bythenumbers
You have forgotten to mention that to achieve the required OEI climb performance mentioned in CAO 20.7.4 para 8.1, then a number of performance criteria must be met. They being:
• Propeller of inoperative engine stopped, i.e. feathered.
• Undercarriage (if retractable) and flaps retracted.
• Remaining engine(s) operating at maximum continuous power.
• Airspeed not less than 1.2 VS.
I am sure you would also be aware that by the time all the above conditions are met plus achieving Vyse (blue line at MTOW) or the decision point if one is used, i.e. from a long runway, the aircraft will be at least 2-300ft. Until then there is absolutely no requirement to achieve a 1% climb gradient. After all the title of CAO 20.7.4 para 8.1 “EN-ROUTE CLIMB PERFORMANCE” implies in itself that the aircraft must be clean.
Having said all that it would appear to me though that other things were at play that may have cause this accident.