HANDS ON
HINTS FOR HOMEBUILDERS
Testing Your Altimeter
and VSI for Leaks
BY CHAD JENSEN
WITHIN MY FIRST TWO WEEKS HERE AT EAA, I had a builder call with
a “problem” he encountered with a DAR during his certification
inspection. The DAR wanted to see proof that the altimeter and
VSI worked as they were supposed to. The test hadn’t been done,
or hadn’t been properly documented that it had been completed,
and the DAR would not sign off until the proper documentation
was available. At this point there may have been miscommunica-tion between the two about how to go about getting the systems
tested, but we got it sorted out, and the inspection was completed
shortly after.
The DAR wanted to see proof that the altimeter
and VSI worked as they were supposed to. The
test hadn’t been done, or hadn’t been properly
documented that it had been completed, and
the DAR would not sign off until the proper
documentation was available.
So how does one test the altimeter and VSI without taking
the unflyable airplane to an avionics shop to have them tested?
The answer is found in AC 90-89A, Section 7. Assembly and
Airworthiness Inspection, Paragraph 4. Field Check, Item b.
Altimeter/vertical speed check.
( 1) To check the static side, apply low suction at the end of
the static vent port. The easiest way to gain access to the static
system is to remove the static line at the static port. If there are
two static ports, tape the unused port closed. Don’t forget to
remove the tape when done. Next, get 2 feet of surgical tubing,
seal one end with a clip, and tightly roll it up. Surgical tubing
works best as it’s extremely flexible, but any flexible tubing
available at your local hardware store will suffice—clear fish
tank tubing works well here, too. Securely attach the open end to
the static line and slowly unroll the tub-
ing. This will apply a suction, or low
pressure, to the static system.
