Deciding how much fuel to put on an airliner is one of the most important planning factors on every flight, for both safety and profit reasons. authorized dispatcher Although recommendations are provided to the captain before each departure, the pilot has the final say on the exact amount of fuel based on an evaluation of the trip. Fuel is ultimately a corporate responsibility. pilot in commandPursuant to Part 121 of the Code of Federal Regulations. In addition to the standard calculations based on distance and time from point A to point B, there are a number of factors that pilots consider.
Firstly, weather is a factor that affects every flight. This is because as adverse conditions increase, fuel consumption also increases. These considerations apply to both default targets and lists. alternative airport In case of transition. Bad weather is one of the most common reasons a captain requests that a plane be refueled before takeoff. Other reasons include the potential for diversions due to single-runway airfields, where noise curfews and ground incidents can lead to longer waiting times or diversions.
Flight crews take all of these emergency factors into account to ensure that the flight crew’s recommendations cover all possible scenarios. As Captain Steve explains, once the captain calculates the exact amount needed, he or she can re-call dispatch and request additional fuel. Airlines want to save as much as possible on gas, but ultimately the safety of the flight is the most important factor, and there can be little question of the captain’s judgment even if he or she thinks the dispatcher’s estimate is too low.
Find the Jet Stream
The biggest weather factors in fuel calculations are: wind speed I found it in the weather forecast. The global weather model is used by flight planning computers around the world to update forecasts on a fixed schedule, with regular updates occurring on average every six hours. This model uses a three-dimensional grid of wind vectors to calculate the headwind or tailwind component, which is then used to find the exact fuel consumption for a specific flight.
This information is a basic estimate from which airline captains begin their own assessment of fuel requirements before takeoff. An experienced captain will not just accept the dispatcher’s wind count. They take that as a benchmark and apply their expert operational knowledge to bridge the gap between computer models and reality. The captain looks at the age of the weather data used in the flight plan.
If the weather model is 6 hours and the fast-moving jet stream has moved 50 miles south, the planned altitude would now place the aircraft directly into a harsh 120-knot headwind instead of a 40-knot vector. If the captain suspects that the jet stream has shifted or intensified beyond what the computer calculated, random fuel is added to offset the accelerated burn rate.
Description of Turbulence
Another factor when considering the slope of how the wind vector changes with distance and in which direction it is projected is finding the boundary. clear air turbulence Typically occurring in the marginal zone of the jet stream core, captains will do their best to avoid rough rides if possible. In many cases, this means descending into lower, denser air to avoid being blown through turbulent, high-speed jet stream winds. At lower altitudes, aircraft burn more fuel because the air itself is denser.
Other forms of turbulence are also likely to occur, so pilots should plan for higher fuel burn. Key geographical features, such as mountains, influence wind behavior in an area, which can create standing waves of strong wind vectors. In some cases, reaching cruising altitude can force the aircraft to quickly adjust power settings to compensate as it passes through turbulence.
Even if the airplane does not need to deviate from course or altitude, fluctuations in engine performance can have a negative impact on fuel consumption. Experienced long-haul captains look at the height of the tropopause relative to their wind vector, knowing exactly when to request an unplanned altitude change from ATC to capture a better wind vector or avoid a headwind. So either way, if such turbulence occurs, additional fuel is needed to compensate for the higher combustion rate.
Headwind Underestimation Bias
Statistically, global weather models tend to err on the optimistic side. They are more likely to slightly underestimate the strength of the headwind than to overestimate it. For ultra-long-haul flights, a 10-knot error in headwind vector over a 14-hour flight will result in a significant shortage of remaining fuel. This is another aspect of fuel calculations and weather forecasts that can be improved over time and with experience.
Captains who regularly fly the same route over very long distances can find the average error by tracking the difference between the weather that actually occurred and the forecast over time. If a veteran captain flies JFK to London 10 times a month and realizes that the actual headwind vector is consistently 15 knots stronger than the dispatch estimate, he will mentally override the computer’s optimism and order additional discretionary fuel to cover the historical margin.
And after you’ve flown that distance, headwinds also factor into your fuel calculations, taking into account conditions when you arrive at your destination airport. Airplanes must land into the wind to minimize ground speed and stopping distance. Because of this, surface wind direction determines the runway configuration of an airport. Many airports around the world have an asymmetric airfield layout with one high-capacity runway and smaller backups. If wind conditions change before the jet arrives, delays will occur.
Air traffic control must reorganize approaches while low-capacity runways slow arrivals. This means that the jetliner will remain in a low-altitude holding pattern until it is cleared to land. During that time, the jet must burn additional fuel, not only for additional time, but also to account for the higher consumption rate as it travels through denser air closer to the ground.
alternative airport elements
Every airline taking off must plan for an alternate airport in case unforeseen circumstances prevent it from landing at its intended destination. Domestic flight policies drawn up by authorities such as the Federal Aviation Administration and the European Aviation Safety Agency set out very clear guidelines, simplified into the ‘1-2-3 rule’. An alternative flight is required by law unless weather at your destination is expected to be at least 2,000 feet and visibility at least 3 statute miles (4.8 km) at least 1 hour before and 1 hour after your scheduled arrival time.
If the weather slides slightly below the forecast’s threshold, operators must add fallback weather. More stringent regulations apply to long-haul aircraft performing transoceanic flights, especially if the destination has only one available runway or no precision approach equipment. Even if your destination meets the criteria to allow takeoff without plans to fly to an alternate airport, the captain may be permitted to carry additional fuel, depending on whether the airline’s policy is more stringent or based on personal experience.
When calculating the fuel needed to reach an alternative airport, there are several steps that determine the final figure. The flight planning computer takes into account missed approaches, altitude gains, cruise moves to alternate routes, descents, and fuel consumed during approaches. One thing to note is that these numbers are calculated based on standard conditions. Here again, the captain may request additional fuel depending on unfavorable conditions or other factors.
ETOPS and other precautions
The physical location of the alternate vessel will change how the captain manages the turn. If the alternatives are very close, the flight planning computer is likely to estimate a very low number. Once again, pilots evaluate the weather and air density at the altitude they will be passing through. If the reserve airfield is very close, climbing to altitude may not be necessary or advisable, so engines flying low to the ground will burn more fuel.
On the other hand, if the alternative airport is 322 km (200 miles) away, calculations for a high-altitude cruise are required. Additionally, when flying over oceans or remote areas such as the Sahara or Pacific, the standard fallback rules do not apply because there are no airports nearby. For twin-engine jets that are several hours from the airfield, dispatchers must list a replacement aircraft during ETOPS, as Foreflight explains.
This means planning for the extreme scenario of flying from 3,048 meters (10,000 feet) to a remote airfield in case of engine failure or cabin depressurization. If you are flying to a remote island, such as Hawaii or Easter Island, where there is no physical alternative airport within a reasonable distance, dispatchers will use the ‘no alternative’ or ‘island quarantine’ rule. Instead of planning a route to a backup airport, the policy mandates that aircraft carry additional fuel, which adds two hours of additional flight time.
