The increasing number of air force incursions from China is starting to fray nerves among ordinary Taiwanese, who wonder if their heavily armed political rival finally plans to attack after decades of threats, polls and analysts say. The People’s Liberation Army Air Force has increased the frequency and number of flights over a median line between the two Asian neighbors in the past four months, according to reports from Taiwan’s Ministry of National Defense. Eighteen Chinese military aircraft passed through Taiwan’s airspace Friday followed by 19 on Saturday, the ministry said. Saturday the planes flew in a formation designed to attack from the front, rear and both sides. Some aircraft were sighted in Taiwanese airspace over waters about 80 kilometers from Taiwan itself, according to maps...