China sent armed trainer jets to drive away Philippine light aircraft over the disputed Scarborough Shoal on Wednesday, in a potentially more cost-effective tactic for its increasingly frequent air confrontations over the South China Sea. At least three JL-10 trainers carrying PL-5 air-to-air missiles were involved in the incident over the shoal, according to a video clip posted to social media by the People’s Liberation Army Southern Theatre Command. The footage showed the Chinese jet’s...