Regarding the CAAs requirement that no design will be certificated if parts can be put in backwards this sounds good in principle but it is not always true. That is my first point.
Regarding the crash of any aircraft the certifying authorities require that something be changed in order to prevent a similar accident from occurring. The manufacturer has the option of changing the design, which is expensive, or to modify or clarify the procedures, which allowed the accident to occur. Another thing to consider is that it was purely a maintenance error and the technician did not follow the existing procedures or in cases illustrated in the accident report the manufacturers technicians installed the scissors incorrectly.
Although this post is aimed at accidents of Agusta designed helicopters the same situation applies not only to all helicopter designs but to fixed wing aircraft as well. Engineers do not take into consideration all aspects of the design although the certification requirements dictate what should be done. The tech writers sometimes minimize the technical detail in the maintenance procedures or they get it wrong or, they too do not consider all aspects of the procedure and what can go wrong. If a maintenance technician performs his job in accordance with the manual and something goes wrong it is not his fault. However if he does not follow the procedure and something goes wrong then it is his fault. But who is at fault if the technician follows the procedures and the procedures are wrong. In that case the procedure is changed or further amplified with words or pictures.
This does not happen, as frequently on military aircraft as the entire maintenance manual must be verified by performing every single maintenance procedure. If a discrepancy is indicated the manual and or the design is changed prior to fielding the system. This does not mean the system is perfect, as problems will arise in the field but not to the magnitude of the problems described in this thread.
Getting back to my first point there are many designs that were approved by the CAA where parts or elements could either be put in backwards or cross connected.
Cases in point: S-55 where the tail rotor controls could be cross-connected. The S-58 where the electrical connectors on the servo control systems could be cross-connected shutting both systems down. A-310 and possibly the A-320 where the electrical controls and sensing and control elements of the secondary flight control could be cross connected causing system failure or possibly causing extreme difficulty in diagnosing technical problems. There are probably many many more.
The manufacturers are not perfect nor are the certifying authorities. However you must end up flying the finished product. As it has been said many times in these threads never buy (or fly) the A model of anything.
