What happened here?

I was driving past PVD on Saturday afternoon. Clear, unhazy weather, no ground wind. On approach to RW5 was a Southwest 737 that I could tell right away was unusual. It appeared to be too high and misaligned. Sure enough I see the aircraft bank to the right, and go into what appeared to be a steep descent. After about 10 seconds, it banked hard to the left, and now it appeared to be heading in a roughly 005 heading rather than a 050 heading. At this point I could see it was in full flaps, gear down. The aircraft made yet another hard bank to the right, this time appearing to be at least heading towards the airport. It was less than a mile away at this point, but it still appeared to not be lined up with the runway.

I found what appears to be the flight in question: flightaware.com/live/flight/SWA2 … /KMDW/KPVD

Obviously go-arounds and missed approaches are commonplace, and can happen even in good weather. My question is why did the pilot wait so long to declare a go-around, and what might have caused such a strange approach attempt in clear weather like this? I would have thought after the first hard bank correction, I’d have abandoned the approach immediately to avoid a possible problem after it is too late.

I should note that RW5 in Providence, AFAIK, doesn’t have any visual approaches published, plus another RW5 arrival 10 minutes prior was a straight-in, so it doesn’t appear that any NOTAM was declared that would have blocked a straight approach. I was thinking that, given the maneuvers at such low altitude it might have been some random training exercise, but I’m pretty sure the flight I linked to, which originated in Chicago-Midway, was a passenger flight.

S-turns for spacing?

That’s possible, although PVD doesn’t get that much traffic. During peak hours it might get 15-20 flights per hour, if that.

Or the turns were done to bleed off speed.

S-Turns are used all the time here at DFW(Dallas/Ft Worth) to provide separation on approach and to bleed off speed. Each visit I make to DFW I see several approaching aircraft do S-Turns as described in you sighting.