To be able to schedule my activities, I sometimes would like to approximate ahead of time the wifi speed and robustness of some onboard wifi to know what kind of work I can do on the plane. Given a flight, how can I approximate ahead of time the speed and robustness of the onboard wifi?
Easy: it will NOT be robust and it will be slow!
I don't think I've ever had a flight without interruptions and/or occasional sluggishness. It varies a lot day to day even on the same exact route.
For US domestic you have a good chance of getting at decent WIFI for at least 50% percent of the flight. Anything else is hit or miss. Actually it's mostly "miss" on international long hauls.
I would say that not only is this information not well defined, I would also posit that this information is fundementally unknowable ahead of time by a passenger.
in the very least the following are critical factors:
- In-flight passenger services are not a part of the planes MEL (Minimum Equipment List), so a plane can be dispatched without working Internet
- Planes can also be substituted at will by the airline, so while one particular plane may have a suitable Internet connection, you may not be seated on that plane.
- The overall Internet connection will have a fixed capacity. So the size of the slice you get will depend on the whims of your fellow passengers.
- The internet connection is provided by radio, so the overall quality of the link will be dependent on local weather and atmospheric conditions.
While other focus on what may be wrong with the connection, I would take the opposite approach. Assume the best case scenario (given the parameters of your trip) and then try to figure out what that scenario looks like. Needless to say that you can follow these steps when you are still considering different airlines and routes.
I'd propose a simple checklist that you will go through for your situation. You may view this analysis as a risk assessment which commonly involves risk and uncertainty. In many cases, you're not going to have a certain answer, but you will be able to get an indication based on information on the internet.
1. Find reviews of the wifi covering your route and airline combo
As other have said, you're going to have different experiences with different airlines and their connection may vary with different routes. Just search for reviews that contain the airline name and their (non-hub) destination (that often captures the route).
This step is meant to get an overall indication of the wifi on flights similar to the one you will be taking. If the connections are bad, there will probably be reviews covering that.
2. Find out about obstacles that will surely interfere with wifi
If your route faces specific obstacles (the Atlantic Ocean, some large countries that may restrict on-board wifi) you use those as a search term as well. For example, the wifi on my Qatar Airways flight to Bangkok cut out when flying over India. That's not a coincidence, that's something you can take as a fact and you can plan around that if you research ahead of time.
3. (more advanced) Research the airline fleet and cross reference with route
A plane that's not retrofitted with wifi capabilities isn't going to give you internet access. Since you know what airline you will be flying with, it makes sense to research how many of their planes actually have wifi capabilities. Do all their planes have wifi access or do only specific models have that technology? Depending on the answer you may have to research which planes are actually used on your route. Some of the flight tracking websites keep records of historical flights which may or may not be available for free.
4. Be prepared for disappointment
This is basically covered by the other answers. Despite your own best research, there may be technical difficulties that prevent you from using the wifi. The previous steps are meant to set your expectations given the flight that you will be taking. For a significant part, those other steps will provide good indicators.
In some cases, the other answers will be correct. In some places you can be sure that the wifi will be slow and spotty. But there is no universal law of crappy wifi, I've had some reliable connections flight after flight on specific routes and that's not a coincidence. It simply depends on the quality of the service and how seriously the airline takes their wifi product.
While this only applies to browser activities, one way to find out what in-flight internet will feel like is to simulate it with Google Chrome or a Chromium-based browser.
If you hit F12 in Chrome or a related browser, you'll get the Developer Tools. These include a Network tab. On that tab, there's a dropdown that initially says "No throttling". You can change that to one of several presets, or you can define your own speed to simulate, and the browser will be slowed down to match that speed.
Of course, this won't help you know exactly what it'll be like on a plane unless you know the plane's internet speed ahead of time, but you can use it to gauge your tolerance with low speeds.