Performance

Airliner performance is planned around one idea: an engine can fail at the worst moment, and the aircraft must still be safe. Transport aircraft are certified in performance class A, which means the take-off, climb, cruise and landing are all calculated with an engine failure in mind and with fixed safety margins.

1. Take-off speeds

Speed	Meaning
VMCG	Minimum control speed on the ground: below it, an engine failure cannot be controlled with rudder alone.
VEF	The speed at which the engine is assumed to fail – one second before V1.
V1	The decision speed: the last moment to start a rejected take-off, and the first from which the take-off can be continued after an engine failure.
VR	Rotation speed.
VMU	Minimum unstick speed: the slowest speed at which the aircraft can lift off.
VLOF	Lift-off speed.
VMCA	Minimum control speed in the air with one engine inoperative.
V2	Take-off safety speed, to be reached by 35 ft and held in the second-segment climb: at least 1.13 × VSR and 1.1 × VMCA.

The order is always V_MCG ≤ V_EF < V₁ ≤ V_R < V_LOF and V₂ ≥ 1.1 V_MCA; V1 cannot exceed VR or the maximum brake energy speed.

2. Take-off distances

• Take-off distance: the longer of (a) the distance to 35 ft with an engine failure at V_EF, and (b) 115% of the all-engines distance to 35 ft. It must not exceed the TODA.
• Accelerate-stop distance: accelerate to V1, then stop (with no credit for reverse thrust on a dry runway). It must not exceed the ASDA.
• Take-off run must not exceed the TORA.
• A balanced field is one where the take-off distance and accelerate-stop distance are equal – it gives the shortest runway for a given mass.

Increasing V1 shortens the go distance and lengthens the stop distance, and the other way round – that is how the performance software optimises V1 for the runway.

3. Take-off climb

The net take-off flight path is divided into segments, all with one engine inoperative:

Segment	From – to	Configuration
1st	Lift-off to gear up	Take-off flap, gear retracting, V2
2nd	Gear up to at least 400 ft	Take-off flap, gear up, V2 – usually the limiting segment
3rd	Level acceleration and flap retraction	Accelerating to final take-off speed
Final	To 1,500 ft or more	Clean, maximum continuous thrust

The minimum gross gradient in the second segment is 2.4% for twins, 2.7% for three engines and 3.0% for four. For obstacle clearance the net flight path (gross minus 0.8% for twins) must clear every obstacle in the departure area by at least 35 ft.

4. What limits the take-off mass

• The field length (TORA, TODA, ASDA).
• The climb gradient (second segment) – worse with heat and altitude.
• Obstacles in the departure path.
• Tyre speed and brake energy limits.
• Structural limits (MTOM) and the landing mass at destination.

The lowest is the limiting take-off mass. On a 40 °C day at Amman (elevation 2,395 ft) the climb limit often becomes the limiting factor.

5. Reduced thrust

When the actual mass is below the limiting mass, a lower thrust can be used to save engine wear: assumed temperature ("flex" on Airbus) – the FADEC sets the thrust for a higher temperature than the real one – or a fixed derate. Reduced thrust is not allowed on contaminated runways or with wind shear expected.

6. Runway surface

• Wet runways allow a lower screen height (15 ft) and credit for reverse thrust in the stop calculation.
• Contaminated runways (standing water, slush, snow, ice) reduce braking and add drag from the contaminant; performance is calculated from the runway condition code (RWYCC 0–6).

7. En-route performance

• After an engine failure in cruise the aircraft drifts down to a lower level. The net drift-down path must clear terrain by at least 2,000 ft all the way to an aerodrome where it can land (or 1,000 ft with a positive gradient when cruising level).
• Cruise speed is chosen with the cost index: CI 0 gives the maximum range (slowest, least fuel); a high CI flies faster to save time.
• Optimum altitude rises as the aircraft gets lighter – the reason for step climbs on long flights.
• At high altitude the margin between buffet at low speed and high speed narrows; the FMS shows the maximum recommended altitude with a 1.3 g buffet margin.

8. Landing

• On a dry runway the required landing distance is the certified distance from 50 ft divided by 0.6 – the aircraft must be able to stop in 60% of the LDA.
• On a wet runway, add 15% to the dry requirement.
• The approach speed is at least 1.23 × V_SR0 (V_REF), plus wind and gust additions.
• Climb gradients for a go-around: the approach climb (one engine out, approach flap) of at least 2.1% for twins, and the landing climb (all engines, landing configuration) of 3.2%.
• At the time of landing (in flight), crews also check the in-flight landing distance for the actual conditions, with a margin of at least 15%.

Flying it at Levant

Use the aircraft's performance tool (or SimBrief's take-off performance) for every departure: enter the runway, wind, temperature, QNH and runway condition, and use the V-speeds and flex temperature it gives. Brief what you will do if an engine fails before and after V1 – and on hot days at Amman, Riyadh or Baghdad, look at which limit sets your take-off mass.

Check yourself

1. What is V1? The decision speed – the last point to start a rejected take-off and the first from which the take-off can continue after an engine failure.
2. What is the minimum gross second-segment gradient for a twin? 2.4%.
3. By how much must the net take-off path clear obstacles? At least 35 ft.
4. On a dry runway, what fraction of the LDA must the landing use? No more than 60%.
5. What does a cost index of 0 give? Maximum range – the lowest fuel burn.

Simulation training material with simplified certification figures. Always use the aircraft's approved performance data.