ANALYZING ENGINE/TRANSMISSION TEST CELL RESULTS.

NAVAIR 17-15-50.3

TM 38-301-3

T.O. 33-1-37-3

CGTO 33-1-37-3

b. Helicopter Gearboxes and Transmissions. Under certain conditions the provisions of Table 2-2,

Decision Making Guidance, may not fully apply. Water in helicopter gearboxes and transmissions may cause

high wear metal indications (normally either high iron and copper or high iron, copper, magnesium, and

aluminum as a result of internal component corrosion. When high wear metal readings of these elements are

obtained, the samples should be examined for water content. If high or abnormal wear metals are detected

and/or the water content of the oil is excessive (normally over 1000 PPM or 0.10%), the laboratory

recommendation should be to drain the gearbox/transmission (and flush if applicable), reservice with new oil,

perform serviceability check in accordance with applicable maintenance manuals, and to submit special oil

samples both after serviceability check and after a specified number of flight hours both wear metal and water

content analysis. Detailed instructions for evaluating a particular gearbox/transmission are included in the

applicable Supplemental Diagnostic Guidance Tables for the specific equipment.

2-4. ANALYZING ENGINE/TRANSMISSION TEST CELL RESULTS. The information contained in the tables of

this manual are not fully applicable to equipment oil samples taken during test cell operational testing following

equipment overhaul due to (1) the overhaul process itself and the different rate of wear metal production of newly

overhauled engines and transmissions, (2) the brief duration of engine run time and the impossibility of

correlating results with trend tables, and (3) the differences between type equipment oil supply during test cell

operation (i.e., some engines, as configured for test cell operation, do not include a complete oil system and an

external oil supply is required).

a. Certain similarities do exist in determining acceptable wear metal levels and production rates for both

test cell and operational engines. Any engine/transmission that exceeds the normal wear metal limit specified in

the applicable Evaluation Criteria tables of this manual should be examined to determine the source of the wear

metal. However, wear metal levels within the normal range as specified in this manual may also be judged as

excessive for test cell purposes at the discretion of the cognizant/controlling engineering authority for the

particular equipment. Since the time between oil samples is normally too brief to be useable as a trend in

accordance with the Evaluation Criteria Tables of this manual, acceptable and unacceptable trend limits shall be

as established by the cognizant/controlling engineering authority for the equipment involved.

b. Engines/transmissions subjected to repair/minor repair in which the oil system remained intact and no

repair was accomplished that would affect the oil system wear metal generating pattern, may be evaluated using

the evaluation criteria of this manual despite the fact that trend values cannot normally be determined due to the

brevity of the test cell operational run. Engines/transmissions in this category are normally subject to post repair

ground run and test flight sampling, and evaluator judgement must again play a large part in determining

equipment acceptability for continued operation until sufficient operation time is accumulated to establish a

documented equipment trend.

c. Questions concerning equipment test cell wear metal limits and trends should be addressed directly to

the cognizant/controlling engineering authority for the particular type/model/series equipment involved.

2-5. USAF/ALC DEPOT OAP EVALUATION CRITERIA. The USAF Depot OAP evaluation criteria contained in

Table 2-4 are for ALC depot level use only. When the guidelines of Table 2-4 are exceeded, the Depot Decision

Logic of Table 2-5 should be used.

2-6. FERROGRAPHY (ARMY). Ferrography is a fluid analysis technique that can be applied to the analysis of

lubricating oils, hydraulic oils, and greases. Ferrography can be used not only to determine the size, shape, and

type of wear metal particles being generated within a component, but also to determine the mode of wear (E.g.,

spalling, cuffing, and rubbing) producing the wear metal particles. Wear metal particles in the size range of 1 to

250 micrometers can be analyzed using ferrography, which makes it an effective supplemental oil analysis

procedure. The ferrographic analysis of a lubricant sample is a three step process: (1) Processing the sample

through the direct reading (DR) ferrograph, (2) Processing the sample through the analytical ferrograph and

preparing the ferrogram, and (3) Examining the ferrogram under the ferroscope. All lubricant samples are mixed

with a fixer solution, which aids in the flow of the sample across the substrate and in the development of the

ferrogram.

2-5