Date: 202108
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Weather elements / visibility: Haze / Smoke; 10
Light: Daylight
Aircraft: Small Aircraft; Low Wing; 2 Eng; Retractable Gear
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Training
Flight phase: Cruise
Airspace: Class E ZZZ; Class G ZZZ
Aircraft component: Engine
Component problem: Failed; Improperly Operated
Reporter organization: Personal
Reporter function: Instructor; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine; Other A&P
Human factors: Communication Breakdown; Situational Awareness; Time Pressure; Training / Qualification; Troubleshooting; Workload
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Detector: Automation Aircraft Other Automation; Person Flight Crew
Result: Flight Crew Diverted
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: The flight was conducted by an experienced ATP-AMEL owner as PIC and training Captain and an experienced commercial AMEL pilot as Trainee. No passengers were on board. The purpose of the flight was a training mission from ZZZ to ZZZ1 and back to ZZZ and for aircraft familiarization and to run an errand in ZZZ3. The flight landed ZZZ1 uneventfully after about 2.0 hours and estimated 28 gallons of fuel burn. Fuel on board at departure from ZZZ was 70 gallons of 84 gallons maximum usable and flight on only the main tanks (48 gal avail; 28 required) was planned. The two pilots parked at the FBO and requested fuel to be topped then proceeded to take the crew car to town for a couple hours to take care of some business in town and get lunch.Upon return to the FBO line service had already serviced the aircraft and a receipt for 26 gallons of fuel was provided. The pilots performed the pre-flight on the aircraft. The ATP checked the fuel quantity visually on the left side and the commercial pilot checked fuel visually on the right side. By verbal agreement the fuel was observed full in all 4 tanks left and right. The receipt for fuel purchase showed approximately the expected amount of 26 gallons burned on the previous flight.Approximately halfway back to ZZZ from ZZZ1; at about 1.3 hours flight time; the right engine failed. The ATP took over controlling the aircraft and completed all of the memorized and checklist emergency procedures and diverted to ZZZ2 in visual conditions. The landing was uneventful with no damage to the aircraft; no injury to the pilots and no passengers nor ground personnel were involved.Upon inspection of the aircraft the problem was determined to be the right main fuel tank was empty. This should not have been the case because it held 27 gallons usable and the 1.3 hour flight should've only burned 8-9 gallons on the right side; flown entirely on the main tanks. The aircraft was fueled at ZZZ2 and the left main took 8.5 gallons commensurate with fuel burn estimates. The fuel selector valves and fuel strainers were tested repeatedly and found to be in working condition. There were no evidences of fuel leakage and the tanks all held fuel properly after refuel. The inescapable conclusion is that the FBO failed to fuel the right main tank. One can account for the volume of fuel added at ZZZ1 prior to departure because auxiliary tanks and main tanks were not full at original departure. This made the quantity placed on board commensurate with the quantity used yet it is inexplicable why the Fueler would have not fueled the right main tank. The right main tank would have had 10 gallons in it. This is commensurate with the one 1.3 hour flight to the point of failure. The pilot in training who checked the right main tank either saw what he expected or saw a glare but didn't properly check fuel quantity on the right main tank. Corrective actions for the future: The PIC should always supervise the personnel during fueling to alleviate any confusion about where the fuel is to be placed. Secondly; the PIC should always check fuel tanks visually himself never trust even another experienced pilot to do that for you. Also; while fuel gauges are properly never to be trusted as a reliable fuel assessment or fuel planning tool and many pilots properly rely on visual checks of fuel and fuel burn calculations; a gauge that show a grossly different from what was visually checked should indicate that a visual recheck is required. Also; stay current on emergency procedures. In this case being absolutely current on engine failure procedures and knowing where VMC alternate were made for an uneventful approach and landing.




Synopsis: Twin Engine Instructor Pilot reported an engine failure in flight due to fuel starvation. One main wing tank ran dry after not being serviced at the FBO.