How in-flight Wi-Fi works, and why your eSIM sits it out

Inside the cabin it is just Wi-Fi

From your seat, nothing is unusual. You join a network with the airline's name, a page opens to sign in or accept the terms, and from then on the phone treats it like any café network. The interesting part is behind it.

Gogo, one of the companies that provides the service, describes the chain on its own aircraft: Wi-Fi access points in the cabin connect to an onboard server, a modem handles the radio link, and antennas on the outside of the fuselage carry the traffic off the plane. Everyone on board shares that same link to the ground. What changes from one airline to another is where the antenna sends the signal: down to towers, or up to satellites.

Route one: towers that point at the sky

In an air-to-ground system, the plane talks to a network of base stations on the ground built to point upwards. Gogo explains that its North American network uses cellular-based towers that point at the sky, with a small antenna mounted on the underside of the aircraft. Because it needs towers below, this approach only works where those towers exist, which means flights over land.

Europe has a hybrid version. The European Aviation Network, run by Viasat and Deutsche Telekom, combines S-band satellite coverage with a ground network that Deutsche Telekom describes as around 300 base stations across the EU member states, Switzerland and Norway. From the seat it is still one Wi-Fi network: which part carries your traffic at any moment is not something you choose or see.

Route two: satellites, high and low

Over oceans and remote areas, the connection goes through satellites. ESA explains the two orbits involved. A geostationary satellite sits at an altitude of 35,786 km and stays fixed above the same spot, which is why ground antennas can point at it permanently and why it suits telecommunications. Low Earth orbit is anything below 2,000 km, and communications satellites there work as constellations of many satellites to give continuous coverage.

Distance is the difference you notice. With a geostationary satellite, a request goes up and down, and its reply goes up and down again, covering that altitude four times. Email and messages do not mind; video calls and anything interactive feel the delay. Satellites in low orbit are far closer, so the trip is much shorter.

Why your eSIM does not connect up there

Mobile networks on the ground are designed for phones on the ground. The FCC explains that its ban on using mobile phones in flight was adopted to protect against radio interference to mobile networks on the ground. That is why, with or without an eSIM, airlines ask for airplane mode, or allow phones on only after their own assessment.

Some aircraft carry a mobile network of their own: the European Commission describes a pico-cell in the cabin linked to the ground network, typically via satellite. The EU's Your Europe portal warns that mobile services provided by satellite fall outside EU roaming rules and have no price caps. A travel data eSIM is made for the ground networks of its country or region, so in the air the plane's Wi-Fi is the connection to use.

Getting the most out of a shared connection

• Keep airplane mode on and switch on Wi-Fi only, so no mobile line connects to a satellite network by mistake.
• On iPhone, turn on Low Data Mode for the plane's network: Settings, Wi-Fi, the info button next to the network. Apple says it pauses automatic downloads, backups and background refresh.
• Download films, music and maps before boarding, not on board.
• Treat it as public Wi-Fi. CISA lists aircraft among the public wireless networks to be careful with, and it is the same advice as in any café.

What is free and what is paid, and whether calls are allowed, is up to each airline. Check its own information for your flight rather than assuming.