Should have been an easy flight for a 139.
Only if the crew were very current in night/IMC operations and understood the correct use of flight director modes and the activation speeds of those modes. I have seen very experienced and current AW139 crews mess up on night overwater or IMC (same thing) take-offs in the sim - especially when even a minor malfunction is introduced.
If the operation is performed by 2 pilots then there needs to be a clear understanding of what will happen during the departure (a full brief) by the pilot flying (both normal and with a failure) and an understanding by the pilot monitoring. This is standard in most offshore/SAR operators SOP's but less so in other operations. If what I understand from previous posts is that this is a private operation normally flown single pilot day/VFR and this particular flight was 2 pilot night/IMC then I am not surprised at the outcome. RIP.