Single-Engine Class B Takeoff and Climb Performance

A single-engine Class B airplane is a single-engined propeller airplane, piston or turboprop, with no more than nine passenger seats and a maximum takeoff mass of no more than 5,700 kg, as classed by the performance rules of EASA's commercial air transport regulation, Part-CAT. Its takeoff rules are short beside those of a Class A airplane: one distance to a 50 ft screen, corrected for the runway surface, slope and wind, then factored. There is no decision speed, no accelerate-stop distance to compute and no regulatory climb gradient; instead the airplane is kept out of conditions in which an engine failure would leave the pilot unable to see where to land.

The rules are a staple of the EASA CPL and ATPL performance examinations, subject 032, which use the data of the UK CAA's CAP 698 examination manual. Landing is covered in single-engine Class B landing performance and the twin's rules in multi-engine Class B takeoff and climb.

What a single-engine Class B airplane is

Annex I to Regulation (EU) No 965/2012 defines performance Class B airplanes as airplanes powered by propeller engines with a maximum operational passenger seating configuration (MOPSC) of nine or less and a maximum takeoff mass of 5,700 kg or less. Both limits must be met. The class takes in singles and twins, piston and turboprop, and its rules form Chapter 3 of the performance subpart of Part-CAT, from CAT.POL.A.300 onward (see performance classes and data). A twin can end up under the single-engine rules: CAT.POL.A.300(b) treats two-engined airplanes that do not meet the climb requirements of CAT.POL.A.340 as single-engined.

For private flights the FAA prescribes no factor either: 14 CFR 91.103(b) requires the pilot to know the runway lengths and the airplane's takeoff and landing distance data.

Operating restrictions: VMC, terrain and SET-IMC

A single whose engine stops can only glide, so Part-CAT keeps commercial singles where a forced landing can be made with the ground in sight. Unless the operator holds a SET-IMC approval:

• CAT.POL.A.300(a): no operation at night, or in IMC except under special VFR;
• CAT.OP.MPA.136: operation only along routes or within areas whose surfaces permit a safe forced landing;
• CAT.POL.A.320: after an engine failure en route the airplane must be able to reach a point from which a safe forced landing can be made, which the AMC places 1,000 ft above the intended landing area; a SET-IMC operator is exempt only while it uses a risk period. EASA guidance adds that relying on a glide to a forced landing is clearly incompatible with flight above a cloud layer extending below the minimum safe altitude (see single-engine Class B en-route performance).

A commercial single therefore departs by day and, except under special VFR, in VMC, with its pilot able to see and avoid obstacles. Its takeoff flight path has no obstacle clearance requirement: CAT.POL.A.310, which has one, applies to multi-engined airplanes only. Where obstacles or a forced-landing area must be seen on departure, the operator's takeoff minima can add conditions such as a ceiling (AMC1 CAT.OP.MPA.110).

SET-IMC, single-engined turbine airplane operations at night or in IMC, is the exception. Introduced by Regulation (EU) 2017/363 and set out in Subpart L of Part-SPA, it is open only to turbine singles whose operator holds an approval. The operator must show engine reliability for the airframe-engine combination, which the AMC sets as a power loss rate below 10 per million flight hours, normally with at least 100,000 hours of in-service experience; engine trend monitoring and a propulsion reliability program; crew training; procedures that include forced landings in all weather; and a safety risk assessment, covering any risk period, a part of the flight during which no landing site has been selected. The airplane must carry, among other items, two separate electrical generating systems, two independently powered attitude indicators, weather-detecting equipment, an area navigation system programmed with the landing sites and a radio altimeter.

For the takeoff, AMC1 CAT.OP.MPA.110 sets SET-IMC minima no lower than 800 m RVR whenever the surface ahead of the runway does not allow a safe forced landing, unless a risk period is used. The surface considered lies under the path from lift-off until the airplane could turn back to the runway or glide to the next landing site.

Takeoff distance requirements

Under CAT.POL.A.305 the takeoff mass must not exceed the flight manual maximum for the pressure altitude and temperature at the aerodrome. The unfactored takeoff distance of the flight manual, the gross distance from the start of the takeoff run to 50 ft above the surface, must then fit the runway:

The rule text, CAT.POL.A.305(b)(2), puts "or" before the last of the three, but read as alternatives the first alone, the unfactored distance within the TORA, would cancel the 1.25 factor wherever any stopway or clearway exists, so all three apply.

The takeoff run available (TORA) is the length declared suitable for the ground run, the takeoff distance available (TODA) the TORA plus any clearway, and the accelerate-stop distance available (ASDA) the TORA plus any stopway (see declared distances). The 1.25 factor lets the gross distance use no more than 80 percent of the TORA. A clearway on its own gains nothing: with no stopway the ASDA equals the TORA, and 1.3 times the distance must fit within it, a stricter test than 1.25.

The operator must account for the mass at the start of the takeoff run, the pressure altitude and temperature, the runway surface condition and type, the slope in the direction of takeoff, and not more than 50 percent of the reported headwind component or not less than 150 percent of the reported tailwind component. The distance the airplane needs to reach the screen in the actual conditions, the flight manual distance with the corrections applied, is what exam texts call the takeoff distance required (TODR).

Part-CAT asks a single for no accelerate-stop distance and no V1, so the ASDA serves only as a check on the takeoff distance. An engine failure after lift-off in a single leaves one option, to land ahead or within about 30° either side (see engine failure after takeoff in a single).

