At sixes and sevens.
It is difficult to say (even for those who know, perhaps) if it was an -06 gear/bearing that failed in G-REDL. The people who should know that are the UK AAIB.
In their report 2-2011, (page 51 Section 1 – Factual Information), Figure 21 shows a photograph of the remaining 7 gears still attached to the 2nd stage carrier. A number of those gear/bearings can be seen in the photo to carry a particular manufacturer’s markings, though that on the inner race of the failed gear is less distinct but similar in position and spacing. In Figure 22 the AAIB showed a “complete undamaged gear for reference”. This can clearly be seen to carry the part number (7 o’clock position) ending 3335-06. The inner race does not appear to carry manufacturer’s markings, unlike those in the previous photo.
At the time this report was published that did not appear to be significant. However in the light of AH mandating the removal from service of all epicyclic modules containing one or more of specific planet gear/bearing part numbers (and return of those to AH for gear replacement), some searching questions need to be asked. Evidently one operator (currently involved in a law suit against AH) chose to hang on to some of those parts and conduct their own examinations.
So, if the failed gear was a type -06 and the reference gear clearly an -06, why would AH maintain the -06 as the only authorised part?
Or, if the failed gear was actually a type -07 (or an -02, -03, or -05 as detailed in EASB 63A030), was the AAIB aware in 2011 that there were differences in the parts and specifically as stated in the above EASB?
“-The detailed design of the planet gear bearing has an increased damage tolerance.
-Modeling and calculation reveal a lower load level on the external race of the planet gear bearing.
-In-service experience shows enhanced reliability”.
The report (1.16.2, page 60) states that “a detailed analysis, using advanced methods, was undertaken by the helicopter manufacturer to build a three-dimensional stress model of the component. A separate analysis tool was used for the Hertzian stresses”
Given the stated differences in damage tolerance and reliability in the EASB, which part number did the manufacturer model and analyse for the AAIB?
The REDL investigation had access to two planet gears from other L2 MGBs (why not EC225s with their higher loading?). These had been “previously sectioned” by the helicopter manufacturer (ref P62) but it does not state when. Which part number was that sectioned 2nd stage planet gear/bearing?
I do not expect anyone on here to answer those questions but I sincerely hope that the Norwegian AIBN and other involved agencies do seek those answers.