Light Aircraft Performance Charts

The performance section of a light airplane's handbook answers the questions every flight raises: is the runway long enough, how quickly will the airplane climb, how fast will it cruise and how much fuel will it burn. The answers come as tables and graphs, each valid only for the conditions and technique printed with it, and each giving a figure that a new airplane achieved in the hands of a test pilot.

Reading them correctly is tested in the PPL and CPL performance examinations and in the FAA knowledge tests. This article covers the charts of a typical light single, the corrections they leave to the pilot and the margins added on top. The physics behind each correction is explained in factors affecting takeoff and landing performance.

What the performance section contains

A typical performance section opens with supporting data, such as the airspeed calibration table, and then gives:

• takeoff distance, as a ground roll and a total distance to 50 ft;
• climb performance: rate of climb, and the time, fuel and distance to climb;
• cruise performance: percent power, true airspeed and fuel flow;
• landing distance, as a total from 50 ft and a ground roll.

The data come from flight tests by the manufacturer with a new airplane and engine, a professional test pilot and precise technique, and they contain no built-in margin. American handbooks mostly present them as tables; European examination data, such as the single-engine piston airplane of the UK CAA's CAP 698 manual, mostly as graphs read across a series of grids, the carpet plots described in performance classes and data.

Every chart states its associated conditions: the power setting, flap setting, runway surface, usually paved, level and dry, the speeds to fly and the technique. A takeoff chart that assumes the short-field technique, with the stated flap, full power before brake release, rotation at the stated speed and a climb at Vx, does not apply to a rolling start with less flap and a climb at Vy, which need more distance. Many handbooks also call for the mixture to be leaned for maximum power before a takeoff from a high-elevation airfield.

The charts are entered with pressure altitude and outside air temperature, never with the airfield elevation. An airfield at 1,200 ft with a QNH of 998 hPa is at a pressure altitude of about 1,650 ft, allowing 30 ft per hPa; with the FAA's 1,000 ft per inch, one at 3,500 ft with 30.42 inHg is at about 3,000 ft. The chart then accounts for the density altitude itself.

Takeoff distance charts and tables

A performance chart in table form lists, for each takeoff weight, rows of pressure altitude and columns of temperature. Each cell gives two figures: the ground roll and the total distance to clear a 50 ft obstacle. Speeds for rotation and at 50 ft are printed with the table, often for each weight, and the distances are valid only if they are flown.

Values between the rows and columns are found by linear interpolation, in proportion to where the actual value lies. If the ground roll at 2,000 ft is 1,050 ft at 20 °C and 1,170 ft at 30 °C, the 10 °C span is worth 120 ft, or 12 ft per degree, so at 24 °C the roll is 1,050 + 48 = 1,098 ft. Taking the midpoint, 1,110 ft, is right only at 25 °C. With two or three variables, interpolate one at a time: temperature at each of the two altitudes, then altitude, then weight. When a figure cannot be read with confidence, the conservative practice is to use the more demanding adjacent entry, never the more favorable one.

Weight matters too. Extra mass raises the lift-off speed and slows the acceleration, so as a rule of thumb a 10 percent increase in mass lengthens the takeoff distance by about 20 percent.

On a graph the same inputs are read in sequence. On the CAP 698 single-engine takeoff graph the first grid combines outside air temperature and pressure altitude, and the line is then carried through the mass, wind and obstacle height grids in turn, following the guide lines from each reference line. The wind grid already contains the regulatory wind factoring, so the reported wind component is entered directly.

Ground roll and distance over a 50 ft obstacle

The ground roll runs from brake release to lift-off. The distance over a 50 ft obstacle adds the airborne segment, from lift-off to the point 50 ft above the runway surface. The difference is large: a handbook giving an 800 ft ground roll may give 1,500 ft to 50 ft, and at a high density altitude the total can be nearly double the ground roll. The 50 ft figure is the one to compare with the runway available, because an airplane that just lifts off at the far end has no margin over the boundary fence.

European Class B rules also measure the takeoff distance to 50 ft above the takeoff surface; Class A airplanes use 35 ft, or 15 ft on a wet runway.

The distinction matters again when corrections are applied. Many American handbooks give the grass correction as a share of the ground roll, for example "increase distances by 15 percent of the ground roll figure". With an 800 ft roll and a 1,500 ft total, the correction is 120 ft, so the roll becomes 920 ft and the total 1,620 ft; the airborne segment is unaffected by the surface. Applying 15 percent to the total, 1,725 ft, overstates the penalty.

Landing distance charts

The landing distance runs from 50 ft above the threshold to a full stop: an airborne segment to touchdown, then the ground roll. The chart assumes a speed at 50 ft, at least 1.3 VS0 for Class B airplanes, and the stated flap and braking technique on a paved, level, dry runway. It is entered like the takeoff chart and has its own notes for wind and surface. A typical grass note for landing reads "increase distances by 45 percent of the ground roll figure": with a 1,150 ft total and a 600 ft ground roll, the total on dry grass becomes 1,150 + 270 = 1,420 ft.

Speed is the variable the pilot controls most. The energy to be dissipated grows with the square of the touchdown speed, so 10 percent too fast lengthens the ground roll by about 21 percent: a 600 ft roll at 55 kt becomes about 726 ft at 60.5 kt, before counting the float in the flare. Crossing the threshold 15 percent fast adds about 30 percent. The same law applies to groundspeed: an airplane touching down at 60 kt IAS with 10 kt of tailwind meets the runway at 70 kt instead of 50 kt with 10 kt of headwind, and needs roughly twice the ground roll. See landing distance for the transport airplane rules.

