The twinjet has a carbon fibre reinforced polymer wing and was to be powered by Aviadvigatel PD-14 turbofans or Pratt & Whitney PW1000G engines.

The standard MC-21-300 has a capacity of 132–163 passengers in a two-class configuration and 165–211 in a single class, and a range up to 6,000–6,400 km (3,200–3,500 nmi; 3,700–4,000 mi).

By early 2024, it had become clear that the design work and additional testing necessary to use Russian-made equipment would delay the launch date to 2025–2026, and that the aircraft would not meet its original weight, range and operating altitude specifications; additionally, industry analysts questioned the feasibility of the revised delivery timeline because the Russian-designed PD-14 engines were unproven and it was unclear if other parts suppliers could meet production targets.

[9] In Russian: МС‑21 "Магистральный Самолёт 21 века" Magistral'nyj Samoljot 21 veka translates as "mainline aircraft of the 21st century".

In 2013, Russian deputy premier Dmitry Rogozin indicated that it would be designated Yak-242 once it enters serial production, the name of a 1990s proposal of an aircraft of similar size.

[17] In February 2012, Russian deputy prime minister Dmitry Rogozin announced it was slated to begin certification tests in 2015/2016 and to enter production in 2020.

Russian protectionism is hampering access to critical western suppliers for the avionics, landing gear, hydraulics, power systems and engines.

[22] Cracks developed at the point of contact between the titanium beam and the composite wing skin in the wingbox.

[24] After completing taxi and runway roll tests, its maiden flight was scheduled for late May 2017 with Pratt & Whitney Geared Turbofan engines, certified in September 2016 in Russia.

[26] Following this maiden flight, trade and industry minister Denis Manturov claimed it will have 12–15% lower operating costs than contemporaries, generating a demand for over 1,000 MC-21s between 2017 and 2037.

[28] In August 2017, the first prototype performed nine test flights, analysing stability and controllability in various configurations, altitude, altitude/speed sensors accuracy and engine operation.

Its software was adjusted by the results as it was fitted with over 500 strain gauges measuring in-flight loading on the airframe, to verify the initial design, for "several weeks".

[38] It made its first flight on 12 May for 1 hour 7 minutes, reaching 3,000 metres (9,800 ft) and 215 knots (398 km/h; 247 mph), checking its landing gear retraction and testing wing configurations.

[42] On 3 December, a fuselage was delivered to the Central Aerohydrodynamic Institute at Moscow-Zhukovsky for fatigue testing: repetitive loads will simulate 180,000 cycles.

[45] The program cost is 438 billion rubles (US$6.6 Bn)[45] In February 2019, the EASA completed initial certification testing with 2.5-to-4-hour flights up to 10,000–33,000 feet (3,000–10,100 m), including high angle-of-attack and stall onset.

[61] Powered by PW1400Gs or possibly PD-14s for the second half, Irkut guaranteed less than 9,865 kg (21,749 lb) fuel burn on a 1,750 nmi (3,240 km; 2,010 mi) route with a 14-knot (26 km/h; 16 mph) tailwind.

By the end of December 2021, Russian type certification was granted for the MC-21-300 variant powered by Pratt & Whitney PW1000G engines, ahead of its planned introduction with its launch operator Rossiya.

[65] In March 2024, Kommersant reported that the design and testing of new Russian-made equipment would delay the aircraft's service introduction until 2025–2026 and that the MC-21 was currently overweight by 5.75 t (5.66 long tons; 6.34 short tons), rendering it incapable of meeting its original specifications for operating weight, range, and altitude.

[13] United Aircraft Corporation (UAC) subsidiary AeroComposit, a Russian firm, developed the vacuum infusion process to produce the wingbox and wing panels.

The vertical and horizontal fins and wingbox are also composite and the high aspect ratio wing is a supercritical airfoil.

By January 2019, U.S. sanctions against Russia had interrupted the supply of foreign raw materials, on which the UAC relied to produce the composite parts.

The UAC started looking for either domestically produced or Chinese replacements, maintaining that the wing box and consoles would still consist of polymeric composites.

[68] In March 2019, AeroComposit reported that it had produced the first fuselage centre section and wing box from domestic materials.

[citation needed] Russia decided to have both an internal and external supplier for the engine and nacelle for greater flexibility in controlling rate and price.

[72] United Engine Corporation (UEC) planned to deliver five PD-14s for the MC-21 by the end of 2018, to start flight tests in 2019 for the MC-21 variant certification in 2021.

[75] In August 2009, Hamilton Sundstrand, a subsidiary of United Technologies, announced it would provide electric power generation and distribution equipment for $2.3 billion over 20 years of production.

Goodrich Corporation, also a subsidiary of United Technologies, along with Aviapribor was initially selected to provide the flight control system actuators.

There were two types of auxiliary power units (APU) designed with specifications suitable for MC-21: the HGT750 from Honeywell Aerospace[79] and the TA18-200 developed by Aerosila.

[84] The cockpit and part of the aircraft's avionics were developed and supplied by the Concern Radio-Electronic Technologies and Rockwell Collins with the participation of personnel from the Russian company Avionika.

[citation needed] In June 2016, Azerbaijan Airlines tentatively signed to lease ten -300s from Ilyushin Finance.