While fooling around on Metropolis at Heroic difficulty, I noticed this crashed Phantom. Normally this Phantom drops off the second Wraith tank when you advance far enough along the bridge. However, in this case, when it appeared, I was with two marines in a Warthog. When the Phantom and its Banshee escorts arrived, I returned to the beginning of the bridge to retrieve the Scorpion tank. When I advanced 3/4 along the bridge, I found the Phantom embedded in the bridge surface, with the Wraith still attached below.

In the first sequence. the marines kill the Wraith pilot, and shortly thereafter, I think you can hear the Wraith fall and hit the ground. In the second sequence, I used the Scorpion to push the Phantom free; the Wraith later falls, more or less intact.

As I wasn't on that half of the bridge when it happened, I don't know how the Phantom got stuck in the bridge to start with.