blade will give more info, was it the spar or skin that failed?

[czheliman]

Thanks boys for PM Looks like company working on it CH-7 Heli-Sport (http://www.ch-7helicopter.com/eng/Bollettini.htm?BollettinoID=127)

http://www.ch-7helicopter.com/eng/GetImageID.asp?IMG2=1&BollettinoID=127

[helisphere]

Hmmm... nice photo, the first thing that jumps out at me is there are no doublers in the highest (bending and tension) stress location where there are also stress concentrations due to the bolt holes.

[czheliman]

It is ugly case, the problem was known more then two years. The investigation shows that the company did not take any action till tragedy happened... Since the case is not closed yet, I cant write more. At the end i post results when published by czech officials..

[czheliman]

Thanks to this valuable phorum we have recieved responses from other people:¨¨

Here is my cracked TR blade which I detected after Helisport had overhauled the Main and Tail rotor gearbox’s. (My pinion gear had failed at 400hrs, so Helisport insisted I post both gearbox’s to them for inspection and overhaul)

I had also experienced some corrosion between the blade and blade grip in 2004 and advised helisport to use anti-corrosion treatment in future blades. As far as I know this is still not being done!

A major problem with Helisport is they do not have a service & maintenance manual with technical information with correct procedures for servicing and maintaining the Kompress. Only when repeated problems occur, do they issue a service bulletin.
By not issuing such proper maintenance manual, this has frustrated many Kompress owners not staying near to factory.

Attached are the photos of my TR corrosion (which I had cleaned & treated with anticorrosion paint) and the cracked blade as I had received it back from Italy and noticed when I was doing at TR balance check after reassembly.

There are other German pilots who experienced severe TR blade cracking in 2007.

[czheliman]

I may be able to help
Hi CZH
I am an expert in adhesive bond failure forensics. I may be able to help. Most rotor blades are adhesively bonded, and if the failure is caused of related to the bonding process maybe I can help.

Firstly, do you have any close-up photos of the blade? Secondly, how is the blade constructed? Is it spar with thin skins and honeycomb core? Next, where were the cracks in the other blades located? Did this blade crack in the same location? What materials were used to make the blade?
Regards
Max
Boys thanks for fantastic support!! Since more people replied with same problem, we have created gallery on Flickr. As you can see the problem is known at least since year 2006 !! Looking close to pictures, there is no spar inside and no honeycomb core. Just and just the thin skins....

Flickr: czheliman's Photostream (http://www.flickr.com/photos/59554164@N08/)

[topendtorque]

Helicopter fatal crash - tail blade fail on Kompress CH-7 please help


Excellent photo log, to be commended.
The answer - that's easy, ground aircraft, no pay no more money, (leverage) Zip and return to sender.
cheers tet

[500e]

I would go with Helisphere No doublers to spread load, & small overlap on grip to support blade either, corrosion not good either, helps to promote cracking, ( not that this is a one make problem, try looking at some certified blades with less than 200 hours corrosion & erosion strips lifting)

[blakmax]

The photos are interesting, but I am curious about the how structure is made. Is there a block to separate the skins, and the fasteners pass through the block and both sides? Also what is the yellow material on the pictures labelled crack 2006 and crack 3? Is it primer or adhesive?

I also note the "stop" drills on German crack 2007. Someone actually flew this after stop drilling?

My personal thoughts are that stop drilling is a very effective means of determining crack growth rates. If you record the dates and hours when the drill holes were made, you can estimate the growth rate by measuing between the repeated drill holes. (I am being fasetious; I have yet to see an exampe where a stop drill actually worked! :rolleyes::rolleyes:)

[czheliman]

Also what is the yellow material on the pictures labelled crack 2006 and crack 3? Is it primer or adhesive?yes primer for alu

I also note the "stop" drills on German crack 2007. Someone actually flew this after stop drilling? As you can see clearly, yes :ugh:

I am being fasetious; I have yet to see an exampe where a stop drill actually worked! Actually I have seen few glider canopys where this was efective solution. But probably becouse is aka plastic material, the crack dont spread any more. But agree with you in case of metal .....

[czheliman]

Kompress has been released to fly today by czech authority after four months of investigation. The condition is obvious - all choppers have to pass factory tail blade inspection before first flight. After each period of 25 hour inspection has to be repeated again using magnifying glass and color-luminiscent-defectoscopy. The main question keeps open: The problem was known several years, why the actions come up after one of us paid the highest price?

[500e]

Had not looked at photos on Flickr
The person who flew the one with stop holes drilled lots of Ba**s but no imagination.
Had a look on web sites tech page there are 3 SB recommendations\ warnings 52. 53. 56. & a picture, regarding TRBs.
Were all these after the Czech crash ?

[czheliman]

ASN Aircraft accident 14-NOV-2010 Elisport CH-7 Kompress OK-JHA 10 (http://aviation-safety.net/wikibase/wiki.php?id=80752)
Fatalities: 1 14-NOV-2010
S.B 52 17-December-2010 one month after crash - too late.....

[piggybank]

Quote "After each period of 25 hour inspection has to be repeated again using magnifying glass and color-luminiscent-defectoscopy."

In the case of the Puma blades involved the visual check did not find cracks early enough. Eddy current inspection was approved for the inspection as the cracks that had caused failure in the past were not visible to the eye with the painted blade.

Blakmax comments on the blade are spot on, how on earth did this design of tail blade get fitted?