Narrative:

[We were] dispatched with tat gauge decaled by maintenance as 50 plus degrees warmer than actual; with the provision that the sat display must operate normally. It was 95 degrees at departure and the sat appeared normal on preflight and takeoff; with a correct crosscheck of N1. During climbout; we were climbing slowly; and were queried by ATC. We looked into performance chapters and determined we were climbing at a reduced setting. The climb to cruise was very slow. Once at FL350; we asked another aircraft for their temperatures and they showed a tat of minus 25 to our 8 plus; and an sat of minus 54 to our minus 24. (They were at FL390 and we were at FL350). Using those temperatures; we determined the EPR was normal for .80 mach at 1.19. We sent a message asking about the effect of both sat and tat being incorrect and giving those numbers. They came back asking is the auto throttles holding your selected speed? We replied yes. They came back with do you have any other EICAS messages or warnings? The MEL for the tat only states sat indication is available. If you suspect sat is not correct the auto throttles may not work correctly. Please keep close watch on speed if using auto throttles. We carefully watched autothrottles setting during the flight and they seemed to work fine. We manually computed a GA EPR setting in case of a go-around. We think both the tat and sat were incorrect; and decided there was no accurate way to determine when to turn on anti ice outside of seeing ice form. The MEL was short of necessary information.

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Original NASA ASRS Text

Title: Flight crew reports being dispatched with a malfunctioning SAT gauge with the provision that TAT functions normally. During climb it is determined that normal climb thrust is not being produced by the ATS and that neither temperature gauge is providing accurate information. Flight continues to destination.

Narrative: [We were] dispatched with TAT gauge decaled by Maintenance as 50 plus degrees warmer than actual; with the provision that the SAT display must operate normally. It was 95 degrees at departure and the SAT appeared normal on preflight and takeoff; with a correct crosscheck of N1. During climbout; we were climbing slowly; and were queried by ATC. We looked into performance chapters and determined we were climbing at a reduced setting. The climb to cruise was very slow. Once at FL350; we asked another aircraft for their temperatures and they showed a TAT of minus 25 to our 8 plus; and an SAT OF minus 54 TO OUR minus 24. (They were at FL390 and we were at FL350). Using those temperatures; we determined the EPR was normal for .80 mach at 1.19. We sent a message asking about the effect of both SAT and TAT being incorrect and giving those numbers. They came back asking is the auto throttles holding your selected speed? We replied Yes. They came back with do you have any other EICAS messages or warnings? The MEL for the TAT only states SAT indication is available. If you suspect SAT is not correct the auto throttles may not work correctly. Please keep close watch on speed if using auto throttles. We carefully watched autothrottles setting during the flight and they seemed to work fine. We manually computed a GA EPR setting in case of a go-around. We think both the TAT and SAT were incorrect; and decided there was no accurate way to determine when to turn on Anti Ice outside of seeing ice form. The MEL was short of necessary information.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.