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Recently I've seen a Cessna 208 Grand Caravan flying as high as 43,000 ft MSL on flightradar24. Perhaps it's still in the air if you look over eastern Canada (the Grand Caravan has a unique shape from the other planes on fr24, looking like a sailplane). The Grand Caravan is unpressurized, does that mean all passengers wore oxygen masks? Or was it just fr24's error to portray a Grand Caravan that high (and if so, how would such error occur)?

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    $\begingroup$ I wouldn't want to fly to FL430 on oxygen. $\endgroup$
    – Zeiss Ikon
    Feb 7, 2022 at 18:23
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    $\begingroup$ You'll likely get the bends after 30 minutes at that altitude. You don't really want to spend significant time above 30k unpressurized. $\endgroup$
    – John K
    Feb 7, 2022 at 18:46
  • $\begingroup$ @ZeissIkon I think it would be a fascinating experience. $\endgroup$ Feb 7, 2022 at 18:59
  • $\begingroup$ Linking to the FR24 track would be very useful in this case. Write down the URL on a piece of paper if you have to, if you can't copy/paste... $\endgroup$
    – randomhead
    Feb 7, 2022 at 19:30
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    $\begingroup$ Voting to close as "needs more details" until you can provide a flight-tracking link or other identifying information. In particular, if you have the registration number of the aircraft we may be able to look it up and see that it used to be assigned to a C208 but is now (e.g.) a Lear 75. In any case, asking a question about a track observed on FR24 and failing to identify it any more than "Over Eastern Canada an hour or so ago" is superbly unhelpful. $\endgroup$
    – randomhead
    Feb 7, 2022 at 19:52

3 Answers 3

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The Wikipedia page for the Caravan family lists the service ceiling at 25,000 feet. I think it's very unlikely someone got one (any version) as high as 43,000, and less likely yet on oxygen in an unpressurized cabin.

That means this is probably an error in altitude reporting. How such an error could occur is difficult to say -- I'm not familiar with fr24, so don't know how they obtain altitude data.

Note also that "At 40,000 feet, 100-percent unpressurized oxygen provides the equivalent of ambient air at 10,000 feet." It would be unnecessarily risky to fly higher than this without some kind of pressure support, and would require full mask oxygen, not the cannula often used by private pilots who venture about 12,000.

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    $\begingroup$ Or the wrong transponder code... $\endgroup$
    – Sanchises
    Feb 7, 2022 at 18:43
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    $\begingroup$ I worked at a busy enroute facility. I would get calls asking that we relay a message to a pilot and the caller would provide the location and altitude. Sometimes, the aircraft would not even be in our facility's airspace, much less the location/altitude given. The online tracking tools are generally fairly good, but do have some problems now and then. A couple of times the caller would argue, and I would point out that I was using a certified ATC system, and they were not. $\endgroup$
    – RetiredATC
    Feb 7, 2022 at 18:47
  • $\begingroup$ It might have been a wrong transponder code indeed, perhaps. $\endgroup$ Feb 7, 2022 at 18:51
  • $\begingroup$ It's also possible that the pilots thought "If our passengers are forced to wear FFP2-masks, why not just let them wear oxygen masks and take them to altitudes they likely never were before in their lives". Service ceiling is not the same as absolute ceiling, after all. $\endgroup$ Feb 7, 2022 at 18:57
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    $\begingroup$ "Service ceiling is not the same as absolute ceiling, after all." While true, they seldom differ by this kind of margin. Usually you can trick, cajole, or coerce an aircraft a few thousand feet above service ceiling -- unless the service ceiling is a limitation of the onboard oxygen system, for instance, which would mean the airplane can fly higher, but crew and passengers cannot. I'm pretty sure oxygen is good above FL300, but it seems to be limited to about FL400 without pressure support. $\endgroup$
    – Zeiss Ikon
    Feb 7, 2022 at 19:07
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Here’s a ForeFlight screen shot of the local flying club’s Cessna 172 pretending it’s a U2 87,500'. So I’m guessing bad data.

Cessna pretending it’s a U2

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    $\begingroup$ Or maybe it's a U-2 pretending to be a Cessna of a local flying club 😏 $\endgroup$
    – Jpe61
    Feb 8, 2022 at 11:26
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Flight Radar 24 works mostly by receiving and decoding ADS-B (Automatic Dependent Surveillance - Broadcast) messages from aircraft. In these messages, there is no data on the aircraft type.

To display the information about the aircraft, Flight Radar 24 has to use the 24-bit address (a code similar to a MAC address in networking) that is uniquely assigned to an aircraft, and look up the aircraft information in a table in their database.

What happened here, is likely one of the following:

  1. the aircraft was flying at 43 000 ft, but was transmitting the 24-bit address of another aircraft (this can happen due to various reasons, from a mechanic putting in the wrong 24-bit address, to electric connection failures). The lookup therefore picked the wrong aircraft (a Cessna Caravan) from the table.

  2. the aircraft was flying at 43 000 ft, and was transmitting the correct 24-bit address, but the table was wrong. This can happen, for example, when a new aircraft is registered on an address that previously belonged to another aircraft (a Cessna Caravan in this case), and the table used by FR24 has not yet been updated.

  3. the aircraft was the Cessna Caravan, but the altitude encoder was erroneously encoding 43000 ft instead of the actual altitude. This occasionally happens, but if the aircraft is receiving Air Traffic Service and is within (secondary) radar coverage the discrepancy would be noticed by ATC very quickly. Depending on the airspace class and the controller workload, the flight may either be allowed to continue based on verbal altitude reporting or the pilot would be asked to land or otherwise leave the airspace.

Without more information about the date, time, location and/or aircraft registration of your observation, it is impossible to discern which of the above cases applied here.

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    $\begingroup$ Would the pilot be asked to land? I thought the controller would ask the pilot to report altitude and proceed with that. $\endgroup$
    – Jan Hudec
    Feb 8, 2022 at 8:42
  • $\begingroup$ @JanHudec It depends a bit on the airspace class and the workload of the controller. If the controller can accommodate the flight based on altitude reporting, then that is an acceptable, albeit temporary, work-around. In other cases, the pilot will be asked to leave the airspace. The pilot may choose to land or proceed to move to Class G airspace or another airspace where no radar services are required for the flight. In any case these kind of errors do not persist for long. $\endgroup$
    – DeltaLima
    Feb 8, 2022 at 8:53
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    $\begingroup$ In the US I would think it exceedingly unlikely that an aircraft would be asked to land or exit certain airspace due to a Mode C failure. There is nothing in the .65 that directly requires that; instead as @Jan said there is a procedure and phraseology to use when the Mode C is off by 300 feet or more (namely, ensure the pilot is using the proper altimeter setting and then trust their reported altitude rather than Mode C). I have even seen a target with Mode C failure permitted to continue flying in Class A airspace. $\endgroup$
    – randomhead
    Feb 8, 2022 at 9:18
  • $\begingroup$ Why does such a good answer have so few upvotes? $\endgroup$ Feb 11, 2022 at 18:50
  • $\begingroup$ @Betternottell that has to do with how this site works. Most of the visits to a question are within the first 24 hours after it was posted. And, as soon as a question has an accepted answer, less people are visiting and voting. My answer came more than 24 hrs after you asked the question. By then, most frequent visitors had seen the question and the accepted answer and so they don't bother to check again. If you want to attract good quality answers, you have to write a good quality question, but also be patient. Don't click the accept mark within 24, perhaps even 48 hours. $\endgroup$
    – DeltaLima
    Feb 11, 2022 at 19:34

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