Definition
A method of estimating an unknown value that falls between two known values in a table or chart by assuming the change between them is proportional. In aviation performance work, interpolation is used when the actual conditions (such as temperature, pressure altitude, or weight) sit between the rows or columns printed in a performance chart.
Plain English
Reading between the lines of a chart. If the chart gives you a number for 2,000 feet and another for 3,000 feet, but you need the value for 2,500 feet, you split the difference to estimate it.
Context Anchor
Pilots encounter interpolation when using aircraft performance charts and tables, especially for takeoff distance, landing distance, climb performance, and weight-related calculations.
Derivation
From the Latin interpolare, meaning 'to refurbish' or 'to insert something between.' The aviation use keeps the 'insert between' sense — you are inserting a calculated value between two values that are already given.
Why Pilots Care
Accurate interpolation produces reliable takeoff, climb, and landing performance numbers when exact chart entries are unavailable.
Analogy
If a ruler marks 4 inches and 5 inches, you can still estimate 4.5 inches halfway between them. Interpolation works the same way with chart values.
Grounding Statement
When a performance chart gives answers for 20°C and 30°C, but the actual temperature is 25°C, interpolation helps you estimate the answer between those two chart lines.
Intuition Check
Interpolation is not just guessing. It is a controlled estimate between known values, not simply rounding to whichever printed value looks easier to use.
Example Sentence 1
The temperature was 25 °C and the chart only listed values for 20 °C and 30 °C, so the pilot used interpolation to find the takeoff distance.
Example Sentence 2
By interpolating between the published fuel-flow rates at 65 percent and 75 percent power, she determined the correct cruise setting.