why has it not been recorded as a possible factor far more frequently than we have been hearing about?
There are a number of reasons why this type of failure has not been reported in other events. Firstly, many safety investigators are ex-pilots and tend to focus on what they are familiar with.
Next, most investigators would not encounter a sufficient number of bond failure causal events to establish an adequate level of expertise in identifying the specific characteristic of a bond failure.
Thirdly, to my knowledge there is no formal training available in adhesive bond failure forensics, and much of the knowledge base is grandfathered within the investigative organisations and that embeds and propagates false knowledge (which is why some investigators use SEM to find the minutest trace of adhesive and then classify the failure as cohesion).
Fourthly as I have said in other postings, there is a deficiency in the FARs and JARs in that there is no mandatory requirement to demonstrate that an adhesive bonding process produces hydration resistance, and what guidance there is in AC 20-107 is weak and only came into existence a few years ago. Hence, there is no regulatory and minimal advisory guidance to the investigator to assist in focussing on that type of bond failure.
These comments are not intended to reflect on the integrity of safety investigators. They simply have not had training and exposure to bond forensics. I am sure that a similar lack of knowledge will come to light when we start to see failure of fibre-composite structures.
Regards
Blakmax