On Mar 18, 7:31*am, Andy wrote:
On Mar 18, 7:00*am, Darryl Ramm wrote:

It is my impression that many piltos with built in loggers like the
Cambridge 302 do not understand that the flight recorder is using
cockpit ambient pressure and not the static line-in on the rear of the
instrument (only used for airspeed calculations). This is a
requirement to prevent the pilot being able to connect to the static
line and tamperer with logged pressure altitude.

I'm aware of that but I see now that what I wrote may be ambiguous.
Perhaps this would have been better:

"loggers (which cannot have an external static connection) will read
lower than
an altimeter which has an external static connection. "

Andy

Andy, I had the sense you did know this. My comment was really to the
overall thread. The near universal situation will be IGC logger with
ambient cockpit pressure (an IGC requirement) and an altimeter with
ships' static (a type certification/airworthiness requirement for many
(all?) gliders). In which case the warnings from the CD make perfect
sense.

A Cambridge 302 or other IGC flight recorder that displays pressure
altitude or a PDA with pressure altitude being displayed from a logger
is the thing to look at if close. But looking for traffic better be
more important. Doing a comparison between an altimeter and Cambridge
302 pressure altitude display at different speeds would be interesting
and something I want to do for other reasons (but related to ambient
cockpit pressure induced altitude errors).

Hopefully most pilots will understand many gliders will have three
static sources, the fuselage static lines (for altimeter and ASI),
static from a multi-function probe (usually for flight computers/
direct reading/digital varios) and ambient cockpit static (used by IGC
fight recorders). Pretty nice redundancy and isolation provided by all
that.

Darryl