The rational behind what covers what may help you understand the 'Why....?'
When things are running normally there's essentially no handling difference between a multi & single. Little bit more complexity but that's just familiarity & training on the type.
Lose an engine & the similarities end. Both a/c lose performance. Once is guaranteed to go downhill, the other may or may not be able to continue flight IF the pilot can keep it under control and the conditions don't require more power than the remaining engine(s) can provide. There is always the option to accept going downhill, just like the single. The skills needed for the single are covered by the skills needed for the twin - hence a twin IR covers a single.
A single suffers no unusual or degraded handling when the engine go awry & so needs no demonstrable ability to cope with such things. A twin losing an engine suffers severe reduction in handling qualities. That's the key point in why a single IR doesn't cover a twin. There's no part of the single IR that covers the controllability aspects of an asymmetric multi.
Interestingly and supporting this concept, in Oz a pilot with a s/e IR is authorised to fly centerline thrust multis eg C337. Oz requires an endorsement for different multi types, but that applies regardless of the flight rules or conditions. If the pilot has a centreline thrust a/c on his licence then gaining a s/e IR embraces that a/c as well.
blody tipos
Last edited by Tinstaafl; 10th December 2003 at 00:46.