To: lomapaseo
The FAA is just being practical in regulating what can be regulated (system safety under 1309). It wouldn't be very practical to require boolean calculations on fuel tank explosions where one doesn't forsee an ignition probability or on a rudder tearing off under overstress.
If a proper FMECA (Failure Mode Effects Criticality Analysis) is performed many of the failures that do occur could be prevented. Case(s) in point: The thrust reverser on the Lauda Air 767, The rudder problem on the 737, the engine explosion on the 737 at Manchester, England as well as many others. TWA 800 could have been prevented if a complete safety hazard analysis were performed.
Another contributor to many crashes is the FAA’s requirement that the safety of a given component or system can be proven by test or analysis. In the case of the Lauda air crash Boeing had the opportunity to demonstrate a thrust reverser deployment during flight test. It was felt that it would be both expensive and it would place the aircraft in jeopardy so they ran a complete computer flow pattern analysis, which proved that the aerodynamic disruption would be survivable and could be controlled safely. In the case of the Sioux City DC-10 crash GE performed an analysis of the fan disc and it proved that it would never fail but their quality assurance program overlooked a flaw in the disc. P&W performed an analysis on the combustor can of one of their engines and that analysis proved the can would never fail. Since the engine would never have an explosive event, which is what was indicated in the P&W FMECA Boeing did not protect the underside of the wing of the 737. The result was in the Manchester catastrophe.
The system is extremely flawed and should be changed and the public should be made aware that commercial aircraft are not as safe as they could be.
One final point regarding the loss of the rudder on the AA A-300. Structures are not placed under FMECA or, Safety Hazards Analyses as it is felt that the static and dynamic tests of the structure prove that it has a reliability of 1. In other words, it will never fail under normal flight profiles.