NEWTON, N.H. — Passengers can send messages, stream videos and browse the internet while flying thousands of feet above the ground. Providing that connection, however, presents challenges that don't exist with Wi-Fi on the ground. Aircraft travel hundreds of miles per hour and cross large geographic areas, making it difficult to maintain a consistent connection.

Maintaining a reliable connection requires engineers to coordinate several systems as the aircraft moves.

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How does in-flight Wi-Fi work?

Most commercial aircraft provide internet access through satellite communications or air-to-ground networks. Inside the cabin, passengers connect their devices to wireless access points, much as they would in a home or office. Those access points connect to onboard networking equipment that manages traffic between passengers' devices and the aircraft's external communications system.

The next step is what makes aviation connectivity different. Aircraft using satellite communications send data through an antenna. The antenna communicates with a satellite, which connects the aircraft to internet infrastructure on the ground.

Air-to-ground systems work differently. They use antennas on the aircraft to communicate with ground-based cellular-style towers. These networks can provide connectivity over land, but their coverage depends on the locations and reach of the towers. While both approaches allow passengers to access the internet, each presents different engineering challenges.

How does antenna placement affect performance?

Aircraft antennas must communicate with equipment outside the cabin while meeting strict requirements for weight, aerodynamics and structural safety. Satellite antennas are typically mounted on top of the fuselage beneath protective covers called radomes, which shield the equipment from airflow and environmental exposure while allowing radio signals to pass through.

Engineers must consider how these installations affect drag and fuel consumption. Antenna placement also influences signal quality, as parts of the fuselage, wings or tail can obstruct communication with a satellite.

Radio-frequency interference presents another challenge. Connectivity equipment must operate alongside navigation, communication and other electronic systems without disrupting their functions. Engineers use careful antenna placement, shielding, filtering and testing to address these concerns.

Why does aircraft movement complicate connectivity?

A passenger aircraft can travel more than 500 miles per hour during cruise, continuously changing its position relative to satellites and ground stations. For satellite systems, antennas must maintain a usable connection despite changes in the aircraft's location and orientation. Some systems use mechanically steered antennas, while others use electronically steered antennas that adjust the direction of the signal without moving the entire antenna assembly.

The type of satellite also affects how the connection works. Geostationary satellites remain in approximately the same position relative to the Earth's surface. An aircraft can communicate with one over a large coverage area, although the signal must travel a considerable distance.

Low Earth orbit satellites operate much closer to Earth and move across the sky relative to the aircraft. They can offer lower communication delays, but the aircraft's equipment must switch between satellites as they move in and out of view.

These transitions are called handoffs. A handoff must transfer the connection from one satellite or ground station to another without unnecessarily interrupting service. Poorly managed handoffs can cause temporary disruptions, even when the aircraft remains within a network's overall coverage area.

Why can't every passenger get the same internet speed?

Bandwidth is another major limitation. An aircraft may carry hundreds of passengers using the internet at once. Some may be checking email, while others are streaming videos or downloading files. All of these activities compete for the same available bandwidth, which can affect connection speeds throughout the cabin.

Unlike a home network, where an internet provider can often deliver service through a fixed cable or fiber connection, an aircraft depends on a wireless link with capacity that can change throughout the flight. Satellite operators must also distribute network resources among multiple aircraft and other customers. When demand increases, individual users may experience slower speeds.

Airlines and connectivity providers use network management software to allocate available capacity. These systems can manage congestion and prevent individual devices from consuming too much bandwidth. However, software cannot increase the available bandwidth when the external connection reaches its limits.

What happens when an aircraft loses its connection?

When an aircraft loses its internet connection, onboard networking equipment may attempt to reconnect through the same system or switch to another available network, depending on the aircraft's configuration. Still, maintaining continuous service requires compatible equipment, available network capacity and successful transitions between connections.

What will improve in-flight connectivity?

Airlines and equipment suppliers continue to develop systems that offer greater capacity and more consistent coverage. New satellite constellations, electronically steered antennas and improved onboard networking equipment are expanding connectivity options.

Multi-orbit systems can provide access to different satellite networks, allowing aircraft to use connections based on coverage and performance.

These improvements come with trade-offs. Airlines must consider equipment costs, installation requirements, aircraft downtime, power consumption and the added weight of onboard hardware.

Reliable in-flight connectivity depends on how well antennas, satellite networks, ground infrastructure and onboard equipment work together to maintain service throughout a flight.