Avionics News March 2013 - 34

TESTING TECHNOLOGY
Continued from page 32

watch,” Dominguez said.
Newer test sets also provide the
inputs necessary for the other appendix E tests. To test for needle friction, the test box creates a 750 feet
per minute descent, and the technician follows the needles’ progress
to ensure it is within the specified
tolerances. The case leak tests runs
the altimeter to 18,000 feet and times
any deviation from that altitude. To
ensure a previous condition does not
affect the accuracy of the current
reading, the hysteresis test simulates
a slam-dunk approach with a decent
rate of 5,000 to 20,000 feet per minute. No later than five minutes after
this test comes the after-affect check,
which tells whether or not the previous tests damaged the altimeter’s
aneroid.
Electronic automation also is part
of transponder test sets, “and the hot
new box is the Aeroflex IFR 6000,
which doesn’t need a test antenna,”
Dominguez said. “Within 15 feet of
the aircraft, it will sense what attenuation you need and then give you a
complete data checkout, frequency,
sensitivity, power, silo protection,
check all those circuits, and gives
you readout.”
Naturally, these features are expensive, but they can cut the test
time by 40 percent, allowing technicians to perform more tests, which
offset their costs.
Because air-data computers derive
their raw data from the same system
as aneroid instruments, glass cockpits undergo the same pitot-static
checks, with additional items specified by the manufacturer of the flight
display.
“RVSM is a pitot-static check on
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march

2013

During the past five or six years, test boxes have
advanced by leaps and bounds. Many include handheld
control pads that allow the technician to set the
required test parameters from the pilot’s seat.

steroids,” Dominguez said, and each
solution is tailored to that jet. Using the same test equipment, it starts
with the appendix E requirements
and adds checks of things like overspeed warnings, altitude preselect
and stick shaker.
Perhaps one of the most welcome
advancements in pitot-static testing
has been the adapters that connect
the text box directly to the pitot tube
and static port.
“AIS introduced the first one in
1998,” Dominguez said, describing a
three-legged spider that used suction
cups with a separate vacuum source
to keep the adapter stuck to the side
of the aircraft. Most test-equipment
manufacturers now make adapters,
and some specialize in them. Today,
many jets wear a “smart probe,”
Dominguez said. A single tube, it
combines the necessary ports for
three separate pitot-static systems,
one for the pilot, one for the co-pilot
and a standby. And companies that
specialize in adapters, such as Cobra
Systems and NavAids Ltd., make
adapters for them.
Before attaching the adapters,
technicians confirm that the pitot
and static ports are properly aligned
with the air pressure they sample, a
relationship that can be soured by
inadvertent modification or using
the pitot-static tube as a handheld. If

equipped, they also check the ports’
heaters that keep ice from forming.
Before adapters, to connect the
test unit, technicians had to tap into
the system’s plumbing with a T fitting, which introduced another possibility for a leak.
“There is no such thing as a perfect airplane,” Dominguez said, adding with a chuckle that “90 percent
of them have problems. In time,
things loosen up, corrode and develop pinholes where dissimilar metals meet. Most airplanes more than
10 years old have leaks that we have
to run down before we can run the
test. You want to make sure the static
plumbing is tight, especially in a pressurized airplane, because all leaks
affect accuracy,” and thereby safety.
Getting hands-on is the only solution, and leaks can be elusive as
their electrical cousins. No matter
the manufacturer, Aeroflex, Barfield,
DFW Instrument Corporation, ATEQ
or Laversab, the technology they
have incorporated in their test boxes
have simplified the inspection process and made it more efficient and
accurate. Dominguez guessed they
have cut the time by 40 percent,
which technicians everywhere appreciate. Now if they could just
devise some technology that would
locate and identify leaks in the
pitot-static system. q
Avionics News March 2013

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