Aircraft Performance: Complete RPL/PPL Study Guide

Australian aviation regulations require pilots to ensure that their aeroplane has adequate performance for all phases of flight. Under CASR Part 91 and the Part 91 Manual of Standards (MOS), specifically Chapters 8 (Take-off) and 9 (Landing), a pilot must determine that the aeroplane can safely take off, climb, approach, and land, clearing all obstacles by a safe margin. These requirements are also supported by the legacy CAO 20.7.4, which details performance requirements for take-off and landing of aeroplanes.

Performance data used for these calculations must be sourced from an approved document, such as the Aircraft Flight Manual (AFM), the manufacturer's data manual, or other data approved under CASR Part 21. Pilots must not rely on unofficial sources or estimations when determining performance figures.

Factors affecting take-off and landing performance

When calculating take-off and landing performance, you must account for the following critical factors:

• Take-off and landing distance available (TODA/LDA): The usable runway length, including any clearway or stopway where applicable.
• Pressure altitude and temperature: These determine density altitude, which directly affects engine power output and aerodynamic performance. Higher density altitudes reduce performance.
• Runway gradient (slope): An uphill slope increases the take-off distance required, while a downhill slope reduces it — and vice versa for landing.
• Runway surface and condition: Grass, gravel, wet, or soft surfaces increase the distance required compared to a dry, sealed runway. The AFM or approved data will provide correction factors.
• Wind direction and speed: A headwind reduces the ground roll required, while a tailwind increases it. When using AFM data, only 50% of a reported headwind and 150% of a reported tailwind should be used as a safety factor, unless the AFM specifies otherwise.
• Aircraft weight: A heavier aircraft requires more distance to take off and land. Performance must be calculated at the planned weight, not merely at maximum take-off weight (MTOW).
• Flap configuration: The use of flap affects both the take-off and landing distances. The correct configuration as specified in the AFM must be used.
• Weather forecasts and actual conditions: Pilots should consider forecast conditions at the time of departure and arrival, including temperature changes and wind variations.
• Obstacles in the take-off and approach paths: The aircraft must be able to clear all obstacles in the flight path by a safe margin after take-off and during approach.

Pilot in command responsibilities

It is the pilot in command's (PIC's) responsibility to ensure that performance calculations are completed before every flight and that the aeroplane can operate safely within the available distances and environmental conditions. If performance calculations show that the available distance is insufficient or obstacle clearance cannot be assured, the pilot must reduce aircraft weight, wait for more favourable conditions, or choose an alternative aerodrome.

Applying safety factors

Pilots should apply appropriate safety factors to the calculated performance figures. For aeroplanes with unfactored performance charts, the Part 91 Plain English Guide recommends applying specific safety factors based on MTOW. For take-off, a factor of 1.15 applies at MTOW ≤ 2,000 kg, increasing to 1.25 at MTOW ≥ 3,500 kg. For landing, a factor of 1.15 applies at MTOW ≤ 2,000 kg, increasing to 1.43 at MTOW ≥ 4,500 kg, with linear interpolation applied between these values.

Pressure altitude (PA) is the height above the standard 1,013.2 hPa datum. A higher PA means reduced atmospheric pressure, requiring a higher True Airspeed (TAS) for a given Indicated Airspeed (IAS), which subsequently increases take-off and landing distances.

Density altitude (DA) is pressure altitude corrected for non-standard temperatures. When the temperature is hotter than the International Standard Atmosphere (ISA), air density decreases. This decrease in air density markedly reduces engine power output and the aerodynamic lift generated by the wings. As a rule of thumb, each 1°C variation from ISA equals a 120 ft variation in DA. Furthermore, high humidity displaces oxygen, further reducing engine power during combustion.

Whenever practicable, aircraft should take off and land into the wind. A headwind reduces the ground speed required to achieve lift-off, thereby significantly shortening the take-off and landing rolls. Conversely, a downwind take-off or landing can add a substantial distance to your required runway length and should be avoided unless operationally necessary.

Headwind and tailwind effects

The direction of wind relative to your runway heading has a direct and significant effect on take-off and landing distances. Understanding this relationship is essential for safe performance planning.