Climb and cruise performance tables

Climb tables give the rate of climb at the stated climb speed, power and configuration for each pressure altitude, temperature and weight. Obstacle clearance, however, depends on the gradient over the ground, and so on groundspeed. At 500 ft/min and a groundspeed of 75 kt, 1.25 NM a minute, the airplane gains 400 ft per NM, about 6.6 percent. A tailwind leaves the rate of climb unchanged but flattens the climb path; a climb graph gives an air gradient that must be corrected for wind before it is used against obstacles.

The time, fuel and distance to climb table is referenced to sea level, so the figures for the departure altitude are subtracted from those for the cruising altitude. If the climb to 8,000 ft takes 14 minutes, 3.2 gallons and 22 NM and the climb to 2,000 ft takes 3 minutes, 0.8 gallon and 4 NM, the climb from a 2,000 ft airport needs 11 minutes, 2.4 gallons and 18 NM. Most tables assume standard temperature and no wind, tell the pilot to add an allowance for start, taxi and takeoff, and ask for an increase in the figures above standard temperature.

The cruise performance table lists, for each pressure altitude and engine setting, the percent of rated power, the true airspeed and the fuel flow, usually in columns for standard temperature and for temperatures above and below it. At a given percent power a warmer day gives a higher TAS and essentially the same fuel flow. Notes may give the correction instead; with a note adding 2 kt per 10 °C above ISA, a table giving 122 kt and 32 liters per hour at 6,000 ft and 126 kt and 31 liters per hour at 8,000 ft gives, at 7,000 ft and ISA +10, 126 kt and 31.5 liters per hour.

At 8,000 ft, 2,400 rpm and 65 percent power, a table giving 128 kt and 9.4 gallons per hour leaves about 41 gallons for the trip from 48 gallons usable after a 45-minute reserve, or about 4.4 hours and 560 NM in still air. Comparing settings needs specific range, distance per unit of fuel: 110 kt for 34 liters per hour is about 3.2 NM per liter, 95 kt for 25 liters per hour about 3.8. In a wind, groundspeed replaces TAS in the division (see range, endurance and gliding).

Corrections for wind, slope, surface and temperature

Temperature and altitude are inside the chart. Humidity is not: the charts assume dry air, so on a hot, humid day performance is somewhat worse than charted, and treating the day as hotter than it is builds in the margin.

Wind is applied as the component along the runway only; the crosswind component is checked against the demonstrated crosswind. Handbook notes typically read "decrease distances 10 percent for each 9 kt headwind; for operation with tailwinds up to 10 kt, increase distances 10 percent for each 2 kt". A 6 kt tailwind then adds 30 percent, turning 1,800 ft into 2,340 ft. The FAA's handbook notes that a headwind of 10 percent of the takeoff airspeed shortens the takeoff distance by about 19 percent, while the same tailwind lengthens it by about 21 percent. For commercial Class B planning, EASA credits no more than 50 percent of a headwind component and assumes at least 150 percent of a tailwind component, unless the chart already includes this factoring.

Slope is often missing from light airplane handbooks. Where the flight manual has no data, the EASA Class B correction increases the takeoff distance by 5 percent per 1 percent of upslope and the landing distance by 5 percent per 1 percent of downslope, with no credit for a favorable slope.

Surface corrections come from the handbook notes or, for Class B planning without flight manual data, from the EASA factors for grass up to 20 cm long on firm soil: × 1.2 for takeoff and × 1.15 for landing on dry grass, × 1.3 for takeoff on wet grass. These factors do not cover longer grass, soft ground or contamination, for which the light airplane handbook usually has no data at all (see wet and contaminated runways).

Corrections are multiplied, never added. A 400 m distance from dry grass (× 1.2) with a 2 percent upslope (× 1.1) becomes 400 × 1.2 × 1.1 = 528 m; adding the percentages gives 520 m and always understates.

Safety factors and personal margins

The corrected chart figure is still a gross figure, and rules and good practice add margins in different ways.

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• EASA commercial air transport, Class B. Under CAT.POL.A.305 the takeoff distance multiplied by 1.25 must not exceed the takeoff run available when there is no stopway or clearway; with them, the distance must fit the takeoff run available, 1.15 times it the takeoff distance available and 1.3 times it the accelerate-stop distance available. The 528 m above therefore needs 660 m of runway. For landing, the airplane must stop within 70 percent of the landing distance available, a factor of about 1.43, with a further 15 percent if the runway may be wet.
• EASA non-commercial flights. NCO.POL.110 requires only, in general terms, that the performance be adequate for the flight and the aerodromes used. The Class B factors are not mandatory for a private flight, but their reasons apply to any takeoff and landing.
• FAA, Part 91. Under 14 CFR 91.103 the pilot in command must, before every flight, become familiar with the runway lengths at the airports of intended use and the flight manual's takeoff and landing distance data, or other reliable information where there is none. No factor is prescribed, and the chart data contain none.

Pilots therefore add a personal margin, a common rule of thumb being 50 percent or more on top of the chart figures for short or obstructed strips, since an older airplane with a tired engine and a less than perfect rotation will not match the test pilot's numbers. A decision point, a landmark by which the airplane must be airborne or the takeoff is abandoned, turns the margin into a plan. On landing, flying the published threshold speed protects it best.

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.