g. Open PRESSURE VENT valve slowly to return airspeed to ambient pressure, and
During all operations, ensure that the vacuum and pressure
selector valves are not moved from their positions and that air
lines are not disconnected while the pump motor is running, or
while any indications other than zero can be observed on the
instruments. (The indications will be zero on the vertical speed
indicator, local ground level on the altimeter, and
approximately 0 on the airspeed indicator.) Failure to observe
this precaution will result in serious damage to the master
instruments and any external instruments connected to the TI.
Before making an accurate test, run each performance check
through its complete range of pressure or vacuum twice. This
exercising of the TI and standard will normalize a small
amount of hysteresis in diaphragms of TI so that correction
card errors will apply when values of function (altitude,
airspeed, absolute pressure) are approached in an increasing
direction. In addition, the operator can see if excessive friction
has developed in instruments. This exercise will also reduce
friction on subsequent test runs. Any leaks detected during
this exercise must be corrected before continuing.
a. Performance Check
Zero the pneumatic pressure standard prior to making any
Ensure to cap shut VAC PORT on TI or altimeter will not
(1) Connect pneumatic pressure standard Ps inlet port to TI PRESS PORT using
hose supplied with TI.
(2) Set the pneumatic pressure standard to altitude/parallel mode; set units to feet.
(3) Close TI VERTICAL SPEED control fully.
(4) Open CROSSBLEED CONTROL valve fully. This prevents airspeed indicator
from increasing. Adjust barometric adjustment knob (on front of TI) for 29.92 in. Hg
(1013.3 mb) indication on barometric indicator.