Narrow-Body Airliner

Overview

A narrow-body airliner is a single-aisle jet built for short and medium-haul routes, the workhorse of the world fleet that flies the dense city-pair networks where most air travel happens. It seats between roughly 130 and 230 passengers in a single aisle and is optimized for short sectors flown many times a day, so quick turnarounds and low cost per cycle matter as much as raw efficiency. The aircraft brings together the same major systems as any jet transport: the Fuselage, two Wing structures, the Empennage, two High-Bypass Turbofan turbofans, the Landing Gear, and the Flight Control System, Avionics Suite, Aircraft Systems and Cabin Interior.

The difference from a wide-body is mostly scale and mission. One aisle, one cargo hold, two smaller engines and a lighter structure suit routes of one to four hours, where the airplane earns its keep by flying often rather than flying far. The sections below follow the structure down through its subsystems.

Airframe: fuselage and wing

The Fuselage is a pressurized aluminium tube of Fuselage Barrel Section barrels, each a Skin Panel skin over Circumferential Frame frames and Stringer stringers, closed by Pressure Bulkhead bulkheads and floored by a Floor Beam Grid beam grid that separates the single-aisle cabin above from the cargo hold below. Plug-type Door (Plug) doors with Evacuation Slide evacuation slides and the window belt complete it. Aluminium alloy remains the usual choice here because the shorter sectors do not reward the extra cost of a mostly composite body the way long-haul flying does.

The Wing is built around a Wing Torsion Box torsion box of Wing Spar spars, Wing Rib ribs and skins that doubles as the Integral Fuel Tank integral tank. Leading-Edge Slat slats and Trailing-Edge Flap flaps give the high lift needed to operate from shorter runways, while Aileron ailerons and Spoiler Panel spoilers handle roll and lift dump, and a Winglet trims the induced drag.

Engines

Each High-Bypass Turbofan is a high-bypass turbofan in the single-aisle thrust class. The Fan Module of Fan Blade blades inside a Fan Containment Case case produces most of the thrust, fed by a core of Compressor (LP+HP) compressor, Annular Combustor combustor and Turbine (HP+LP) turbine. The engine hangs from a Engine Pylon inside a Nacelle & Inlet with a Thrust Reverser, runs under a FADEC Engine Control digital control, and drives its pumps and generators through an Accessory Gearbox.

Because a narrow-body may fly five or six sectors a day, its engines accumulate cycles fast, takeoff to landing being a cycle, and that cycle count, not just hours, drives the maintenance and life-limited-part schedule. The hot section in particular is designed for that high-cycle duty.

Landing gear and flight controls

The Landing Gear is a retractable tricycle arrangement: two twin-wheel Main Landing Gear Leg legs and a steerable Nose Landing Gear, each on an Oleo-Pneumatic Strut shock strut with carbon Carbon Wheel Brake brakes. Like the engines, the gear is built for high cycle counts, since it touches down far more often per flight hour than a long-haul aircraft.

The Flight Control System system on this generation is fly-by-wire: Flight Control Computer computers take inputs from the Control Yoke / Sidestick and Rudder Pedal Assembly, combine them with data from the Air Data Inertial Unit, and command Control Surface Actuator actuators on the surfaces. The architecture mirrors the wide-body but with fewer surfaces and actuators to match the smaller wing.

Avionics and systems

The Avionics Suite suite is a glass cockpit: Flight Deck Display Unit displays, dual Flight Management Computer flight management computers, a Radio Communication Suite of radios, weather radar, transponders and the Flight Data / Voice Recorder data and voice recorders. It supports the two-pilot crew through the high-tempo short-haul day, where the workload is concentrated in frequent departures and arrivals rather than long cruise.

The Aircraft Systems group keeps the aircraft powered and habitable with three Hydraulic System circuits, an Electrical Generation fed by engine Integrated Drive Generator generators, an Environmental Control System that conditions and pressurizes the cabin through its Air Cycle Machine (Pack) packs, an Auxiliary Power Unit for ground power, an Oxygen System for decompression protection, and an Ice Protection System system.

Cabin and use

The Cabin Interior is a single-aisle layout of Passenger Seat seats, with Galley galleys and Lavatory Module lavatories at the ends, overhead Overhead Stowage Bin bins and a Passenger Service Unit service unit above each row. Cabins on this class are designed for fast cleaning and boarding because the airplane spends so little time on the ground between flights.

In service a narrow-body flies a tight schedule, often turning around in well under an hour and completing several round trips a day, with the two-pilot crew working the busy departure and arrival phases that dominate a short sector. Airlines run them in large fleets because a common type across many routes simplifies crews, spares and maintenance. The economics favor frequency and flexibility over the long range and large capacity of a wide-body, which is why the single-aisle jet carries the majority of the world passengers even though it flies the shorter distances.