Vilas,
The option to obtain approval for 10 mins use of take-off thrust OEI was introduced in both US and EU regulations IIRC somewhere in the 1970's or 1980's. Approval is not automatic but requires specific substantiation from both the engine manufacturer and the airframe manufacturer. For some older aircraft that did not have that option in the original certification the manufacturers may have obtained approval later and offered it to their customers as a 'retrofit'.
Last edited by HazelNuts39; 2nd Mar 2013 at 10:29.
Reason: missing plural 's'