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I was looking for air brake pictures on different fighters, and then I saw a Tornado using afterburner and air brake at the same time! Air brake duty is to reduce speed, isn't it? So why would a fighter burn so much fuel to increase thrust and then use speed brakes simultaneously?

Afterburner and Air brake

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The first photo is from the Tornado Role Demonstration Team's display at RAF Leuchars in September 2012 (source).

That Sep '12 show or its preparation is on YouTube. Most of the instances of the air brakes as seen from the cockpit (looking behind) are followed by the swing-wing extending and the afterburner turning off (you can tell from the sound of the variable nozzle actuators).

While the photos are cool, I'd say it's just perfect timing before the pilot turned off the afterburner while slowing down.

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Such example (above) can be seen after 7:40 in this video. Notice the wing position, and from the video notice the aforementioned sound once the wing is extended.

Another possible reason is slowing down for the spectators to see and hear the afterburner. That can also coincide with the fake bomb drop – a pyrotechnic wall of fire, the smoke of which can be seen in the first photo in the question (example below).

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An RAF Tornado GR4 carries out a mock bombing run (BBC)

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While the pictures above are most likely a result of the reason posited by ymb1 (showing off max blast while staying subsonic for the crowd), using afterburner with speedbrakes to reduce weight is a known practice in the fighter community, in line with Kolom's answer. Even if an aircraft is equipped with a fuel dump system, environmental restrictions and standard operating procedures limit the altitude at which fuel may be dumped; if already below that floor, using afterburner with speedbrakes extended is a practical way to reduce landing weight. I don't have any specific sources to cite, just drawing on my experience as a naval aviator.

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  • $\begingroup$ In KSP I've had to use brakes as control surfaces when things go wrong. Is there any possibility this is poor man's thrust vectoring? Say, if you wanted to do a back-flip into a stall on a dime. $\endgroup$ – Mazura Sep 17 '19 at 2:55
  • $\begingroup$ @Mazura: I'd guess that's unlikely; fighters have large control surfaces that give plenty of control authority even at low speed. Possibly if your elevators are damaged, and the speed brakes aren't at the centre of gravity or lift... If you wanted to perform a cobra maneuver you'd maybe have afterburners on (for thrust to hold up the plane's weight) and speed brakes on (for the speed-limiting effect, not extra control authority). But according to Wiki, you normally apply thrust part way through. $\endgroup$ – Peter Cordes Sep 17 '19 at 3:30

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