Helicopter performance
The helicopter was operating close to its maximum operating weight when it approached the helideck on the accident flight. The commander believed that the helicopter’s performance at that weight was such that it would not be possible for it to hover OGE with the power available. Changes in airflow around and through the rotor disc of a helicopter hovering close to the surface in ground effect (IGE) lead to increased rotor blade efficiency. Less power is therefore required to hover at a given weight when compared to a higher, OGE hover. In situations where performance is limited, the helicopter needs to make a continuous and steady approach to a landing site, so that it gains the benefits of ground effect before losing the extra lift that is a function of forward airspeed.
I was quite surprised to see this commentary in the accident report. Notwithstanding which side was used with respect to the obstacle environment (and it would appear that the P2’s side might have been better - but it is the Commander's decision), there is an absolute requirement for AEO HOGE to be planned. This was contained in guidance up to the time of revision 5 (NPA-38), at which time it was brought into the rule material (note to AAIB; please ensure that you have an up-to-date copy of the regulations).
In addition, and as indicated (indirectly) by the accident investigator, taking the landing from the P2s side would also have added at least 10kts to the accountable wind (shown in the report as 12kts – 20kts), as the committal point - on that side - would have been achieved with at least 10kts more airspeed (one of the benefits of the dynamic over the offset procedure).
Jim