The type of contamination present in a system determines the method by which a system is decontaminated. Normally, recirculation cleaning is the most effective decontamination method, considering maintenance man-hours and material requirements. This method should be used whenever possible. However, if a system is contaminated by some substance other than readily filterable particles, it may be necessary to flush the system, or in certain very extreme cases, to purge it. Refer to table 4-3. The table contains information to help you select an appropriate decontamination method. The table refers to chemical analysis and particle counting, as well as to the normally performed patch testing and visual tests. You may request chemical analysis and actua  particle counts of fluid samples from the NADEP materials engineering laboratories. You may use these test results to select a decontamination method. 

CONTAMINATION CONTROL SEQUENCE 

System decontamination is one operation of a contamination control sequence that includes hydraulic fluid sampling and analysis. Decon-tamination is performed when the results of sampling and analysis indicate an unacceptable contamination level. Then, additional testing determines when an acceptable level is reached. There are many operations required during the contamination control sequence, and these operations interact during the sequence. Figure 4-7 is a basic contamination control sequence chart for aircraft system decontamination. It is a guide for decon-taminating all naval aircraft and portable hydraulic test stands. The procedures outlined in the chart reflect basic requirements of periodic maintenance,

Table 4-3.Aircraft Decontamination Requirements

periodic aircraft rework, and maintenance performed as a result of actual or suspected malfunctions.