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Currently, there is an ongoing Search and Rescue mission being conducted by Canada, the United States, and commercial operators to find and rescue the crew of the OceanGate Titan submersible vessel (submarine) in the area of the Titanic.

Reportedly, this Search and Rescue mission involves multiple aircraft from Canada and the United States, including multiple C-130 aircraft as well as at least one aircraft providing sonar equipment.

Why are these aircraft not visible on sites like ADS-B Exchange?

For reference, this is a snapshot of the air traffic reported on ADS-B Exchange at 10:35 UTC on 21 June 2023 (daylight for over an hour in the search area):

ADS-B Exchange screenshot of OceanGate Titan Search and Rescue Area

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2 Answers 2

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ADS-B is line-of-sight. For an aircraft to be visible to an ADS-B receiver, it needs to be above the horizon. The wreck of the Titanic is 600 kilometers from the nearest land, so in order to be visible, an aircraft would need to be flying at an altitude of 28 kilometers/90,000 feet. Going the other direction, an aircraft doing a search pattern at 3000 meters/10,000 feet would only be visible out to 200 kilometers/120 miles.

As DeltaLima notes, many military aircraft don't transmit ADS-B messages, but I don't think that's the case here. I live near a flight path for USAF aircraft, and my ADS-B receiver regularly spots "cargo-like" military aircraft such as the P-8 Poseidon and C-130 Hercules being used here. It's only the combat aircraft that usually fly with ADS-B off.

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    $\begingroup$ You are absolutely right. I was under the impression that ADS-B exchange had some feed from a few satellite based ADS-B receivers, but it turns out all the intermittent oceanic reports are over ADS-C. ADS-B can see a bit beyond the horizon though. At 1090 MHz the signal is following the curvature of the earth a little bit. Under good conditions I have had messages from 700 km away (aircraft at cruise altitude of 38000ft, receiver antenna at ~15 m AMSL) $\endgroup$
    – DeltaLima
    Jun 22, 2023 at 8:57
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    $\begingroup$ I was under the impression that most military aircraft do transmit ADS-B when they don't need to be worried about being tracked, this includes fighter jets and other combat aircraft. I would assume this is for safety so civilian aircraft can stay out of their way. $\endgroup$ Jun 22, 2023 at 16:04
  • $\begingroup$ Since the only aircraft that regularly approaches 90.000 feet is the SR-71, it's handy that it came equipped with all sorts of high resolution cameras. Unfortunately, flying examples are fairly few and far between... $\endgroup$
    – FreeMan
    Jun 22, 2023 at 19:03
  • $\begingroup$ @DeltaLima, you can get the occasional over-the-horizon message (that's probably how G-XLEK is visible in the screenshot in the question), but nothing reliable enough to track the search aircraft. $\endgroup$
    – Mark
    Jun 22, 2023 at 20:42
  • $\begingroup$ @Crazymoomin I see Blackhawks regularly flying by which show up on commercial ADS-B sites, but have never seen a fighter jet... of course, if there's already airspace restrictions in place they probably don't have to worry about civilian aircraft staying out of their way as much. $\endgroup$
    – Michael
    Jun 23, 2023 at 0:41
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The aircraft probably do not transmit ADS-B messages, many military aircraft don't. The only way ADS-B exchange can locate these aircraft in such case is by using multilateration.

Multilateration only works if the aircraft is transmitting messages on 1090MHz AND there are multiple receivers receiving those messages. ADS-B exchange seems to only have intermittent signals from satellites over the ocean.

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Since there is no abundance of receivers in the ocean, multilateration cannot work. Hence nothing is shown.

Please see this answer from Mark as well, it points out that the aircraft are out of the range of terrestrial ADS-B receivers. Since ADS-B-Exchange does not have a feed from satellite based ADS-B receivers, their website does not cover the aircraft over the oceans unless the aircraft report over ADS-C.

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