Curtain. Very strange. Why would there be extra restrictions placed on two engined aircraft if they are as safe as three or four engined?
To ensure equivalence of safety.
You can have four engines maintained to a lesser standard, or two to a higher standard. Manufacturers & airlines concluded the best overall cost optimisation for
equivalent safety or better was to go with the twinjet system.
One large operator used to take the engine cores from an ETOPS twin once it went out of spec and then install it on it's four engine aircraft.
In 400+ sectors on a four engine jet, I had 3 inflight shutdowns. I've spent 9 hours in cruise across the pacific on 3 engines. In 4,500+ sectors on a twinjet, I've never had an engine miss a beat, never.
So, about the Certification Specifications critique...