Reliability: a measure of the success with which a system conforms to some authoritative specification of its behaviour.
Safety: Freedom from those conditions that can cause death, injury, occupational illness, damage to (or loss of) equipment (or property), or environmental harm. Given that interpretation, it is then fair to say that there is no safe airplane.
When the behaviour of a system deviates from that which is specified for it, this is called a
failure. Failures result from unexpected problems internal to the system that eventually manifest themselves in the system's external behaviour. These problems are called
errors and their mechanical or algorithmic cause are termed
faults. Systems are composed of components which are themselves systems: hence;
> failure -> fault -> error -> failure -> fault
Software doesn’t deteriorate with age: it is either
correct or
incorrect but faults can remain dormant for long periods. Ada is very much alive and well. I find it considerably amusing to read posts where the author assumes Ada to be a stale dinosaur - they seem to be quite far removed from reality. We use Ada for commercial projects achieving superior results in comparison with other languages - fewer bugs reach binary, easier to maintain code, certified and tested compilers, self documenting, and standards that read with legal precision... to name a few benefits.
I don't have a problem with the software engineering practices used in avionics. But I am weary of impacts on safety caused by time-cost demands.
There is a list of mechanisms that could make aircraft 'safer' but they aren't implimented because of cost savings.
http://www.computersociety.it/wp-con...c653_final.pdf