MD Helicopters 369-500, Maintenance Instructions Manual

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CSP-HMI-3
MD Helicopters, Inc
.
MAINTENANCE MANUAL
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95-10-10
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The information disclosed herein is proprietary to MD Helicopters, Inc.
Neither this document nor any part hereof may be reproduced or transferred to
other documents or used or disclosed to others for manufacturing or any other
purpose except as specifically authorized in writing by MD Helicopters, Inc.
Copyright
©
1999 − 2016 by MD Helicopters, Inc.
HEATED PITOT TUBE
MAINTENANCE PRACTICES
1. Heated Pitot Tube
(Ref. Figure 201 for 369D helicopters,
Figure 202 for 369E/FF - 500/600N helicop­
ters) The heating element in the heated pitot
tube is used to eliminate ice formation and
moisture in the pitot system. The coil heating
element in the heated pitot tube provides a
load for the full 28 Vdc load provided by the
battery/generating system or an auxiliary
power unit (APU). Sufficient heat is generated
in the coil element to melt ice in 180 seconds at
an ambient temperature of -25
°
F (-32
°
C). The
heating coil can withstand an overload of up to
250 watts at -35
°
C (-31
°
F). Continuous
operating limits are -25
°
to +150
°
F (-32
°
to
+66
°
C).
A. Wiring Diagrams
(Ref. Figure 203 thru Figure 207) Wiring
diagrams are provided for the three heated
pitot tube configurations. These diagrams may
be used in conjunction with the helicopter
basic interconnection diagram and terminal
board interconnection diagram (Ref. Chap. 96).
Know your helicopter. Compare
these diagrams with your heli­
copter carefully. Be sure you are using the
correct diagram and following the correct
maintenance or modification procedure.
2. Heated Pitot Tube Troubleshooting
(Ref. Table 201 for troubleshooting informa­
tion) Information is provided to simplify fault
determination by providing a set of probable
causes and remedies for all malfunctions likely
to be encountered during normal operation of
the system.
A. Wire Identification Numbers
NOTE:
Before stripping wire insulation for re­
pairs or replacements, observe wire identifi­
cation numbers stamped on the insulation
and sleeves. When wire insulation must be
stripped back far enough to obliterate iden­
tification numbers, tag the wires carefully
with their identification numbers.
(Ref. Figure 203 thru Figure 207 for wire
numbers, component reference designations,
and terminal letters or numbers for each
heated pitot tube configuration.
(1). Refer to the appropriate figure for your
helicopter before disconnecting a wire
whose identification numbers have
already been obliterated.
(2). Determine the identification number by
carefully observing what the wire is
connected to (observe both the compo­
nent reference designation and the
terminal letter or number) and refer­
ring to that component and terminal in
the appropriate wiring diagram.
(3). Tag the wire before disconnecting it.
3. Heated Pitot Tube Replacement
(Slim − Line Instrument Panel)
(Ref. Figure 201)
A. Heated Pitot Tube Removal (Slim − Line
Instrument Panel)
(1). Raise copilot's heel strips and raise
access door in copilot's floor.
(2). Disassemble ground terminal E24
sufficiently to remove black 20 gauge
lead to pitot tube heating element. This
lead is un-numbered.
NOTE:
Terminal on end of black heater ele­
ment lead is MS25036-103.
(3). Remove five screws securing left or
right lower section panel of instrument
panel lower support assembly.
(4). Disconnect pressure tube threaded
fitting, or remove clamp securing
pressure tube to rear of pitot tube.
(5). Detach cable ties securing red and
black leads.
(6). Detach two strap, remove tubing from
knife splice SP140 and disengage knife
splice. Knife splice of SP140 connects
red wire from pitot tube heating
element to wire F504B16.
CAUTION