The MiG-25 underwent substantial design sacrifices in order to achieve high speed, altitude and rate of climb. However, it lacked maneuverability at interception speeds and was difficult to fly at low altitudes. The MiG-25's speed was limited to Mach 2.83, but it could reach a maximum speed of Mach 3.2 or more with the risk of engine damage.
Development of the MiG-25's replacement began with the Ye-155MP (Russian: ?-155) prototype which first flew on 16 September 1975. Although it bore a superficial resemblance to the MiG-25, it had a longer fuselage to accommodate the radar operator's cockpit and was in many respects a new design. An important development was the MiG-31's advanced radar, capable of both look-up and look-down/shoot-down engagement, as well as multiple target tracking. This gave the Soviet Union an interceptor with the capability to engage the most likely Western intruders (low flying cruise missiles and bombers) at long range. The MiG-31 replaced the Tu-128 as the Soviet Union's dedicated long-range interceptor, with far more advanced sensors and weapons, while its range is almost double that of the MiG-25.
Like its MiG-25 predecessor, the introduction of the MiG-31 was surrounded by early speculation and misinformation concerning its design and abilities. The West learned of the new interceptor from Lieutenant Viktor Belenko, a pilot who defected to Japan in 1976 with his MiG-25P. Belenko described an upcoming "Super Foxbat" with two seats and an ability to intercept cruise missiles. According to his testimony, the new interceptor was to have air intakes similar to the Mikoyan-Gurevich MiG-23, which the MiG-31 does not have, at least in production variants.
Serial production of the MiG-31 began in 1979. The MiG-31 is able to maintain combat effectiveness despite the potential use of active and passive radar jammers and thermal decoys by adversaries. A group of four MiG-31 interceptors is able to control an area of air space across a total length of 800 to 900 kilometres (500 to 560 mi); its radar possessing a maximum detection range of 200 kilometres (120 mi) in distance (radius) and the typical width of detection along the front of 225 kilometres (140 mi).
The MiG-31 was designed to fulfill the following mission objectives:
Intercept cruise missiles and their launch aircraft by reaching missile launch range in the lowest possible time after departing the loiter area;
Detect and destroy low flying cruise missiles, UAVs and helicopters;
Long range escort of strategic bombers;
Provide strategic air defense in areas not covered by ground-based, air defense systems.
MiG-31 production ended in 1994. The first production batch of 519 MiG-31s including 349 "baseline models" was produced at the Sokol plant between 1976 and 1988. The second batch of 101 MiG-31DZs was produced from 1989 to 1991. The final batch of 69 MiG-31B aircraft was produced between 1990 and 1994. From the final batch 50 were retained by the Kazakhstan Air Force after the dissolution of the Soviet Union. Of the "baseline models", 40 airframes were upgraded to MiG-31BS standard.
Upgrades and replacement
Some upgrade programs have found their way into the MiG-31 fleet, like the MiG-31BM multirole version with upgraded avionics, new multimode radar, hands-on-throttle-and-stick (HOTAS) controls, liquid crystal (LCD) color multi-function displays (MFDs), ability to carry the R-77 missile and various Russian air-to-ground missiles (AGMs) such as the Kh-31anti-radiation missile (ARM), a new and more powerful computer, and digital data links. A project to upgrade the Russian MiG-31 fleet to the MiG-31BM standard began in 2010; 100 aircraft are to be upgraded to MiG-31BM standard by 2020. Russian Federation Defence Ministry chief Colonel Yuri Balyko has claimed that the upgrade will increase the combat effectiveness of the aircraft several times over. 18 MIG-31BMs were delivered in 2014. The Russian military will receive more than 130 upgraded MiG-31BMs, and the first 24 aircraft have already been delivered, Russian Deputy Defense Minister Yuri Borisov told reporters on 9 April 2015.
