Here are a couple of articles that describe the isolation of APV.
Links provided for each article.
A modified enzyme-linked immunosorbent assay for the detection of avian pneumovirus antibodies Journal of Veterinary Diagnostic Investigation, Vol 12, Issue 4, 381-384
S Chiang, AM Dar, SM Goyal, MA Sheikh, JC Pedersen, B Panigrahy, D Senne, DA Halvorson, KV Nagaraja, and V Kapur
Link:
http://jvdi.org/cgi/reprint/12/4/381?ijkey=980184e7e3b9bf1441a41f8541f6d84e0e421fd2Isolation of avian pneumovirus from an outbreak of respiratory illness in Minnesota turkeys Journal of Veterinary Diagnostic Investigation, Vol 12, Issue 2, 166-168
SM Goyal, SJ Chiang, AM Dar, KV Nagaraja, DP Shaw, DA Halvorson, and V Kapur
Link:
http://jvdi.org/cgi/reprint/12/2/166?ijkey=778bb6e8ee74b0bc0f0bfaf8d465942c7d6e673d