A320 Limitations

The A320 limitations are the boundaries within which the aircraft is certified and must be operated, from speeds and weights to wind, engine, system and autopilot limits. Certification sets them and the flight manual (AFM) records them; the flight crew operating manual (FCOM) gathers them for the crew in its Limitations chapter, together with recommendations that are not limitations at all.

This article follows the A320 FCOM. Weights are those of one weight variant, and engine figures those of the CFM56-5B of the A320ceo; the IAE V2500 and the neo's LEAP-1A and PW1100G have their own. The operator's AFM and FCOM always govern.

How the FCOM presents the limitations

The Limitations chapter opens with the general limitations: operational limits such as runway slope, altitude and wind, speeds, weights and load factors. The systems follow, one section each: air conditioning, autoflight, APU, engines, fuel, landing gear, oxygen, surveillance and others. The autoflight section separates the general AP/FD and FMGS limits from those for CAT II and CAT III approaches and automatic landing.

Not every entry carries the same weight. Some are prohibitions: reverse thrust may not be selected in flight, and bleed air from the APU and from a high-pressure ground air start unit may not be used together. Others are recommendations. Airbus states that the maximum demonstrated crosswind is not an AFM limitation but the strongest crosswind met during the certification campaign, and with passengers on board it is only "not recommended" to exceed 20 minutes without air conditioning, because cabin air quality falls significantly.

The chapter is also specific to a fleet: weights depend on the weight variant, engine limits on the engine, and some entries apply only to options.

Load factors and operating speeds

The flight maneuvering load factor limits are −1 g to +2.5 g in the clean configuration, the standard CS-25 design limits for a transport airplane, and 0 g to +2 g with slats or flaps extended (see load factor and flight envelope). Normal law keeps the aircraft within them. The maximum altitude with slats or flaps extended is 20,000 ft.

VMO and MMO cross at about FL245 in ISA; above it the Mach number is the limit. The PFD shows VMAX, the maximum speed in the current configuration, as a red and black strip at the top of the speed scale (see A320 characteristic speeds), and a placard on the center panel repeats the flap speeds (VFE) and gear speeds. VLO is lower than VLE because, while the gear is moving, the doors are open and the legs are not yet locked.

Other speed limits: 200 kt with a cockpit window open, 230 kt with the wipers sweeping, and, above 76,000 kg (167,550 lb) takeoff weight, a taxi speed of 20 kt in turns.

Weights, altitudes and runways

One A320ceo weight variant gives these weights:

Other variants differ; the AFM lists them all. The EASA type certificate data sheet (TCDS) sets the maxima: for the A320ceo a takeoff weight of 75,500 to 78,000 kg depending on the model, a landing weight of 66,000 kg and a zero fuel weight of 62,500 kg; for the A320neo 79,000 kg, 68,400 kg and 65,300 kg (see maximum structural and regulated masses).

View full schematic

An overweight landing is allowed only in exceptional cases: after an in-flight turnback or a diversion, an immediate landing above the maximum landing weight is permitted provided the crew follow the overweight landing procedure (see overweight landing).

The TCDS gives the A319, A320 and A321 a maximum operating altitude of 39,100 ft, raised to 39,800 ft by a modification. The maximum runway altitude is 9,200 ft and the maximum mean runway slope ±2 %. The nominal runway width is 45 m and the minimum 30 m. The passenger doors may be operated in winds up to 65 kt and the cargo doors up to 40 kt, or 50 kt nose into wind or with the doors leeward; the cargo doors must be closed before the wind exceeds 65 kt.

Wind limits and crosswind by runway state

The tailwind limit is 10 kt for takeoff and for landing. The maximum demonstrated crosswind is 38 kt, gusts included, for both, which Airbus recommends not exceeding intentionally. A contaminated runway gives the tires less side force, so Airbus publishes maximum recommended crosswinds by reported braking action and runway condition code (RWYCC), the same for takeoff and landing. They include:

Automatic landing has tighter limits, the same for ILS and MLS CAT II and CAT III and for GLS CAT I autoland: 30 kt headwind, 10 kt tailwind and 20 kt crosswind. They apply to the surface wind reported by ATC. If the wind on the navigation display exceeds them but the tower reports a wind within them, the autopilot may stay engaged; if the tower reports a wind beyond them, only a CAT I automatic approach without autoland may be flown.

Minimum control speeds VMCG, VMCA and VMCL

The minimum control speeds are the lowest speeds at which the aircraft remains controllable after a sudden failure of the critical engine: VMCG on the takeoff run, using the rudder without nosewheel steering; VMCA in the air, with no more than 5° of bank; and VMCL in the landing configuration.

