The Il-86 is an all-metal low-wing land monoplane with four jet engines.[64][65][66][67] Its wing is a cantilever three-spar structure of modified trapezoid planform. Centre section integral with the fuselage, inboard sections, outboard sections and detachable leading and trailing edges. High-lift devices include full-span six-segment leading edge slats (contiguous past the engine pylons) at up to 17.5% of chord (drooping to 35°), two-segment fixed vane double-slotted trailing edge flaps occupying some 75% of the span (deploying to 40°) and five-segment spoilers (outboards used as spoilerons at high speeds, inboards used as lift dumpers on the ground). Boundary layer fences over pylons. Two-segment outboard ailerons for low and intermediate speed roll control. Engines suspended from the wing on pylons act as anti-flutter weights. Trim range is 16-33% of mean aerodynamic chord.

The fuselage is of conventional circular section structure of frames and stringers with a continuous main deck and lower decks fore and aft of the wing centre section. Rectangular windows in most interframe bays, eight ICAO Type 1a passenger doors on the main deck and three more on the lower deck portside; two freight hold doors and a galley supply door on the lower deck starboard. The main deck houses the flightdeck, two wardrobes, eight toilets, two pantry units and a three-section passenger cabin. The lower deck houses three entry vestibules/luggage stores with hydraulic boarding stairs to ground level and fixed stairs to the main deck, a midships galley linked with the main deck by an electric lift, two freight holds (fore and aft of the passenger facilities), an avionics bay and two technical bays. The entire accommodation is pressurised và air-conditioned with "earphones for music or on-board cinema."[68]

The empennage is conventional cantilevered trapezoid planform swept-back surfaces. Two-segment elevators and rudder. Tailplane area 96.5 m² (1,039 ft²); incidence adjustable between 2° and 12° by electric motors commanded by yoke trim thumbwheels and console trim wheels. Fin area 56.06 m² (603.4 ft²). Its landing gear use a near-conventional layout, with a twin-wheeled nose gear leg and three four-wheel bogie main gear units (centre and two outer legs. Track is 9.9 m (/32 ft 5.5 in).

The Il-86 is powered by four Kuznetsov NK-86 two-spool turbofans. Five-stage LP compressors, six-stage LP compressors, annular combustor cans, single-stage HP turbine, two-stage LP turbine. Cascade thrust reversers canted 15° from the horizontal. Pneumatic starters (airborne relights use the windmill effect). Forward-facing air ejectors blow away detritus during taxi. A VSU-10 APU generates power and heats/cools the interior on the ground, provides engine start air. International Standard Atmosphere hourly fuel consumption per engine is 7.7 t (16,975 lb) at maximum continuous rated thrust, 6 t/13,230 lb at nominal maximum thrust, 5.1 t (11,243 lb) at 85% thrust, 4.2 t/9260 lb at 70%, 3.6 t (7,937 lb) at 60%, 2.45 t (5,400 lb) at 40% and 1 t (2,205 lb) at idle. Overall hourly fuel consumption at long-range cruise and 190 t (419,000 lb) is 9.75 t (21,495 lb) reducing to 7.79 t (17,174 lb) at 140 t (308,650 lb).

The inputs to all control surfaces are through hydraulic channels. An SAU-1T-2 automatic flight control system offers assisted manual and automatic flight modes, with no pure manual control option. Automatic coupled runway approaches to ICAO Category II conditions. It has four independent hydraulic systems power all flight controls and the built-in airstairs. Fluid is to the NGZh, rather than AMG, formula.

The aircraft's avionics include a Pizhma-1 navigational system with Omega inputs. GPS transceivers and TCAS fitted retrospectively during the 1990s. Pizhma-1 can be used throughout the flight from departure terminal area to landing and taxy to stand. Airfield approach aids enable instrument landing system approaches to ICAO Category II weather minima. Other radio aids include VOR và DME receivers, a weather radar và Warsaw Pact identification aids. Pizhma-1 has full-time roll and yaw dampers. Cockpit voice recorders and flight data recorders fitted as standard. Four GT-40PCh6 engine generators, the APU or ground sources supply 200/115 V, 400 Hz current to the primary system or two secondary systems (36 V/400 Hz AC and 27 V DC). Consumers include the high-lift devices, tailplane trim, deicing, galley lift and interior services.