It wasn’t MSNBC’s chopper, but WNBC’s. This shot is titled MSNBC since it aired LIVE on that channel. This angle was seen for the first one second on NY Channel 4, if that. It was LIVE on MSNBC for the last seconds of the disaster, between the [FOX LIVE] NBC West St. view and the NBC GE Building cam, the latter of which only showed dust. Throughout the day, the NBC network broadcast bits of the shot, which I had to piece together to create a complete version (link 3 above [UPDATE: Quality recording newly available Oct. 2010. Link to come.]).
The LIVE broadcast was made available online at today.msnbc.msn.com, as well as on TV for the 6 year anniversary. It replayed (for example) at 1:21, 2:52 and 6:34 pm on 9/11 (the versions I pieced together).
Raw NIST Cumulus file: WNBC Dub6 22, NBC Atlanta3 28
MSNBC – Chopper4
YouTube 1, 2 & 3
