Performance: take-off, climb, cruise and landing

There must be a V1 that makes both the accelerate-stop and the accelerate-go distance fit, and 115 % of the all-engines distance must also fit. Longer runway, headwind, downhill slope and cooler air all raise this limit.

With one engine out a twin must have a gross gradient of at least 2.4 % in the second segment (gear up, take-off flaps, V2). This limit does not depend on the runway at all, only on mass, temperature and pressure altitude.

The net flight path, the gross path reduced by 0.8 % for a twin, must clear every obstacle in the take-off funnel by at least 35 ft. A close, tall obstacle needs a steep path and limits the mass.

The ground speed at lift-off may not exceed the tyre rating (typically 195 kt). V1 may not exceed VMBE, the speed above which the brakes cannot absorb the energy of a stop. Both bite at high, hot aerodromes and with tailwind.

The certified maximum take-off mass, independent of the day. For this teaching aircraft 78 t. The planned mass may also be limited by the landing mass at destination.

When the actual mass is below the limit, reduced thrust saves engine wear. Flex (assumed temperature): performance is calculated as if it were hotter, and TOGA is still available at any time. Derate: a certified lower thrust rating with its own, lower VMC; TOGA cannot simply be selected without losing those margins.

Climb gradient depends on excess thrust: (T − D) / W. Rate of climb depends on excess power: (T − D) × V / W. For a jet, thrust is nearly flat, so the best angle (Vx) is close to the minimum-drag speed and the best rate (Vy) is clearly faster.

Fuel flow follows drag, so the most distance per kilogram comes at the highest ratio of speed to drag, about 1.32 × the minimum-drag speed, until the drag rise near the critical Mach stops it. Long-range cruise gives up 1 % of the range for a few percent more speed.

Time costs money too (crew, maintenance, connections). The cost index is the ratio of time cost to fuel cost. CI 0 gives the maximum range speed; a higher CI flies faster and burns more fuel to save time.

The optimum altitude gives the best range for the present mass and rises as fuel is burnt. The maximum altitude is the lowest of the certified ceiling, the altitude with a 0.3 g buffet margin, and the altitude where the residual climb rate drops to 300 ft/min. Step climbs follow the optimum upwards.

Range is distance over the ground. Into a headwind it pays to fly faster than the still-air best range speed, and with a tailwind slightly slower. A strong headwind can also make a lower level with less wind the better choice.

At idle, the descent gradient is about drag / weight, the inverse of L/D. Each aircraft flown at its own best-L/D speed (higher when heavier) has the same L/D, so the still-air glide distance is the same. The A320 descends at a fixed managed speed above that best-L/D speed; there the heavier aircraft is closer to its best L/D, so it descends more shallowly and its top of descent comes earlier. An early, idle, continuous descent is the most fuel-efficient.

The gross path is what an average aircraft would fly. The net path is the gross gradient reduced by 1.1 % for a twin (1.4 % and 1.6 % for three and four engines). It is a fictitious, deliberately pessimistic path, and the terrain rules are applied to it, not to the gross path.

Either the net path is still climbing (gradient positive) at least 1000 ft above all terrain within 5 NM either side of track, or the net path from cruise level to a suitable aerodrome clears all terrain in that corridor by at least 2000 ft. The corridor grows to 10 NM if the navigation accuracy does not meet the 95 % containment level.

Green dot (best L/D with one engine out) at MCT gives the shallowest descent and the highest level-off: the obstacle strategy. Where terrain is no problem, a faster standard strategy (M.78/300 kt on the A320) reaches lower levels sooner but gets to the diversion aerodrome faster.

Over the Alps, and on some routes over Scandinavian mountains, the planned track may not satisfy the rules at high mass on a warm day. Operators then publish escape routes: pre-computed tracks along valleys to an en-route aerodrome, with decision points that tell the crew which way to turn after a failure.

Speeds and thrust come from the performance application on the EFB, calculated for the runway or intersection, wind, temperature, QNH, runway state and configuration. Both pilots compute or cross-check independently and enter V1, VR, V2 and the flex temperature on the MCDU PERF TAKEOFF page. A gross error check against the expected values catches typing mistakes.

With a flex temperature entered, the thrust levers go to the FLX/MCT detent. If more thrust is needed, TOGA is always available by pushing the levers fully forward, because VMC is based on TOGA. TOGA is used when the runway is contaminated, when wind shear is expected, or when the margins are not there for flex.

A typical Airbus procedure: the captain keeps a hand on the thrust levers until V1. At low speed the take-off is rejected for any significant failure; at high speed only for major ones such as engine failure, fire or a sign that the aircraft is unsafe to fly. At V1 the hand comes off and the decision is go.

The runway condition report (in Europe via SNOWTAM and ATIS) gives an RWYCC for each third of the runway, for example 5/5/3, with contaminant type, depth and coverage. The crew enters the condition in the performance application. Flex is not used on a contaminated runway.

Before the descent the crew calculates the landing distance at the time of arrival with the expected runway condition, wind, autobrake and reverse, and checks it plus 15 % against the landing distance available. A failure such as a reverser or brake inoperative, or a change in runway condition, means a new calculation.

The cost index is entered on the INIT A page and the FMS flies the ECON speed and Mach. The PROG page shows the optimum flight level (OPT) and the recommended maximum (REC MAX). Green dot on the speed scale is the best lift-to-drag speed in clean configuration, used for an engine-out climb or drift-down.

NADP 1 (close-in): at or above 800 ft above the aerodrome, reduce to climb thrust and keep take-off flaps at V2 + 10 to 20 kt up to 3000 ft, then accelerate and retract. It protects neighbours close to the runway. NADP 2 (distant): from 800 ft or higher, lower the nose and accelerate, retracting flaps on schedule, with the thrust reduced during or after the retraction, then climb clean to 3000 ft. It reduces noise further out and saves fuel. Either way the noise procedure never overrides the obstacle and engine-failure requirements.

The A320 is operated as a Class A aeroplane: an engine failure at any point of the take-off is covered by scheduled data, through V1, the accelerate-stop and accelerate-go distances, the net take-off flight path with obstacle clearance and the en-route drift-down rules on this page. Class B aeroplanes, by comparison, use simpler factored charts with no V1.