Narrative:

While flying an owner trip conducted under part 91 in a part 135 gulfstream iv; we ran into a low fuel situation which required a diversion. The flight planning was conducted using online flight planning software with a series of step climbs and a random routing across the north atlantic with a routing around [the destination] to the west which would bring us in on the ILS; the predicted arrival runway in use with 9hrs and 2 minutes of flight time. The software gave us an estimated landing fuel number of 3600 lbs; which included the fuel to the alternate; 45 min reserve; and an additional 200 lbs of extra fuel with a departure fuel number of 29500 lbs.we climbed to an initial altitude of FL400; which was the highest altitude possible at our weight. After coasting out over the atlantic we requested FL430 as soon as we were able but the request was denied for traffic. Again; we requested a climb to FL430 or FL450 but both were denied; we were given a climb to FL410. When we coasted in they allowed us to climb to FL430; but it was too little; too late at that point; as our fuel computer showed us landing with 2600 lbs. Shortly after contacting center we were issued a descent to FL260; this was more than an hour from our destination. I asked the controller if we could maintain a higher altitude for fuel concerns; and he gave us a level off at FL300. At this point our fuel landing number dropped again to 1600 lbs.; but he informed us that we'd have to descend to 16000 after zzzzz intersection; which would've put us in a dangerously low fuel situation. In the interest of safety I decided to divert for fuel and the controller; who was extremely helpful; recommended [another airport]; as they had customs and fuel available; and were directly under our route. He gave us a heading and a descent clearance; and we were vectored around for the ILS; landing with a comfortable 3200 lbs. This all could've been avoided if I had planned a fuel stop from the beginning; in light of the risks that ATC would keep us so low across the atlantic; and descend us so soon. Another major contributing factor to this situation was the fuel reserve requirements under 14 crash fire rescue equipment 91.167 which states only that you have enough fuel to fly to your destination; your alternate; and 45 minutes at normal cruise. This is what flight planning software takes into consideration when calculating fuel requirements. The problem with this is that in an aircraft such as the gulfstream; altitude makes a huge difference in fuel burn; and while you may have no problem completing a flight with the calculated fuel burns at the filed altitudes; if ATC requires altitudes lower than those at which you filed or an early descent; you may not have an adequate amount of fuel to complete the mission. I will; from now on; plan for a higher fuel burn than computed in order to avoid unplanned deviations in the future.

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Original NASA ASRS Text

Title: GIV Captain elected to divert for refueling after ATC had been unable to approve flight-planned higher altitudes on a westbound transatlantic flight.

Narrative: While flying an owner trip conducted under part 91 in a part 135 Gulfstream IV; we ran into a low fuel situation which required a diversion. The flight planning was conducted using online flight planning software with a series of step climbs and a random routing across the North Atlantic with a routing around [the destination] to the west which would bring us in on the ILS; the predicted arrival runway in use with 9hrs and 2 minutes of flight time. The software gave us an estimated landing fuel number of 3600 lbs; which included the fuel to the alternate; 45 min reserve; and an additional 200 lbs of extra fuel with a departure fuel number of 29500 lbs.We climbed to an initial altitude of FL400; which was the highest altitude possible at our weight. After coasting out over the Atlantic we requested FL430 as soon as we were able but the request was denied for traffic. Again; we requested a climb to FL430 or FL450 but both were denied; we were given a climb to FL410. When we coasted in they allowed us to climb to FL430; but it was too little; too late at that point; as our fuel computer showed us landing with 2600 lbs. Shortly after contacting center we were issued a descent to FL260; this was more than an hour from our destination. I asked the controller if we could maintain a higher altitude for fuel concerns; and he gave us a level off at FL300. At this point our fuel landing number dropped again to 1600 lbs.; but he informed us that we'd have to descend to 16000 after ZZZZZ intersection; which would've put us in a dangerously low fuel situation. In the interest of safety I decided to divert for fuel and the controller; who was extremely helpful; recommended [another airport]; as they had customs and fuel available; and were directly under our route. He gave us a heading and a descent clearance; and we were vectored around for the ILS; landing with a comfortable 3200 lbs. This all could've been avoided if I had planned a fuel stop from the beginning; in light of the risks that ATC would keep us so low across the Atlantic; and descend us so soon. Another major contributing factor to this situation was the fuel reserve requirements under 14 CFR 91.167 which states only that you have enough fuel to fly to your destination; your alternate; and 45 minutes at normal cruise. This is what flight planning software takes into consideration when calculating fuel requirements. The problem with this is that in an aircraft such as the Gulfstream; altitude makes a huge difference in fuel burn; and while you may have no problem completing a flight with the calculated fuel burns at the filed altitudes; if ATC requires altitudes lower than those at which you filed or an early descent; you may not have an adequate amount of fuel to complete the mission. I will; from now on; plan for a higher fuel burn than computed in order to avoid unplanned deviations in the future.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.