Franz Stephan Strambach, a 31-year-old psychology student, sparked a major security alert in early January as he flew the plane menacingly around some of Frankfurt's tallest buildings, threatening at one point to crash into the European Central Bank.

Speaking to a German news channel live while still in the air, relayed via air traffic control, Strambach said he wanted to pay tribute to Judith Resnik, who died in the 1986 Challenger space shuttle disaster.

He said he did not want to harm anyone but was ready to kill himself. He eventually surrendered.

Doctors at the Clinic for Forensic Psychiatry in the western town of Haina have diagnosed the suspect as mentally ill and thus unable to face a criminal trial, a spokesman for the public prosecutor's office in Darmstadt said.

A final medical report is to be issued in four weeks, after which Strambach is expected to be remanded into a psychiatric hospital.

SPACE.WIRE