CASA Performance Chart Figure 3: How to Read the Take-off Weight Chart (RPL Exam)

If there's one skill that separates students who pass the CASA theory exam from those who don't, it's reading performance charts. Figure 3 — the take-off weight chart — appears in virtually every RPL and PPL theory exam, and getting it right is worth multiple marks.

This guide walks you through Figure 3 step by step, explains what each section and reference line means, and gives you the method you need to confidently answer performance chart questions on exam day.

What is Figure 3?

Figure 3 is the take-off weight performance chart used in Australian CASA theory exams. It determines the maximum take-off weight for an aircraft given the current conditions, or alternatively, the minimum take-off distance required for a given weight. The chart accounts for:

• Outside Air Temperature (OAT) — hotter air is less dense, reducing performance
• Pressure Height — higher altitude means less dense air
• Take-off Distance Available (TODA) — the runway length available for take-off, in metres
• Surface type — short dry grass, short wet or long dry grass, or long wet grass
• Runway slope — level, upslope, or downslope
• Wind component — headwind improves performance; tailwind reduces it

The chart is based on a specific aircraft type (typically a Cessna 172 or similar trainer). The method for reading it is always the same.

Two types of exam questions

Exam questions using Figure 3 come in two forms:

1. Maximum take-off weight — "Given these conditions and runway, what is the heaviest the aircraft can be at take-off?" (answer in kg)
2. Minimum take-off distance required — "Given these conditions and aircraft weight, what is the shortest runway you need?" (answer in metres)

Both use the same chart — you read it in a slightly different direction depending on which value you are solving for.

The layout of Figure 3

Figure 3 is a multi-panel nomogram — a chart with several linked sections that you navigate using reference lines. The main sections are:

1. Atmosphere section (bottom-left) — pressure height on the left axis, with temperature lines running through it
2. TODA section (upper) — take-off distance available curves, in metres
3. Surface correction section — reference lines for different runway surfaces
4. Slope correction section — adjustments for runway gradient
5. Wind and weight section — wind component lines leading to the final weight reading on the weight scale

A separate climb-limit section (bottom-right) uses the wind component to determine whether the aircraft can safely climb after take-off. Your final answer is the lower of the distance-limited weight and the climb-limited weight.

Step-by-step method: finding maximum take-off weight

Here is the standard method for the most common question type — finding the maximum take-off weight. Practise this sequence until it becomes automatic.

Step 1 — Enter at pressure height and temperature

Find your pressure height on the left axis of the atmosphere section. Move horizontally right until you reach the line for your given temperature. Mark this intersection point.

Tip: If the question gives you QNH and aerodrome elevation instead of pressure height, calculate it first: PH = Elevation + (1013 − QNH) × 30.

Step 2 — Move up to the TODA curve

From your atmosphere intersection, move vertically upward into the TODA section. Find the curve that corresponds to your take-off distance available (in metres) and mark where your vertical line crosses it.

Step 3 — Apply surface correction

Move horizontally right to the surface reference line. If your surface is short dry grass (the reference condition), continue straight through. For wet or long grass conditions, follow the diagonal reference lines to the appropriate surface line — this effectively reduces performance to account for the softer surface.

Step 4 — Apply slope correction

Continue horizontally right through the slope section. Find the line for your runway gradient (level, 2% upslope, or 4% upslope). Upslope reduces performance; downslope improves it.

Step 5 — Apply wind and read weight

From the slope section, move vertically downward to your wind component line. Headwind improves performance (allowing more weight); tailwind reduces it. From the wind intersection, move horizontally left to the weight scale and read your answer in kilograms. This gives you Weight A — the distance-limited weight.

Step 6 — Check the climb limit

In the separate climb-limit section at the bottom-right, enter at your wind component value and read the climb-limited weight (Weight B). Your final answer is the lower of Weight A and Weight B — the aircraft is limited by whichever constraint is more restrictive.

Worked example

Here is a sample question in the style used on the CASA RPL theory exam:

Given: Temperature 20°C, Pressure Height 4,000 ft, TODA 1,000 m, level slope, short dry grass surface, headwind 10 kt. Determine the maximum take-off weight.

Working through Figure 3:

1. Enter the atmosphere section at PH 4,000 ft — move right to the 20°C temperature line
2. Move vertically up to the 1,000 m TODA curve
3. Surface is short dry grass (reference condition) — move straight through
4. Slope is level — move straight through
5. Move down to the 10 kt headwind line — move left to the weight scale to read Weight A
6. Check the climb limit for the 10 kt headwind — read Weight B
7. Take the lower value — answer: approximately 1,000 kg

The exact numbers depend on the specific Figure 3 in your exam, but the method is identical every time. Try this exact question on our interactive Figure 3 chart to see the solution path traced step by step.

Finding minimum take-off distance required

For the reverse question type — "what distance do you need?" — you work through the chart in the opposite direction:

1. Start at your known take-off weight on the weight scale
2. Move right to the appropriate wind component line
3. Move up through slope and surface corrections (in reverse)
4. Read the TODA value where your trace crosses the TODA curves
5. Verify that your atmosphere conditions (temperature and pressure height) support this result

This question type appears regularly in exams. Our interactive Figure 3 practice tool generates both question types randomly so you are prepared for either.

Common mistakes on Figure 3 questions

• Confusing pressure height with elevation — if given QNH and elevation, you must calculate pressure height first: PH = Elevation + (1013 − QNH) × 30.
• Ignoring surface type — wet or long grass significantly reduces the maximum weight. Always check the surface condition given in the question.
• Forgetting the climb limit — even if the runway distance allows a heavy weight, the climb limit may be more restrictive. Always check both and take the lower value.
• Reading TODA in feet instead of metres — the TODA scale on Figure 3 uses metres. Do not confuse it with altitude values in feet.
• Using the wrong direction on the wind scale — headwind allows more weight; tailwind means less. Make sure you follow the correct wind line direction.
• Not interpolating between reference lines — if your value falls between two TODA curves or weight lines, estimate proportionally. Do not just round to the nearest line.

Why performance charts matter for safety

Beyond the exam, performance charts are a critical pre-flight tool. Before every take-off, pilots calculate whether their aircraft can safely depart from the available runway given the conditions. Incorrect performance calculations are a contributing factor in numerous aviation incidents.

The RPL and PPL theory exams emphasise performance chart reading because CASA wants pilots who understand — not just pass — this material.

How many performance chart questions are in the exam?

The RPL theory exam typically includes 3–5 questions on performance and loading topics, which includes Figure 3, Figure 4 (landing distance), and weight and balance calculations. Getting these right is often the difference between passing and having to resit.

Performance chart questions are also predictable — the method does not change. Unlike knowledge-recall questions where you may not know the answer, performance chart questions reward students who have practised the technique.

Summary: reading Figure 3

1. Enter at pressure height and temperature — find the intersection in the atmosphere section
2. Move up to your TODA curve — the take-off distance available in metres
3. Apply surface correction — wet or long grass reduces performance
4. Apply slope correction — upslope reduces performance
5. Apply wind and read weight — headwind helps, tailwind hurts
6. Check the climb limit — take the lower of the two weight values

Practise this method 10–15 times with different values using our interactive chart tool until you can do it in under two minutes. On exam day, Figure 3 will be marks you can bank.

Related Resources

• Performance Charts Overview
• Performance Study Guide