The Jet Stream

The Jet Stream
Have you ever wondered why is it faster to fly from America to Europe than the other way around? The answer is the Jet stream. This ‘river’ of air flowing through the Earth plays a big role in aviation. Airlines have learned how to take advantage of it and plan their flights accordingly.


The discovery of the Jet Stream is often attributed to Wasaburo Ooishi, a Japanese meteorologist. Back in 1923, he observed that strong winds aloft would deviate atmospheric balloons as they gained altitude. By tracking their position, he was able to determine the wind speed. Although it was only a prediction, he was able to record a trend over the years and determined that these winds followed a pattern. His observations remained mostly unnoticed as he published them in Esperanto.

During World War II, Ooishi’s observations allowed Japan to launch “Operation Fu-go”. Using his prediction on winds aloft, the Japanese launched nearly 10,000 hydrogen balloons carrying bombs over the Pacific Ocean to America. Predictions of 190 knots (350 km/h) in wind speed (between 30,000 and 38,000 feet) would carry the balloons to the United States west coast in 3 days. His predictions turned out to be inaccurate and only some balloons arrived and didn’t cause the intended effect.

Balloons loaded with bombs. Photo:
Balloons loaded with bombs. Photo:

American aviator Wiley Post is also attributed the discovery of the Jet Stream. Post achieved the first around-the-world solo flight in 1931, developed the pressure suit and explored the limits of high- altitude flying. In 1935, while flying at 30,000 feet in his supercharged Lockheed 5C Vega “Winnie Mae”, he experienced speeds up to 340 miles per hour. Flying in the Jet Stream he was able to cover 2,035 miles between Burbank, California and Cleveland, Ohio in 7 hours and 19 minutes, proving the benefits of high-altitude flights. The same distance, at sea level, would have taken 12 hours and 42 minutes.

Wiley Post en su "Winnie Mae"
Wiley Post and his Lockheed 5C Vega “Winnie Mae”. Photo: Hulton Archive


The air acts like a fluid, just like water. And so, it flows and it is affected by external forces, modifying its behavior and shaping its patterns.

On earth, due to the differential heating along its latitude, the vertical development of the atmosphere changes. Close to the Equator the air is warmer, so it ascends creating an area of low pressure near the surface. The surrounding air tends to fill in this ‘gap’, so it flows from the higher pressure area to the lower. The ‘gap’ created by the air moving to the low pressure area at surface, creates a sinking motion for the air that is up at the Tropopause. Thus, creating a circulation.

Circulation of the Hadley, Ferrel and Polar cell. Photo: NASA – Wikimedia
Circulation of the Hadley, Ferrel and Polar cell. Photo: NASA – Wikimedia

There are three circulation cells per hemisphere. The Hadley, the Ferrel and the Polar cells. These cells find their top at the Tropopause, the layer at which the air stops rising. Close to the equator, the air is warmer and ascends much higher, elongating the Tropopause further up. The average (it varies during the year) altitude of the tropopause at the equator is 56,000 feet, and 30,000 feet at the poles.

Cross-section of the Cells and its circulation. Photo: Sleske – Wikimedia
Cross-section of the Cells and its circulation. Photo: Sleske – Wikimedia

The Jet Stream originates at the boundary of these cells. Due to Earth’s rotation, the air traveling to this boundary is forced sideways. This is called the Coriolis effect. In the Northern hemisphere, the air traveling North will be forced to flow East. This is why the Jet Stream flows primarily in that direction. The greater the air velocity, the greater the deviation. If the difference in temperature is high between cells, the Jet Stream speed increases, up to 200 Knots (370 Km/h).

The Jet Stream is like a continuous ‘river’ of air, meandering. This is due to the difference in Coriolis effect at different latitudes. These are called Rossby waves, and it’s the reason why we often see Jet Streams that are not directly heading East.

Rossby waves
Rossby waves. Photo: NASA


With all this knowledge, aviation can take advantage of a given atmospheric condition at any time. By using meteorologic and satellite information, we can predict future weather phenomena, winds aloft and more. Airlines use hourly updated information to plan their flight avoiding dangerous weather worldwide.

When dealing with Jet Streams, flight planning departments take into account the position, height, extension and speed of the wind on their planned route. Therefore, anticipating themselves and being able to modify the route to, for example, avoid a strong headwind o a turbulence area associated with it.

