The main problem here is that the crew have just landed and shut down in order to take a patient off. The APU is still running, so there is a lot of noise. If you start approaching the helicopter at this point, unless you are known to the crew or have a radio, they will have very little idea of who you are or what you want, so all you will do is cause confusion. Waving hands and trying to catch someones eye will just add to the confusion. Wait until the machine is completely shut down and it is obvious that they are not still occupied with other duties before you come and say hello. At that point most will be more than happy to entertain you if they have the time. For what it is worth it is very unlikely the engines were running and the rotor stopped if they had just landed. It would have been the APU. In the S92 you cannot apply the brake with the engines still running. You can start up the engines with the brake on, and take them up to ground idle, but cannot do the reverse on shutdown. Yes the APU really does make that much noise!