A300
Flight Crew Air Transport Pilot (ATP)
Confusion; Distraction; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Gate; Flight Crew Took Evasive Action; General Maintenance Action
Aircraft; Company Policy; Procedure
Normal preflight and taxi-out.  We were instructed to hold short of Runway XXR at the ILS critical area.  We noted that there were runway sweep vehicles on the runway; so we anticipated a slight delay until they had cleared the runway.  After several minutes; I noted the total fuel onboard at approximately 94.4.  We had blocked out with 98.2.  94.4 was below minimum required for takeoff and also did not agree with the fuel used counter that showed approximately 800 burned. The discrepancy was found to be in the Right Inner Tank quantity.  The Right Inner Tank was now showing approximately 2;400 lbs less than the Left Inner. Given the wing-to-wing fuel load split limit exceeded and the minimum fuel requirement not met; we contacted Tower and told them we needed to hold our position to work a problem.  Believing this to be a quantity indication problem; we contacted Maintenance and attempted to restore proper fuel indications.This eventually came to be; and the resulting revelation was chilling!  We were unsuccessful in restoring proper fuel quantity indications and returned to the ramp so that the Right Inner Tank Quantity Indication System could be MEL'ed.  On the way to the ramp; the Right Inner Quantity indication dropped another 12;500. This convinced us that we had a serious indication problem; but what we were soon to learn; was that this final indication was the correct indication! We very nearly took off with an actual fuel split on the order of 15;000 lbs. Further investigation of the refueling slip shows that essentially no fuel was added to the Right Inner Tank during refueling because it was indicating about 13;000 lbs high. The plane was refueled to a significantly unsafe imbalance due to an indication problem and it was purely by stroke of luck that we noticed a slight discrepancy due to a delay while holding short. Had we not had a delay of a few minutes at the hold short; we would very likely have taken off with a wing-to-wing imbalance on the order of 15;000 lbs. Even if assuming a controllable aircraft; depending on how the indication problem played itself out; the fuel at destination/alternate situation could have been disastrous. This was caused by a simple indication malfunction; where the Right Inner was indicating much higher than actual prior to refueling.This situation would have been prevented had we not recently changed the fuel slip review procedures.  Previously; the block in fuel was noted; and the pre-fueling amount was also noted.  The First Officer was required to compare these two numbers for disparity.  Had this procedure still been in effect; this discrepancy would have been caught early in the pre-flight. The two refueling slips associated with this flight are attached for reference. Note that the original refueling added fuel the left inner and a significantly less amount to the Right Inner due to the pre-fueling indication problem.  The second slip pre-fueling amount is accurate; therefore significantly more is pumped into the Right Inner to balance the load and bring it up to the required fuel load.  Strongly recommend we revert to logging the block-in fuel load in addition to the pre-fueling fuel load.
An A300 Captain noted a fuel quantity discrepancy while holding short for takeoff and discovered after returning to the ramp that the Right Inner Tank Quantity was indicating 15;000 lbs more than actually on board.