Originally Posted by
212man
I hadn't realised how much of a rise there is. Just found this video where this whole process - both the initial mag check, and the check of the mag switch position and MAP before lifting - is discussed at length, including a demo of the MAP rise on one versus the expected normal figure. He does say that there is hardly any RPM drop during the mag check, and says that means they are healthy. My recollection from FW training is that you want to see a positive drop to confirm you have actually isolated one - not seeing a drop when selecting either L or R would seem to match the fault in the original accident topic.
I had also been looking for a good video of R44 (or even R22) mag checks and have yet to find one. This particular video is actually quite poor. He does not provide a good visualization of the engine RPM gauge during the checks and therefore it is difficult for those who are not familiar with piston helicopters to truly appreciate how the engine RPM responds during these checks. Then he addresses the MAP rise as an afterthought well past the mag checks.
You may have missed it, but way back in post 131 I did observe that the MP was way up at 20" when they were on the skids and read to pick up. I also previously addressed the issue that one may need to wait several seconds (more than 2) to detect an RPM drop to confirm a good P lead.
For those that know, and can be bothered to watch, why do the rotors start turning after start, with the clutch switch off - residual tension in the belts?
Yes, exactly. This is particularly apparent with new belts and it's a fine line between running to MX, stretching them per S/N 33, or just making a couple of flights. One also has to be careful not to start up with the clutch partially engaged. If the previous pilot did not perform the shutdown properly the clutch may not be fully disengaged and if you are quick at starting things up this can happen, particularly on the R22 or Raven I because no electric priming is necessary. However in this case when the master came on the clutch light was out so not an issue.