(7) Keep vise jaws covered with soft metal
maintenance in a hangered environment shall not be
considered to be in storage. Tasks applicable to short
term storage shall be performed as necessary to prevent
deterioration of the aircraft. Selection of the required
tasks is at the discretion of the maintenance officer based
on local conditions. Aircraft stored in an outside
environment awaiting parts shall be preserved for the
appropriate storage category as described above.
4-3. Powertrain. Powertrain systems for single rotor and
tandem rotor helicopters are explained in the following
a. Single Rotor Powertrain. The single rotor
powertrain consists of gearboxes, drive-shafts, and
clutches. The system carries torque from the engines to
the main and tail rotors. A typical single rotor powertrain
system is shown in figure 4-1.
b. Tandem Rotor Powertrain. The tandem rotor
powertrain delivers torque from the engines to both rotors.
A typical tandem rotor powertrain is shown in figure 4-2.
4-4. Drive Components. The components that make up
the power drive system are gearboxes, clutches, free-
wheel units, engine cooling fans, rotor brakes, and drive
shafting. Power drive components shall be serviced at
normal operating oil temperature with the oil specified in
the applicable aircraft maintenance manual.
a. Gearboxes. The gearbox is coupled to the
engine by the main driveshaft and provides drive angle
change and speed reduction to drive the main rotor mast,
through a train of spiral bevel gears and two-stage
(1) Inspection. Refer to the applicable
maintenance manual for specific inspection procedures.
The following paragraphs contain general instructions for
(a) Oil contamination. When metal
particles are found in oil or gearbox and are readily
identified as fragments of gearbox parts, such as gears,
nuts, bearings, slingers, thrust washers, snap rings, and
lockwire, the gearbox shall be replaced in accordance
with the applicable aircraft maintenance manual. If the
gearbox has an external oil cooler, the oil cooler shall be
replaced and the lines flushed.
(b) Identification of metal particles.
When foreign substances are found and not readily
identified, perform the serviceability check described in
the following procedures:
1 Drain and flush gearbox with
specified operating oil.
Drycleaning solvent is flammable and
solvent vapors are toxic. Use P-D-680,
Type II Solvent in a well-ventilated area.
Keep away from open flames. Avoid
prolonged solvent contact with skin.
2 Remove, clean, and reinstall
filter, finger screen, and magnetic plug. Clean with
drycleaning solvent, Federal Specification P-D-680.
When removing screen or filter, catch oil
which comes from around screen and
filter in a clean white cloth. Dip cloth and
its contents into dry cleaning solvent,
Federal Specification P-D-680. Examine
foreign material found in cloth, as well as
that adhering to screen, as a means of
determining condition of gearbox.
3 Service gearbox, with grade
and specification of oil specified in applicable aircraft
4 Inspect gearbox after 5, 10,
and 15 hours operation. If amount of particles has
increased, remove gearbox for overhaul. If amount of
particles has decreased, gearbox will be continued in
(c) Overspeed inspection. When a
gear box has been subjected to overspeeding, it shall be
inspected in accordance with the applicable aircraft
inspection requirements manual.
(d) Sudden speed reduction inspection.
When a sudden reduction in speed or sudden stoppage is
encountered, gearbox shall be inspected or replaced as
specified in the inspection requirements of applicable
(e) Leaking seals. Inspect gearbox for
leaking seals. Leaking seals can be replaced in some
gearboxes. These seals shall be replaced as outlined in
applicable maintenance manual. Damaged or leaking
fittings will be replaced.
Change 2 4-3