Cessna T188C - Blowing out Lines; Pitot System Inspection and Leakage Test; Removal and Installation; Trouble Shooting Pitot Static System

MODEL 188-&
T188 SERIES
SERVICE
MANUAL
15-12.
PITOT SYSTEM
INSPECTION
AND LEAKAGE
Like
the pitot lines,
static pressure
lines must be
TEST.
To check pitot
system for leaks,
place a piece
kept clear
and connections
tight. Static
source sumps
of
tape over small
hole in lower
aft end of pitot tube,
collect
moisture and
keeps system
clear. However,
fasten a piece
of rubber
or plastic
tubing
over pitot
when
necessary,
disconnect
static
line at first
instru-
tube,
close opposite
end of tubing
and slowly roll
up ment
to which it is connected,
then blow
line to clear
tube
until airspeed indicator
registers
in cruise range.
with low
pressure air.
Check all static
pressure line
Secure tube
and after a
few minutes recheck
airspeed
connections
for tightness.
If hose or hose
connec-
indicator. Any
leakage will have
reduced the
pres- tions
are used, check
for general
condition and clamps
sure
in system,
resulting in a lower
airspeed
indica- for
security. Replace
hose which
have cracked,
tion. Slowly
unroll tubing
before removing
it, so
hardened
or show other
signs of deterioration.
pressure
is reduced
gradually.
Otherwise
instru-
ment
may be damaged.
If test reveals
a leak in
sys- 15-14.
REMOVAL
AND INSTALLATION
OF COM-
tem, check
all connections
for
tightness.
PONENTS.
(Refer to
figure 15-2).
To remove
the
pitot mast, lower the access cover, then disconnect
15-13. BLOWING OUT LINES.
Although the pitot
line and heater wires (if installed).
Pitot and static
system
is designed to
drain down to
pitot tube open-
lines are
removed in the
usual manner,
after remov-
ing,
condensation
may collect at
other points in
sys- ing
access plates.
Installation of the
tubing will be
tern and produce
a partial
obstruction.
To
clear the
simpler
if a
guide wire
is drawn in
as tubing
is being
line,
disconnect
it at airspeed indicator.
Using
low removed.
When replacing
components
of the pitot
pressure
air, blow from
indicator
end of
line toward
and
static pressure
systems,
use anti
seize compound
the
pitot tube.
sparingly
on male
threads, avoid excess
compound
which
might
enter
lines.
Tighten
connections
firmly,
CAUTION
but
avoid
overtightening
and
distorting
the
fittings.
If twisting of plastic tubing is encountered when tight-
Never blow
through pitot or
static lines
ening fittings,
VV-P-236 (USP
Petrolatum),
may be
toward the instruments,
applied sparingly
between tubing
and fittings.
15-15. TROUBLE
SHOOTING --
PITOT-STATIC
SYSTEM.
TROUBLE
PROBABLE CAUSE
REMEDY
LOW
OR SLUGGISH AIRSPEED
Normal altimeter and vertical
Repair or replace
damaged
INDICATION.
speed - leak or
obstruction in
Line.
pitot line.
INCORRECT OR SLUGGISH Both instruments - leaks or Repair or replace line.
RESPONSE.
obstruction
in static
line.
15-16. TROUBLE SHOOTING-- PITOT TUBE HEATER.
TROUBLE PROBABLE CAUSE REMEDY
TUBE DOES
NOT HEAT OR
Switch turned "OFF."
Turn switch
"ON."
CLEAR ICE.
Circuit breaker "Open". Reset breaker.
Break in wiring. Repair wiring.
Heating
element burned
out.
Replace element.
15-5