Narrative:

On engine start at abq, elev 5400', both engine N2 stabilized at 46-47 percent. Generally idle RPM N2 is 'approximately 53 percent', according to our operating manual. This lower idle caused the right generator to cycle on an off. There is a procedure in the manual which calls for advancing the affected engine(south) to attempt to close a bleed valve which may cause the lower RPM. I attempted this procedure to no avail and concluded that I did not have a bleed valve stuck open. I also concluded that I did not have a hung start because all other indications were normal. I was especially careful to monitor egt's and acceleration rates as I advanced the throttles. My conclusion was that I had low idle RPM's on both engines due to high elevation (5400') and barometric pressure (low). I had seen low idle RPM's on this aircraft before at high elevations. Prior to departing abq, I advanced both throttles to maximum takeoff power, noting smooth, proper acceleration on both engines, with egt's normal as well as normal indications on all other engine parameters. These normal indications remained throughout all regimes of flight. At cruise I contacted our technical advisors by radio. The tech rep felt that the N2's were low and advised me to write it up for maintenance action at destination. I entered the write up in the logbook. Upon arrival at destination (elev 667') both N2 RPM's were 52 percent at idle on the ground. In flight, engine idle was normal. The mechanic at destination, after reviewing the logbook questioned my decision to depart abq. I then called the tech advisor on the phone. He agreed that, since acceleration and other parameters were normal, that my decision was safe. However, he informed me that using his charts (not available in the operating manual) that N2 should have been about 52 percent. Maintenance approved the aircraft for further service with no limitation. Recommendation. Since there are no definite idle RPM lower limits, I recommend either including the charts available to maintenance or stating a definite lower limit. This would remove the vague references such as 'approximately 53 percent' for stabilized idle. Also, in talking to other pilots of this aircraft, I have discovered that the low idle condition at high altitude airports is fairly common. If it in normal/abnormal, there should be some guidance for the pilot.

Google
 

Original NASA ASRS Text

Title: FLT CREW CONCERNED REGARDING IDLE ENGINE READINGS AT HIGH ALT AT ABQ. NORMAL READINGS FOR TKOF. GND PERSONNEL INDICATED FLT CREW SHOULD NOT HAVE TAKEN OFF.

Narrative: ON ENG START AT ABQ, ELEV 5400', BOTH ENG N2 STABILIZED AT 46-47 PERCENT. GENERALLY IDLE RPM N2 IS 'APPROX 53 PERCENT', ACCORDING TO OUR OPERATING MANUAL. THIS LOWER IDLE CAUSED THE R GENERATOR TO CYCLE ON AN OFF. THERE IS A PROC IN THE MANUAL WHICH CALLS FOR ADVANCING THE AFFECTED ENG(S) TO ATTEMPT TO CLOSE A BLEED VALVE WHICH MAY CAUSE THE LOWER RPM. I ATTEMPTED THIS PROC TO NO AVAIL AND CONCLUDED THAT I DID NOT HAVE A BLEED VALVE STUCK OPEN. I ALSO CONCLUDED THAT I DID NOT HAVE A HUNG START BECAUSE ALL OTHER INDICATIONS WERE NORMAL. I WAS ESPECIALLY CAREFUL TO MONITOR EGT'S AND ACCELERATION RATES AS I ADVANCED THE THROTTLES. MY CONCLUSION WAS THAT I HAD LOW IDLE RPM'S ON BOTH ENGS DUE TO HIGH ELEVATION (5400') AND BAROMETRIC PRESSURE (LOW). I HAD SEEN LOW IDLE RPM'S ON THIS ACFT BEFORE AT HIGH ELEVATIONS. PRIOR TO DEPARTING ABQ, I ADVANCED BOTH THROTTLES TO MAX TKOF PWR, NOTING SMOOTH, PROPER ACCELERATION ON BOTH ENGS, WITH EGT'S NORMAL AS WELL AS NORMAL INDICATIONS ON ALL OTHER ENG PARAMETERS. THESE NORMAL INDICATIONS REMAINED THROUGHOUT ALL REGIMES OF FLT. AT CRUISE I CONTACTED OUR TECHNICAL ADVISORS BY RADIO. THE TECH REP FELT THAT THE N2'S WERE LOW AND ADVISED ME TO WRITE IT UP FOR MAINT ACTION AT DEST. I ENTERED THE WRITE UP IN THE LOGBOOK. UPON ARR AT DEST (ELEV 667') BOTH N2 RPM'S WERE 52 PERCENT AT IDLE ON THE GND. IN FLT, ENG IDLE WAS NORMAL. THE MECH AT DEST, AFTER REVIEWING THE LOGBOOK QUESTIONED MY DECISION TO DEPART ABQ. I THEN CALLED THE TECH ADVISOR ON THE PHONE. HE AGREED THAT, SINCE ACCELERATION AND OTHER PARAMETERS WERE NORMAL, THAT MY DECISION WAS SAFE. HOWEVER, HE INFORMED ME THAT USING HIS CHARTS (NOT AVAILABLE IN THE OPERATING MANUAL) THAT N2 SHOULD HAVE BEEN ABOUT 52 PERCENT. MAINT APPROVED THE ACFT FOR FURTHER SVC WITH NO LIMITATION. RECOMMENDATION. SINCE THERE ARE NO DEFINITE IDLE RPM LOWER LIMITS, I RECOMMEND EITHER INCLUDING THE CHARTS AVAILABLE TO MAINT OR STATING A DEFINITE LOWER LIMIT. THIS WOULD REMOVE THE VAGUE REFERENCES SUCH AS 'APPROX 53 PERCENT' FOR STABILIZED IDLE. ALSO, IN TALKING TO OTHER PLTS OF THIS ACFT, I HAVE DISCOVERED THAT THE LOW IDLE CONDITION AT HIGH ALT ARPTS IS FAIRLY COMMON. IF IT IN NORMAL/ABNORMAL, THERE SHOULD BE SOME GUIDANCE FOR THE PLT.

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.