The A320 FCOM gives VMCG and VMCA at sea level and without thrust bump, a function some engines have (see A320 autothrust and thrust levers), and a single VMCL:

• VMCG: 111 kt in CONF 1+F, 109 kt in CONF 2 and CONF 3;
• VMCA: 110 kt;
• VMCL: 113 kt.

On runways narrower than 40 m, VMCG is increased by 1.5 kt for a 35 m runway and 2.5 kt for a 30 m one. The speeds set floors: V1 may not be less than VMCG, VR not less than 1.05 VMCA, V2 not less than 1.10 VMCA, and VREF not less than VMCL.

Autopilot and approach minimum heights

The autopilot minimum engagement height after takeoff is 100 ft AGL, and at least 5 seconds after liftoff. Elsewhere the minimum height for AP/FD use depends on the phase and the guidance mode:

DES or OP DES may be used on approach only with the FCU altitude set at or above the higher of the MDA (MDH) and 500 ft AGL.

The CAT II and CAT III limits follow the capability shown on the FMA (see A320 auto flight: approach, landing and go-around):

• CAT II: decision height at least 100 ft; at least one autopilot in APPR mode with CAT 2 or better on the FMA; for a manual landing, autopilot off by 80 ft AGL.
• CAT III fail-passive (CAT 3 SINGLE): decision height at least 50 ft; at least one autopilot, and the autothrust in use.
• CAT III fail-operational (CAT 3 DUAL): alert height 100 ft; both autopilots and the autothrust; decision height at least 20 ft, or RVR at least 75 m without decision height.

Automatic landing is approved in CONF 3 and CONF FULL. It was demonstrated with glideslopes between −2.5° and −3.15°, at airport elevations up to 2,500 ft and below the maximum landing weight, and is not allowed below −1,000 ft pressure altitude. Automatic rollout is approved on dry and wet runways only. With an engine out, CAT II and CAT III fail-passive autoland are approved only in CONF FULL, with the engine-out procedures completed before 1,000 ft.

Engine, APU and air conditioning limits

For the CFM56-5B:

Up to three automatic start attempts count as one starter cycle; ground starts need 20 seconds between cycles and 15 minutes of cooling after four failed cycles, and the starter must not run above 20 % N2. Reverse thrust may not be used to back the aircraft, and maximum reverse should not be used below 70 kt. FLEX temperature may not exceed ISA + 53 °C or be below the flat-rating temperature or the actual OAT, and FLEX is not permitted on contaminated runways. A derated takeoff is permitted whatever the runway condition, dry, wet or contaminated, but never combined with FLEX, and TOGA is then selected only if an abnormal or emergency procedure calls for it (see reduced and derated takeoff thrust).

The APU operational envelope is not one figure but several. The APU may be started throughout the normal flight envelope, but its bleed may assist an engine start only up to 20,000 ft and supply air conditioning and pressurization up to 22,500 ft with one pack or 15,000 ft with two; it may never be used for wing anti-ice. After three consecutive start attempts the crew wait 60 minutes (see A320 APU).

The maximum cabin differential pressure is 9.0 psi positive and 1.0 psi negative, with the safety valves set at 8.6 psi. Conditioned air from the packs and from a low-pressure ground unit may not be used together.

Fuel, oxygen and other system limits

The minimum fuel for takeoff is 1,500 kg, with no wing tank low-level alert displayed. JET A1 may not be colder than −43 °C and JET A than −36 °C, and fuel may not exceed 54 °C, or 49 °C for JET B and JP4. At takeoff, full inner tanks may differ by 500 kg and the outer tanks by 370 kg; in flight and at landing, full inner tanks by 1,500 kg, with no limit once the heavier holds less than 2,250 kg, and the outer tanks by 690 kg under conditions. A fuel system failure may push these out without significant effect on handling (see A320 fuel system).

The minimum crew oxygen bottle pressure covers the preflight checks, use by one pilot alone in the cockpit, the unusable quantity and normal leakage, plus the more demanding of two cases: after a loss of cabin pressure, with the masks on diluted oxygen, an emergency descent for all crew members and observers for 13 minutes followed by cruise at FL100 for two pilots for 107 minutes; or smoke protection with 100 % oxygen for all crew members and observers for 15 minutes at 8,000 ft cabin altitude.

Among the remaining limits:

• Brakes: 300 °C maximum for takeoff with the brake fans off; the brakes are not designed to hold the aircraft with high thrust on an engine.
• Navigation: IRS ground alignment between 82°N and 82°S only.
• Surveillance: the terrain display is a situation awareness tool, never a basis for navigation. The predictive GPWS functions should be inhibited (TERR off) within 15 NM of an airfield whose runway is not in their database, or on procedures the operator has identified as causing spurious terrain alerts, and the decision must not rest on crew judgment alone.

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.