An air force helicopter crash that killed India’s military chief and 13 other people was caused by an unexpected change in weather that disoriented the pilot, a military court said in preliminary findings released Friday.The helicopter was flying through a valley last month with General Bipin Rawat, his wife and 12 other army and air force personnel on board when a change in weather led the pilot to fly into clouds, the court of inquiry said.“This led to spatial disorientation of the pilot…