Date: 201709
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Military
Operator: Military
Operating under: Part 91
Mission: Refueling
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Fuel Storage System
Component problem: Improperly Operated
Reporter organization: Military
Reporter function: Check Pilot
Reporter qualification: Flight Crew Flight Instructor
Human factors: Human-Machine Interface; Time Pressure
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: During aerial refueling (A/R); our augmented crew (composed of an extra pilot and an extra navigator) noticed the incremental fuel onloads passed by the tanker were not matching the planned gross weight of our aircraft given the fuel taken from the tanker at each increment. The navigator recalculated the fuel in the totalizer and checked it against the planned gross weight for that fuel quantity and noticed a discrepancy. The crew was not able to identify the source of the error and elected to continue taking fuel required for the remaining mission. The tanker crew was sympathetic to our fuel requirement and passed us an additional 10;400 pounds for a total of approximately 91;400 pounds of JAA. The pilot flying noted shortly after completing the post A/R checklist that the aircraft was sluggish in its handling. After thinking about the disparity in the numbers for another 10 minutes; the crew reached the conclusion that the basic aircraft weight was entered into the aircraft performance computer incorrectly. Upon closer examination; the actual number and the entered number differed by 20;000 pounds; making the performance computer think that the aircraft was 20;000 pounds lighter than it actually was. As a result; the extra fuel taken from the tanker resulted in the crew exceeding the published aircraft gross weight listed in the aircraft's technical order and caused a potentially dangerous situation. The crew then contacted our dispatcher (Operations Supervisor) for assistance while keeping the aircraft in smooth air and at 1 G. The dispatcher contacted base maintenance; depot engineers; manufacturer engineers; and the depot test pilot all for input; assistance; and guidance. The consensus was that our aircraft limit was predicated on a 2 G increment and that since the aircraft did not experience turbulence or exceed 1 G; the structure of the aircraft was fine and there was no structural event to worry about. In fact; the consensus from all parties; now including unit leadership; was that we could elect to continue the entire planned mission; including a subsequent A/R should the crew choose. At this point; the crew elected to decline the second aerial refueling and accomplish as much of the mission with the fuel we had in order to return to base within a comfortable fuel margin.In the future; the navigator (or another crew member) should verify the basic aircraft weight variable entered into the aircraft's performance computer during preflight. In this situation; the copilot accomplishes this task while the left-seat pilot accomplishes the exterior walk-around. The navigator would be the obvious choice to verify this data. In this case; the navigator elected to enter the weight and balance information but did not verify the basic aircraft weight entry made previously by the copilot. Again; in this case; the basic aircraft weight had already been entered into the APC by the copilot (indicated by a color change in the entry field from yellow to green) and the aircraft weight and balance data publication was sitting on the navigator's table. Given these two pieces of information; the navigator assumed that the data had been entered and verified against the aircraft weight and balance data publication. In hindsight; this would have been the easiest link in the chain to break.




Synopsis: A Navigator of a military aircraft reported that due to a miscalculation of aircraft weight; they received an excessive amount of fuel from the tanker aircraft.