• A headwind reduces ground speed for a given airspeed, meaning the aircraft reaches flying speed over a shorter ground distance. This reduces both take-off and landing rolls.
• A tailwind increases ground speed for a given airspeed, requiring a much longer ground roll to accelerate to flying speed (or to decelerate after landing). Even a small tailwind component can have a disproportionately large effect on take-off and landing distances.
• As a general rule of thumb, a headwind component of 10% of the lift-off speed reduces the take-off roll by approximately 19%, while a tailwind component of 10% of the lift-off speed increases it by approximately 21%. The effect is not symmetrical — tailwinds are more penalising than headwinds are helpful.

Crosswind considerations

Pilots must evaluate the crosswind component before every take-off and landing. Each aircraft type has a maximum demonstrated crosswind component published in the Pilot's Operating Handbook (POH) or Aircraft Flight Manual (AFM). Exceeding this limit is hazardous and must be avoided.

To estimate the crosswind component, pilots can use the crosswind component chart in the POH, or apply simple trigonometric rules:

• Wind angle 30° off the runway — crosswind component is approximately 50% (half) of total wind speed.
• Wind angle 45° off the runway — crosswind component is approximately 70% (sin 45° ≈ 0.71) of total wind speed.
• Wind angle 60° off the runway — crosswind component is approximately 87% of total wind speed.
• Wind angle 90° off the runway — the full wind speed acts as crosswind.

Windsock indications

Visual cues like windsocks are vital at all aerodromes, particularly at non-controlled aerodromes (CTAFs). The standard windsock used in Australia, in accordance with CASA's Manual of Standards (MOS) Part 139 (Aerodromes), is designed to be fully extended (horizontal) at approximately 25–30 kt. Key windsock indications include:

• Fully extended (horizontal) — wind speed of approximately 25–30 kt.
• At approximately 45° below horizontal — wind speed of roughly 15 kt.
• Drooping (nearly vertical) — calm or very light winds.

The windsock also shows wind direction — it points downwind, meaning the wind is blowing from the opposite end (the wide, open end of the sock faces into wind). Pilots should select the runway that allows take-off and landing into the direction the windsock's mouth is facing.

Operational considerations

Good performance planning requires up-to-date wind information and awareness of how conditions can change between the surface and circuit altitude. The following points are important for safe operations at all aerodrome types.

• Always check the latest ATIS, AWIS, or area forecast for wind information before flight.
• Be aware that surface wind can differ significantly from wind at circuit altitude or on approach.
• Wind shear and gusty conditions near the surface — particularly in the lee of obstacles or terrain — can dramatically affect aircraft performance and controllability.
• At non-towered aerodromes, if no windsock is visible or conditions are uncertain, consider overflying the field to assess conditions before joining the circuit.

The characteristics of the runway surface heavily influence an aircraft's acceleration during take-off and its deceleration during landing. Understanding how different surfaces affect both rolling resistance and braking friction is essential for accurate performance planning.

Rolling resistance during take-off

While concrete and bitumen offer minimal rolling resistance, natural surfaces like grass, gravel, or mud resist the aircraft's forward motion during the ground roll. Long, dense, or soft grass significantly increases rolling resistance, retarding acceleration and extending the take-off roll. However, it is important to note that wet short grass may actually reduce rolling resistance slightly during the take-off acceleration phase, as the moisture acts as a lubricant between the tyres and the grass surface. Despite this, pilots should not assume a shorter take-off roll on wet grass, as the surface may be soft underneath and other factors — such as reduced braking ability in the event of a rejected take-off — must be considered.

Braking friction during landing

The effect of surface conditions on landing differs significantly from take-off. During landing, the pilot relies on braking friction to decelerate the aircraft. Wet grass, even if short, severely reduces braking effectiveness because the water film between the tyres and the surface drastically lowers the coefficient of friction. This means that while wet short grass may slightly ease the take-off roll, it substantially increases landing distance due to degraded braking performance. Pilots must account for this increased landing distance when planning approaches to grass strips in wet conditions.

Aquaplaning

Free water on any runway surface — whether sealed or natural — can build up in front of the wheels, causing additional resistance during acceleration. More critically, standing water can lead to aquaplaning (hydroplaning), where the tyres ride on a film of water and lose contact with the surface entirely. This results in a near-complete loss of braking and directional control. Aquaplaning can occur on both sealed and natural surfaces and is more likely at higher speeds and with worn tyres or lower tyre pressures.