Significant Weather Chart of the Atlantic Ocean. Photo:

Pilots also receive weather information in form of SIGWX (Significant Weather Chart) and wind charts. Then, they can also judge the situation, discuss and decide the better course of action. On long haul flights, a route deviation implies a great deal of considerations: Fuel planning can be affected, ETOPS operation may restrict certain deviations, en-route alternate airports may have to be adjusted, the airline may have to consider schedule affectations on connecting flights, etc.


As we have seen the Jet Stream is a fast-flowing stream of air. The air surrounding it is, by comparison, slower or even still. When an aircraft is approaching a Jet Stream area and the wind suddenly increases, it suffers from what is called Windshear. This is a sudden change in relative speed between two adjacent air masses. A change in wind speed causes instability within the air mass. As it flies through it, the aircraft is subject to those disturbances, suffering from turbulence. Also, as the Jet Stream flows right next to the border of the Cell, we find a transition between air temperatures, thus changing the density of the air and creating instability as well.

This type of turbulence is not associated with clouds, that’s why it’s called CAT, Clear Air Turbulence. Usually the turbulence is reduced to a mere bumpy road-like feeling. With short and repetitive shaking, this kind of turbulence is unpleasant for passengers rather than dangerous for flight safety. Nevertheless, there have been situations in which moderate and severe turbulence has been encountered as a result of CAT.

Depiction of a cell boundary, Jet Stream and Area of CAT
Depiction of a cell boundary, Jet Stream and Area of CAT

From the flight planning stage, with help of the aforementioned maps & charts, pilots do their best to avoid such areas. CAT areas are marked and their vertical extent also advised. As we can see in the map, the blue dotted line over Sardinia (Italy) represents an area of potential clear air turbulence. In the legend we can see it ranges from FL210 to FL410. We can also see how it is associated with a Jet Stream that is flowing from North to South (Red line) at 120 knots (Every triangle represents 50kt and every line 10kt).

Significant Weather Chart showing the Jet Stream and associated CAT areas. Photo:
Significant Weather Chart showing the Jet Stream and associated CAT areas. Photo:

When an aircraft is subject to moderate and severe turbulence, the pilots shall report it to the ATC —Air Traffic Control— to help other traffic in the surrounding area and raise awareness of potential hazardous areas. A simple change of Flight Level (Altitude) shall suffice to get out of the turbulent area. Often times, pilots ask the ATC for an altitude change to avoid the uncomfortable shaking.


As a little example of the big influence the Jet Stream can have on a given flight, we are going to take a look at a flight from Los Angeles to Tokyo-Haneda, and how we can take advantage of our knowledge.

We can see that the Jet Stream, the same that instigated the Japanese balloon project, flows along the Pacific Ocean. If we were to follow the standard routing, we would find ourselves right in the middle of the Jet Stream. Let’s take a look at the effect of it.

When flying through the Jet Stream, we are experiencing a sustained headwind of up to 120kt along he whole route. This would result in a flight time of 12 hours and 45 minutes to cover 4835 Nautical Miles, and an estimated fuel burn of 94,800 Kg of fuel. Allowing for contingency, final reserve and alternate fuel we would need roughly 108,000 Kg of fuel on departure.

Conversely, if we decide to deviate further North, even though we will fly a longer route (123 Nautical Miles longer) we will avoid the Jet Stream and the effects are very noticeable. Let’s see:

Flying the Northern route we would fly a distance of 4958 Nautical Miles, it would take only 11 hours and 25 minutes. 1 hour and 20 minutes and nearly 10 tones of fuel less. This represents a massive time and fuel cut, even when flying a longer route. Of course, this is a perfect example, some days the difference would be less. But, all in all, it means millions of dollars in savings when thousands of flights are scheduled on a yearly basis. This is how important is to have an effective operations & flight planning team supporting the flight operation.


Aviation is a complex, ever-changing business. Crew schedules, route network, customer service or staff management. Every aspect of it is subject to sudden changes and continuous adjustment. Airlines sometimes find it difficult to strive in this ultra-competitive world. Mergers, acquisitions and bankruptcies are no strangers to many airlines. We, the people behind this circus, are sometimes caught in the middle of it all.

This is a tale of a pilot’s last flight for an airline.

