1. Why the Same Plane Flies at Different Speeds Going and Returning
According to pilots at Japan Airlines (JAL), strong winds called jet streams blow at altitudes of about 10,000 meters in winter. Flights heading west must fight against these headwinds, sometimes managing only about 500 km/h. However, flights returning east ride the same wind, reaching speeds of 900 km/h, and sometimes nearly 1,000 km/h [1]. A difference between 500 km/h and 900 km/h means the speed is roughly 1.8 times faster (900 ÷ 500). These figures are estimates shared by pilots and do not happen every time. Still, if the difference is this large, ignoring the wind and drawing a straight line on a map seems wasteful. This raises a question: Is it sometimes better to take a detour on the map if it means riding the wind?
2. Why a Curved Route on the Map Can Be Shorter Through the Air
Think of walking in a flowing pool. If you walk with the current, you move easily even with the same number of steps. Airplanes move through moving air, not on the ground. When an airplane rides a tailwind, its speed through the air increases, which can make the flight time shorter even if the path on the map is longer. Shorter flight times mean arriving sooner. Explanations also note that riding a tailwind can save fuel or allow for more passengers or cargo [2]. It is also explained that world tour routes can be planned so that both the outbound and return legs take different paths to catch the wind. The relationship with fuel is clarified in a research paper. If speed and altitude are constant, the fuel used per hour is nearly constant. Therefore, if speed and altitude are constant, the route with the shortest flight time uses the least fuel. This study calculated the shortest-time route from wind distribution using a mathematical method called optimal control theory [5]. So, who actually decides the path that rides the wind?
3. How the North Atlantic Flight Routes Were Set Twice a Day
Between Europe and North America, over the North Atlantic, there was a route system called the "Organized Track System" (OTS). It was decided by control agencies based on that day’s wind. It was created twice a day and redrawn to match the movement of the jet stream [3]. Although called a "track," there are no lines on the ground. It is a path in the sky set over the sea. By setting routes according to the daily wind, they prepared paths over the sea where many airplanes gather. Is this daily path truly the best one?
4. How Much Longer the North Atlantic Routes Were Than the Best Paths
The mechanism for these tracks had not changed much since 1961 [4]. Researchers at the University of Reading in the UK compared the actual tracks with fuel-optimal routes calculated from wind distribution. They studied flights between New York and London from December 1, 2019, to February 29, 2020, covering about 3 months in winter, or 91 days. The results showed that the actual tracks were usually hundreds of kilometers longer than the optimal routes, with an average difference of about 200 km [5]. A press release stated that this average of about 200 km meant it was possible to reduce carbon dioxide by about 6.7 million kg (6,700 tons) over the 3-month period [6]. The paper also shows room to reduce the distance through the air. For westbound flights, it is 0.7–7.8%, and for eastbound flights, 0.7–16.4%. This range varies depending on flight speed and which route is used that day [5]. While some write "fuel reduced by 16%," this is the upper limit for the best eastbound conditions, not the average. This research became one basis for reviewing North Atlantic operations. From March 1, 2022, the pre-set OTS routes were abolished for altitudes below 33,000 feet (about 10,000 m) [4]. With the pre-set routes in lower airspace removed, airlines can more easily choose their flight path considering that day’s wind. However, only the part below this altitude was abolished; OTS continues at higher altitudes. Choosing your own path without using OTS was already allowed before the abolition. So, what changed was not that freedom to choose was new, but that pre-set paths were removed in lower airspace.
5. How More Pacific Flights Choose Their Own Wind Paths by Calculation
Over the Pacific Ocean, connecting Japan and the US West Coast, there is also a system for using wind paths. According to a report by ALPA Japan, flights over the ocean generally use fixed air routes (NOPAC), plus routes created by controllers called PACOTS, and UPR (User Preferred Routes chosen by the operator) [7]. In recent years, computer calculations have become faster, and UPR is spreading. Using UPR allows for more flexible and fuel-efficient flight plans to be calculated in a short time compared to PACOTS. In this trend, the abolition of 2 PACOTS routes for United Airlines flights between Japan and Texas was agreed upon [7]. The shift is from controllers preparing daily paths to each company calculating and choosing their own path. This direction is similar to the change in the North Atlantic.
6. Why Altitude, Restrictions, and Forecasts Matter Besides Wind
Air routes are not decided by wind alone. JAL pilots explain that routes are somewhat fixed, and altitude is adjusted accordingly [1]. Dealing with wind is done not just by turning sideways, but by choosing height. There are other constraints on choosing a path. The ALPA Japan report states that both Japanese and US sides say PACOTS is still a useful tool for handling restricted airspace due to military activities or rocket launches, and for responding to volcanic ash [7]. Even if calculation allows free choice, not everything in the sky is free. Wind forecasts are also issued by the Japan Meteorological Agency (JMA) for aircraft. Upper-air charts for altitude, temperature, and wind over the Asia-Pacific and North Pacific are published [9]. A NASA technical brief from 2004 calculated that using wind-optimized shortest-time routes could shorten flight times for US transcontinental flights by an average of about 7 minutes, and up to 1 hour during strong jet streams [8]. The difference per flight seems small, but with many flights every day, it adds up.
7. How to Compare Outbound and Return Flight Times Yourself
You can try this today: Look at an airline schedule and compare flights between the same two airports for the outbound and return trips. See if there is a difference in travel time and which is longer, thinking about the relationship with wind. Sometimes the difference is small. If you have the chance to fly, record the actual flight times for the outbound and return trips and compare them with the schedule numbers. For official information, the JMA aviation meteorology page has a list of upper-air wind forecast charts. The University of Reading research page is a good entry point to understand the review of North Atlantic routes.