ADS-B diversity in AK, HI being considered?

[Rich]

I received a link from AOPA to an equipage questionnaire from the FAA. It appears they are considering utilizing a space-based system in these states. I don't know that it's being considered a mandate, but basically I think they are considering the (presumably) Aerion system to augment coverage in these states due to the difficulty of getting desired coverage using ground-based towers. The questionnaire basically asked if I fly in those states (no) and what kind of transponder/antenna I have in the plane.

[Lou]

I agree Rich, sounds like they are looking at Aireon for coverage.

This antenna diversity thing is going to be a sleeper issue I feel, and when it wakes up it’s going to create a bunch of compliance issues again. I am getting my GTX345R this week. Based on another thread here on the forum, my guy used an internal antenna that I understand is mounted in the tail. He says he’s tested it and it works great. If so, I hope that the powers that be won’t impose a diversity requirement when a performance requirement would make a lot more sense, ie a tail mounted antenna in a composite aircraft must be equally visible from above or below.

[Rich]

I wonder about the efficacy of the space-based solution. Something to consider is the relative distance you'd typically be from the nearest satellite and how many are in view at any given moment. There are 66 satellites in polar orbits about 420 nautical miles above the surface. (This is far lower than GPS satellite height.) The likelihood of one being directly overhead any given airplane at any given moment is nil. So say the typical distance is 600 nm slant-range. So the signal strength seen by one of these satellites would be 1% of the strength seen by a surface station 60 nm away. They seem to be targeting latency of 8 sec. max. This would suggest to me they are expecting to miss some of these signals and start to approach the latency of ground-based radar systems.

I see they figure to support transponders emitting at 125 Watts. My KT74 is supposedly 240 W and the GTX units 200 W. That suggests to me that possibly a single internal antenna mounted in the tail of our glass-fiber planes might suffice, if even that's necessary. (Maybe put dummy antennae on top and bottom for the busybodies?) When I do my next transponder re-certification I might look into having the technician also measure signal strength above the airframe.

[Colin]

Elon Musk has a constellation that would be much more useful. He is already doing a bunch of government contracts and it wouldn't surprise me if he was working out a broadband deal for ATC in there as well.

[Rich]

Elon Musk has a constellation that would be much more useful. He is already doing a bunch of government contracts and it wouldn't surprise me if he was working out a broadband deal for ATC in there as well.

I wonder about this. He currently has permission to deploy 12,000 satellites in different orbital shells. The constellation is primarily designed to supply broadband internet traffic and are not currently licensed for the frequency band used by transponders. The financial success of this venture is not assured.

Canada, BTW, has a 51% stake in Aerion.

[CFIDave]

Elon Musk has a constellation that would be much more useful. He is already doing a bunch of government contracts and it wouldn't surprise me if he was working out a broadband deal for ATC in there as well.

The antenna required for this service is at least the size of a large pizza box, so it might be tough to put on top of your DA42.

[Rich]

Elon Musk has a constellation that would be much more useful. He is already doing a bunch of government contracts and it wouldn't surprise me if he was working out a broadband deal for ATC in there as well.

The antenna required for this service is at least the size of a large pizza box, so it might be tough to put on top of your DA42.

Need to look like the Millenium Falcon

[Colin]

I can put the antenna in the tail cone since it is composite. I'm all set.

[CFIDave]

I can put the antenna in the tail cone since it is composite. I'm all set.

Nope, not unless you want to go back to your DA40. The DA42 fuselage is made of carbon fiber that blocks RF signals, which is why DA42s and DA62s all need an external ELT antenna on top. The fiberglass DA40 gets by with an internal ELT antenna.

[ememic99]

The DA42 fuselage is made of carbon fiber

All DA42 or just newer ones?