Story ID: 
AINsight: Goldilocks Approach to Aircraft Fuel Planning
By: Stuart “Kipp” Lau
Caption: How to calculate an aircraft fuel load that is just right
Word Count: 1586
Preflight fuel planning and proper en-route fuel management are critical to flight safety. For pilots, calculating the correct amount of fuel for their aircraft requires a balance between comfort, operational requirements, and economic sense. It’s the proverbial Catch-22—too much or too little fuel has consequences.
Too much fuel may result in an aircraft exceedance such as maximum takeoff or landing weight, and it reduces the available payload. Likewise, excess fuel increases the weight of the aircraft, which creates a higher fuel burn and increases the direct operating cost of a flight.
Too little fuel has many negative outcomes, such as returning to the ramp for additional fuel due to taxi delays, an aircraft turnback, or an en-route diversion due to insufficient fuel. Other negative consequences of too little fuel may result in insufficient reserve fuel that can result in a minimum fuel (pan pan) or mayday fuel declaration or regulatory enforcement action against the pilot or operator. Worst-case scenarios may result in an engine failure due to fuel exhaustion.
The NTSB found that personnel issues such as planning and aircraft familiarity contributed to 95% of fuel management accidents. A 2017 report found fuel system failures or malfunctions in less than 5% of investigations.
According to the NTSB, fuel management accidents are completely preventable. Pilot complacency and overestimation of flying ability can play a role in these accidents.
Fuel management accidents typically occur due to inadequate pilot planning or monitoring, or a misunderstanding of aircraft fuel systems. “Prudent pilot action can eliminate these issues,” the Safety Board said.
Pilot experience does not affect fuel management accidents, with incidents nearly evenly divided between commercial- or ATP-rated pilots (48%) and private or sport pilots (50%). Only 2% of fuel management accidents involve student pilots.
A Natural Conflict
For the professional pilot, fuel planning is more art than science. There is a reasonable amount of fuel for every flight—“topping it off” isn’t a practical answer for modern jet aircraft unless the plan is to fly halfway around the globe.
As an example, the pilot of a Gulfstream G700 or Bombardier Global 7500 could likely fly 10 flights between Chicago and New York (about 700 nm) on just one full load of full upload before the first of these flights. Obviously, this is too much fuel—in this scenario, there would likely be issues with reduced payload, exceeding maximum landing weights, and increased cost on the first nine of these legs.
For flight operations leaders, fuel planning is more science than art. Operators employ many tactics to save fuel, such as purchasing the most fuel-efficient aircraft, software technology, improved flight profiles, fuel trading and hedging strategies, and weight savings measures that include minimizing fuel uploaded before each flight.
This is because, for aircraft operators globally, fuel represents their most significant expense. The International Air Transport Association (IATA) reports that, on average, fuel and oil comprise 28.7% of operating costs for airlines, though this percentage may vary considerably by geographic region. In general, Latin America and the Caribbean are expensive; North America is cheap.
Bottom line: Pilots want more fuel, while management wants to reduce fuel. This creates a natural conflict in flight operations between front-line operators (pilots and dispatchers) and management. In the end, the final agreed-upon fuel load will be a compromise that takes several factors into account, including cost and potentially even carbon footprint.
On a recent flight, I heard an interesting exchange between a regional jet and New York Center:
Airliner: “New York, [regional] 3465 climbing FL190 to FL230 declaring minimum fuel.”
Center: “Roger, [regional] 3465 understand you are minimum fuel climbing to FL230…Didn’t you just take off?”
This one radio exchange highlighted the poor state of fuel planning with some operators. So, how bad is it? This bad. In the above example, regional 3465 had zero margin for error in their fuel planning.
What’s Your Number? Internal or Inner Struggles
In a multicrew operation, as the captain/pilot-in-command, I like to ask, “What’s your number?” No, I’m not hitting on the first officer; I simply want to initiate a conversation and ensure that we’re in agreement on the planned fuel load during preflight and during other phases of flight.
