Housing corrosion

NAVAIR 17-15-50.3

TM 38-301-3

T.O. 33-1-37-3

CGTO 33-1-37-3

MH-60A/UH-60L/MH-60L/MH-60K (U.S. ARMY ONLY) (Cont.)

TAIL ROTOR GEARBOX

b. Housing corrosion - Housing corrosion is identified by an increase in magnesium wear metal levels in

spectrometric analysis results. At the first instance of an upward trend in magnesium levels, recommend the unit

drain and flush the tail rotor gearbox (reference paragraph 7) to insure any water contamination is removed. If

magnesium wear metal levels increase past the high range, recommend the unit remove the tail rotor servo and

inspect the servo bore area and the gearbox ID for signs of corrosion. If corrosion is found it should be repaired

per TM55-1520-237-23. If the corrosion cannot be repaired in the field, the gearbox should be replaced. If

corrosion cannot be identified, and magnesium wear metal levels continue to increase into the abnormal range,

the gearbox should be removed. Lab personnel may require more frequent sampling if a trending analysis

indicates the magnesium wear metal level may exceed the abnormal range before the next regularly scheduled

sampling is due.

c. Inboard retention plate/output gear spline wear - Wear of the inboard intention plate/output gear splines is

characterized by an increase in the levels of Ti (titanium), Al (aluminum), and Ag (silver) wear metals. An increase

in aluminum wear metal levels alone, without an accompanying rise in titanium wear metal levels, does not

explicitly indicate spline wear. Titanium and/or aluminum levels may be in the marginal/high range on new

gearboxes (less than 100 flight hours since new/overhauled) due to normal break-in wear of the internal

components. If spline wear is suspected (titanium in the high/abnormal range), recommend that the unit perform

an inboard retention plate nut bolt torque check, and report their findings (bolt torques) and observations to the

lab. Do not recommend removal of the inboard retention plate to inspect the split cones/splines. This action

should only be taken as a direct result of the torque check. If no action is required from this check, continue to

track titanium levels. Do not recommend further action unless titanium levels increase over an additional 100 flight

hours. If the levels increase over this interval, recommend another inboard retention plate nut bolt/input flange nut

torque check be accomplished.

d. Split cone wear - Wear of the split cones is not easily identified in the tail rotor gearbox. Wear of the split

cones would result in an increase in copper and aluminum wear metal levels. However, increases in copper wear

metal levels due to wear of the pitch control shaft bushing usually masks any increase in copper levels associated

with wear of the split cones. The presence of high levels of aluminum in spectrometric analysis is not indicative of

split cone wear. Wear of the inboard retention plate spline and of the pitch control shaft bushing also contribute to

high aluminum wear metals levels.

e. Pitch control shaft bushing wear - Wear of this bushing is characterized by high (in some cases, extremely

high - up to 200 ppm) levels of copper wear metal in the oil samples. This is especially common on newer

gearboxes. This wear is expected due to normal wear-in and is not cause for additional maintenance. The unit is

required to perform a dimensional inspection of this bushing for wear every 500 hours. A dimensional inspection

of the bushing OD may also be recommended when the copper level exceeds 75 ppm for two consecutive

sampling periods.

7. Field units should use the following drain and flush procedures to insure all contaminants/wear metals are

removed from the inside of the gearbox.

Remove filler cap.

Drain gearbox.

Remove chip detector self-closing valve.

Place a funnel under the chip detector self-closing valve opening. Place a 2 gallon container under the

funnel.

A157