How Does In-Flight Wi-Fi Really Work?

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Wi-Fi access has become an expected feature when flying for either work or pleasure. Using Melanie Wynne’s The Future of Inflight High-Speed Wi-Fi as a launching pad, new TPG Contributor Rick Mitacek, operations manager of an avionics modification team, takes a closer look at the technical side of Wi-Fi in the sky. (All photos by the author, unless otherwise specified.)

Prior to the integration of in-flight Wi-Fi, most airline passengers passed their time at 30,000 feet completely disconnected from the world below them — but these days, that’s a highly uncommon occurrence. For instance, while writing this article on a short-haul United flight with broken Wi-Fi, I realized that I couldn’t remember the last time I’d been rendered email-less for even a couple of hours. Since this service has become so important in our lives — everywhere we go — I’d like to offer a closer look at in-flight Wi-Fi and how it actually works.

Let’s start with a look at the three types of in-flight Wi-Fi:

ATG (Air To Ground)

ATG connection uses ground based towers for connection. Photo curtesy of LinkedIn.
ATG connection uses ground-based towers for connection.

Designed for domestic travel over land, the ATG system of Wi-Fi requires two antennas that are installed on the belly of an aircraft in order to pick up signals from land-based cell towers. When the flight attendant flips the switch on the ATG system to “On,” the aircraft begins to pick up the different cell towers and allows users within the plane to start sending and receiving signals.

The ATG antenna based at the bottom of the plane. Photo by the author.
The ATG antenna installed at the bottom of the plane.

At present, most ATG service is only providing users with a Wi-Fi speed of approximately 3 Mbps, which suffices for emails, checking Facebook and of course, reading TPG. Gogo’s latest ATG-4 system supports up to 10 Mbps, but it isn’t available on as many planes as the slower ATG-3.

Ku-Band

Satellite based Wi-Fi. Photo courtesy of OnAir.
Satellite-based Wi-Fi. Image courtesy of OnAir.

Satellite-based Ku-Band service, popular with airline providers like Gogo, Panasonic and Row 44, covers a much greater area, keeping you connected even when flying out of range of ground-based cell towers or over the ocean. The Ku-Band antenna is housed in a big dome-shaped “saucer” that sits on top of the plane, and similar to a rooftop TV dish on a house, this antenna has to be directed toward the transmitting satellite as the plane flies.

Panasonic Avionics’ Ku-band eXConnect antenna. Photo courtesy of Panasonic.
Panasonic Avionics’ Ku-band eXConnect antenna. Image courtesy of Panasonic.

Once the antenna picks up the satellite signal, the plane provides users with Wi-Fi speeds of up to 30-40 Mbps. Although this is much improved over the ATG system, speeds depend on how many aircraft one satellite is serving. Ku-Band isn’t going to provide you with the capability to stream movies off of Netflix, for example, but as TPG contributor Sarah Silbert found on a recent United flight, you could run a Google Fi call, view some picture-heavy websites and maybe even stream some music. Because of the distance a signal must travel, satellite Wi-Fi suffers from latency issues that don’t affect ATG, so while content will load faster overall, initial page elements will take up to a second to appear.

Ka-Band

ViaSat Ka and Ka/Ku-Band satellite antennas. Photo courtesy of ViaSat.
ViaSat Ka and Ka/Ku-Band satellite antennas. Image courtesy of ViaSat.

Formally used for military communications, satellite-based Ka-Band is currently the fastest Wi-Fi service available for airlines and is popular with JetBlue, Virgin America and some United 737s. Satellite and wireless-service provider ViaSat powers Ka-Band with its new ViaSat-1 satellite, which is much more powerful than Ku-Banded satellites and promises speeds of up to 70 Mbps to each aircraft. This is similar to the speed you’d find in your home and allows you to stream videos, as well as upload photos to websites and social media platforms like Instagram and Facebook. There’s presently only one ViaSat Ka-Band satellite, so the service is limited to the US, however, ViaSat plans to launch a second Ka-Band satellite in 2016, which will cover Canada and parts of Europe.

Virgin America allows streaming of Netflix through Ka-Band service. Photo courtesy of Virgin America.
Virgin America allows streaming of Netflix through Ka-Band service. Image courtesy of Virgin America.

Since Ka-Band is currently only available in the US, Virgin America has opted to use a Ka-/Ku-Band hybrid receiver for the time being on its newly delivered A320 aircraft. This hybrid receiver allows the airplane to switch between Ku- and Ka-Bands based on the best signal strength available. Virgin America claims that this combination of satellite-serviced Wi-Fi will allow its passengers to watch shows and movies on Netflix and stream music from Spotify.

Exede

ViaSat's ViaSat-1 satellite provides both Ka-Band and Exede Wi-Fi service on planes. Photo courtesy of ViaSat.
ViaSat’s ViaSat-1 satellite provides both Ka-Band and Exede Wi-Fi. Image courtesy of ViaSat.

Also provided by ViaSat’s ViaSat-1 satellite is the 12 Mbps Exede service, which JetBlue uses to offer free “Fly-Fi” Wi-Fi service for all its passengers, along with the speed-enhanced Fly-Fi+ service available at $9 per hour. JetBlue also recently announced that it has teamed up with Amazon to offer Amazon Prime members the opportunity to stream movies to their own devices. JetBlue has completed Wi-Fi installation on all of its A320 family, but only 2% of the new E190 aircraft.

