EMB ERJ 140 ER/LR
Flight Crew Air Transport Pilot (ATP)
Distraction; Time Pressure; Training / Qualification; Communication Breakdown; Confusion
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Aircraft Equipment Problem Dissipated; General Maintenance Action
Aircraft; Company Policy; Equipment / Tooling; Procedure
I was in command of a flight.  Approximately 10 minutes prior to departure; the GPU suddenly and without warning failed while connected to aircraft.  Because the APU had been previously MEL'ed and was not available; we quickly powered the aircraft off and noted that the GPU voltage now showed 0.0V while both Main Battery #1 and Main Battery #2 showed 22.2V.  We contacted Operations about the GPU failure and they connected an operational GPU.The problem we then observed was the low voltage on both Main Batteries.  With the Main Batteries below 23.5V; the AOM-1 Manual prescribed that a Main Battery Recharge Procedure would have to be applied.  A Mechanic; who had been flown in the night before to perform a tire change on the same aircraft overnight; suggested that he would contact Maintenance Control (MOC) to see if they would authorize him to clear the APU MEL so that we could use the APU to recharge the batteries.  We witnessed the conversation the Mechanic had over the phone.  The Mechanic asked the person on the other end of the phone if there were any previous mechanical discrepancies in the APU's history that prevented the APU MEL from being cleared.  The Mechanic indicated that the APU MEL could be cleared and the Mechanic was apparently given authorization by MOC to start the APU.  The Mechanic started the APU and the APU seemed to run normally.  The Mechanic then stated that he was going to clear the APU MEL so that he could document the APU's working status and balance the required AML paperwork.  The Mechanic then removed the applicable MEL stickers and returned the APU to service with his AML entry and MOC's approval.With the APU operational; the Main Battery Recharge Procedure as outlined in AOM-1 was applied.  After 30 minutes of the running the APU (as required by the procedure); the Mechanic then informed us that he was told by MOC that the APU MEL could not be cleared and that he had to reinstate the APU MEL.  This information was troubling and the APU was manually shutdown.  We asked the Mechanic and the Manager on Duty of MOC why the APU had been allowed to be started if the APU MEL could not be cleared.  He stated that previous downloaded data received from the maintenance computer log indicated that the APU had a previous APU FADEC Fault and a previous APU Overheat that required the APU to go through a Borescope prior to being cleared for operation.  We were perplexed because the Mechanic had been given authorization from MOC to clear the APU MEL and to start the APU.  The Mechanic never at any time retrieved the aircraft's electronic maintenance messages (CMC messages) from either the MFD or through a download with the use of a computer and cables.  The APU FADEC Fault and the APU Overheat downloaded messages had been retrieved on a different day previous and was information available prior to MOC authorizing the APU's use and subsequent return to service.These events appear to indicate questionable judgment by MOC in authorizing the use of the APU when substantial safety risks existed.  MOC qualified their actions of starting the APU as troubleshooting.  However; why did the APU need to be troubleshot if it was known that a Borescope of the APU was required prior to safe operation?  And if MOC was troubleshooting the APU; why did they allow it to be run a full 30 minutes?Our primary concern after the realization of these complications was focused on determining the aircraft's airworthiness; specifically concentrating on possible damage caused by the effects of starting the APU.  After we required the Mechanic to perform a detailed visual inspection of the APU; APU compartment; and surrounding areas/compartments; the Mechanic stated that he did not find any evidence of damage or any other unsafe condition.  We further consulted the MOC MOD and Flight Management to determine that the aircraft was airworthy.  We complied with all applicable policies and procedures outlined in AOM-1 and FM-1 and the flight operated and landed safely at our destination; without further incident.
[Report narrative contained no additional information.]
A GPU failed while supplying an EMB-140 electrical power. When the aircraft batteries went below 23.5V; Maintenance Control authorize a Mechanic to start the MEL'ed APU but after the batteries were charged said the APU could not operate because of a previous overtemp and was re-MEL'ed.