EVALUATING SAMPLE RESULTS

NAVAIR 17-15-50.3

TM 38-301-3

T.O. 33-1-37-3

CGTO 33-1-37-3

d. The Decision Making Guide (Table 2-2) provides a logical sequence of action for the evaluator to follow

in determining appropriate laboratory recommendations during the evaluation process. This table is structured

so that a laboratory recommendation may be derived from a comparison of the latest oil sample analysis with the

analysis of the previous sample with consideration of the trend as a factor. Table 2-2 is intended for use as a

guide for the evaluator. When making a final determination of the appropriate recommendation, the evaluator

must consider all the factors involved in the evaluation process. A recommendation for maintenance action is

normally considered only after a special sample confirming the previous analysis. However, the evaluator may

desire to issue a "do not fly, do not operate" recommendation following an abnormal routine sample pending an

evaluation of the special sample if the circumstances warrant such a recommendation. The laboratory

recommendation codes in Table 2-2 are defined in Table 2-3 and are standard throughout the JOAP for

aeronautical equipment. A recommendation code that is the most appropriate for the situation shall be assigned.

However, the descriptive text accompanying the recommendation code may be modified to fit the situation,

provided the basic definition of the code selected remains unchanged.

e. Sampling frequency is directly related to the probability of detecting impending failure which is, in turn,

related to the rapidity of the failure mode. Although oil analysis is intended to provide a high probability of

detection of impending failure, a reduced probability of detection may be tolerated in some cases for equipment

with built in redundancy such as multi-engined aircraft, or for systems with low safety risks associated with

equipment malfunction or failure, such as aircraft auxiliary power units. Normal sampling frequency

requirements, however, are determined by higher authority within each service, are mandatory, and are not

subject to modification by laboratory or operating activities without official direction. Laboratories may, however,

recommend increased sampling frequency for special samples when analysis results indicate the need for closer

equipment monitoring on a temporary basis.

2-2. EVALUATING SAMPLE RESULTS. Fully automated laboratories will receive a computer generated

recommendation based on limits entered in the computer program. Although these limits are statistically correct,

the computer generated recommendation is considered as a guide and is not binding upon the evaluator.

Evaluator experience and judgement are extremely important factors in determining an effective recommendation

since the evaluator may use additional information not contained in the computer statistical program in order to

arrive at a more accurate decision for a particular set of circumstances. The following procedure will be used by

the evaluator in evaluating sample results:

NOTE

Investigate missing or unusual oil servicing records (such as no oil addition, or excessive oil

addition) as these records are an important part of the sample evaluation process.

a. Determine the range for each critical wear metal concentration in the sample result from the appropriate

engine/component wear metal Evaluation Criteria Table in Appendix A.. Critical wear metals (elements) which

require oil analysis monitoring for the particular equipment have numerical criteria provided in the applicable

equipment wear metal Evaluation Criteria Table. Data on the average concentration of other elements (listed

below the table) are provided for information purposes. However, if unusual concentrations of these non-critical

elements are found, they may also be used as a basis for maintenance recommendations or resampling

requests.

b. Compare the wear metal concentration levels of the current sample with the levels of the previous

sample to determine if changes are occurring which indicate developing or impending equipment problems.

2-2