No matter the size of the aircraft, every experienced pilot knows that it is always up to the weather when it comes to flying. Pilots are taught that a headwind is terrible for cruising conditions. Still, they can be quite beneficial for take-off and landings. Aviators can strategically use a headwind to their advantage to help them reach altitude faster.

Airports change runways direction because taking off and landing into the wind can be done at lower speeds and in less time. Simply put, when taking off, a headwind will create more lift. When landing, winds at your nose will also act as a speed break by creating drag against the airframe to slow the aircraft down.

Taking off and landing into the wind provides a sometimes much needed a lift to make a safer departure/arrival. When there is no wind, an aircraft may have to accelerate 25 percent faster to achieve the same lift it would if it where heading into the wind.

This becomes especially crucial when landing heavy planes at smaller airports or airstrips, where runway length is limited.

In this article, we are going to look closer at why airports change takeoff and landing directions.

But before that, we need to understand the very basics of flying…

Basics of Flying

To understand why airports consistently switch runways for take-off and landing, you must understand the 4 forces of flight. The forces acting upon the aircraft and its aerodynamics play a vital role in the aircraft’s ability to generate lift.

• Thrust: Thrust is created by the propulsion system and is the force that moves an aircraft through the air. Thrust counteracts drag by pulling the plane through the air and sending the wind in the opposite direction.
• Drag: Drag is the force that counteracts thrusts.  Friction creates drag that tends to slow the aircraft down during flight. Therefore a plane must have powerful enough engines to overcome the forces acting against it.
• Weight: Weight is the force of gravity on the plane’s airframe. The aircraft’s weight is counteracted by its ability to generate lift.
• Lift: Contrary to weight, the lift is the force that helps the plane get airborne. The airfoils generate lift by decreasing the pressure on top of the wing and increasing air pressure below it. The pressure difference creates a lifting force that is often greater than the weight of the aircraft.

The second and last thing you need to get a grasp of before understanding how airports decide which runway to use for takeoffs and landings, is how wind affects airplanes.

How does wind affect planes?

 

Wind will affect every aircraft differently depending on its design and ability to move through the air.

However, in short, there are three basic concepts you need to be familiar with:

Headwinds

Headwinds are a wind force that blows toward the aircraft during flight. They can be great for take-off and landing, but work against the plane at cruising altitude.

Tailwinds

Tailwinds are more favorable during cruising conditions because the wind helps push the aircraft in the direction of flight rather than work against it. Flying with a tailwind can lower operating costs because it saves both time and fuel.

However, during take-off and landing, a tailwind can increase the speed at which it is needed to gain altitude. I can also increase the distance required to take off and land.

Crosswinds

Crosswinds are wind forces that blow perpendicular to the aircraft. Crosswinds can make take-off and landing more difficult because it can sweep the plane off the runway into surrounding structures. In level flight, wind forces can blow a plane off course.

How wind impacts landing and takeoff

Departing with the wind to your nose (Headwind) allows the pilot to take off in the shorter distance and use less engine power to get airborne.

When a plane takes off in opposing winds, it maximizes airflow under the wings to achieve flight more efficiently and reduces fuel consumption.  Airports generally utilize the prevailing headwinds during departure in all directions.

Much like the take-off, landing into a headwind is strategic by the pilots. Landing into the opposing wind allows pilots the make a slower approach, and makes landing safer.

As an aside, for a helicopter, it is equally essential to land into the wind. If it lands in a tailwind, it will increase the aircraft’s chances of getting into settling with power.

So, what determines in which direction a runway is used?

 

 

Weather and wind direction is the main factor in determining which runway is used for departure and landing. All airfields are equipped with an anemometer and windsock, which, when combined, help ground control assess wind direction and speed.

Winds are monitored at all times, as weather can change without warning. Sometimes, reports of upper-level winds by aviators that differ from those on the ground can also be a determining factor for runway selection as well.

It is the responsibility of air traffic control to continuously monitor the weather and try and anticipate developing trends to accurately select a runway. When choosing a runway air, traffic control must consider:

• The number of planes designated to land
• Runway length
• Coming weather conditions
• Visibility
• Runway conditions
• Taxiing distances
• Exessive Noise on the surrounding areas

Larger airports generally have more than one runway that runs perpendicular with the other so that a runway facing the wind is always available. Such an example is shown below.

Some airports have a primary runway system when conditions are right because it reduces noise pollution around the surrounding areas.

Noise reduction and runway selection.

Noise can also be a factor when designating a primary airstrip. Air traffic control will nominate a specific runway to avert excess noise downwind of the surrounding area during noise abatement hours. Since most airports have an agreement with the city, air traffic control tries to be mindful of sound when selecting a primary runway.

Excess noise cannot always be averted. Seasonal trends in weather may result in using a specific airstrip to utilize the prevailing winds. This can sometimes lead to excess noise in the surrounding areas during certain times of the year.

Airport Placement

Airport locations are generally picked because of their geographic location to the current populus of a region. However, runways are designed with both prevailing winds and land structures in mind.

In the Continental United States, most prevailing winds run east to west and visa versa due to the Coriolis Effect of the earth’s rotation. Wind direction is important because it will dictate which way aircraft depart and land.

Why are the numbers different on each side of the runway?

Airports are bi-directional and can be used in both directions. The numbers at the end of the runway indicated the course you are taking off or landing relative to its compass bearing. For example, Runway 09 is 90 degrees on the compass running west to east. Conversely, Runway 27 faces 270 East.

The numbers will always differ by 180 degrees on the same runway. Some airports have perpendicular runways to utilize wind in all directions.

Do planes take off and land in the same direction?

Yes, as discussed, it is always best for a plane to both depart and land into the wind.

Sometimes they will depart and land on the same runway, but other times they may have to land on a different one. This happens because winds can shift direction while the aircraft is in flight, causing them to have to approach the airport in a different direction.

Can planes take off and land with a tailwind?

Yes, aircraft can take off and land with a  tailwind, but it is not recommended. When a plane takes off with the wind at its back, it takes more speed and runway length to achieve lift.

This means if an aircraft has to take off or land with a tailwind, the pilots must ensure that they have enough runway, and enough engine power to achieve flight. It is only recommended to land with the wind at your back when the conditions are unknown if you are in an emergency.

Do planes have to land into the wind during an emergency?

During an emergency, planes should land into the wind because it will allow them to make a slower approach. Touching down into a  headwind can shorten landing distance and will also create drag to help slow down the aircraft.

However, in an emergency, getting the plane to the ground safely and quickly is the main objective, even if it means landing with the wind at your back

Do helicopters have to take off and land in the same direction as planes?

Unlike planes, helicopters can take off vertically. However, they can gain altitude faster and easier with a headwind. Helicopters often have their own take-off and landing helipads at the airport because they operate differently.

It is more critical for a helicopter to land into the wind because when it touches down into a tailwind, it increases their chances of entering settling with power.  This could cause the aircraft to inadvertently descend without the pilot input on the controls.

Some helicopters that are equipped with wheels are capable of performing a rolling takeoff. However, they do not require a lot of runway to generate lift unless they are severely weighed down.

Summary

• Wind and weather will always dictate which runway a pilot uses. Still, aviators must always be able to adapt to the changes in weather trends.
• Although ground control continuously monitors weather data, winds can shift without warning.
• This means the runways can change as well. No matter the size of the aircraft, a headwind can make take-offs and landings more efficient.