Airbus and Boeing Flight Deck Philosophies

Airbus and Boeing build airliners to the same certification standards for the same airlines, yet their flight decks differ in ways a pilot notices within minutes. In an Airbus A320 the pilot flies with a sidestick that gives no feedback, inside limits the computers will not let anyone exceed in normal law, while the thrust levers stay still as the autothrust works. In a Boeing the pilot holds a control column and wheel, trims the airplane, watches the thrust levers move and, on the fly-by-wire 777 and 787, can override the protections with enough force.

Each set of choices expresses a flight deck philosophy, the principles a manufacturer designs its cockpit, automation and procedures around. Both have their traps, and accidents on both sides teach the same lessons about mode awareness and monitoring. This article compares the A320 family with the Boeing 737 NG, 777 and 787, and ends with what changes for a pilot moving between them.

Two design traditions

Airbus describes a safe flight as the result of effective interaction between its cockpit philosophy, its procedures and its pilots. The philosophy rests on ten high-level design requirements: the first makes the flight crew ultimately responsible for the safe operation of the aircraft, and the second lets the crew, if required, exercise full authority through intuitive actions while aiming to eliminate the risks of overstress and overcontrol. The A320, which entered service in 1988 as the first airliner with digital fly-by-wire flight controls and flight envelope protection, built those ideas into sidesticks, control laws and protections, and every airliner Airbus has designed since has been fly-by-wire (see A320 flight deck design philosophy).

Boeing's tradition grew out of its conventional airliners. The 737's wheels and columns still drive cables to hydraulic power control units, with artificial feel. When Boeing adopted fly-by-wire for the 777, its first such airliner, it kept the column and wheel with artificial feel and had the autopilot move the controls, and the 787 follows the same pattern. Authority is explicit there too: the 737 FCOM makes the captain the final authority for all tasks directed and done.

The alerting systems have their own lineage: ECAM first appeared on the A310, EICAS on the 757 and 767. And a philosophy belongs to the design house, not the badge: the A220, designed by Bombardier as the CSeries, has sidesticks but uses EICAS, thrust levers that move and manual pitch trim in manual flight.

Sidestick and control laws versus yoke and feel

The A320's sidestick sits on each pilot's outboard console. The sticks are spring-loaded to neutral, give no feedback from the control surfaces and are not mechanically coupled, so neither pilot feels the other's input; with the autopilot engaged they lock at neutral, and a firm push disconnects it. The stick commands not a surface angle but a response set by the control law. In normal law fore and aft stick demands a load factor, with automatic trim, and sideways stick a roll rate of up to 15° per second; released, the stick leaves the aircraft holding its flight path and, up to 33°, its bank, while the pitch trim wheels turn by themselves.

Inputs from both sticks are added algebraically, with green lights and a DUAL INPUT voice message, so the procedures insist on one pilot flying: the pilot taking over says "I have control" and presses and holds the takeover pushbutton, and the last pilot to press gets priority. On Air France 447 the BEA found that priority was taken without a callout and that both pilots made simultaneous inputs.

The Boeing inceptor is the control column with its control wheel, often called the yoke. On the 737 the two columns and wheels are connected, with transfer mechanisms to bypass a jam, and an elevator feel computer builds column forces from airspeed and stabilizer position. The pilot trims with electric switches or the stabilizer trim wheels, which rotate whenever the stabilizer moves. On the 777 the pitch law, C*U, blends pitch rate and load factor with a speed term that returns the aircraft toward a trim reference speed, so the pilot trims much as in a conventional airplane. Its controls are backdriven, so both pilots see and feel what the autopilot and the protections are doing; the 787 has autopilot backdrive actuators on the wheel, column and rudder pedals.

Envelope protection and pilot authority

Flight envelope protection is the part of the control laws that keeps the aircraft within its limits, or resists inputs that would take it beyond them (see fly-by-wire). Airbus uses hard limits: in normal law no input can exceed them, so a pilot can pull fully back in a terrain escape or windshear and get the aircraft's best performance without stalling or overstressing it. The A320 holds the load factor between +2.5 g and −1 g clean, or +2 g and 0 g with slats or flaps out, limits pitch to 30° nose-up (less at low speed and in CONF FULL) and 15° nose-down and bank to 67°, never lets the angle of attack pass alpha max even with full aft stick, and applies a nose-up demand above VMO/MMO. Alpha floor, an autothrust function, commands takeoff and go-around thrust whatever the lever position when the angle of attack passes a threshold.

Boeing's fly-by-wire types use soft limits. Near a limit the protections raise the force the pilot must apply, for example on the wheel beyond a set bank angle, but enough force overrides them. The 787's protections cover bank angle, thrust asymmetry, underspeed and overspeed, and its MMEL counts bank angle protection as inoperative when the wheel's backdrive actuator is, a sign that the protection works through the pilot's control. The 737 has none. The stick shaker and the overspeed clacker warn, and its autothrottle's approach speed floor is held with thrust, not angle of attack protection.

