Narrative:

We departed cos on time with a normal pushback and engine start. We taxied out to runway 17L with an OAT of 65 degrees F and a takeoff weight of 112000 pounds. We elected to use maximum thrust on takeoff with a reduced climb (climb-2) preselected in the FMC. As takeoff power was applied by the autothrottles, we noticed considerable 'searching' by the autothrottles. Target N1, was 97.3 percent and an excursion to 100.7 percent N1, on the #2 engine was noted at one point. The captain pulled the thrust lever back on the #2 engine at approximately 100 KIAS, to get it back close to 97.3 percent N1, with all other parameters being normal. We then rotated, noting some hot air balloon activity about 2-3 mi off the departure end of the runway 17L. The balloons were drifting quite quickly into our path due to the stronger winds aloft. We had to deviate left of course to keep an appropriately safe distance from the traffic. This traffic dictated that our scan be primarily outside the aircraft. Once safely clear of traffic, we then returned our scan to the cockpit and noticed that both engine overtemp lights were on with a corresponding egt on both engines of approximately 965 degrees to 980 degrees C. We immediately selected climb thrust (climb-2) and cleaned up the aircraft. As engine parameters returned to normal we then resumed a normal climb out to cruise altitude. During climb out and cruise we diligently monitored all engine parameters with no abnormalities noted. After discussing the event between us, and given the normal indications and operations of both engines, we agreed that we could safely complete the flight to phx. All other phases of flight were uneventful. Maintenance control was notified prior to arrival and thoroughly briefed upon arrival at the gate. After discussing this event and comparing prior experiences, the likelihood of a temperature inversion was very likely. This would not have occurred while the autothrottles were in 'throttle hold' where the aircraft servo motors are unpowered. At that time they would not have been able to respond to an increase in egt caused by the temperature inversion. As we were looking outside to avoid the balloon traffic our attention was diverted from the engine parameters. The temperature inversion was later confirmed by the DFDR. We had an increase of 8 degrees in the first 1000 ft. Both engines had to be removed from the aircraft for complete 'hot sections.'

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Original NASA ASRS Text

Title: ACFT ENG OVERTEMP WHEN GOING THROUGH INVERSION WHILE RPTR WAS TRYING TO AVOID BALLOONS. THE FLC LEFT THE THRUST SETTING IN TKOF PWR AND THUS THE ENGS ARE LOCKED AND CANNOT ADJUST FOR INVERSION (TEMP) EFFECTS.

Narrative: WE DEPARTED COS ON TIME WITH A NORMAL PUSHBACK AND ENG START. WE TAXIED OUT TO RWY 17L WITH AN OAT OF 65 DEGS F AND A TKOF WT OF 112000 LBS. WE ELECTED TO USE MAX THRUST ON TKOF WITH A REDUCED CLB (CLB-2) PRESELECTED IN THE FMC. AS TKOF PWR WAS APPLIED BY THE AUTOTHROTTLES, WE NOTICED CONSIDERABLE 'SEARCHING' BY THE AUTOTHROTTLES. TARGET N1, WAS 97.3 PERCENT AND AN EXCURSION TO 100.7 PERCENT N1, ON THE #2 ENG WAS NOTED AT ONE POINT. THE CAPT PULLED THE THRUST LEVER BACK ON THE #2 ENG AT APPROX 100 KIAS, TO GET IT BACK CLOSE TO 97.3 PERCENT N1, WITH ALL OTHER PARAMETERS BEING NORMAL. WE THEN ROTATED, NOTING SOME HOT AIR BALLOON ACTIVITY ABOUT 2-3 MI OFF THE DEP END OF THE RWY 17L. THE BALLOONS WERE DRIFTING QUITE QUICKLY INTO OUR PATH DUE TO THE STRONGER WINDS ALOFT. WE HAD TO DEVIATE L OF COURSE TO KEEP AN APPROPRIATELY SAFE DISTANCE FROM THE TFC. THIS TFC DICTATED THAT OUR SCAN BE PRIMARILY OUTSIDE THE ACFT. ONCE SAFELY CLR OF TFC, WE THEN RETURNED OUR SCAN TO THE COCKPIT AND NOTICED THAT BOTH ENG OVERTEMP LIGHTS WERE ON WITH A CORRESPONDING EGT ON BOTH ENGS OF APPROX 965 DEGS TO 980 DEGS C. WE IMMEDIATELY SELECTED CLB THRUST (CLB-2) AND CLEANED UP THE ACFT. AS ENG PARAMETERS RETURNED TO NORMAL WE THEN RESUMED A NORMAL CLB OUT TO CRUISE ALT. DURING CLBOUT AND CRUISE WE DILIGENTLY MONITORED ALL ENG PARAMETERS WITH NO ABNORMALITIES NOTED. AFTER DISCUSSING THE EVENT BTWN US, AND GIVEN THE NORMAL INDICATIONS AND OPS OF BOTH ENGS, WE AGREED THAT WE COULD SAFELY COMPLETE THE FLT TO PHX. ALL OTHER PHASES OF FLT WERE UNEVENTFUL. MAINT CTL WAS NOTIFIED PRIOR TO ARR AND THOROUGHLY BRIEFED UPON ARR AT THE GATE. AFTER DISCUSSING THIS EVENT AND COMPARING PRIOR EXPERIENCES, THE LIKELIHOOD OF A TEMP INVERSION WAS VERY LIKELY. THIS WOULD NOT HAVE OCCURRED WHILE THE AUTOTHROTTLES WERE IN 'THROTTLE HOLD' WHERE THE ACFT SERVO MOTORS ARE UNPOWERED. AT THAT TIME THEY WOULD NOT HAVE BEEN ABLE TO RESPOND TO AN INCREASE IN EGT CAUSED BY THE TEMP INVERSION. AS WE WERE LOOKING OUTSIDE TO AVOID THE BALLOON TFC OUR ATTN WAS DIVERTED FROM THE ENG PARAMETERS. THE TEMP INVERSION WAS LATER CONFIRMED BY THE DFDR. WE HAD AN INCREASE OF 8 DEGS IN THE FIRST 1000 FT. BOTH ENGS HAD TO BE REMOVED FROM THE ACFT FOR COMPLETE 'HOT SECTIONS.'

Data retrieved from NASA's ASRS site as of July 2007 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.