Tyre condition and pressure

Under-inflated tyres increase rolling resistance during take-off and are more susceptible to heat build-up, increasing the risk of tyre blowout during take-off or landing. A tyre failure at speed can cause a catastrophic loss of directional control. Pilots should ensure tyres are correctly inflated and in good condition during pre-flight inspections.

Summary of surface effects: take-off vs landing

The table below summarises how common surface conditions affect rolling resistance during take-off and braking friction during landing. Note that the same surface can have opposing effects across the two phases of flight.

• Dry long or dense grass: Increases rolling resistance, extending the take-off roll. Braking friction is reduced compared to sealed surfaces but remains better than wet grass, resulting in a longer landing roll than sealed surfaces.
• Wet short grass: May slightly reduce rolling resistance during take-off acceleration, but severely reduces braking friction on landing — significantly increasing landing distance.
• Wet long or dense grass, or mud: Increases rolling resistance during take-off and reduces braking friction on landing — an adverse effect in both phases.
• Gravel or soft ground: Increases rolling resistance substantially. May provide some braking friction but performance can be unpredictable and may cause directional control issues.
• Sealed surfaces (concrete or bitumen) when wet: Minimal change to rolling resistance, but reduced braking friction and an increased risk of aquaplaning.

Pilots operating from natural surface aerodromes should always apply appropriate performance corrections as specified in the aircraft's Pilot Operating Handbook (POH) and consider the current surface condition when calculating both take-off and landing distances. When in doubt, always apply conservative safety factors.

Aircraft performance is not just about having enough runway to leave the ground; it is also about clearing terrain safely after departure and during approach. Understanding Weight Altitude Temperature (WAT) limitations and obstacle clearance requirements is essential for safe flight planning.

WAT Limitations

WAT limitations are designed to ensure that an aircraft maintains a minimum prescribed climb performance after take-off, particularly in the event of an engine failure. Formally, WAT limits apply specifically to multi-engine aeroplanes and are defined under regulatory frameworks (including CAO 20.7.4 and CASR Part 91) to guarantee that, following the failure of one engine, the aircraft can still achieve an adequate climb gradient. The WAT limit defines the maximum weight at which the aircraft can meet the required climb performance for a given pressure altitude and temperature.

WAT limit charts are typically presented in the Aircraft Flight Manual (AFM) or the aircraft's performance data supplement. The pilot enters the chart with the aerodrome pressure altitude and the ambient temperature, and the chart yields the maximum permissible take-off weight that ensures the required climb gradient can be met with one engine inoperative (OEI). If the actual aircraft weight exceeds the WAT limit, the take-off must not be attempted until weight is reduced (by offloading fuel, passengers, or cargo) or conditions change favourably.

For single-engine aeroplanes, formal WAT limits as defined for multi-engine aircraft do not apply in the same regulatory sense, because there is no second engine to sustain flight following an engine failure. However, the underlying principle remains critically important: pilots of single-engine aeroplanes must still ensure that their aircraft has adequate climb performance after take-off to clear obstacles and terrain. This is achieved by consulting the AFM performance charts, which account for the effects of weight, altitude (density altitude), and temperature on climb performance. If conditions result in a climb gradient that is insufficient to clear obstacles on the departure path, the take-off should not be attempted.

Density Altitude and Its Effect on Performance

Density altitude is the altitude in the International Standard Atmosphere (ISA) at which the air density equals the actual air density at the location. It is the single most important factor in determining aircraft performance because it combines the effects of pressure altitude and temperature into one value. A high density altitude means the air is less dense, which results in:

• Reduced engine power output (less air mass entering the engine per cycle)
• Reduced propeller efficiency (less air mass being accelerated)
• Reduced lift generated by the wings at any given true airspeed (requiring a higher true airspeed and therefore a longer ground roll)

Density altitude increases with higher elevation, higher temperature, lower atmospheric pressure, and higher humidity. Pilots must always calculate density altitude — or use the AFM charts entering with pressure altitude and temperature — when planning take-off and landing performance, especially at elevated or hot-and-high aerodromes.

Obstacle Clearance — Take-off

For light single-engine aeroplanes, the take-off distance required as published in the AFM is typically measured from the start of the take-off roll to the point at which the aircraft reaches a height of 50 ft above the runway surface (the screen height). This 50 ft screen height is the standard reference for light aeroplanes under CASA regulations. Pilots must ensure that all obstacles on the extended centreline of the departure path can be cleared with an adequate margin.