It hasn’t been an easy summer. Rumours in the office, cockpit talks, hints on the news… We all know something is cooking. Some colleagues are already searching for a way out, others keep the faith and will stay. During this week my schedule has changed several times. The airline is adjusting and re-adjusting the flights, some aircrafts have been impounded by their owner, the lessor. Others are still on maintenance. It looks bad, but we’ll keep on fighting until the end.

I check my roster and my flight has been changed. I will fly to Tirana, stay the night and come back in the morning. As I drive to the airport, I can’t help but think it can be the last time. I’m going to enjoy this flight like it’s the last. I will try to remember every little detail and make the best out of it. When I make it to the office, the captain is nowhere to be seen. Our aircraft is late by more than an hour and he will probably show up right before it lands. I take the flight briefing folder and start to prepare the flight. The office is quiet, nobody dares to speak more than the necessary, everyone suspects we won’t be around much longer. Finally, the captain arrives and, we brief the flight together. It’s looks like a smooth ride over the Balkans on our way to Albania. We check the technical status of the aircraft and decide how much fuel we will take. It looks like the flight is further delayed, so the captain decides we won’t have time to go to the hotel in Tirana. We will stay in the aircraft, as we will have a little longer than two hours until we will have to come back to Ljubljana.


We make our way to the terminal, pass the security control and walk to the aircraft. The apron is quiet, we can see three of our airplanes grounded, sealed. It’s sad we won’t see them flying anymore. We agree he will fly the first leg and I will fly the way back tomorrow morning. Finally, we arrive to our Bombardier CRJ-900. S5-AFA has only been with us for 2 years. It came from Air Nostrum, where it was registered as EC-JNB. We open the doors and I start with the initial checks.

Milky way seen from the first officer seat.

One hour later, we are cruising at FL350. A moonless night brings us wonderful views of the milky way. The purser brings the dinner to the flight deck. I’m not hungry, thoughts race through my mind, I feel uneasy. Nevertheless, this might be the last dinner onboard, so I decide to eat. The flight progresses as usual. We land in Tirana and passengers disembark the plane. It’s 1:30 AM and the captain is powering down the aircraft. Meanwhile, I close the door and set the alarm.

Wake up call. The screen of my phone illuminates the passenger cabin, pitch-black, it’s 4 AM. Swollen face, red eyes, better make some coffee. I pick up the ATIS, prepare the route and calculate the performances, as the passengers start boarding the plane. They probably have no idea of what’s going to happen with the airline and some of them might not be able to come back home after their holidays. Captain asks for the checklist and we start up the engines. “ADRIA727, wind is 020 at 2 knots, runway 35 cleared for take-off”. AFA starts rolling, illuminating the runway as speed increases. “V1, rotate” and I gently pull the yoke to lift up the nose. The aircraft leaves the asphalt slowly and starts climbing into the dark of the night.

It’s 5:30 and the stars are disappearing in favour of a dark blue twilight. The weather is perfect in Ljubljana and we will be the first inbound flight this morning. One of the cabin crew brings coffee. You can’t say no to a cup of coffee with the best views in the world.

Sunrise over Zagreb, Croatia.

As we start our descent, the sun rises over the Balkan skies, calm as ever. We can’t talk to each other, gutted.

Gear down”, we feel this could be our last landing in Ljubljana.

Adria 727, Cleared to land runway 30, wind calm”.

50, 40, 30 – Thrust idle – 20, 10 – Flare…” And we kiss the runway for the last time.

A smooth approach and landing put an end to it. As always, we bring our passengers home, safely, but this time, it feels different. As I step out of the cockpit, I look back and take a last glance at it. Here is where it all started. This airline gave me my first chance, my first job as an airline pilot. I learned how to fly a masterpiece of an aircraft.

Bombardier CRJ900 departing from Ljubljana, Slovenia. (Photo: Adria Airlines)

Two days after Adria Airways ceased operations temporarily. A week later, on September 30th, the airline filed for bankruptcy. This article is dedicated to the people of Adria Airways (1961-2019).

Edgar Domenech Llinares is an airline pilot rated on Bombardier CRJ700 and 900 series. He has been based in Slovenia flying for Adria until vert recently.

He started his career as a cabin crew. He worked for 6 years based in Palma de Mallorca where he managed to get his pilot licenses and ratings.

His passion for aviation drove him to make his dream to come true, learning a lot in the process, and looking forward to learn more in the future.