Task: Summarization / Bullet points
User instruction:
The Learjet 50 series was first announced at the 1977 Paris air show with larger cabins than the existing Learjets. The series was to have three variants, the Learjet 54, 55 and 56 but only the Learjet 55 was built. The Learjet 55 was a low-wing cantilever monoplane with NASA-developed winglets. The aircraft has a T-tail and is powered by two Garrett TFE731 turbofans mounted each side of the rear fuselage. It has a retractable tricycle landing gear and an enclosed cabin for up to ten passengers and a cockpit for the two crew. Construction of the Learjet 55 began in April 1978 after extensive testing and work on the wing design which came, initially, from the Learjet 25. The Learjet 55 first flew on 19 April 1979. The first production aircraft were produced starting 18 March 1981. In total, 147 Learjet 55 aircraft were delivered. 
Summarize in bullet points in chronological order in Korean.

Evaluation criteria:
In the summary, the events of 1977 (Paris Air Show announcement), 1978 (airframe design launch), 1979 (first flight), and 1981 (start of mass production) must be mentioned in chronological order.
The summary must be in bullet points.
The summary must be in Korean.