To: Genghis
I can't speak for the CAA but FAA design guidelines state that all single point failures that can result in death or loss of the aircraft must be designed out of the system. If this is not possible, then the failure can occur no more frequently than 1 10-9 or, one time in a billion hours of fleet operation.
In making this calculation, you can only deal with the inherent failure modes of the system or component under analysis. In the case of the tires (tyres) failing due to a puncture caused by a part falling off of another aircraft, this cannot be considered in calculating the failure rate.
This type of induced failure can be considered in the safety hazards analysis but, it is extremely difficult to assign a rate of ocurrence as it is assumed that the runway is clear of debris.
In the case of the underskin of the wing you can only consider an inherent failure of the skin itself. Normally in any reliability calculation you assume that the structure has a reliability of 1 which means that the structure will not fail which is proven in the structural and flight testing prior to entering service. Of course, structure does fail but due to design redundancy the failure does not effect the overall reliability assuming that the failure is caught in a check and repaired. However, it is well known that tires (tyres) and wheels fail and as a result throw up a great deal of debris with a large ammount of kinetic energy and as a result, the wing skin should have been protected
You can take that one step further and assume that the repair was not done correctly resulting in the ultimate crash of a 747 in Japan.
Many years ago a USAF F-86 was lost when upon landing the nose wheel struck an upturned empty tin that had previously contained some type of adhesive tape. The tin lid hit at just the right angle cutting deeply into the tire (tyre) causing it to fail during roll-out.
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The Cat
[This message has been edited by Lu Zuckerman (edited 18 November 2000).]
[This message has been edited by Lu Zuckerman (edited 18 November 2000).]
[This message has been edited by Lu Zuckerman (edited 18 November 2000).]