Airspeed Indicator Accuracy Tolerance

Bob Gardner wrote:

If there is no means of adjustment, the question answers itself. Keep in
mind that the blue line is not sacrosanct...actual Vyse will vary with
weight and density altitude. The vertical speed indicator is a much more
accurate means of determining best rate of climb.

Well, not really. My question is whether their is a good way to measure
the absolute accuracy of a ASI. And my concern is that 6 nts is too far
off when it could make a significant difference in performance in
critical situations, like single engine operation.


Bob Gardner

"O. Sami Saydjari" wrote in message
...

In my Cessna 421C, the pilot-side airspeed indicator reads 6 nts below the
co-pilot-side airspeed indicator. When I pointed this out to a mechanic,
he said that it was "within toleraance." He said it was possible that one
was 3 nts high and the other 3 nts low and so both could be within
tolerance. He added that there is no real internal adjustment, so there
is not much he could do about it anyway.

Seems to me that when you are talking about a possible 6nt difference and
given the need for accurately maintain blue-line speed in case of a
single-engine failure, it is important to know that one's airpseed
indicator is accurate. Isn't there a way to judge true accuracy of speed
indicators (just as there is for altimeters)? Should I be satisfied with
my mechanic's answer and move on?

-Sami
N5554G, Cessna 421C