Cessna T188C - And Leakage Test; Description; Installation; Instruments

MODEL
188 &
T188
SERIES
SERVICE
MANUAL
15-5. INSTRUMENTS.
b. Ensure
no alterations
or deformations
of air-
frame surface have been made which would affect
15-6. REMOVAL.
Most instruments
are
secured to
the relationship
between air pressure
in static
pres-
the panel with screws inserted
through the panel face.
sure system and true ambient static
air pressure for
To remove
this
type instrument,
disconnect
plumbing
any
flight configuration.
or
wiring, remove
the
mounting
screws, then
remove
c.
Seal one static
source
port with
pressure
sensi-
instrument
from behind
the
panel.
Other instruments
tive
tape. This
seal must
be air
tight.
are held
in place by
metal brackets
that
seat against
d. Attach
a source of
suction to
the remaining
static
the panel from
behind. To remove
this type
instru-
pressure source
opening. Figure
15-3 shows
one
ment, disconnect
wiring
or plumbing,
remove
nuts
method of
obtaining suction.
securing
the bracket
to the
instrument,
then remove
e. Slowly
apply
suction until
altimeter
indicates
a
instrument
from the front
side of
the panel. The
1000-foot increase
in altitude.
same
procedures
apply
to
the cluster
after
the plastic
cover has been removed for access. In all instances
when an
instrument
has been
removed,
the lines
or
wires disconnected
from it
should be
protected.
Cap
When
applying
or releasing
suction,
do not
open lines and
cover pressure
connections
on the in-
exceed range
of vertical
speed indicator
or
struments
to prevent thread
damage and the entrance
airspeed
indicator.
of foreign
matter.
Wire terminals
should be insu-
lated
or tied up so
they will not
ground accidentally
or f.
Cut off suction
source to maintain
a "closed"
short-circuit
on another terminal,
system for one
minute. Leakage
shall not exceed
100 feet of altitude loss as indicated on altimeter.
15-7.
INSTALLATION.
Generally,
installation
pro-
g. If
leakage rate
is within
tolerance,
slowly
re-
cedure
is the
reverse of
the removal
procedure.
lease
suction source
and
remove tape
from static
Make
sure mounting
screw nuts are tightened
firmly,
port.
but
do not overtighten
them,
particularly
on instru-
ments having
plastic cases. The
same rule generally
NOTE
applies to
connecting plumbing
and wiring.
If thread
lubricant
or sealer
is used
on plumbing,
it should
be
If leakage
rate
exceeds the
maximum
allowable,
applied
sparingly
and only
on the
male threads.
first
tighten
all connections,
then
repeat
leak-
age test.
If leakage
rate still exceeds
the maxi-
15-8. PITOT AND STATIC SYSTEM. (See figure mum allowable, use following procedure.
15-2.)
h.
Disconnect
static
pressure
lines from
airspeed
15-9. DESCRIPTION.
The
pitot system
conveys
ram
indicator and
vertical
speed indicator.
Use
suitable
air pressure
from
the pitot
mast, mounted
beneath
fittings
to connect
lines together
so altimeter
is
the
the left
wing, through
plastic tubing
to
the airspeed
only
instrument
still
connected
into
static
pressure
indicator.
The
static
system
vents
the altimeter,
system.
which is
connected
to the
airspeed
indicator,
through
i.
Repeat
leakage
test to
check whether
static pres-
a
source
button
located
on each
side
of the
tailcone
sure system
or the
bypassed
instruments
are
cause
of
aft
of the
cockpit.
A
static
line sump
is
installed
at
leakage.
If
instruments
are
at fault,
they
must
be
each
source
button
to
collect
condensation
in
the sys-
repaired
by
an "appropriately
rated
repair
station"
tem.
A
pitot
mast
heater
may
be installed.
The
or
replaced.
If
static
pressure
system
is at
fault,
heating element
is
controlled
by a switch
on the
in-
use following
procedure
to locate
leakage.
strument
panel
and power
is
supplied
by the
electrical
j. Attach
a source
of
positive
pressure
to
static
system.
source
opening.
Figure
15-3 shows
one
method
of
obtaining
positive
pressure.
15-10. MAINTENANCE.
Proper maintenance
of
pitot and
static system
is essential
for proper
opera-
CAUTION
tion of
altimeter,
vertical
speed
and
airspeed
indi-
cators.
Leaks,
moisture
and obstructions
in pitot
Do not apply
positive
pressure
with airspeed
system
will
result
in false
airspeed
indications,
while
indicator
or vertical
speed
indicator
connect-
static
system
malfunctions
will affect
readings
of all
ed
to static
pressure
system.
three instruments.
Under instrument
flight
condi-
tions,
these instrument
errors
could
be hazardous.
k. Slowly
apply
positive
pressure
until
altimeter
Cleanliness
and security
are the
principal
rules for
indicates
a
500-foot decrease
in
altitude and
main-
system
maintenance.
The pitot
tube and static
ports
tain
this altimeter
indication
while checking
for
leaks.
MUST
be kept
clean and
unobstructed.
Coat
line connections
and
static source
flange
with
LEAK-TEC
or
a solution
of
mild
soap and
water,
15-11. STATIC PRESSURE
SYSTEM INSPECTION
watching for
bubbles to locate leaks.
AND LEAKAGE
TEST.
The
following
procedure
out-
1. Tighten
leaking
connections.
Repair
or replace
lines
inspection
and
testing
of static
pressure
system,
parts
found
defective.
assuming
altimeter
has
been tested
and inspected
in
m. Reconnect
airspeed
and
vertical speed
indicators
accordance
with current Federal
Aviation
Regulations.
into static pressure
system
and repeat leakage
test
a.
Ensure
static
system
is free
from
entrapped
per
steps
"c"
thru
"g".
moisture
and
restrictions.
15-4