Russia plans to start development of a replacement for the MiG-31 by 2019. The aircraft will be called PAK-DP ( , ? - Prospective Air Complex for Long-Range Interception). Development of the new aircraft, designated MiG-41, began in April 2013. Such development is favored over restarting MiG-31 production. In March 2014, Russian test pilot Anatoly Kvochur said that work began on a Mach 4 capable MiG-41 based on the MiG-31. Later reports said that development of the MiG-31 replacement is to begin in 2017, with the first aircraft to be delivered in 2020, and the replacement entering service in 2025.
The wings and airframe of the MiG-31 are stronger than those of the MiG-25, permitting supersonic flight at low altitudes. Like the MiG-25, its flight surfaces are built primarily of nickel-steel alloy, enabling the aircraft to tolerate kinetic heating at airspeeds approaching Mach 3. The MiG-31 airframe comprises 49% arc-welded nickel steel, 33% light metal alloy, 16% titanium and 2% composites. Its D30-F6 jet engines, each rated at 152 kN thrust, allow a maximum speed of Mach 1.23 at low altitude. High-altitude speed is temperature-redlined to Mach 2.83 - the thrust-to-drag ratio is sufficient for speeds in excess of Mach 3, but such speeds pose unacceptable hazards to engine and airframe life in routine use.
The MiG-31 was equipped with RK-RLDN and APD-518 digital secure datalinks. The RK-RLDN datalink is for communication with ground control centers. The APD-518 datalink enables a flight of four MiG-31 to automatically exchange radar-generated data within 200 km from each other. It also enables other aircraft with less sophisticated avionics, such as MiG-23,25,29/Su-15,27 to be directed to targets spotted by MiG-31 (a maximum of four (long-range) for each MiG-31 aircraft). The A-50AEW aircraft and MiG-31 can automatically exchange aerial and terrestrial radar target designation, as well as air defense. The MiG-31 is equipped with ECM of radar and infrared ranges, and is capable of performing combat tasks.
The flight-navigation equipment of the MiG-31 includes a complex of automatic control system SAU-155?P and sighting-navigation complex KN-25 with two inertial systems and IP-1-72A with digital computer, electronic long range navigation system Radical NP (312) or A-331, electronic system of the long-range navigation A-723. Distant radio navigation is carried out by means of two systems: Chayka (similar to the system of Loran) and «Route» (similar to the system of Omega).[clarification needed]
Similarly to the complex S-300 missile system, aircraft group with APD-518 can: share data obtained by various radars from different directions (active or passive scanning of radiation) and summarize the data. The target can be detected passively (through noise posed to protect themselves / active search radar (target)) and (or) actively simultaneously from many different directions (active search radar of MiG-31). Every aircraft with the APD-518 will have the exact data, even if it is not involved in the search.
interacting with ground-based automated digital control system (ACS «Rubezh» Operating radius of 2,000 kilometres (1,200 mi), can control multiple groups of planes), operating modes of remote aiming, semi-automated actions (coordinate support), singly, and also: to direct on the target missiles launched from the other aircraft.
Digital immune system provides the automatic exchange of tactical information in a group of four interceptors, remote one from another at a distance of 200 km and aiming at the target group of fighters with less-powerful avionics (in this case the aircraft performs the role of guidance point or repeater).
Adopted in 1981 RP-31 N007 backstop (Russian: Zaslon).
the range of detection of air targets with Zaslon-A: 200 km (for the purpose of a radar cross-section of 19 m2 on a collision angle with probability 0.5)
Able to intercept and destroy cruise missiles flying at extremely low altitudes.
The basic differences between other versions and the MiG-31BM are:
The onboard radar complex of the MiG-31BM can track 24 airborne targets at one time, six of which can be simultaneously attacked by R-33S missiles.
Modernized variants of the aircraft can be equipped with anti-radiation missiles Kh-31, Kh-25MR or MPU (up to six units), anti-ship Kh-31A (up to six), air-to-surface class missiles Kh-29 and Kh-59 (up to three) or Kh-59M (up to two units), up to six precision bombs KAB-1500 or eight KAB-500 with television or laser-guidance. Maximum mass of payload is 9,000 kilograms (20,000 lb).
