Airfix,
Your view is as valid as any other. You will know that not one of us here holds that it is impossible that the pilots were negligent. We simply ask that it be proved to the standard required that they were.
If you have indeed read everything available, then how can you assert that the helicopter should have been climbed (presumably to SALT). To the best of the pilots' knowlede, the +4 deg C isotherm (Chinook Mk2 limit) was at 2500', well below SALT.