TM 1-1520-240-MTF4-43NOTEThe 20 degrees subtracted from the PTIT for initialTEAC is not subtracted from subsequent TEACS.(4) To determine the lower limit baselineenter figure 5-9 at the prevailing FAT,proceed vertically to a value 20_C lessthan the measured PTIT. The lower limitbaseline is identified as the number ofdegrees above the applicable referenceline 1, 2, 3 or 4 on figure 5-9. When theengine lower limit baseline has beendetermined, record the line number andthe number of degrees above the line inthe remarks section of the HistoricalRecord For Aircraft (Form 2408-15TEAC overprint).ExampleDuring the TEAC, PTIT was recorded at 800_C, N1speed was 103%, FAT was-14_C.PTIT=800_CTolerance=-20_CEngine Lower Limit Baseline=780_CThe engine lower limit is 5_C above line 3 at all ambi-ents. Record lower limit in the Historical Record ForAircraft as shown below.NOTEThe purpose of the lower limit is to validate theaccuracy of the PTIT temperature measure-ment system, as mentioned in the trouble-shooting chart. A PTIT temperature below theestablished lower limit, with all other indica-tions correct, is an indication of temperaturesystem problems.
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