The MiG-31M, MiG-31D, and MiG-31BM standard aircraft have an upgraded Zaslon-M radar, with larger antenna and greater detection range (said to be 400 kilometres (250 mi) against AWACS-size targets) and the ability to attack multiple targets - air and ground - simultaneously. The Zaslon-M has a 1.4 m (4.6 ft) diameter (larger) antenna, with 50-100% better performance than Zaslon. In April 1994 it was used with an R-37 to hit a target at 300 kilometres (190 mi) distance. It has a search range of 400 km for a 19-20 m2 RCS target and can track 24 targets at once, engaging six, or 282 km for five m2. Relative target speed detection increased from Mach 5 to Mach 6, improving the probability of destroying fast-moving targets. The MiG-31BM is one of only a few aircraft able to intercept and destroy cruise missiles flying at extremely low altitude.
Front seat cockpit of older MiG-31 variant
The aircraft is a two-seater with the rear seat occupant controlling the radar. Although cockpit controls are duplicated across cockpits, it is normal for the aircraft to be flown only from the front seat. The pilot flies the aircraft by means of a centre stick and left hand throttles. The rear cockpit has only two small vision ports on the sides of the canopy. The presence of the WSO (weapon systems operator) in the rear cockpit improves aircraft effectiveness since the WSO is entirely dedicated to radar operations and weapons deployment, thus decreasing the workload of the pilot and increasing efficiency. Both cockpits are fitted with zero/zero ejection seats which allow the crew to eject at any altitude and airspeed.
One Kh-47M2 Kinzhal high-precision hypersonic aeroballistic missile with a range of about 2,000 km, Mach 10 speed, and an ability to maneuver at every stage of flight.[verification needed] It can carry both conventional and nuclear warheads. This gave the MiG-31 long range strike capabilities for the first time, alongside its primary interceptor role. 
A side view of a MiG-31 from 790th Fighter Order of Kutuzov Aviation Regiment on the runway of Khotilovo airbase, Tver region.
A MiG-31B on left and MiG-31BM on right flying in formation.
With the designation Ye-266, a re-engined Ye-155 set new world records. It reached an absolute maximum altitude of 37,650 metres (123,520 feet) in 1977, and set a time to height record of 35,000 metres (115,000 feet) in 4 minutes, 11.78 seconds, both of which were set by the famous MiG test pilot Alexander Fedotov. Pyotr Ostapenko, his deputy, set a time to height record to 30,000 m (98,000 ft) in 3 minutes and 9.8 seconds in 1975.[clarification needed]
On 26 April 2017, a MiG-31 crashed during a training exercise over the Telemba proving ground in Buryatia; both crew members successfully ejected. While Russian state media did not offer any details, independent investigators discovered from a leaked government document that the aircraft was in fact shot down by an R-33 missile fired from another MiG-31, and that pilot error from both planes were at fault. The report also suggested problems with the Zaslon-AM radar and Baget-55 fire control system that might increase the risk of more accidental shootdowns occurring in the future.
Syria ordered eight MiG-31E aircraft in 2007 for the Syrian Air Force. The order was suspended in May 2009 reportedly either due to Israeli pressure or lack of Syrian funds. On 15 August 2015, Turkish news media reported that six MiG-31s had been delivered to the Syrian Arab Air Force, but Russia denied making MiG-31 deliveries to Syria.
A front view of a MiG-31 on the ramp of Khotilovo airbase, Tver region
Prototype modification of the early MiG-31. First flight in 16 September 1975.
First variant which entered in serial production. 349 aircraft were built.
Development of a more comprehensive advanced version, the MiG-31M, began in 1984 and first flew in 1985, but the dissolution of the Soviet Union prevented it from entering full production. One piece rounded windscreen, small side windows for rear cockpit, wider and deeper dorsal spine. Digital flight controls added, multifunction CRT cockpit displays, multi-mode phased array radar. No gun fitted in this model, refueling probe moved to starboard side of aircraft, fuselage weapon stations increased from 4 to 6 by adding two centre-line stations. Maximum TO weight increased to 52,000 kg using increased thrust D-30F6M engines instead of the D-30F6 engines. 1 prototype and 6 flyable pre-production units were produced.