Interior Equipment Required to Make Wi-Fi Work on a Plane

There are several miles worth of wiring for the Wi-Fi and In-Flight Entertainment alone! Photo by author.
The average commercial aircraft has several miles’ worth of wiring in order to enable its Wi-Fi service.

The Wi-Fi and in-flight entertainment systems used on most commercial aircraft are fairly simple when compared with many other aircraft systems. For example, in 1984, Delta Air Lines outfitted a Lockheed L-1011 to carry the first seat-imbedded in-flight phones — and today, airplane Wi-Fi relies on similar technology.

Tucked behind the wall panels of an aircraft, lining one side of the plane and set slightly above the windows, a series of black boxes (not to be confused with flight recorders) serve as in-flight Wi-Fi access points.

Black boxes called Wireless Access Points (or WAPs) line the interior of the starboard side of an airplane.

Called Wireless Access Points (or WAPs), these black boxes function similarly to Wi-Fi routers that would be found in a home, but because they’re on an airplane, they cost 10 times more and break 10 times more easily. Each WAP is connected by a QuadRax cable, which is essentially formed of wires within wires within wires.

To see how an airplane is outfitted from the inside out with the technology required to enable satellite Wi-Fi in the sky, check out this cool two-minute, 33-second video made by United Airlines:

An aircraft’s interior Wi-Fi equipment is actually capable of far greater speeds than the exterior antennas are capable of receiving, which is why some airlines (e.g., Delta, United and Southwest) opt to use a pre-loaded computer that’s based on board the aircraft and allows a user to stream entertainment to their own device.

The Limitations of In-Flight Wi-Fi

In-flight Wi-Fi has the potential to be quite fast, but all aircraft (regardless of service type) keep it “auto-throttled,” so that data will be equally distributed among its active users. As a result, in-flight internet service will be a lot faster with four users as opposed to 40.

All speed aside, though, the onboard hardware that enables in-flight Wi-Fi has some limitations. For example, the ATG system only has front- and rear-facing antennas and the Ku satellite receiver can only connect to one satellite at a time, which means that both systems can cause a Wi-Fi user to experience short “hiccups” between towers or satellites.

A lonely cell-tower landscape can equal a brief lack of service in the sky. Photo courtesy of Sy / Flickr.
A tower-free landscape can equal a brief lack of service in the sky. Image courtesy of Sy / Flickr.

Technology on the ground has its own constraints. While the US generally has good cell-tower coverage, in states with large stretches of remote land and relatively small populations (e.g., Montana, Nebraska, etc.), cell towers are more spread out, often causing antenna signals to disconnect until the next connection is made. Meanwhile, in the North and South Pole, cell towers aren’t available and satellite connection is fairly difficult to achieve. Along the same lines, in Russia and China, restricted Wi-Fi access is generally due to political policy. Most of the time, your flight crew is aware of where you’ll lose connection and they’ll disclose that early in the flight.

Wi-Fi systems break every day, but most of the time it’s due to something simple, such as a loose wiring connection or a broken antenna. Inoperable Wi-Fi isn’t a safety-critical aspect of flight, so unless there’s a major problem, it will never cause a delay of departure. Typically, inoperable Wi-Fi requires some mild troubleshooting at an overnight maintenance check — and unfortunately, flight attendants aren’t avionic technicians and generally can’t do more than give it the old “turn it off and turn it back on again” trick. So please, be nice to your flight attendant when your Wi-Fi goes out — they may not be able to repair it, but they can still save your life in the event of an emergency!

Looking Toward The Future 

The new ATG-4 service, which adds two additional side antennas to the side of the airframe and increases the connectivity with the ground, is currently being added to some commercial aircraft. Testing of ATG-4 on Gogo’s 737-500 flying test bed proved that its connection was strong enough to stream video. However, the auto-throttle feature mentioned above is likely to reduce the available data depending on passenger usage.

An ATG 4 antenna located on the side of the aircraft, increases ground based connectivity. Photo by the author.
An ATG-4 antenna located on the side of the aircraft increases ground-based connectivity.

Meanwhile, the dome-shaped Ku-Band housing that sits atop aircraft is steadily getting thinner. Gogo claims that its new satellite-based 2Ku service will have a dome that’s only 17mm thick and delivers speeds of up to 70 Mbps. Although the dome’s size might not seem like a big deal to a passenger, it’s of great concern to an airline — the current dome models carry a 400- to 600-pound fuel penalty for each flight! Reducing the size and weight of these domes could save thousands of gallons of fuel in a year and reduce aircraft emissions.

As aircraft such as the Boeing 787 and Airbus A350 enter service, the airlines will continue to push the envelope of in-flight amenities. Wi-Fi providers have made strides to mimic the speeds offered in homes and offices in order to provide a seamless in-flight transition for both business and leisure travelers. When booking your next airline ticket, look for the little Wi-Fi symbol in the aircraft’s details to save you the headache of guessing if you’ll be able to send emails, surf the web or simply get some work done on your next flight.

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