Bob,
I must say your outburst came as a complete surprise because nowhere in my post were Europe or the UK mentioned.
The standard of certification for flight in IMC (Appendix B) comes from US regulations - FAR 27/29 (written well before Europe adopted these regulations in 'preference' to their own - in the interest of commonality and cost). The ICAO Standard is one that we (world-wide) develop in harmony, and show compliance with, in accordance with the Chicago Convention.
Redundancy is usually called for when the failure rate of the component is reasonably probable:
Reasonably probable events...are based on a probability on the order of between 10**-3 to 10**-5.
and the outcome of any failure is likely to be hazardous/catastrophic.
Hughes500,
The engine failure rate has remained steady at 1 x 10**-5 (or above) per flying hour for several decades. This number is based upon engine manufacturer's data and shows no bias towards the installation number.
For Category A twins, independence of the engines is provided by the certification code (Appendix C of Part 27 and integral to Part 29) as far as is practical. Double engine failures have been caused by issues such as: simultaneous ingestion of (large amounts of) salt water; FOD events (bird ingestion); volcanic dust; and of course fuel exhaustion. These double failure events cannot be controlled by certification and are therefore addressed by the operational code and training - they are extremely rare.
Jim