Learjet 36
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Communication Breakdown
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Aircraft
I departed ZZZ for ZZZ1. My flight plan showed that I should arrive at ZZZ1 with 1;453 pounds of fuel. From the start of my taxi to take off on [Runway] XR was twelve minutes. After a couple of vectors and a brief level off at 10;000 feet; we were cleared to climb to FL370 and given direct ZZZZZ intersection. However; the flight plan called for FL390 for our initial altitude. At ZZZZZ; I was three minutes behind the flight plan and 248 pounds behind on fuel. I was later cleared to climb to FL390 about 1:10 into the flight. I reached FL390. At this time my fuel was falling further behind. When I crossed ZZZZZ1; my fuel gauge showed that I was nearly 600 pounds behind the flight plan. Shortly after; I requested and received permission to climb to FL410. At my next waypoint; ZZZZZ2; the flight plan calculated 4;098 lbs. Thirty-six minutes from ZZZZZ2; the fuel gauge was showing 4;100 lbs. The Point of Safe Return was 2:12 into the flight. A little less than two hours into the flight my co-pilot and I decided to return to ZZZ. I requested a turn from HF Radio. I informed the radio operator that if I did not get an amended clearance as soon as possible that I would have to notify ATC. The operator was unable to receive the amended ATC clearance as quickly as I had hoped. Therefore; I notified ATC and instructed my co-pilot to make a left turn towards R464. Shortly after we completed the turn; we received a new clearance to proceed via to ZZZ2. I canceled the emergency once we were heading toward the ZZZZZ3 intersection. (We chose to return to ZZZ2 because it was nine minutes closer than ZZZ.) The accuracy of the fuel gauge came into question on our return leg to ZZZ2. The fuel numbers on the flight plan began to agree with the quantity on the gauge once we were below 4;000 lbs. The actual fuel flow numbers were close to flight plan fuel flow numbers. When we landed at ZZZ2; we indicated 1;500 lbs. Total flight time was 4:44.
During a ferry flight; the Captain elected to divert due to unreliable fuel quantity indications.