This is my first post on this topic. To establish myself, I put in over fifty years in aircraft maintenance in positions from mechanic to vice president and I managed Quality Control as well.
The controversy over whether the missing spacer contributed to the accident is impossible to settle. It does show a shocking lack of adherence to process and poor quality control at Air France. Work of this nature in the USA is mandated as a "Required Inspection" which is a warning sign to the Inspector. I believe the British used a “Double Inspection” to ensure compliance. What failed here is not fully explained. I might also add, I found the cavalier attitude toward an overweight takeoff and in a downwind direction disturbing. The corporate safety culture apparently failed all around.
The titanium repair spacer from the DC-10 engine was apparently not installed in accordance with the Structural Repair Manual (SRM). Continental also is at fault for shoddy work.
All these aside, the bigger issue is the failure of the relevant regulatory agencies and the manufacturer to prevent the chain of events caused by a tire failure. As an example, early on in the B727 history there were some tire failures that punctured the composite material tank access plates on the bottom of the wing in the gear area. I seem to remember Boeing Service Bulletins and an Airworthiness Directive mandating their replacement with metal tank access plates to prevent puncture. Every time we purchased a used B727 we had to check to see the AD was complied with to get the aircraft on our certificate.
After Concorde suffered a major tank rupture at Dulles, what regulatory action was taken? Apparently there were tire improvements. But tire failures continued. Every single tire failure was a roll of the dice as to where the shrapnel would go. It took the CDG crash to finally come up with some measure of protection which I believe was lining the tank bottom with Mylar fabric material. It took all those years from Dulles to CDG to drive the point home that the aircraft was vulnerable to a simple tire failure.
Lord knows I have seen many tire failures. Early on it was a B720 that wiped most of the hydraulics off the strut, a B747 that damaged the horizontal stabilizer (the mechanics on duty never thought to look back there until I told them to take a peek). I have seen landing gear doors badly damaged, etc, all of these from failed tires that threw pieces or chunks or even entire recaps but they didn't bring the aircraft down.
The real cause of the crash was the failure of the regulators and the manufacturer to take definitive corrective action to prevent a repeat of the Dulles tank rupture. If it was impossible to do so, then the aircraft certificate of airworthiness should have been pulled. The Concorde was a magnificent flying machine but it had a fatal Achilles Heel. They had adequate warning at Dulles, they should have taken action.