It is important to understand the distinction between take-off distance and take-off run:

• Take-off run: The horizontal distance from the start of the take-off roll to the point at which the aircraft becomes airborne (lifts off the ground).
• Take-off distance: The horizontal distance from the start of the take-off roll to the point at which the aircraft reaches 50 ft above the runway surface. This includes the take-off run plus the distance to climb from lift-off to 50 ft.

AFM performance charts typically present take-off distances for specific conditions (ISA sea level, hard dry runway, zero wind, level runway). Pilots must then apply corrections for actual conditions. Factors that increase take-off distance and reduce climb performance include:

• High aircraft weight — increases stall speed, requires greater lift (and therefore a longer ground roll and higher speed before rotation), and reduces climb gradient
• High density altitude (high elevation, high temperature, low pressure) — reduces engine power, propeller efficiency, and lift
• Tailwind component — increases groundspeed at lift-off and therefore increases ground roll distance
• Upslope runway gradient — the component of gravity opposes acceleration during the ground roll
• Soft, wet, or contaminated runway surfaces — increase rolling friction and increase ground roll
• Use of grass runways versus sealed surfaces — grass surfaces typically increase take-off distance by a significant factor (commonly around 1.2 to 1.3 times the distance on a sealed surface, depending on grass condition)
• Failure to use the recommended flap setting — incorrect flap settings can increase take-off distance
• Low wind or calm conditions — no headwind benefit to reduce ground roll

Pilots should also apply a safety factor to the calculated take-off distance. CASA recommends (via AC 91-02) that pilots factor their AFM-derived performance figures to account for variables such as pilot technique, aircraft condition, and less-than-ideal surface conditions. A common practice is to add a factor of 1.15 (15%) or more to the AFM take-off distance to provide a safety margin.

Climb Gradient After Take-off

Clearing the 50 ft screen height at the end of the take-off distance is only the beginning. Pilots must also ensure that the aircraft's climb gradient is sufficient to clear all obstacles along the intended departure path. The climb gradient is the ratio of height gained to horizontal distance covered, usually expressed as a percentage or in feet per nautical mile.

The climb gradient is affected by:

• Aircraft weight
• Density altitude
• Aircraft configuration (flaps, gear)
• Wind (a headwind improves the climb gradient over the ground; a tailwind degrades it)

If terrain or obstacles along the departure path require a climb gradient that the aircraft cannot achieve under the prevailing conditions, the pilot must either reduce weight, wait for more favourable conditions (e.g., cooler temperatures), or choose an alternative departure path or aerodrome.

Obstacle Clearance — Landing

For light aeroplanes, the landing distance required in the AFM is calculated from a height of 50 ft above the landing threshold, at a speed of 1.3 V_SO (1.3 times the stall speed in the landing configuration), to a complete stop with maximum braking applied. V_SO is the power-off stall speed in the landing configuration (gear down, flaps fully extended).

The approach at 1.3 V_SO provides an adequate margin above the stall to account for gusts, turbulence, and minor speed variations during the approach. Approaching faster than 1.3 V_SO will increase the landing distance required, as the aircraft will float further before touching down and will have more energy to dissipate during the ground roll.

Factors that increase landing distance include:

• High aircraft weight — increases stall speed (and therefore approach speed) and increases kinetic energy to dissipate
• High density altitude — increases true airspeed for a given indicated airspeed, increasing groundspeed and ground roll
• Tailwind component — increases groundspeed at touchdown, significantly increasing ground roll
• Downslope runway gradient — gravity assists the aircraft's forward motion during the ground roll, increasing stopping distance
• Wet or contaminated runway surfaces — reduce braking effectiveness
• Higher than recommended threshold speed — increases float distance and ground roll
• Grass runways — while grass increases rolling friction (which can shorten dry ground roll), a wet grass surface significantly reduces braking action and can increase landing distance
• Late or incomplete use of braking — delays deceleration
• Failure to use the correct flap setting — affects approach speed and descent gradient

As with take-off, pilots should apply a safety factor to their calculated landing distance. CASA guidance in AC 91-02 recommends factoring AFM landing distances. A common factor for a dry, hard surface is 1.15 (15%). For heavier aircraft, higher factors apply: aircraft with a Maximum Take-off Weight (MTOW) between 2,000 kg and 4,500 kg use linear interpolation between 1.15 and 1.43, while aircraft with an MTOW of 4,500 kg or above use a factor of 1.43. Additional factors (e.g., for wet grass) may also be appropriate. The specific factors depend on the surface condition and the guidance applicable to the operation.

