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Comment by madrox | Hacker News Reader

I once forgot to put my cell phone in airplane mode during a flight from London to SFO (and didn't use my phone during the flight). I was rather alarmed to see a flood of text messages from my carrier welcoming me to Iceland, Canada, and the US upon my landing.

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That sounds... Improbable. When you were passing over Iceland you must have been far too far above the antennas to receive any sort of signal, unless it landed there on the way across the ocean?

Can't speak for Iceland specifically, but can confirm that if you fly from Seattle or Portland down to SFO, you follow a corridor of fairly strong mobile coverage most all the way, and it's occasionally usable at cruising altitude for a moment here and there. Definitely enough to get text messages.

This is in fact the real reason that we still have the airplane mode restriction.

A phone at cruising altitude can see and try to connect to a huge number of cell towers at once. Like, orders of magnitude more towers than it would be able to see even from the top of a mountain. Plus, you're constantly disconnecting from some towers and connecting to new ones. This puts a strain on the cell network systems.

One person won't have a negative impact but then you multiply the problem by the number of people who fly daily.

Definitely possible, 100%. Can confirm getting texts at 25k feet while not in airplane mode. I was on a flight from JFK->SEA and got welcome to Canada texts above Toronto area.

I too have gotten similar sorts of texts on my last trans-Atlantic flight from DIA to Frankfurt.

Being 6 miles up and 8 miles horizontally is only 10 miles from a cellphone tower. As rural cells can easily be more than 20 miles this seems reasonable.

I would think the antennas on cell towers are polarized to limit radiated power up.

Curvature of the earth means that an airplane may be horizontal at 20+ miles out, while a surface vehicle is blocked by ground.

Not so much polarised as aimed. I'm not familiar with 5G (which I believe uses phased array beam aiming), but earlier generations had provision to physically tilt aerials in the vertical plane to optimise beam direction.

They are.

Would that do much for multi path bounces etc?

Depends on the base station. We usually point them down and try to adjust the power output not to "spray" the signal all over the place but rather be focused (and save operator costs), however some stations are set on max power and a lot can bounce away, indeed.

The bandwidth required for the initial handshake is very, very, very low. I'm not surprised that in areas with strong enough networks (especially considering there's no visual obstruction towards the skies) that a portion of the connection process would succeed, but it wouldn't be sufficient for anything else (thus the welcome SMSs only arriving far later).

A long time ago when we found out that iPhones were keeping track of where you went, I learned that my phone had associated with some Russian cell towers when I flew over Russia flying from Newark to India, or somewhere like that. It’s highly probable.

This also happens passing over Sydney to Auckland from Singapore.

Yep, flying Sydney to Perth occasionally passes over Adelaide and I’ll notice my phone change Timezone to Adelaide and get a notification or two come through

I have received messages over Russia (traveling from US to India, 2-3 years back). And I received from one more country that I do not recall. It happens.

I have AirTags in a case that is shipped by air a lot (without me being on the same flights) and once I got an updated location in midflight.

I was as surprised as you. We did not land. I do not have an explanation.

This happens to me, too, particularly when I fly in Asia. I collect screenshots of notifications welcoming me to countries I've never been to.

Had the same happen a couple of times on flights to Alaska from the US west coast. Surprised to see messages from Bell Canada

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