13.3 Supplemental Fuel Requirements & Holding Fuel Management

Supplemental Fuel, Flight Watch, and Tankering

Supplemental fuel planning begins by identifying propulsion type and geography. The word supplemental does not establish a universal 45-minute reserve for every airplane worldwide. Sections 121.643 and 121.645 have distinct applicability, and § 121.645(e) expressly sends supplemental turbine operations within the contiguous states/DC to § 121.643. The approved flight-following and operational-control system determines who performs each planning and monitoring function.

Select the correct rule

For nonturbine and turbopropeller supplemental airplanes, § 121.643(a) generally requires fuel to land at the released destination, then the most distant listed alternate, then 45 minutes at normal cruising fuel consumption. The stated day-VFR/nontransport exception has its own conditions and is not the ordinary transport-jet rule.

For those propulsion types on flights other than from one contiguous-U.S. point to another, paragraph (b) requires the destination/alternate portions and thereafter 30 minutes plus 15 percent of normal-cruise time to destination and alternate, or 90 minutes, whichever is less. On an applicable no-available-alternate route under § 121.623(b), paragraph (c) requires destination fuel plus three hours cruise.

For turbine jets outside the contiguous states/DC, § 121.645(b) ordinarily requires destination fuel, the ten-percent destination-time component, most-distant-alternate fuel where required, and 30 minutes holding at 1,500 feet above the alternate or destination as specified. Paragraph (c) provides the applicable approved no-available-alternate two-hour cruise requirement. Special OpSpecs treatment must be actually authorized; never infer it from aircraft size or charter status.

Reserve calculations and fuel components

A hypothetical contiguous-U.S. supplemental jet has trip fuel of 12,000 pounds, required most-distant-alternate fuel of 2,000, normal cruise flow of 4,000 pounds/hour, and taxi allowance of 500. The ordinary 45-minute component is 0.75 × 4,000 = 3,000 pounds. Minimum takeoff fuel for these supplied assumptions is 17,000 pounds; ramp fuel including taxi is 17,500. Any required additional operational allowance and chosen discretionary fuel are added separately.

For a hypothetical applicable turboprop outside the contiguous-point route, total destination-plus-alternate normal-cruise time is five hours. The paragraph (b) reserve duration is 30 + 0.15 × 300 = 75 minutes, below the 90-minute cap. Convert that time using the appropriate approved fuel-consumption data. Do not multiply a time percentage directly by a pounds total unless the exercise explicitly supplies a constant rate making them equivalent.

Monitor fuel without treating estimates as measurements

Fuel-quantity indications and an FMS calculated fuel estimate are different information sources. An FMS prediction depends on route, winds, speed, altitude, aircraft configuration, and the accuracy of its inputs. Compare indicated fuel, planned checkpoint fuel, actual elapsed time, and updated destination/diversion predictions. A disagreement can reflect modeling error, a sensor issue, an aircraft defect, a leak, or an unrecorded route change.

If the projected margin is eroding, promptly coordinate with the PIC and the authorized operational-control personnel. Assess current weather and field conditions at reachable diversion airports, update the route and performance calculation, and decide before the remaining choices become unsafe. Do not wait until entering a destination hold merely because the original release included adequate fuel at departure. Do not prescribe a universal emergency declaration from a discrepancy alone; assess whether priority is needed to ensure safe landing.

Minimum fuel and emergency priority

A minimum-fuel advisory tells ATC that the flight cannot accept undue delay. It does not itself request emergency priority. If priority is needed to ensure a safe landing, the PIC declares an emergency and advises fuel remaining in minutes as appropriate. The dispatcher supports the assessment, informs the appropriate company/ATC contacts, and arranges suitable ground assistance.

Do not promise that emergency priority instantly removes every aircraft ahead or guarantees an unrestricted straight-in approach. ATC coordinates priority handling while managing other traffic and hazards. The practical distinction is the need for an emergency declaration when safety requires priority, rather than hoping that “minimum fuel” creates that priority automatically.

Tankering economics with explicit assumptions

Tankering carries extra fuel from a lower-cost station to reduce a later purchase. Extra weight can increase trip burn, reduce payload capability, increase landing weight, and affect runway or climb margins. The cost-to-carry factor is aircraft/route-specific. No regulation says every flight burns a fixed 3.5 percent of tankered weight per hour, and payload displacement is an economic/operational decision subject to limits rather than a universal federal prohibition.

In a simplified hypothetical model, buy an extra 8,000 pounds and burn 700 carrying it. Delivered extra fuel is 7,300 pounds. Ignoring other costs, tankering is worthwhile only if 8,000 × origin price is less than 7,300 × destination price. The required destination/origin price ratio is therefore greater than 8,000 / 7,300 ≈ 1.096. This exact comparison for the stated model differs from adding a burn percentage to one without accounting for the delivered quantity.

Finally verify zero-fuel, ramp, takeoff, landing, CG, and performance limits; fuel capacity and fuel distribution; airport constraints; and any revenue or scheduling effects. A profitable arithmetic result does not authorize an overweight landing or inadequate reserve. Use the approved planning system to recompute the final flight, because changing uplift also changes the weight and burn inputs.

Official References

Source check: 2026-10-12. Part 121 dispatch, fuel, and amendment rules; FAA AIM clearances and priority. For operational use, apply current issued authorizations and the assigned aircraft’s approved data.