jgg     2014 34 (4):  149-152    ISSN: 0412-1961  CN: 21-1139/TG STUDY ON THE METHOD TO EVALUATE HELIPORT CLEARANCE  BASED ON AUTOCAD VBA 1）Air Force Engineering University，Xi’an 710038 2)Air Force Logistics，Beijing 100005 3）Air Force Defence Six，Hengyang 421001 Received: 2014-04-09  Revised: null  Online: 2014-07-22 Supporting info