On Dec 7, 12:14*pm, Darryl Ramm wrote:

Bzzzttt I've got to shoot myself here for getting missing the critical
regulation....

I hope you are healing but the abuse may not have been justified.

The full text of 14 CFR 91.217 is as follows:

"§ 91.217 Data correspondence between automatically reported
pressure altitude data and the pilot's altitude reference.

(a) No person may operate any automatic pressure altitude reporting
equipment associated with a radar beacon transponder—

(1) When deactivation of that equipment is directed by ATC;

(2) Unless, as installed, that equipment was tested and calibrated to
transmit altitude data corresponding within 125 feet (on a 95 percent
probability basis) of the indicated or calibrated datum of the
altimeter normally used to maintain flight altitude, with that
altimeter referenced to 29.92 inches of mercury for altitudes from sea
level to the maximum operating altitude of the aircraft; or

(3) Unless the altimeters and digitizers in that equipment meet the
standards of TSO-C10b and TSO-C88, respectively.

(b) No person may operate any automatic pressure altitude reporting
equipment associated with a radar beacon transponder or with ADS–B Out
equipment unless the pressure altitude reported for ADS–B Out and Mode
C/S is derived from the same source for aircraft equipped with both a
transponder and ADS–B Out."


Note that (a)( 3) is "or-ed" with condition (a)(2). Also note that
for a glider no altimeter is used to maintain flight altitude since
maintaining flight altitude is not a requirement for gliders.

I would conclude that 91.217 imposes no requirement for the altimeter
to be TSO C10b compliant. If the OP can't argue that the altimeter is
not used to maintain flight altitude then a correspondence check with
a non TSO certified altimeter will meet the requirement of 14 CR
91.217 (a)(2). The correspondence check only needs to be done to the
"maximum operating altitude of the aircraft" which may be defined for
the OP's motor glider but isn't for any unpowered glider.

I would further argue that, if there is no requirement to maintain
flight altitude, then the altimeter is not part of the automatic
pressure altitude reporting equipment. If this is accepted then the
only requirement left from 14 CFR 91.217 is that the encoder is TSO
C88b compliant. That's a no brainer since they all are.

It's much easier to install the equipment yourself than argue the
regulations with someone you pay to do the work for you!

Andy