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I’ve racked my brain and Google for a few years and can’t find an answer. I’m hoping someone here can help. In 1979 I flew from Chicago to Cologne, Germany. I distinctly remember the pilot informing us in an announcement that in a minute we would hear a loud boom and to not be alarmed. It was the sound of us breaking the sound barrier. It was my first ever flight when I was 17. I thought I kept the ticket, but can’t locate it. Any idea what the plane would have been? Concorde? Or were there other planes that did this is ‘79 over the ocean?

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  • $\begingroup$ Was this a scheduled flight? $\endgroup$ Jan 11 at 20:49
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    $\begingroup$ Umm... You don't hear a boom if you are inside the airplane. $\endgroup$ Jan 11 at 20:51
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    $\begingroup$ In a strong enough tail wind conventional airliners have had a groundspeed faster than the speed of sound, but of course it's the airspeed that matters: washingtonpost.com/weather/2019/02/19/… $\endgroup$ Jan 12 at 12:44
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    $\begingroup$ That's not how sonic booms work. The sonic boom is continuous. That is, it is not a single boom but a constant loud RAWRWRRRWWRRR from the moment the plane breaks the sound barrier to the time it slows down below the speed of sound. The reason people on the ground hear a single "BOOM" is because the're standing at a single place. If you place an array of microphones along the flight path and combine all their outputs it would not be a single boom but a non-stop RAWRRWWRRWRRR. Of course, you cannot hear this if you are on the plane generating the "BOOM" $\endgroup$
    – slebetman
    Jan 13 at 4:28
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    $\begingroup$ The more likely cause of that boom would be another plane nearby flying past at more than Mach 1. $\endgroup$
    – Hobbes
    Jan 14 at 20:02

3 Answers 3

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Although Concorde flew to many cities on charter flights, including to Cologne and Chicago, it is pretty unlikely that you flew on Concorde between those two cities. Not that it was impossible, as in theory there could have been charter flights between Chicago and Cologne with refueling stops in New York and either London or Paris. And of course the over land segments would not be supersonic. Not really practical from a time savings standpoint, but that wasn't the point, people just wanted to ride on Concorde.

However as explained in this answer, no you would not have heard a sonic boom if you were on Concorde. And since all Concorde pilots knew this they would not have made such an announcement.

What I suspect happened is that you were on a regular flight across the Atlantic, and your pilot became aware that Concorde would be passing relatively nearby (likely at a much higher altitude), and they thought that there might be a sonic boom heard and that it might alarm the passengers, so they made an announcement about it. In that case you either misheard or misremembered exactly what the pilot said.

See Did Concorde's sonic booms affect other air traffic?

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  • $\begingroup$ This makes even more sense based on the other answer saying ATC would warn nearby traffic about it. $\endgroup$ Jan 15 at 3:00
  • $\begingroup$ There's be a separation of at least about 10km between Concorde and any other airliner on the route because of the different cruise altitudes, not even taking into consideration the different airways. $\endgroup$
    – jwenting
    Jan 15 at 6:24
  • $\begingroup$ @jwenting - so does that make it unlikely, extremely rare, or just not something that happened every day? Concorde cruised between 55 and 60,000 feet, airliners typically between 35 and 40,000 feet. That's a vertical distance ranging between 4.5 and 7.6 km. During climbout Concorde went supersonic at around 40,000 feet, not sure how low it remained supersonic during descent. Concorde's sonic boom was clearly heard on the ground when it was cruising at 18 km, otherwise it wouldn't have had land overflight restrictions. Of course the boom diminishes as you get further away from the flight path. $\endgroup$ Jan 15 at 7:37
  • $\begingroup$ @StevePemberton at the time airliners rarely flew higher than 35000ft. Most flew around 30000. You simply wouldn't see or hear Concorde. The overland restrictions were because a) it'd fly a lot lower there (takes time to climb) and b) politics (mostly b) $\endgroup$
    – jwenting
    Jan 15 at 10:06
  • $\begingroup$ @jwenting - I think the U.S. restrictions were mostly based on public sentiment in an environment where everyone from Juan Trippe on down thought that supersonic airliners would soon replace many if not most subsonic airliners, just as jets by that time had pretty much replaced piston props. The thought of enduring multiple sonic booms per day was not appealing. Of course in reality the Concorde flight rate was minimal. Was Concorde allowed to fly supersonic over Europe or was it prohibited there also? I am only aware of the Malaysia and India restrictions, which some suspect was political. $\endgroup$ Jan 15 at 18:42
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It is extremely likely that you misremembered this, or alternatively that the pilot was making a joke.

Reasons for this:

  • There has only ever been one supersonic airliner in the western world, and that is Concorde.
  • Concorde was only operated by British Airways and Air France. Neither of them flew scheduled flights from or to either Chicago or Cologne. It's technically possible that you misremembered a flight that flew something like Chicago->New York->London->Cologne with Concorde as the middle leg, but I assume you would have remembered that detail.
  • While Concorde did fly charter flights, such a flight would have been extremely memorable, far above the level of "I'm going to Cologne and it happens to be on a Concorde".
  • When you are inside a supersonic aircraft you do not actually hear the sonic boom.
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    $\begingroup$ Actually Concorde flew to a lot of different cities on charter flights, hundreds actually, including both Cologne and Chicago. In fact roughly half of all Concorde flights were charters, especially holidaymaker flights during the tourist season. Of course they would not be supersonic during the land portion of the flights. And to your point there would not have been a nonstop flight between Chicago and Cologne. But there could have been a direct charter flight between those two cities, refueling in New York and either London or Paris. $\endgroup$ Jan 12 at 0:28
  • $\begingroup$ If you think that's possible then it would make a good answer. $\endgroup$ Jan 12 at 0:48
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    $\begingroup$ I think your answer is correct because sonic booms are not heard in the plane creating them. $\endgroup$ Jan 12 at 1:39
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The most likely explanation is that the pilot knew that he had taken off one or two planes sooner than either Concorde, Tu144, or (much less likely that he would know) a military jet, and therefore knew that it was about to be overtaken.

As others have already said, you wouldn't hear a boom inside the aircraft that caused it, but the boom is essentially three-dimensional, so propagates all round, (not just towards the ground) so would be audible to any aircraft nearby.

There are so many reasons why you would have known that it was Concorde that you were on, that it is totally unreasonable to think that it was indeed Concorde that you were flying on.

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