TAIPEI (Reuters) - Taiwan’s air force is no longer scrambling each time Chinese aircraft encroach on its air defence identification zone but tracks the intruders with ground based missiles instead to help save resources, a senior official said on Monday. Taiwan’s air force has repeatedly scrambled to intercept Chinese jets in recent months, and the United States approved in July a possible $620 million upgrade package for Patriot surface-to-air missiles to Taiwan.. Twenty Chinese military aircraft entered Taiwan’s air defence identification zone (ADIZ) on Friday, in the largest incursion yet reported by the island’s defence ministry and marking a dramatic escalation of tension across the Taiwan Strait. Though they have not flown over Taiwan itself, the flights have ramped up pressure, both financial and physical, on the air force to ensure its aircraft are ready to go at any moment in what security officials describe as a “war of attrition”. Speaking in parliament, Deputy Defence Minister Chang Che-ping said that initially fighter jets were sent out each time to intercept the Chinese aircraft, whose missions are concentrated in the southeastern part of Taiwan’s ADIZ. As that took up valuable time and resources that was then changed, with Taiwan sending slower aircraft up if China did too, but that has changed too, Chang added. “So we now largely use land-based missile forces to track them. We are considering the war of attrition issue,” he said. China claims democratic Taiwan as its own territory and has never renounced the use of force to bring the island under its control. While Taiwan’s air force is well trained, it is dwarfed by that of China’s. Taiwan’s Defence Ministry has spoken of the repeated missions, along with its aircraft being “middle-aged”, leading to a huge increase in maintenance costs not originally budgeted for. The defence minister said in October that Taiwan had spent almost $900 million so far in 2020 on scrambling its air force against Chinese incursions, describing the pressure they are facing as “great”.