context: At the time, Kai Mellén, who had about 50 hours of flying experience, flew to Tumpu on a 15-minute first flight on March 15, 1953. Esko Halmeen, a test pilot from a state aircraft factory, was initially supposed to fly the first flight of a prototype that received the OH-YMA license, but due to Halme's delay, Mellén decided to wait and fly the first flight, which had a positive first impression. Despite the possible flaws in the designers' minds, the aircraft's flight performance turned out to be better than expected and no aerodynamic changes were needed. After a few short flights the same day, Mellén flew through Tampere to Malmi Airport in Helsinki. The test flights continued and minor modifications were made to the aircraft to correct minor bugs. Towards the end of the month, the machine was introduced to a guest of invitation, including Professor Bernard Wuollee, Secretary to the Board K. T. B. Koskenkylä and Jorma Serlachius, PIK's first chairman. A couple of months later, on May 1st, 1953, the plane flew over Helsinki in a student rally, including the Praga E.114 OH-PRB of the Academic Aircraft Club. PIK flew a prototype after the first test flights, a fairly thorough test flight program based on US CAR part 3 airworthiness requirements. The aircraft was also flown by Eero Juurikkala, a journalist from the Technology World, whose article on the machine was published in issue 5/1960. [3]
question: When did Tumppu fly his first flight?
answers.text: March 15, 1953