MJKTuck@cs.com wrote:
>
> Hi Folks,
>
> Is there any way of testing the transponder annually without
> having to remove the panel and give it to a radio shop to do
> the testing? For Mode C testing my radio shop attaches a harness
> to the transponder as well as a vacuum to the static system then
> checks the readout of the transponder/encoder every 100 ft
> increment. While interesting to watch and quite satisfying to
> see its all a bit of a hassle to get the panel out and back in again.
>
> I wonder how other homebuilts (RV's) which do not have removable
> panels are able to check functionality and satisfy the FAR's. Is
> there a 'minimal' test which will satisfy the regs for Experimental?
There's no exception for homebuilts; the test must be done "as installed" (or
quickie
checked after re-installation if both xponder/encoder bench checked); but
for Mode C and VFR, it should be a simple test. If you observed checks every
100' all the way up to like 20,000, it sounds as though the shop owner had a
boat payment due. :-)
For VFR they need only check a "sufficient number of test points," and the
details
as to how they can easily check all Mode C data lines are not important here,
except to note there's a limited range where the guy should check every 100'.
Vacuum can easily be pulled at the static port, sealing the other port if two
ports
- necessary to complete test if for IFR. Problem is how much you can pull
out of the static system and not harm the airspeed, so they have to break into
the static system appropriately.
Re panel removal problem, if the airspeed static were brought out under the
panel
and then back in, with an exposed in-line fitting, the guy could connect there
and seal the static port. However, if there's some system leakage - allowable
for VFR, the tech guy may not like that, and often they don't like suggestions
as to how to do their job! Worth plumbing it that way just in case.
Regards,
Fred F.
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