Cell Phone and Data Service at 8,000’? Surprise!

Bill Watson

Bill Watson

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Flying back from a trip to Nova Scotia I was surprised to receive a phone call while cruising at 8,000’. We’ve occasionally received a notification or text message while cruising at altitude over the US but never received a phone call (long and clear). I regret not trying an outgoing call but Facebook worked well at all using 5G or LTE.

It seems to me that Canada cell companies don’t do the mumbo jumbo that the companies do in the US to disable cell service at altitude.

Is it justified? Don’t know but it sure was nice!


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Was it a rural area? How fast were you going? These are probably some significant factors in how good your cell coverage is at altitude. In denser areas, the cell antennas will tend to have more downtilt or be aimed more at the ground in order to prevent interference with nearby cells. In rural areas they will be setup to propagate farther. LTE capability is also limited by speed due to such things as cell hopping and doppler effect. If you were in a less dense area doing 120knts, you should have better coverage for instance. I doubt the carriers are artificially limiting aircraft in the US.
 
Vertical pattern main lobe of a cell tower antenna group has beam height of only about 10 degrees. Typical install within a high traffic area, the center of the lobe is depressed a few degrees from the horizon. Out in the boonies, maybe level with the horizon.

Best guess is you were catching a reflected signal from a very distant tower, maybe a hundred miles or more from your flight path.
 
I get signal pretty regularly at 8k. 13k is the highest I've seen anything
 
Even though you were cruising at 8,000 ft did you fail to mention that ground level was 6,000 feet? Therefore cell towers were within reach?

I assume not since you were surprised :)
 
kujo806 said:
Was it a rural area? How fast were you going? These are probably some significant factors in how good your cell coverage is at altitude. In denser areas, the cell antennas will tend to have more downtilt or be aimed more at the ground in order to prevent interference with nearby cells. In rural areas they will be setup to propagate farther. LTE capability is also limited by speed due to such things as cell hopping and doppler effect. If you were in a less dense area doing 120knts, you should have better coverage for instance. I doubt the carriers are artificially limiting aircraft in the US.
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Yes, Nova Scotia by definition is pretty rural. I was doing 155knots plus/minus 10.

I thought cell phone coverage and use in the US was purposefully limited by canceling out calls hitting too many towers at the same time (I swear I heard about that here) but the tilt thing makes some sense. Just totally surprised. It all stopped when we hit rural Maine.

It was a high quality, multi-minute call. And my spouse got on Facebook and enjoyed the time. Oh well.

How do things work in N. Dakota, Montana, etc?


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I can often get coverage at 7.5/9.5 flying over Kalamazoo Michigan and Youngstown Ohio.

I usually aim for urban areas when I need service at altitude so my experience differs from yours.
 
Bill Watson said:
I thought cell phone coverage and use in the US was purposefully limited by canceling out calls hitting too many towers at the same time (I swear I heard about that here) but the tilt thing makes some sense. Just totally surprised. It all stopped when we hit rural Maine.
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The "too many towers" issue was part of the rationale for not allowing cell phones in airline flights. It was more of an FCC issue than an FAA one. I don't believe that anything was done technically to limit it, just regulatory limits. I also believe it's not an issue with more modern systems, can't provide a technical explanation.
 
I think many years back there was a "ping ponging" issue when the phone saw multiple sites at a time and was traveling fast. I tend to remember CDMA having this limitation pretty bad due to soft hand offs. It was primarily a computational limitation i think. Now a days computing power is much higher and lte is more forgiving with such things in how it works.
 
The restriction is buried in the FCC regs for the original AMPS system. The way frequency reuse worked in that was that the system would command your phone to lower its power as necessary to minimize the number of cell towers it hit. If you got a little altitude on the system, you messed that up badly as you lit up the entire system even at the lowest power settings.

The various spread spectrum technologies used in the past two decades don't have that issue. The reason it doesn't work well at altitude is simply that the antennas are designed not to radiate energy where they don't expect there to be any customers.
 
I was flying about 9000' south of Tucson when I made a successful phone call; however, the call was made via a Flagstaff cell tower hundreds of miles away. Flag is 7000' altitude and the tower could have been on a higher hill top.
 
Snowmass said:
I was flying about 9000' south of Tucson when I made a successful phone call; however, the call was made via a Flagstaff cell tower hundreds of miles away. Flag is 7000' altitude and the tower could have been on a higher hill top.
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How do you know what tower was used?
 
I got a burst of notifications (texts, emails, voicemail) at FL380 yesterday. Oops. It was all bad news, totally ruined my enjoyment of an inflight movie, so that’s the real reason to use airplane mode.
 
SMS (texts) works with a lot less signal capacity than what is necessary to get voice or real data through.
 
Snowmass said:
I was flying about 9000' south of Tucson when I made a successful phone call; however, the call was made via a Flagstaff cell tower hundreds of miles away. Flag is 7000' altitude and the tower could have been on a higher hill top.
Click to expand...

I'd be impressed to know that a three-watt cell phone made a 200-mile trip to a tower, even if the signal was line-of-sight.
 
Rgbeard said:
I'd be impressed to know that a three-watt cell phone made a 200-mile trip to a tower, even if the signal was line-of-sight.
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This, exactly.....so I get receiving bounced or "reflected" signals....but it also hasta make the round trip and be transmitted back.

btw....I regularly am able to call at 5,000 feet over the flat lands.
 
Bill Watson said:
How do things work in N. Dakota, Montana, etc?
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I live in ND and always have service up to at least 6-7000. Sometimes higher. I cruised to MN once at 9500 and service was spotty, but usable enough.
 
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