Photographer: Chris Stowers/AFP/Getty Images

Taiwan has grounded its entire fleet of F-5 fighters after two of the jets disappeared over the ocean, renewing worries about the island’s aging military hardware.

Rescuers are searching for one of the pilots after the Taiwanese F-5 fighters collided at 3:06 p.m. Monday during training, the National Rescue Command Center said in a text message. The pilot of the other plane was found unconscious at sea and later died of his injuries.

The jets disappeared from radar screens 1.4 nautical miles east of Mudan Township, in the southern county of Pingtung.

Taiwan’s Presidential Office said in a text message that the air force had been ordered to clarify the cause of the accident.

Taiwan manufactured 242 single-seat F-5s and 66 two-seaters under license from Northrop Corp. between 1973 and the mid 1980s, making it at one point the world’s biggest user of the plane, the island’s defense ministry said in a Facebook post in 2014.

A Taiwanese F-5 fighter crashed and its pilot was killed during a training exercise east of Taiwan in October last year. The pilot, who had ejected and was rescued, later died despite hours of emergency treatment.

The next month, an F-16 was lost off the east coast minutes after taking off from a base in Hualien.

Taiwan plans to retire its F-5 jets in 2026, when the U.S. completes delivery of 66 F-16Vs ordered in 2020, CNA reported in October, citing an unidentified military source.

Last January, the island’s most senior uniformed officer and 12 others were killed when the helicopter they were traveling in went down in bad weather in mountains south of Taipei. Two pilots also died when their helicopter crashed following military exercises in July.