Narrative:

We picked up aircraft in ZZZ and flew to ZZZ1. I noticed nothing unusual on the first flight. On the return flight to ZZZ at 17000 ft at an extremely cold temperature; captain did an engine trend and noticed the right engine delta delta T to be higher than normal. After conferring with maintenance; the decision was made to take another trend reading since the information gathered at 17000 ft with such a cold temperature may be unreliable. This was further reinforced by flight operations manual. On the next flight we flew into WX which required the engine anti-ice to be turned on. We did a full approach and were unable to do a trend. On the way back we came back out of the WX system and did a trend at a lower altitude. The results were the same so captain wrote it up and I believe maintenance did an inspection. If a delta delta T shift over 40 degrees is noticed at altitudes above 15000 ft; do not write up the shift until the delta delta T is again checked between 12000 ft and 15000 ft. If a shift of over 40 degrees remains at the lower altitude; a write-up and compliance with the avoidance ranges is then required. This is due to engine characteristics at high altitude; especially cold air. During a routine trend check; an abnormal temperature was noticed but deemed unreliable due to the altitude and outside temperature. A second trend was done to verify. As far as I knew we had operated in accordance with the flight operations manual. We followed the guidance in the flight operations manual and referenced the QRH. After landing maintenance was called a second time and it was written up. The flight operations manual states 'do not write up the shift until the delta delta T is again checked.' it sounds as though it shouldn't be written up until the next time that a trend can be done and it can be again verified. I think this leaves room for clarification in the event that a trend can not be accomplished on the next immediate flight. Should it be written up without a second trend done (which seems contrary to that statement); or should it be flown again to accomplish the second trend? I prefer the first.

Related reports:

Google
 

Original NASA ASRS Text

Title: A SAAB-340B FLT CREW; AT 17;000' FT IN EXTREME COLD; DID AN ENG TREND CHK. NOTICED R ENG DELTA; DELTA -T; TO BE HIGHER THAN NORMAL.

Narrative: WE PICKED UP ACFT IN ZZZ AND FLEW TO ZZZ1. I NOTICED NOTHING UNUSUAL ON THE FIRST FLT. ON THE RETURN FLT TO ZZZ AT 17000 FT AT AN EXTREMELY COLD TEMP; CAPT DID AN ENG TREND AND NOTICED THE R ENG DELTA DELTA T TO BE HIGHER THAN NORMAL. AFTER CONFERRING WITH MAINT; THE DECISION WAS MADE TO TAKE ANOTHER TREND READING SINCE THE INFO GATHERED AT 17000 FT WITH SUCH A COLD TEMP MAY BE UNRELIABLE. THIS WAS FURTHER REINFORCED BY FLT OPS MANUAL. ON THE NEXT FLT WE FLEW INTO WX WHICH REQUIRED THE ENG ANTI-ICE TO BE TURNED ON. WE DID A FULL APCH AND WERE UNABLE TO DO A TREND. ON THE WAY BACK WE CAME BACK OUT OF THE WX SYS AND DID A TREND AT A LOWER ALT. THE RESULTS WERE THE SAME SO CAPT WROTE IT UP AND I BELIEVE MAINT DID AN INSPECTION. IF A DELTA DELTA T SHIFT OVER 40 DEGS IS NOTICED AT ALTS ABOVE 15000 FT; DO NOT WRITE UP THE SHIFT UNTIL THE DELTA DELTA T IS AGAIN CHKED BTWN 12000 FT AND 15000 FT. IF A SHIFT OF OVER 40 DEGS REMAINS AT THE LOWER ALT; A WRITE-UP AND COMPLIANCE WITH THE AVOIDANCE RANGES IS THEN REQUIRED. THIS IS DUE TO ENG CHARACTERISTICS AT HIGH ALT; ESPECIALLY COLD AIR. DURING A ROUTINE TREND CHK; AN ABNORMAL TEMP WAS NOTICED BUT DEEMED UNRELIABLE DUE TO THE ALT AND OUTSIDE TEMP. A SECOND TREND WAS DONE TO VERIFY. AS FAR AS I KNEW WE HAD OPERATED IN ACCORDANCE WITH THE FLT OPS MANUAL. WE FOLLOWED THE GUIDANCE IN THE FLT OPS MANUAL AND REFED THE QRH. AFTER LNDG MAINT WAS CALLED A SECOND TIME AND IT WAS WRITTEN UP. THE FLT OPS MANUAL STATES 'DO NOT WRITE UP THE SHIFT UNTIL THE DELTA DELTA T IS AGAIN CHKED.' IT SOUNDS AS THOUGH IT SHOULDN'T BE WRITTEN UP UNTIL THE NEXT TIME THAT A TREND CAN BE DONE AND IT CAN BE AGAIN VERIFIED. I THINK THIS LEAVES ROOM FOR CLARIFICATION IN THE EVENT THAT A TREND CAN NOT BE ACCOMPLISHED ON THE NEXT IMMEDIATE FLT. SHOULD IT BE WRITTEN UP WITHOUT A SECOND TREND DONE (WHICH SEEMS CONTRARY TO THAT STATEMENT); OR SHOULD IT BE FLOWN AGAIN TO ACCOMPLISH THE SECOND TREND? I PREFER THE FIRST.

Data retrieved from NASA's ASRS site as of January 2009 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.