# Can a sonic boom arrive before the source?

I'm on the ground, a fast jet flies from very near to the ground, I hear the sonic boom soon, but after the plane passes my point, right?

The real question I'm trying to solve is this:

I just heard an explosion-like sound, and then heard a jet pass. So this means there was an explosion. Am I correct?

One thing I doubt is that the "normal" sounds I heard after could also be "lagged", so it might have confused me about the timing, but I think that wouldn't make a big difference.

• If you were standing in a road and a car travelling faster than the speed of sound came at you, it would hit you before you heard it. Perspective may change this when you add in altitude and curvature of the earth. Unless you are talking about military aircraft I doubt what you heard was a sonic boom. Commented Jul 16, 2016 at 1:49
• For all I know, you could have heard the sound of the jet engine. They don't allow planes flying at supersonic speed over the US unless you are outside of it, then it might depend of what country you are in. Commented Jul 16, 2016 at 4:05
• The airplane could break the sound barrier, then slow down again, be overtaken by its shockwave and follow it, right? (I guess that's just a special-case of a non-linear trajectory already mentioned by @mins , anyway.) Commented Jul 16, 2016 at 11:32
• If you were at your house and you heard a sonic boom, someone broke a law/FAA regulation (assuming USA). If what you did hear was a sonic boom, followed by seeing and hearing a jet fly by at low altitude, there would have been 2 planes - you heard, but never saw, the first one, then, alerted by the sound, you looked up and saw & heard the second one. Commented Jul 16, 2016 at 12:51
• Did the OP say that he ever saw the plane? Seems like he describes exactly how a supersonic flyby would sound. 1) aircraft passes overhead before any sound 2) Shock wave would arrive first 3) followed by the sound of the jet. Only one plane required. It may not have occurred in the US and, legal or not, I've heard sonic booms at my home twice. Once there were four in quick succession at the wee hours of the morning. I say wee hours because I nearly peed myself they were so loud. Commented Jul 17, 2016 at 5:16

Assuming the aircraft you saw was traveling in a straight line, then the sonic boom you heard (assuming it was a sonic boom) could not have been generated from that same aircraft. This is because the sonic boom is experienced at an angle back from the flight path of the aircraft.

Many aircraft which are capable of generating sonic booms also happen to fly in groups. Fighter jets are a good example of this. Fighter jets often train in groups of more than one aircraft.

It's possible you may have heard a sonic boom from another aircraft at a higher altitude which you did not see, then you later saw a new aircraft. This is actually very likely, because sonic booms are much more common at high altitude. The atmospheric conditions for creating sonic booms are favorable at high altitude. This is because the speed of sound is much lower at high altitude compered to the speed of sound at low altitude. It is difficult to see military aircraft at high altitude against a blue sky background because the military intentionally paints the skin of the aircraft in a grey color to make it difficult to see against a blue sky. So without a con trail you likely did not see the fighter jet which was flying at high altitude.

Other commenters asserted supersonic flight is not allowed inside the US, but this is not entirely correct. Many restricted airspaces in the US allow supersonic flight. The restrictions on supersonic flight are generally put in place to balance the concern of noise pollution for the population. Some MOA (military operating area) also allow supersonic flight, although usually only at high altitude. Some areas of the eastern US which allow supersonic flight require the pilots to fill out a log stating supersonic flight occurred. However, supersonic flight is easy to do accidentally in many fighter aircraft. The pilot may not realize he was supersonic until reviewing the tapes after the flight. Most airspaces allowing supersonic flight are over sparsely populated deserts of the western US.

Picture credit to Wikipedia

• Thanks for your explanation. Nothing happened that night was assumed to be compliant with the law. And from what we heard, there were 2 jets, but I thought they were flying separately. But you are right, it can be the two of them passing consecutively. Unfortunately I have (or anyone has) too little information to confirm any of this :) But still, thanks.
– jeff
Commented Jul 17, 2016 at 20:00
• Military jets often fly at night with their exterior lights set to only emit in the range which is visible to someone wearing infrared googles. That way the pilots can see each other, but the enemy cannot see them without NVG equipment. Such a scenario is another reason you might not have seen all of the aircraft. Commented Jul 17, 2016 at 20:07
• @Lnafziger this might be theoretically possible, but in practice the aircraft would not be able to slow down sufficiently during the time the last sonic boom emission travels to the listener. Fast moving aircraft have a great deal of momentum, and deceleration happens slowly. Even if the plane changed speed from 800 knots to 0 knots instantly, the sound would reach the observer in just a couple seconds. And the aircraft would still be in view. A better question is "could the aircraft turn around 180 deg fast enough?" I don't know if it could turn fast enough, but maybe. Commented Jul 17, 2016 at 20:25
• re "other commenters asserted supersonic flight is not allowed inside the US..." -- the OP confirmed in the comments above that they live in Turkey, and this was part of the recent failed coup. I would hazard a guess that a fighter pilot who is involved in a violent overthrow of their country's government is not concerned about a bit of noise pollution. :) Commented Jul 17, 2016 at 20:45
• @yshavit Yea he has other things to worry about now Commented Jul 17, 2016 at 20:50