Surface, slope and wind corrections

Unless the flight manual says otherwise, AMC1 CAT.POL.A.305 gives these surface factors, applied in addition to the regulatory factor:

The grass runway factor covers only grass up to 20 cm long on firm soil, which the AMC defines as showing wheel impressions but no rutting; longer grass and soft ground are not covered. The AMC warns that on grass the pilot of a single should assess the rate of acceleration and the distance it adds, and that a rejected takeoff on very short wet grass over firm subsoil can be slippery enough to increase distances significantly. A wet paved runway, one with visible dampness or water up to 3 mm deep, needs no takeoff correction, because the wet surface barely affects the acceleration; the flight manual chart itself assumes a dry runway. EASA guidance calls takeoffs from contaminated runways inadvisable, best delayed until the runway is cleared (see wet and contaminated runways).

The runway slope correction of AMC2 CAT.POL.A.305 adds 5 percent to the takeoff distance for each 1 percent of upslope. A downslope earns no credit, which adds margin. Corrections for slopes beyond 2 percent need flight manual or operations manual data, procedures and crew training shown to the competent authority.

The factors multiply. A worked example, with the wind already factored in the chart:

• gross takeoff distance from the chart: 520 m;
• dry grass: 520 × 1.2 = 624 m;
• 1 percent upslope: 624 × 1.05 = 655 m;
• regulatory factor: 655 × 1.25 = 819 m of TORA required.

On a TORA of 800 m the 1.25 test fails. With a 100 m stopway and a 100 m clearway, giving a TODA and an ASDA of 900 m, the alternative tests pass: 655 m fits the TORA, 655 × 1.15 = 753 m the TODA and 655 × 1.3 = 852 m the ASDA. Without the stopway the ASDA would be 800 m and the third test would fail.

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Screen height and takeoff speeds

The Class B takeoff distance ends at a screen height of 50 ft, for singles and twins alike, against 35 ft, or 15 ft on a wet runway, for Class A. Under CS-23 up to Amendment 4 a single-engine landplane's rotation speed VR may not be less than VS1, the stall speed in the configuration concerned, and its speed at 50 ft not less than the higher of a speed safe under all reasonably expected conditions and 1.2 VS1. Twins add margins above the minimum control speed (see V-speeds).

The flight manual graph prints the rotation and 50 ft speeds in an inset box, and its distance holds only if those speeds and the stated technique are flown. The main variables (see factors affecting takeoff and landing performance):

• mass: the distance grows roughly with its square, about 20 percent for 10 percent more mass;
• pressure altitude and temperature: less power from a normally aspirated engine and a higher true airspeed at the same indicated speed, so a longer run;
• flap: takeoff flap lowers the speeds and shortens the ground run, but its drag flattens the climb, so with obstacles close ahead the distance to 50 ft and the climb for each setting decide;
• tailwind: as a rule of thumb, 10 percent of the lift-off speed adds about 20 percent.

Takeoff climb requirements

Part-CAT sets no climb gradient for a single after takeoff: the climb requirements of CAT.POL.A.340, including 4 percent with all engines operating, apply to two-engined airplanes, and the obstacle clearance of CAT.POL.A.310 to multi-engined ones. The single relies on its CS-23 certification climb performance.

The pilot still needs the climb data, because a distance to 50 ft says nothing about the trees beyond the boundary. Rate and gradient of climb both fall as mass, altitude and temperature rise.

Obstacles are fixed to the ground, so the gradient that matters is the ground gradient (see climb performance). In feet per nautical mile it is the rate of climb in ft/min × 60 ÷ groundspeed in knots. At 700 ft/min and 84 kt TAS in still air that is 500 ft per NM, about 8.2 percent. A 12 kt tailwind raises the groundspeed to 96 kt and lowers the gradient to about 440 ft per NM, 7.2 percent; a 12 kt headwind gives about 580 ft per NM, 9.6 percent. A downwind departure toward rising ground is penalized twice: a longer run and a flatter climb.

Over a close obstacle the pilot climbs at Vx, the best angle of climb speed, then accelerates to Vy, the best rate of climb speed, which is the higher of the two; they converge with altitude and meet at the absolute ceiling (see Vx and Vy).

Using the CAP 698 SE graphs

CAP 698, the UK CAA's examination performance manual, contains the data of the single-engine piston airplane of the European theory examinations, SEP1. Its takeoff graph is a carpet plot, read from left to right through four grids: outside air temperature and pressure altitude, takeoff mass, wind component, and obstacle height or the 50 ft screen. At each grid the line runs from the reference line parallel to the guide lines, then across to the next. The wind grid already contains the 50/150 factoring, which is why its tailwind lines are steeper, so the reported wind is entered as it is.

Before using the graph, check its associated conditions: full takeoff power, the flap setting it was drawn for, a paved, level and dry runway, and the speeds in the inset box. The graph gives the gross distance; the surface and slope corrections and the regulatory factor follow. Questions often ask for the maximum takeoff mass instead: divide the TORA by 1.25 and by the corrections to find the largest gross distance allowed, then work back through the graph from that distance to the mass. With a TORA of 1,000 m on level dry grass, the gross distance may not exceed 1,000 ÷ 1.25 ÷ 1.2 = 667 m.

The climb graph, drawn for one climb speed, power setting and configuration, is entered with temperature, pressure altitude and mass; its still-air result must be corrected for wind before the gradient is used against obstacles. Common exam errors: applying the wind rule twice, adding factors, using the 1.43 landing factor and crediting a downslope.

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.