Ever looked at how a flight operates on a map and wondered why it takes the path that it does? These days, with features such as interactive maps on the aircraft’s in flight entertainment and flight tracking software, it is easy for people to monitor how an airplane flies. Often, it is noticeable that the aircraft do not fly in the most direct manner, which often adds duration to the flight.

This guide dives deeper into the matter and explains how the shortest and fastest routes might not always be the most practical route for an aircraft to fly on.

Great-Circle Perception On A Flat Map

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Perhaps one of the greatest misconceptions of flight paths is why an aircraft often does not fly on a straight line from its point of origin to the destination. This is a common thought for passengers when viewing a flight path on a flat map, especially on long-haul flights, which would indicate the aircraft initially flying more to the north (in the Northern Hemisphere) or south (in the Southern Hemisphere), before turning towards the destination. This is also known as “Mercator Projection”.

While this might appear to be odd, the aircraft is in fact flying the shortest distance and is in fact flying on a direct path. This becomes more evident if the flight path is viewed on a spherical map, which more airlines these days are increasingly introducing into their IFE systems. The aircraft (when possible) flies the most direct path, following the curvature of the Earth, also known as the great circle path. This track over the curvature, when transposed on a flat map, makes the flight path appear odd.

That being said, in real-life airline operations, there are a lot of complexities, which could result in airlines often choosing to operate longer routes for efficiency reasons, or sometimes due to safety reasons. That being said, sometimes the airlines are also “forced” to operate longer routes due to regulatory reasons as well.

Jet Streams – A Force Of Nature

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In the simplest of terms, jet streams are bands of high-speed winds, generally flowing west to east, which can be found at higher altitudes, within certain regions of the planet where air masses meet and interact with each other. With these streams often exceeding speeds of several hundred miles per hour, aircraft often utilize them to fly faster and more efficiently, even if it means taking longer routes.

An aircraft flying to the east can often travel faster by utilizing a flight path through the jet stream than if it followed the typical great-circle path. The added tailwind allows the aircraft to fly faster, utilizing lower power, which subsequently results in lower fuel burn and better operational efficiency. This is also why easterly flights generally record lower flight durations than westerly flights, with the difference in duration being more evident as the distance increases. Here are a few examples of block times listed by various airlines on long-haul routes offered:

The above-mentioned block times are what airlines use for marketing, but the actual flight times can be of lower or higher duration depending on operational conditions. That being said, in the case of Singapore Airlines’ service from its hub to New York JFK Airport and back, the carrier harnesses the range of the specially designed Airbus A350-900ULR aircraft and operates both legs of the flight in an easterly direction, maximizing the use of jet streams.

Weather Events Can Cause Rerouting

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Apart from operational efficiencies, another reason why aircraft might opt to operate a longer flight path instead of a direct one could be attributed to weather-related safety. Although modern aircraft are technologically advanced and can operate in various scenarios, some atmospheric weather conditions are avoided due to the risk to flight safety they can pose.

Weather conditions such as the formation of cumulonimbus clouds are avoided because within these clouds are severe thunderstorms and turbulence. Furthermore, operating in and around these areas can also cause icing-related issues, such as ice build-up on aircraft’s pitot tubes and sensors, which can result in erroneous readings on flight deck instruments and can also result in aircraft damage. In extreme cases, the aircraft can also get caught in microbursts, which are extremely dangerous and can cause injuries to passengers and crew members onboard.

Therefore, pilots are always encouraged to reroute their aircraft around dangerous weather activities. The weather-related data and information are always briefed to the pilots before the flight, and they also have access to live data in flight using onboard weather radar systems. These sophisticated systems not only show cloud formations, but also indicate information regarding potential storms and their intensities.

Mountain Ranges Are Also Avoided

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Apart from atmospheric weather, another natural feature which airlines prefer to avoid and fly around where possible is large-scale mountain ranges. While one might think most jet aircraft can fly at altitudes much higher than that of mountains (which they can), the decision to route around the area is not related to ground clearance, but the safety risks that mountains can pose to flight operations.

Mountain waves are a threat

These are phenomena that are caused by airflow over mountains, wherein winds traveling in straight lines are forced to oscillate up and down by the presence of the mountain, subsequently causing airflow at higher altitudes to oscillate as well. An aircraft caught in mountain waves can experience severe turbulence, often experiencing updrafts and down-drafts as well. There is also the added risk of an airplane already at high altitude being caught in an updraft, which could send it over the aircraft’s operational ceiling.

Emergency descent

Another issue with large-scale mountain ranges such as the Himalayas is, in fact, the presence of the mountains. It is never predictable as to when there could be an emergency, such as cabin depressurization, and the aircraft has to perform an emergency descent to lower altitudes (below 10,000 feet). The problem with mountain ranges such as the Himalayas or the Alps is that there are mountain peaks within the ranges which exceed the safe altitude, which therefore prevents an aircraft from performing an emergency descent to the required altitudes altogether.

ETOPS & Suitable Airport Requirements

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Although one might assume it is easy to fly a direct route, especially when traveling for extended periods over vast bodies of water, this is not necessarily the case. One of the key factors kept in consideration when charting a route for a flight is the availability of suitable en-route airports the aircraft can divert to in the event of any emergency. This is particularly focused on routes that fly over the oceans or deserted areas.

Modern aircraft have Extended-range Twin-engine Operational Performance Standards ( ETOPS) ratings, which determine how long an aircraft can safely operate with only one engine, from the nearest suitable airport. This essentially means aircraft with lower ETOPS ratings will be forced to operate longer routes, which are less efficient, to ensure the aircraft remains within the minimum required flight duration to a suitable airport, at any point in flight.

That being said, modern systems and technology have allowed for better reliability in recent years, which has subsequently pushed the ETOPS ratings to allow aircraft to operate more efficient routes. Airbus’ latest generation widebody aircraft, the Airbus A350, holds an ETOPS rating of 370 minutes. This allows the twin-engine aircraft to fly at distances over six hours from the nearest suitable airport.

Some Airspaces Are Entirely Avoided

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Sometimes, geopolitical reasons can force an aircraft to operate using longer and less efficient flight paths due to safety or geopolitical reasons. Considering current world affairs, inaccessibility to a few strategic airspaces in recent times has been creating significant impacts, reshaping global aviation markets.

In terms of safety factors, whenever there is civil unrest, tensions, or conflicts on the ground, there can be repercussions in the air. Such events often bring flight safety into question, especially if military activities are involved, or even technological warfare, such as GPS jamming. These pose high levels of risk to commercial flights. In many cases, airspaces are closed off by the nation entirely. But in the event they are not, airlines would still prefer to circumnavigate the region, prioritizing safety over efficiency.

On the other hand, when it comes to geopolitical reasons, airlines sometimes have to avoid certain airspace, not necessarily due to safety reasons, but due to regulatory reasons, such as being banned from operating within certain airspace. A prime example that can be used is the fact that Russian Airspace is off-limits to airlines registered in several Western nations, and vice versa. This means airlines (such as those in Europe) wishing to operate flights to destinations in Southeast or Far East Asia are forced to avoid Russian Airspace and utilize inefficient flight paths flying around Russia, rather than the great circle route.

The closure of Russian airspace resulted in several airlines reducing their long-haul services to Asia because of the added costs related to using an inefficient flight path. On the other hand, airlines from countries such as China are still able to utilize Russian airspace, giving them an operational advantage of continuing to use the most efficient flight path. In fact, in recent years, East Asian airlines have been able to continue to expand their network to Europe.