Jet extreme turns over SJ downtown approach to SJC?

A few minutes before PDT Fri 2006-09-29T20:00-0700 I was in San Jose
coming up US-Ca-I-280 from US-101 towards 7th St and Ca-87 exits, and
saw a large airplane (commercial passenger airline sized, although
could have been fedex?) take a hard turn (I am pretty sure a turn to
the right), somewhere between 50 and 70 degrees away from horizontal,
wings looking from my angle close to buildings, then level out within
a second or two, then a few seconds later, a hard turn in the opposite
direction about same angle from horizontal, also leveling out within a
second or two again, and both times very close to the buildings.
After the second turn, I couldn't see it any more since it was
shrouded by ground features, when I was approaching US-Ca-I-280 N -
Ca-87 N exit lane, nor did I see it later as I entered Ca-87 exit
ramp.

It was so strange that I drove to the airport to see if anything
happened. Everything seemed normal; I didn't see any smoke, fires on
the way by the freeway or at the airport when I got there, crazy
acting people, equipment on the airstrip, etc.. Because of nazi
driving and parking rules in the airport, I couldn't pick a random
person for a conversation to ask stuff about it. It was extremely
busy at the airport at that time.

Why would a plane do such a maneuver?

What is the experience of those on the plane?

How safe is such a maneuver?

Sunday night (2006-10-01) at 20:15, I saw a similar plane come into
the SJC airport landing approach queue at a sharp angle, with a
similar type of flying behavior to the one I saw Friday. This time it
was somewhere between Willow Glen and I-280 when it came in to its
slot. I didn't see it after that.