Note: Transport category aeroplanes use a screen height of 35 ft for take-off obstacle clearance calculations. For RPL/PPL purposes with light aeroplanes, the standard screen height is 50 ft for both take-off and landing.

Close-in Obstacles and Visual Illusions

Obstacles located close to the runway on the departure or approach path can force pilots to adopt abnormal pitch attitudes to clear them. This can create dangerous situations, particularly at low speed and low altitude. Attempting to climb steeply at low speed to clear an obstacle can lead to an aerodynamic stall or a loss of control.

On approach, obstacles such as trees, buildings, or rising terrain near the threshold can also create visual illusions. These illusions can cause pilots to misjudge their height, approach angle, or distance from the runway. For example:

• An upsloping runway or rising terrain on approach can create the illusion of being too high, tempting the pilot to fly a lower approach path — risking an undershoot.
• A downsloping runway can create the illusion of being too low, leading to an excessively high approach — risking a long landing and overrun.
• Narrow runways may appear longer than they are, giving the illusion of greater height — tempting the pilot to descend below the correct approach path.
• Wide runways may appear shorter, giving the illusion of being lower than actual — leading to an excessively high approach.
• Featureless terrain on approach (e.g., water, desert, snow) can remove visual references, making it difficult to judge height accurately — this is known as the "black hole" effect at night.
• Rain on the windscreen can refract light and make the runway appear further away than it is, tempting the pilot to fly a lower approach.

Pilots must always cross-reference visual cues with instruments (altimeter, VASI/PAPI if available) and use published approach procedures to maintain safe obstacle clearance. At unfamiliar aerodromes, thorough pre-flight planning using the En Route Supplement Australia (ERSA), NOTAMs, and aerodrome charts is essential to identify obstacles and terrain on departure and approach paths.

Planning Considerations — Summary

Before every take-off and landing, pilots should work through a structured performance assessment. This ensures that all relevant factors have been accounted for and that the operation can be conducted safely within the aircraft's demonstrated performance capability.

• Calculate the take-off and landing distances required using the AFM performance charts for the actual weight, pressure altitude, temperature, wind, runway slope, and surface condition.
• Apply appropriate safety factors to the AFM figures as recommended by CASA guidance.
• Compare the calculated distances with the available runway length (take-off distance available and landing distance available) as published in ERSA or on the aerodrome chart.
• Ensure the aircraft's climb gradient is sufficient to clear all obstacles along the departure path.
• For multi-engine aeroplanes, ensure the aircraft weight does not exceed the WAT limit for the prevailing conditions.
• Review ERSA and NOTAMs for obstacle information, terrain, and any relevant warnings for the aerodrome.
• Consider a go-around or missed approach plan in case obstacles or conditions prevent a safe landing.

Regulatory References

Performance requirements for take-off and landing in general aviation are found in CASR Part 91, specifically within Subpart 91.F (which addresses aircraft performance). Key regulations include regulation 91.795 (take-off performance) and regulation 91.800 (landing performance), which require pilots to ensure that their aircraft can comply with the performance requirements for the intended operation. Advisory Circular AC 91-02 provides detailed guidance on aircraft take-off and landing performance assessment for general aviation pilots, including recommended safety factors and methods for calculating performance.

The legacy CAO 20.7.4 also contains performance requirements applicable to certain aircraft operations, including WAT limitations for multi-engine aeroplanes. Note that Chapters 8 and 9 relating to take-off and landing performance are found in the CASR Part 135 Manual of Standards (for air transport operations with smaller aircraft), not in the Part 91 MOS. For RPL/PPL general aviation operations, pilots should refer to CASR Part 91 (Subpart 91.F), AC 91-02, the AFM, and CAO 20.7.4 (where applicable) to ensure compliance with performance requirements.

Related Resources

• Weight & Balance
• Aerodynamics
• Performance Charts Blog