Narrative:

During the preflight; we noticed that the engine #1; N1 gauge was rolling up and down from 0- 11.1 percent; with the engine off. We notified maintenance and wrote it up. We were told that; this is a no-go item. Upon further troubleshooting; it was discovered that the problem seemed to go away when switching from APU power to external power. It was apparent that maintenance's line of thinking was to disable the APU; thereby removing the problem. The first officer and I questioned this thinking based upon our concerns that the actual cause of the problem was still unknown and that the planned fix was merely a way to get the airplane out of town rather than diagnosing the real problem; which turned out later to be a wire chafe near the N1 transducer. I called maintenance control; through dispatch; to discuss our concerns: what was causing the N1 fault despite that it would go away when switching power sources? Maintenance control: yet unknown? What official maintenance guidance was maintenance control using to inop the APU to fix the problem? Maintenance control: none? What MEL references would apply? Maintenance control: (chapter) 49-11 or 24-21. Neither of these mentions N1. What would be the ramifications of an N1 signal failure once we were airborne? Would the engine continue to run normally with the loss of the N1 signal? Maintenance control: could not say.this last concern was most troubling. Maintenance control could not definitively tell us if the engine would continue to run. Therefore; if we were to accept this fix; we would possibly be putting ourselves into an engine-failure scenario. How could we possibly justify this type of fix? I expressed my concerns to dispatch and maintenance control; having already decided that I would not be agreeable to depart without a clear answer that the engine would continue to run normally. There is no guidance in the flight manual that addresses this issue. It seems to me; that this lack of guidance needs to be corrected. Ultimately; the flight canceled; because the N1 continued to fluctuate excessively during an engine run. However; I am convinced that; absent our inquiries and advocacy with maintenance control; this flight would have been allowed to continue with an unsafe condition; in this case; a wire chafe; and a potential engine failure. I have been very concerned for some time about this maintenance philosophy of performing just enough diagnosis to get the airplane out of town; without actually confirming the fault. This is evidenced; for example; by my previous report; wherein the aircraft had a deferral; which required the gear to be raised; by performing a flight manual irregular procedure. I refused to take this aircraft. Ultimately; it was found that the deferral was inappropriate and that there were inoperative gear sensors; which had to be replaced. This aircraft had been flying around in this condition for some time. Also; it is very common to see maintenance clear a fault by stating; unable to duplicate? Or reset cmc? Or cycled circuit breaker; fault cleared; only to have the fault reoccur on a subsequent leg. Usually; it seems that a component is found to be defective sometime down the road; and these temporary maintenance fixes; only delay the diagnosis and repair of actual defects. Is this appropriate and in accordance with existing regulation? In addition; our aircraft had to be completely depowered electrically; during the troubleshooting process. Station personnel and mechanics were unaware that passengers must be deplaned if the aircraft is to be depowered to facilitate a potential evacuation. I have observed that this is a widespread phenomenon and guidance should be issued to clarify existing requirements.

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Original NASA ASRS Text

Title: During a preflight of his B747-400 at an international station; a flight crew noticed the #1 engine N-1 gauge on their B747-400; was rolling up and down; with the engine off. The Captain further reports on the inadequate troubleshooting procedures used by his carrier's Maintenance Controller; and the rush to sign-off; or defer; the rolling N1 gauge; without understanding the cause or consequences.

Narrative: During the preflight; we noticed that the engine #1; N1 gauge was rolling up and down from 0- 11.1 percent; with the engine off. We notified Maintenance and wrote it up. We were told that; this is a No-Go item. Upon further troubleshooting; it was discovered that the problem seemed to go away when switching from APU power to external power. It was apparent that Maintenance's line of thinking was to disable the APU; thereby removing the problem. The First Officer and I questioned this thinking based upon our concerns that the actual cause of the problem was still unknown and that the planned fix was merely a way to get the airplane out of town rather than diagnosing the real problem; which turned out later to be a wire chafe near the N1 transducer. I called Maintenance Control; through Dispatch; to discuss our concerns: What was causing the N1 fault despite that it would go away when switching power sources? Maintenance Control: yet unknown? What official maintenance guidance was Maintenance Control using to inop the APU to fix the problem? Maintenance Control: none? What MEL references would apply? Maintenance Control: (Chapter) 49-11 or 24-21. Neither of these mentions N1. What would be the ramifications of an N1 signal failure once we were airborne? Would the engine continue to run normally with the loss of the N1 signal? Maintenance Control: Could not say.This last concern was most troubling. Maintenance Control could not definitively tell us if the engine would continue to run. Therefore; if we were to accept this fix; we would possibly be putting ourselves into an engine-failure scenario. How could we possibly justify this type of fix? I expressed my concerns to Dispatch and Maintenance Control; having already decided that I would not be agreeable to depart without a clear answer that the engine would continue to run normally. There is no guidance in the flight manual that addresses this issue. It seems to me; that this lack of guidance needs to be corrected. Ultimately; the flight canceled; because the N1 continued to fluctuate excessively during an engine run. However; I am convinced that; absent our inquiries and advocacy with Maintenance Control; this flight would have been allowed to continue with an unsafe condition; in this case; a wire chafe; and a potential engine failure. I have been very concerned for some time about this maintenance philosophy of performing just enough diagnosis to get the airplane out of town; without actually confirming the fault. This is evidenced; for example; by my previous report; wherein the aircraft had a deferral; which required the gear to be raised; by performing a flight manual irregular procedure. I refused to take this aircraft. Ultimately; it was found that the deferral was inappropriate and that there were inoperative gear sensors; which had to be replaced. This aircraft had been flying around in this condition for some time. Also; it is very common to see Maintenance clear a fault by stating; unable to duplicate? Or reset CMC? Or cycled circuit breaker; fault cleared; only to have the fault reoccur on a subsequent leg. Usually; it seems that a component is found to be defective sometime down the road; and these temporary maintenance fixes; only delay the diagnosis and repair of actual defects. Is this appropriate and in accordance with existing regulation? In addition; our aircraft had to be completely depowered electrically; during the troubleshooting process. Station personnel and Mechanics were unaware that passengers must be deplaned if the aircraft is to be depowered to facilitate a potential evacuation. I have observed that this is a widespread phenomenon and guidance should be issued to clarify existing requirements.

Data retrieved from NASA's ASRS site as of April 2012 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.