The Aero L-39 Albatros represents a second generation jet aircraft desgined and produced by Czechoslovak avation industry during the last thirty years of the 20th century. The L-39 type was designed in close cooperation with the Soviet Union – the likely future main user and client, which planned to use the L-39 as its Air forces basic attack/interceptor jet trainer. The new type was designed to have more powerful engines than the Delfin, and because Czechoslovakia then did not have such an engine, a Soviet engine, the Ivtchenko AI-25 with a thrust of 14,21 kN was selected. This engine was already in use in the Yak-40 jetliner. The AI-25 was modified and upgraded for light combat use by a Czech company Motorlet (Walter).

The first aircraft selected for flying test was the second prototype L-39X-02. Taxi tests started on 25th October 1968, and these were soon followed by the aircrafts maiden flight on 04th November 1968. During flying tests was found that it was necessary to enlarge the engine air intakes to allow better air flow into the engine. Boundary layer control flaps and additional air intakes were tested and installed. Thus the final appearance of the air intakes was changed – they became larger and were moved slightly forward. Company tests were concluded at the end of 1970. After ten more pre-production machines were built, the first aircraft were officially delivered to the Czechoslovak Air Force on 7th September 1971.

The whole initial batch of aircraft were allocated to the Czech Air Force training School in Kosice on 28th March 1972. The prototype L-39X-07 was dispatched to the Soviet Union for Harsh Weather and other flight tests by Soviet Air Force in March 1973. As a result of these tests, the Soviet Union, as the largest potential costumer asked for some changes to the design to be made. These changes were made on X-07 which then served as a basis for design on which all production machines were made for the Soviet Union.

The L-39ZO, in fact a modified L-39X-011 prototype, was demonstrated at the Paris Airshow in 1977. The Albatros made a good impression on the professional aviators at the show. L-39 has been further modified during its production life, and various new versions have entered series production. It was found in early 1980’s that a more powerful variant of L-39 jet trainer was needed. The new L-39MS was the result of that thinking, which was later designated L-59. The L-39/L-59 family is definitely the World’s most widespread jet trainer of its type. Almost 3,000 planes have been produced and in total they have logged more than 4,000,000 flying hours to date.

The L-39 Albatros is two-seat, single engined low-wing monoplane of all metal construction with tricycle undercarriage. The tapered wing is made as one piece with a pair of 1-litre wingtip tanks. Whing mechanisation is with double-slotted flaps. Tail has a tapered horizontal elevator and slightly swept-back vertical fin. The pair of the air brakes is mounted under fuselage in place of the fuselage-wing connection. The fuselage is divided to three parts. In the front part blocks of avionics and communications are located. The center part is pressurized and includes a crew cockpit, followed by fuselage fuel tanks with total capacity of 1,100 litres and engine air intakes. The rear part with tail surfaces is detachable, what allows bettwe access to the engine. The cockpit is accessible by two separate canopies opened to the right (L-39 only). The crew seat on two indigenous VS-1-BRI ejecting seats with parameters h=0, v=150 km/h. Seats can be ejected even through the closed canopy in case of its seperation failure. Both cockpits are fully equipped with flying, engine and systems instruments and communication, weapons and navigation control elements. The instrument equipment differs by aircraft versions according to specific client’s requests and purpose of individual version. All versions and modifications are fully equipped for night and day flying including the bad weather conditions. The undercarriage is retractable, tri-cycle type with low-pressure tires. Main undercarriage legs are equipped with hydraulic brakes and are retracting to the centre of the fuselage. The powerplant is AI-25 (AI-25W or AI-25TL) jet engine with axial compressor with Saphir APU. All L-39 versions are equipped with two or four wing pylons, according to the version. A various weapons and special equipment can be attached on those underwing pylons, like drop tanks, bombs, unguided ocket pods, machine gun pods, reconnaissance pods, and Air-to-Air missles.

The L-39 remains into the 21st century a primary interceptor fighter and combat trainer in much of Eastern Europe, Africa and South America.