I'm not so sure. The same data packet claims that the flight has 2h 25m of flight time left to cover 1167 miles. That works out to 483 mph, which is pretty close to the stated 487 and might be explained by some padding added to the time to account for taxiing.
Unless that 1167 figure is in a different unit it doesn't even come close to working out at 487 knots ground speed.
The blog says the destination was Oakland. The Oakland International Airport is at 37°43′17″N 122°13′15″W. The data packet also contains the current lat and long of the flight as 40.201 and -100.755 respectively. Plugging that in to a distance calculator [2] gives 1163 miles, 1010.6 nautical miles, or 1871.6km. So the distance value of 1167 appears to be miles.
At 487mph covering 1163 miles would take 2.3963039014 hours or ~2h23m. If the speed is knots then it would be 2.08233112598 hours or ~2h5m at 560.4296mph. So mph makes the most sense given an estimated time of arrival of 2h25m.
So I think you are right, the distance appears to be miles and the speed MPH. This makes sense for an in-flight infotainment system on a US domestic flight.
The difference between 1167 and 1163 can probably be explained by the fact that the plane is 6.5 miles in the air traveling at 8 miles per minute and we don't know update interval or if the distance is in the air or on the ground.
I have been on (international?) flights where the in-flight display gave me a choice. It may still be done on the backend but doing that kind of conversion in the UI is at least arguable.
Your ground speed plot hovering around 500 mph would be ~800 km/h which is oddly slow for an airliner, unless you were facing strong headwinds the entire way.
The nautical mile is historically the common unit for marine and air navigation.
Knots are typically used for aviation. Also different planes have their own optimal speeds for efficiency that the airlines aim for so if you know the airframe you can derive what they are most likely targeting. You can also compare the value to the filed flight plan and see if it is similar.
Knots are used for aviation, but this data looks like it's being consumed by the in-flight UI, and most _people_ are not familiar with knots in terms of speed. Indeed, using the UI shows MPH vs. knots. My money is this speed being mph.
One reason I think it could be MPH despite that is because some of the other data seems like it's been processed so that it doesn't need to be transformed any further on the client side before using it in the UI, and the UI displays the speed in MPH.
If I were still on the flight, I could just compare the numbers in these payloads to the MPH number in the UI and confirm.
Based on the lat/long of your destination and the coordinates of the plane I believe the distance and speed actually are in miles and mph: https://news.ycombinator.com/item?id=37694487
Well, most airlines. I think both China and Russia already switched to SI units (so km/h), and supposedly ICAO recommends using km/h but there is exception for using knots and there is also no end date to stop using knots, so everyone just continues to use knots.
It's not that they 'already switched', but rather that early Russian aircraft had used the metric system for instruments and China acquired much of their early aircraft from the USSR.
In the West, it was well into the 50s before knots became conventional. Many (but not all) British and American aircraft used miles per hour, and most of non-communist mainland Europe used the metric system. I am not aware of whether there was some agreement to choose knots, but by the 60s almost all western aircraft had instruments in knots and nautical miles.
