Narrative:

During descent in visual meteorological conditions at app. 13;000 feet and 9 minutes until ETA; the flight crew received a red cur lim master warning followed shortly thereafter by a right gen caution. A check of the electric power monitor (epm) showed 0 amps on the right dc amps indication; which the crew discussed as being a failure of the right 275 current limiter and possible overload of the right generator as a result of the failure or vice versa. The crew proceeded to the QRH procedure for the cur lim master warning on page E-5 which indicated; based upon epm readings; that only 1 current limiter had failed and that flight could be continued with reduced electrical loads. The crew next proceeded to the QRH procedure for the right gen caution found on page A-8. This QRH procedure advises the crew to check electrical loads; circuit breakers; gen switch position; and then attempt multiple resets of the affected generator in an effort to bring the generator back online. However; given the fact that the crew was dealing with what they believed at the time to be a possible overload situation with a blown current limiter; they elected to leave the generator off and not attempt a reset; thereby avoiding the potential to reintroduce an overload into the already compromised electrical system.with the red cur lim and yellow right gen messages still displayed; the crew discussed the need to land the airplane as soon as possible and further reduce electrical load due to the unknown nature of the electrical issue at hand. With the destination less than 5 minutes away at this point; the crew reduced the electrical load by shedding the AC; flood & cabin fans; etc. And made an expeditious approach and landing in VMC; shutting the right engine down after clearing the runway to further reduce the possibility of more issues arising from the right generator. Further investigation by maintenance after shutdown revealed the root cause of the messages to be a loose stud on the right generator bus of the power distribution panel (pdp) inside the tail cone of the aircraft; and not a failure of the current limiter or right generator as was presented to the flight crew by the associated warning and caution annunciators. The flight crew had been led to believe by the warning messages and QRH procedures that the system had worked as designed and isolated the electrical problem by blowing the 275 current limiter; when indeed the current limiter had not blown and the overheating bus had continued to receive power; furthering the overheat situation and leading to the erroneous display of the right gen caution msg from the overheating bus. Had the right gen msg not been displayed; directing the crew to take the generator offline and reduce electrical load; the bus would have continued to receive power and overheat; leading to the potential for a catastrophic electrical fire or total electrical failure. All of this would have occurred without any indication to the crew of the severity of the developing situation; due to the fact that the cur lim master warning is not a direct indication of the status of the current limiter (blown or intact) as the QRH assumes; but rather an indication that a circuit breaker on the bus sensed the overheat situation caused by the loose stud and tripped; triggering the cur lim master warning. The current limiter was still intact and powering the bus with the cur lim master warning displayed; a truly dangerous and potentially catastrophic detail had the flight been continued; allowing the overheat event to propagate along the pdp.

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Original NASA ASRS Text

Title: Learjet 31 pilot reported having an electrical issue with a generator and supporting warning lights. Crew engaged in troubleshooting and elected not to restore the generator on line. The destination airport was close enough so as to land normally there.

Narrative: During descent in Visual Meteorological Conditions at app. 13;000 feet and 9 minutes until ETA; the flight crew received a Red CUR LIM Master Warning followed shortly thereafter by a R GEN Caution. A check of the Electric Power Monitor (EPM) showed 0 amps on the right DC Amps indication; which the crew discussed as being a failure of the right 275 Current Limiter and possible overload of the R Generator as a result of the failure or vice versa. The crew proceeded to the QRH procedure for the CUR LIM Master Warning on page E-5 which indicated; based upon EPM readings; that only 1 Current Limiter had failed and that flight could be continued with reduced electrical loads. The crew next proceeded to the QRH procedure for the R GEN Caution found on page A-8. This QRH procedure advises the crew to check electrical loads; circuit breakers; GEN Switch position; and then attempt multiple resets of the affected generator in an effort to bring the generator back online. However; given the fact that the crew was dealing with what they believed at the time to be a possible overload situation with a blown current limiter; they elected to leave the generator off and not attempt a reset; thereby avoiding the potential to reintroduce an overload into the already compromised electrical system.With the Red CUR LIM and Yellow R GEN messages still displayed; the crew discussed the need to land the airplane as soon as possible and further reduce electrical load due to the unknown nature of the electrical issue at hand. With the destination less than 5 minutes away at this point; the crew reduced the electrical load by shedding the AC; flood & cabin fans; etc. and made an expeditious approach and landing in VMC; shutting the right engine down after clearing the runway to further reduce the possibility of more issues arising from the R Generator. Further investigation by maintenance after shutdown revealed the root cause of the messages to be a loose stud on the R Generator Bus of the Power Distribution Panel (PDP) inside the tail cone of the aircraft; and NOT a failure of the Current Limiter or R Generator as was presented to the flight crew by the associated warning and caution annunciators. The flight crew had been led to believe by the warning messages and QRH procedures that the system had worked as designed and isolated the electrical problem by blowing the 275 current limiter; when indeed the current limiter HAD NOT blown and the overheating bus had continued to receive power; furthering the overheat situation and leading to the erroneous display of the R GEN Caution msg from the overheating bus. Had the R GEN msg not been displayed; directing the crew to take the generator offline and reduce electrical load; the bus would have continued to receive power and overheat; leading to the potential for a catastrophic electrical fire or total electrical failure. All of this would have occurred without any indication to the crew of the severity of the developing situation; due to the fact that the CUR LIM Master Warning is not a direct indication of the status of the Current Limiter (blown or intact) as the QRH assumes; but rather an indication that a circuit breaker on the bus sensed the overheat situation caused by the loose stud and tripped; triggering the CUR LIM Master Warning. The Current Limiter was still intact and powering the bus with the CUR LIM Master Warning displayed; a truly dangerous and potentially catastrophic detail had the flight been continued; allowing the overheat event to propagate along the PDP.

Data retrieved from NASA's ASRS site 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.