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Comment by jollybean | Hacker News Reader

The airplane reported both 500AGL and 1NM (nautical mile) which is oddly the exact lower limit for altitude, and the exact limit to distance for 'advanced operating' drone from the airport, as far as I understand. Why those exact legal limits? What are the odds of that?

If the drone operator reported those numbers, they'd only be 100ft outside of where they should be legally.

Since both '500' and '1' are pretty arbitrary numbers, any reasonable margin of error puts a ton of range for the drone to be flying in safety while the pilot being at error. Or both.

This seems to be a 'threshold' issue, not some arbitrary invasion of space, but we'll have to wait for Transport Canada, hopefully the drone will have precise information. Correct me if I'm wrong.

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This is not a threshold issue (other than a Boolean threshold of the drone operator needing to comply with the law and not doing so).

There is no lower limit for aircraft in the process of taking off or landing. I’m much more familiar with US aviation law, so I’ll give you US citation there, but it’s not likely to be wildly different elsewhere.

A fairly typical approach slope is 3°, which would put an aircraft around 320’ above touchdown zone elevation at 1 nm. There is of course some variation above and below that.

There’s no incentive for the pilot to shade or cheat their reported position. They would be legal at 419 feet and 1.625 nm just as well as 500’ and 1 nm.

Canadian regs (US are different here) require that if this were an airport without a control tower, the drone would need to be a minimum of 3 miles away from it. With an operating control tower, the drone operator needs permission and active radio contact with the tower.

The general safe altitude law in the US is 91.119*, which begins: Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes: (Necessary is consistently interpreted somewhat broadly rather than extremely narrowly.)

* https://www.law.cornell.edu/cfr/text/14/91.119

I would mostly attribute it to what the pilots are likely to notice - 500' AGL is a standard call-out on landing approach (not that light aircraft pilots necessary 'call it out' but their Foreflight or whatever very well may have), and the airport in question is actually uncontrolled so "one mile final" would be a common point to make a radio call.

So it's probably that it happened somewhere near those numbers, and they were the references the pilot readily knew of.

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