The NBC News article Next-generation satellites gave federal officials key data in Boeing 737 Max investigation says:

The Federal Aviation Administration, or FAA, grounded Boeing's 737 Max airplanes on Wednesday, after receiving data from air traffic surveillance company Aireon about the deadly crash of Ethiopian Airlines Flight 302.

Aireon's system piggybacks on Iridium's network of 75 satellites. Expected to become fully operational in a few weeks, Aireon can track airplanes anywhere on the planet. But the company's data is already proving to be critical, as Aireon said in a statement to CNBC that "the system was able to capture information associated with Flight 302."

While Aireon declined to make company officials available for an interview while the investigation is ongoing, the company said it is working with federal officials to provide them with raw data. Even though the Aireon system has not been fully rolled out, the company is able to provide investigators with information about an aircraft's location, velocity, altitude and more.

Since the Aireon systems are physically attached to the Iridium Next satellites, they share the same orbit and attitude control, and most likely power and some other bus functions as well like thermal management.

But do the Aireon systems use Iridium systems to communicate to the ground, or do they make their own contact with their own ground stations?

I wonder if being attached to a data communications and IoT-like service-providing satellite, the Aireon systems could just use Iridium's data messaging service directly?

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    $\begingroup$ I have no info from Aireon, I haven't tracked them at all in the news (I'll fix that shortly). But this should be the seed of an answer - the NEXT birds are operating now: spacenews.com/… $\endgroup$ – Saiboogu Mar 15 '19 at 0:14
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    $\begingroup$ @Saiboogu Thank you for that! I guess the question in its current form is moot. I'll quickly decide if there's any surviving permutation. I didn't realize that almost all of the earlier satellites have already been de-orbited. I guess I'll never see an Iridium flare. How much longer will we be able to see Iridium satellite flares? $\endgroup$ – uhoh Mar 15 '19 at 0:35
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    $\begingroup$ @Saiboogu based on your news, I've modified the question. Thanks again! $\endgroup$ – uhoh Mar 15 '19 at 0:40

The Aireon Hosted Payload is a 1090ES ADS-B receiver that is attached to Iridium NEXT as a "Hosted Payload".

The paper "Iridium NEXT SensorPODs: Global access for your scientific payloads" by Dr. Om P. Gupta of Iridium Communications Inc. describes in general how Iridium Next payloads communicate with the ground:

Mission data and sensor telemetry and command data for these missions can be transported in near real-time utilizing the K-band network of cross-links between satellites, feeder links to the ground, and teleports connecting the satellites through earth stations to a Multiprotocol Label Switching (MPLS) cloud called the Teleport Network.

[...] Iridium enables a hosted payload command and data path to an MPLS cloud. A customer designated sensor operations facility would manage the hosted payloads in-orbit on the Iridium NEXT satellite using the command and data path provided by Iridium operations.

The Aireon Technical Overview Brochure states:

The Aireon space segment consists of the Aireon receiver, known as the Aireon Hosted Payload (AHP), which is located on each of the 66 Iridium satellites distributed over six polar orbital planes. The AHP receives, demodulates and transfers received ADS-B messages through the Iridium main mission payload, which is routed over crosslinks between Iridium satellites and downlinked to an Iridium teleport network before reaching the Aireon ground segment.

To summarize, the Aireon Hosted Payload transfers the ADS-B data it received from planes to the host Iridium satellite, which then transmits the data via crosslinks with other Iridium satellites to an Iridium ground station. It does use Ka band for this, which is used with larger, stationary receivers on the ground, and not the L band, which typical satellite phones use. Iridium's Teleport Network (TPN) then transmitts the data to Aireon's Hosted Payload Operations Center.

According to this pdf by Iridium the data rate for a hostes payload is 100Kbps on average and the payload gets 50 W of power on average.

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    $\begingroup$ @uhoh I meant by wire. 'transmit' might be a poor word choice, due to me not being a native speaker. There exists an Interface control definition for how exactly the hosted payload communicates with the spacecraft, but it might not be publicly available. $\endgroup$ – KarlKastor Jan 16 at 14:12
  • $\begingroup$ I changed it to "transfers", is that okay? $\endgroup$ – uhoh Jan 16 at 15:15
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    $\begingroup$ @uhoh that is probably a better word, thanks! $\endgroup$ – KarlKastor Jan 16 at 21:59

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