Originally Posted by
arcticbull
Important note: The new policy concerning the use of the NEXUS card as proof of identity and documents that denote citizenship does not pertain to the air mode of transportation. Members of the NEXUS program will still be required to carry the appropriate documentation when travelling by air.
To add one more detail, there is an exception to the above if using a NEXUS kiosk at Canadian Preclearance airports. Under that circumstance you don't need a passport for entry by air. As noted earlier in this thread though, it could be problematic if the kiosks aren't working and, again, I wouldn't do it.
http://www.getyouhome.gov/html/lang_eng/eng_at.html