TAIL ROTOR GEARBOX (Cont) - TM-38-301-30190

NAVAIR 17-15-50.3

TM 38-301-3

T.O. 33-1-37-3

CGTO 33-1-37-3

SH-60B, SH-60F, HH-60H, MH-60S, MH-60R (Cont.)

TAIL ROTOR GEARBOX

Mg -

With a new or freshly reworked gearbox, magnesium usually indicates minor

manufacturing/assembly debris from housings. Otherwise, magnesium

contamination indicates internal corrosion or abrasive wear. Magnesium

components in the tail rotor gearbox include the input housing, center

housing, output housing, and the lubrication spiral that provides oil to the

output bearing on the bevel gear. To date, most internal tail rotor gearbox

corrosion has originated at the servo bore area, which is accessible for

inspection after removal of the tail rotor servo and pitch change shaft

assembly.

Due to moisture accumulation, vulnerability to corrosion is increased if the tail

rotor gearbox has been serviced but has not been operational for an

extended period. If corrosion occurs due to moisture contamination,

magnesium is sometimes accompanied by iron. If the magnesium level

enters the marginal or high range, the recommendation shall be "Sample at

approximately 10 flight hour interval for next 30 flight hours. Do not change

oil at this time. If magnesium level does not increase to abnormal range and

no abnormal upward trend occurs in the initial 30 flight hour period, return to

normal sampling". Maintain a normal sampling interval thereafter until an

abnormal level or abnormal upward trend occurs. Due to the relative softness

of magnesium alloys in this gearbox, risk of abrasion is not sufficient to justify

oil change unless an abnormal upward trend occurs or the magnesium level

enters an abnormal range. If the magnesium level enters the abnormal range

or if an abnormal upward trend occurs, the recommendation shall be

"Change oil, submit turn-up sample, and submit samples approximately each

10 flight hours for next 30 flight hours. If magnesium level remains below

marginal level and no abnormal upward trend occurs within this 30 flight hour

period, return to normal sampling". If the magnesium level returns to the

marginal range or above, or if an abnormal upward trend occurs, the

recommendation shall be "Remove tail rotor servo and pitch change shaft

assembly at next phase inspection and inspect servo bore area of tail rotor

gearbox housing, as well as visible internal areas of tail rotor gearbox, for

evidence of corrosion. If corrosion is found, repair in accordance with H-60

aircraft corrosion control manual. If no corrosion is evident, serviceability

check is recommended in accordance with general aircraft information

manual.

Titanium wear particles can be extremely serious in this gearbox. Titanium

particles may be indicative of wear in the splines between the inboard

retention plate and the output bevel gear, or in the splines between the input

flange and the pinion gear. Aluminum wear particles should accompany the

titanium, since there is aluminum in the titanium alloy for both the inboard

retention plate and the input flange. If inboard retention plate spline wear is

the cause of wear particles, aluminum and copper will usually be contributed

through wear on the aluminum-bronze split cones.

If titanium level enters the marginal or high range and is accompanied by

aluminum levels in the same range, the recommendation shall be, "Submit

samples approximately every 10 flight hours for the next 30 flight hours. Do

not change oil at this time." If contamination does not increase to abnormal

range and no abnormal trend occurs at any time within this period, change oil

and return to normal sampling. If the titanium level enters the abnormal range

or if an abnormal upward trend occurs and is accompanied by aluminum

levels in the same range or greater, verify immediately with a second sample.

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