10% + 7 is the one quoted in the books. The instructor that gave me the 15% rule instead insisted that it was more reliable at the lower airspeeds helis work at (he was previously a heli instrument instructor in the military). I tested his calculation at 80kts on the R22 (so 12 degrees instead of 15 degrees) and it was pretty much spot on. You pays your money and takes your choice
I've never seen it presented that way, but your instructor is indeed correct that 15% gives a closer approximation (using AOB tables). Every day is a school day!
Joined: Feb 14, 2008 Posts: 888 Location: Stavanger, Norway
Posted: Wed Jun 29, 2011 6:23 pm Post subject:
During pre-start checklists we go through an instrument check. During this all 3 altimeters are cross-checked for errors. I do a second check on the standby (clockwork one).
Set QNH and note reading
Add 10mb and check approx 250-300 increase
Subtract 10mb and check approx 250-300 decrease
Old habbit, but a good check for a duff altimeter.
We always have the same setting on all 3 altimeter and there is an SOP to cross-check them after any change. We also give altitude call outs (500ft to go and 100ft to go) when climbing or descending. Only ever use local/regional QNH or 1013 for flight levels.
If we have a difference in settings between the two pilots altimeters by >5mb then a yellow arrow will appear on both of them to indicate a miscompare of information being fed into the computer things.
Does anyone use QFE anymore?
Radalt and minima bugs change depending which phase of flight we are in, but I won't bore you with all that.
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