For the single pilot, according to Sigmund Freud’s psychoanalytic theory, your id, ego, and superego are all going to have to align to come up with the right number. In this case, the charts and graphs from the aircraft pilot operating handbook and a dose of skepticism are going to be the tiebreaker.
It’s a healthy exercise if “your numbers” aren’t exact. Operating a larger jet, a difference in total fuel in hundreds of pounds could be a rounding error. If there is a discrepancy of more than a thousand pounds, it is time to pause and have a more in-depth conversation. Each total fuel value comes with a different perspective or experience. The goal is to reach a consensus.
During flight, if you’re asking for the first time the “what’s your number” question while entering a holding pattern, it might be a little too late. At this point, you’re likely a candidate for an in-flight diversion or declaring minimum or mayday fuel.
Goldilocks Principle Applied to Fuel Planning
All too often, preflight fuel planning discussions focus on the minimum amount of fuel required to take off. Earlier, we discussed the consequences associated with too much or too little fuel; if only there were a happy median like the Goldilocks principle. As the fairytale suggests—and as outlandish as it sounds—a fuel load that is just right.
For academic discussions, the minimum fuel required for an IFR flight is sufficient fuel to fly from point A to B and an alternate, if required, plus a required 45-minute fuel reserve.
So, in this case—if all goes according to plan, with no delays, deviations, alternate routing, or holding—a pilot will land with the legal reserve fuel. If there is a single hiccup, then the flight lands with less than the legally required reserve fuel.
On the other end of the scale, the maximum fuel required for an IFR flight is sufficient fuel to fly from point A to B and an alternate, if required, and a required 45-minute fuel reserve, as well as some arbitrary amount with no legitimate justification that makes the dispatcher scratch their head.
Personally, I approach fuel planning as a contrarian. I address fuel calculations in reverse order, placing greater emphasis on ensuring my required personal minimum landing fuel (PMLF)—or the Goldilocks fuel—is available for landing at my destination or alternate airport.
My PMLF includes the required reserve fuel (45 minutes) and, for peace of mind, the amount of fuel to execute a go-around and fly an additional approach to landing (about 15 minutes). If an alternate is required, that amount is included. This personal minimum number satisfies and exceeds the legal requirements for FAA reserve fuel (45 minutes) and ICAO’s minimum diversion fuel.
Using this technique, prior to takeoff, the total fuel on board must equal the required fuel burn to the destination, fuel burn to the alternate (if required), known fuel for delays, MELs, and/or other items, along with my personal minimum landing fuel (the Goldilocks Fuel), then I am satisfied that I can legally, and comfortably, depart.
En route at my first fuel crosscheck, I am happy if the fuel onboard equals the required fuel to the destination, the alternate, and my personal minimum landing fuel. En-route fuel checks (the “fuel score”) are important, even on short flights. On a recent flight, the actual winds were 85 to 95 knots above forecast winds.
Similarly, if ATC issues holding instructions, once established in the hold, it’s a familiar exercise: Fuel on board - fuel to alternate - personal minimum landing fuel = amount of time in minutes to hold.
Just to recap. To come up with the Goldilocks fuel value, a pilot should understand the amount of fuel (in pounds, kilos, or whatever your fuel-quantity gauges indicate) required to satisfy the legal requirements for reserve fuel (45 minutes) and, for peace of mind, ascertain the amount of fuel to execute a go-around and fly an additional instrument approach to landing.
Other good-to-know fuel burn numbers for your aircraft include fuel burn in cruise for the first hour, second hour, and subsequent hours. Likewise, an understanding of fuel burn in the terminal area and the effects of configuration changes is important.
For strategic/planning purposes, fuel is often expressed in time. But for tactical purposes on the flight deck, I personally express the amount of available fuel in pounds, equal to my fuel quantity indicators.
Conclusion
The purpose of this discussion is to generate a practical conversation on how you and your organization plan and manage fuel. For pilots, the goal is to operate safely. Understanding the consequences of having too much or too little fuel should help you arrive at a number that is just right.
The opinions expressed in this column are those of the author and are not necessarily endorsed by AIN Media Group.