From what I remember of flying the 146-200 many years ago, with a TOB of 77, you would not be wanting to fly much more than 2 1/2 hours plus reserves to remain comfortable. The RJ85 was not that much more efficient, 4:22 endurance sounds very, very optimistic to me unless this aircraft had a singnificant increase on the 146-200's MTOW of 42T.