View full schematic

Protection is only as good as its sensors. After some failures an Airbus reverts to alternate law, which keeps load factor limitation but loses pitch and bank protection and replaces high angle of attack protection with a stability function the pilot can override, or to direct law, with none. On Air France 447 an A330 reverted to alternate law after ice crystals most likely blocked its pitot probes, and was stalled. Boeing's fly-by-wire types have flight control modes of their own, in which the FAA requires 787 pilots to be trained, initially and recurrently.

Autothrust and thrust lever feedback

Back-driven thrust levers are moved by the automation itself. Boeing autothrottles drive the levers with servo motors, so their position always shows the thrust commanded; the 787's MMEL lists two autothrottle servo motors. The 737 autothrottle stops moving the levers at 84 kt on the takeoff roll (THR HLD), and on an autoland starts retarding them at about 27 ft radio altitude so that they reach idle at touchdown. Because an engaged autothrottle could drive a lever away from where the pilot puts it, the 737 recall items for engine fire, overheat and limit or surge begin by disengaging it.

Airbus chose non-back-driven levers. The levers have detents, TOGA, FLX/MCT, CL and IDLE, and each lever position is a thrust demand to the FADEC. With both engines running the autothrust works between idle and the CL detent, where the levers sit from the thrust reduction altitude, and the lever position caps what it may command. The crew judge energy from speed, speed trend and engine parameters instead of lever movement. In a manual landing a "RETARD" callout at 20 ft reminds the pilot to close the levers, and the autothrust disconnects when both reach idle (see A320 autothrust and thrust levers).

Moving levers are a cue, not a safeguard. In 2009 a faulty radio altimeter put a Turkish Airlines 737-800's autothrottle into its retard mode on approach to Amsterdam, and the crew did not notice the lack of thrust until the aircraft neared the stall. In 2013 the autothrottle of Asiana 214, a 777, went to HOLD after the levers were pulled to idle and stopped controlling speed. On both makes the flight mode annunciator and the speed are the references.

Alerting: ECAM and EICAS

ECAM, the electronic centralized aircraft monitor, uses the A320's two center screens: the engine/warning display shows engine parameters, alerts and memos, the system display the system pages and the STATUS page. Level 3 red warnings come with a continuous repetitive chime or a specific sound and a flashing MASTER WARN light, level 2 amber cautions with a single chime and MASTER CAUT, level 1 amber messages with neither. A caution calls up the affected system page, and the procedure appears as action lines. On the overhead panel, dark when all is normal, the failed system's pushbutton lights to lead the hand to the corrective control.

EICAS, the engine indicating and crew alerting system, shows Boeing alerts as messages at three levels: red warnings with master WARNING lights and a distinctive aural, amber cautions with master CAUTION lights and a tone, and advisories, amber but indented, with neither. CANCEL removes cautions and advisories but never warnings, and RECALL brings them back. The 737 has no central alerting display: two system annunciator panels with twelve lights repeat the overhead systems and trigger the MASTER CAUTION lights.

CS 25.1322 and 14 CFR 25.1322 make warnings red and cautions amber or yellow on both makes, but blue differs: on the A320 overhead it marks a system in temporary use, on the 737 information such as a valve position (see flight warning and alerting systems).

Checklists and procedures

Much is shared. Both write normal procedures as flows around the panels followed by a short checklist, split duties between a pilot flying and a pilot monitoring, and have both pilots confirm any action that cannot be undone, such as shutting down an engine (see standard operating procedures and checklists).

The difference is how a failure reaches the checklist. On the A320 the ECAM displays the procedure. The pilot flying flies and takes the radio; the pilot monitoring reads each action aloud, performs it and obtains the pilot flying's confirmation before clearing the alert. After a failure on takeoff or go-around the actions wait until at least 400 ft unless the flight path is safe earlier. The QRH covers events the ECAM cannot detect, such as many smoke and fumes cases.

On the 737 the crew identifies the failure from lights and indications and takes the non-normal checklist from the QRH: recall items from memory, then reference items read step by step. The 787's electronic checklist is the primary means of access to the normal and non-normal checklists; items the system senses as complete are not normally read aloud, and a current paper backup must be carried.

Moving between the two

Within each manufacturer, commonality between types is recognized and credited. The draft Revision 7 of the FAA's A320 Flight Standardization Board report designates the A330 and A340, and for currency only the A350, as related aircraft: a current A330 or A340 pilot, normally with at least 300 hours of line experience on the type, can move to the A320 through related aircraft differences training, and mixed fleets are flown with differences currency every 90 days. EASA gives the 777 and 787 a single type rating, B777/787, while the FAA keeps separate ratings with commonality and level D differences training. The FAA defines related aircraft as aircraft of the same make, so such credit stops at the manufacturer: moving between an Airbus and a Boeing means a full type rating course (see class and type ratings).

Habits change more slowly than ratings:

• Thrust levers. On a Boeing they move; on an Airbus they stay in the detent, the FMA and engine parameters show the thrust, and the pilot closes them in the flare, with the RETARD callout as a reminder.
• Trim and feel. Normal law trims automatically; a Boeing pilot trims, and the column gives feel and, on the 777 and 787, moves with the autopilot.
• Authority. Hard limits do not travel: a 737 has none, a 777 or 787 lets a strong input through, and on an Airbus the active law decides what is still protected.
• Alerting. ECAM displays the procedure; on a 737 the crew finds it in the QRH.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.