Boudreaux Bob - oooh we have a feisty one here with you don't we. Where have you been all these years me old?
Here - go to bed early tonight and take this with you - you'll be asleep within minutes
Where does the UK/JAR "twin only" mentality come from? [Archive] - PPRuNe Forums
The main post being:
There is no twin-only mentality; the restriction on flights over a hostile environment (and specifically a congested hostile environment) arises from compliance with the ICAO Annexes - you know, the Chicago Convention to which all States agree to comply:
Specifically:
ICAO Annex 2 - Rules of the Air; and Annex 6 - Operation of Aircraft.
Respectively, the need to 'land clear' (protection of third parties) and the requirement for a 'safe-forced-landing' (protection of crew and passengers).
There is also linkage to the the certification principle that no hazardous outcome should be permitted with an event which has a classification of 'Reasonably Probable' (which is based upon a probability on the order of between 1:1,000 and 1:100,000). Because engines tend to fail within that probability spectrum, ICAO SARPs attempt to keep the helicopter away from an area where the effect of the failure could be hazardous.