Two aircraft were designated as Type 31D and were manufactured as dedicated anti-satellite models with ballast in the nose instead of radars, flat fuselage undersurface (i.e. no recessed weapon system bays) and had large winglets above and below the wing-tips. Equipped with Vympel ASAT missiles. Two prototypes were built.
Special modification used as a flying laboratory for testing of ejection seats during flight.
Two-seat all weather, all altitude interceptor. Designated as MiG-31 01DZ when fitted with air-to-air refueling probe. One hundred produced of DZ variant.
Second production batch with upgraded avionics and in-flight refueling probe introduced in 1990. Its development was the result of the Soviet discovery that Phazotronradar division engineer Adolf Tolkachev had sold information on advanced radars to the West. A new version of the compromised radar was hastily developed. MiG-31B also have the improved ECM and EW equipment with integration of improved R-33S missiles. Long range navigation system compatible with Loran/Omega and Chaka ground stations added. This model replaced the 01DZ models in late 1990.
Export version of the MiG-31B with simplified avionics. Never entered in serial production.
Designation applied to type 01DZ when converted to MiG-31B standard.
After passing state testing in 2008 this modernized variant of MiG-31B was approved for introduction into air force of Russia. 50 planes are modified to MiG-31BM (Bolshaya Modernizatsiya/Deep Modernization) standard in accordance with 2011 contract. Efficiency of modernized MiG-31BM is 2.6 times greater than basic MiG-31. The MiG-31B?'s maximum detection range for air targets was increased in the upgrade to 320 km. It had the ability to automatically track up to ten targets, and the latest units can track up to 24 targets and simultaneously engage up to eight targets. The on-board Argon-K is replaced with new Baget 55-06 computer that selects four targets of highest priority, which simultaneously are engaged by long-range R-33S air-to-air missiles. New long range missile R-37 (missile) with speed of Mach 6 and range up to 400 km is developed during modernization process for use with newly modernized MiG-31. MiG-31BM has multi-role capability as is capable of using anti-radar, air to ship and air to ground missiles. It has some of avionics unified with MiG-29SMT and has refueling probe. MiG-31BM broke world record while spending seven hours and four minutes in the air while covering the distance of 8,000 km.
An upgrade of the BS version, it is the latest modernization variant first time contracted in 2014 for modernization of 60 aircraft, it is very similar in some aspects to the BM standard. Unlike the BS standard, aircraft modernized into the BSM standard are equipped with air refueling probe. Improvements were made to the aircraft canopy, where new and better heat resistant glass was used, thus enabling the MiG-31BSM to fly with cruise speed of 3000 km/h at long distances without any damage. Furthermore, new faster central computer Baget-55-06 is used with addition of multi-functional displays, one for pilot and three for weapons operator-navigator. Also there is a new set of navigation equipment. The MiG-31BSM has multi-role capability with ability to use anti-radar, anti-ship and air-to-ground missiles. Main visible difference between the BS and BSM standards is adding of the rear-view periscope above the front cockpit canopy.
Modified MiG-31BM variant capable to carry the hypersonic Kh-47M2 KinzhalALBM. Ten aircraft have been modified as of May 2018. With this modification and with removed APU for air-to-air missiles, the aircraft gained a sole role of an attack aircraft.
Planned fighter-bomber intended for use with TV, radar and laser-guided ASM weapon systems. Never entered in serial production.
Russian Air Force - about 250 in inventory and approximately 120-132 (MiG-31B/BS/BM/BSM) in service as of 2017. Modernization of the MiG-31s is carried out by the Sokol Aircraft Plant under two contracts signed in 2011 and 2014. In total, 113 aircraft will be modernized to the MiG-31BM/BSM standards by the end of 2018-2019. Approximately 110 aircraft were modernized as of August 2017. Ten jets have been modified to the MiG-31K version and carry the Kh-47M2 Kinzhal missile as of May 2018.