Latest from NZ on R44 blades
 

Mods please move if appropriate..

The latest letter from NZ CAA (states that is not from a manufacturing defect.)

26 May 2015
Dear Sir/Madam
DCA/R44/32B Robinson R44 Main Rotor Blades P/N C016-7 – Failure initiated by fatigue crack
As the registered owner of an aircraft that is possibly affected, you are advised of the following.
On 23 January 2015 a significant crack was found in a P/N C016-7 main rotor blade fitted to a Robinson R44 Raven II helicopter on agricultural spraying operations.
During a spray run the pilot experienced vibration through the cyclic control. The vibration increased when the helicopter was brought to the hover. The pilot immediately landed the helicopter and found a signification crack in one of the main rotor blades. The photograph in DCA/R44/32B shows the area where the crack was found. No main rotor blade defects were found by the pilot during any preceding pre-flight inspection(s).
Both main rotor blades were subsequently removed and shipped to RHC for examination. This examination was undertaken with oversight from the National Transport Safety Board (NTSB), the Federal Aviation Administration (FAA) in the USA, the Transport Accident Investigation Commission (TAIC) and the CAA of New Zealand.
The preliminary investigation determined that the main rotor blade failure was due to a 50mm fatigue crack initiating at the trailing edge of the blade. The time taken to progress to this length is unknown. Once the crack reached 50mm the remaining blade cross-section began to fail rapidly in a combination of fatigue and overload (mixed). Finally the remaining section failed in overload once the blade chord had reduced to approximately 50% of original. The original fatigue crack was not due to a manufacturing defect.
The multi-agency investigation is ongoing and if any other significant information becomes available further communication will follow.
To assist the CAA with this investigation please report any Robinson R44 Main Rotor Blades P/N C016-7 incidents or defects to the CAA by completing a CA005 Defect Report form. Please provide as much detail as possible. The form can be obtained from http://www.caa.govt.nz/Forms/CA005D_Form.pdf
The completed form can be emailed to the CAA at [email protected]

The original fatigue crack was not due to a manufacturing defect.
 

Then what caused it? Are they saying it was the operator's fault? What did the operator do to cause it so everyone can avoid doing the same procedure which initiated this crack? Cracks just don't "happen"!

If the crack was not due to a manufacturing fault, then t he alternatives are:

1. The blade design and certification testing may have been deficient.
2. There may have been an issue with the heat treatment for the alloy sheets used to make the blade skin.
3. There may have been an issue with orientation of the rolling direction of the metal. (Sheet metal is strongest in the rolling direction.)
4. The investigators may not have examined all alternatives which may have initiated the crack. For example did they consider the possibility that a bond defect may have led to a redistribution of stress which caused the crack to initiate?

It has been my experience that the level of understanding of adhesive bond failure forensics within the aviation safety investigation community and even manufacturers is open to question.

Regards

Blakmax

Blak

I read it as 1 in your list. No manufacturing defect basically means the blade was built to design. It is the design that is inadequate.

The Sultan

The original fatigue crack was not due to a manufacturing defect. ?
Strange that Robinson implemented a modification if there was no cause & effect then.

Blade issues
 

Sultan, I agree to some extent, but I think that the other possibilities need to be investigated or excluded.

What really worries me is that this finding strongly reflects the typical manufacturer's response: See.... I told you it was not our problem.

Until we know why the crack initiated, the manufacturer is still not off the hook. I have seen so many excuses for the older blades which grasp at straws and are then taken as "reasonable explanations".
So I place as much weight on the "it is not a manufacturing problem" as I would place on Sepp Blatter's defence "I know nothing"! Who knows? Maybe the next explanation will be that these failures were due to impact with a kiwi!

What really troubles me is that four months has passed since the first cracking occurrence and several months since an in-flight break up at Queenstown NZ and yet the only interpretation of the entire problem is that it is not a manufacturing defect. In the mean time, operators, pilots and passengers wait for a plausible explanation of the cause of these failures. Doesn't ICAO require timely investigation of these events?

I think it is time for CAANZ and TAICNZ to bring in the people in areas where they may not have appropriate expertise, and I say this with no reflection on the expertise of the investigators. If they have never had appropriate training how can they know what the significant factors are in a bond-related failure? I know those capabilities exist in NZ, and I would be happy to back these people up.

The earlier -5 blades have an AD which permits use for another five years, yet in the case of DQ-IHE the IIC found that the most probable cause of the crash was due to failure of the MRB due to low bond strength. That blade had been in service for only 34 months before it failed. So how can a five year service life be justified? Worse yet, the blade had been inspected TWICE using the approved tap test and once visually within about 80 hours of failure. See http://www.adhesionassociates.com/pa...ES%20final.pdf

If NDI can not assure bond integrity, and if there are examples of failures in a time frame well below the 5 year period of grace, then I hope someone can explain how continuing airworthiness can be managed before the lawyers have a field day in the mean time after some poor innocent people pay the price for a "She'll be right" management philosophy.

And before I get the "Robbo bashing" comments, I state again that the same analysis applies for any bonded principle structural element where the overlap length is amazingly short. See the paper.

Regards

Blakmax

The original fatigue crack was not due to a manufacturing defect
 

My first idea when reading was that the blade had a rendezvous-vous with the hangar door or something similar which caused a dent / notch which later on resulted in the crack.
But then again English is not my mother tongue.

So apparently there was a blade having the robbie mod (tin snips and glue) being done in NZ and the engineer found it was debonding.
Came from a reliable source.

From the horse's mouth
 

Sorry Hughsey, but I have it directly from the people involved that it was definitely not disbonded. I also got the incorrect version and posted elsewhere along those lines before receiving the correct info directly from the technician and the company.

Regards

Blakmax

However you cut the cake, it boils down to 1.
Any deficiency in design, durability, fitness for application, should have been revealed at that stage.

As I don't have a Skygod's certificate, I won't comment further. Mr. Blakmax will let you know if my opinion is worthless! ;) :8

Hi Cockney Steve. I won't discount your comments but I also won't discount the other options.

Spunk, if it was due to a hangar rash they why would every operator need to modify their blades? Vielen danke!

Regards Max

Copy that Blakmax.

Would be good to get some actual answers though. From my understanding the first blade that was sent to the US is yet to be looked at.

I am astounded
 

If this is true then it is an amazing situation. We have a blade that failed in flight and fortunately the aircraft was able to land, and the manufacturer issues a change for the blade to be reworked. Is this the blade that hasn't been looked at? If so, what is the basis for the modification for the blade? Just a knee jerk "it must be a stress concentration problem" by the manufacturer without any engineering forensics on the failure? Really?

Add to that, we have had a fatal crash with the same blade type. I would have thought that would add impetus to the investigation of the first blade.

Even then, I bet that the analysis will concentrate on the fatigue crack itself without investigation other possible initiating factors. I would like to see a thorough forensic assessment on any contribution of adhesive bond issues, even if it is to exclude such causes.

Regards

blakmax

Blakmax, as a well credentialed poster, what do you make of the "Mod it yourself with some sandpaper wrapped around the roll of quarters you will use to tap it" video?

As a soon to be minted (:eek:) CPL(H) with a BE Mech. and a higher degree in things with blades that look a lot like helicopters turned 90 degrees I am aghast RHC can issue a video on April Fools Day that suggests "whack a bit off, she'll be right mate".