10.performance-charts. Performance Charts
Performance charts allow a pilot to predict the takeoff, climb, cruise, and landing performance of an aircraft for a given set of conditions. The data are derived from actual flight tests conducted by the manufacturer using a new airplane flown by an experienced test pilot. Because production aircraft accumulate wear and tear, pilots should consider book values as best-case numbers and apply a margin of safety in real-world planning.
Types of Performance Charts
Performance information in the Pilot's Operating Handbook (POH) or Aircraft Flight Manual (AFM) is typically organized in Section 5 and includes:
- Takeoff charts — ground roll and total distance over a 50 ft obstacle.
- Climb charts — fuel, time, and distance to climb; rate of climb.
- Cruise performance charts — true airspeed, fuel burn, and endurance at various power settings and altitudes.
- Range and endurance charts — maximum distance or time aloft.
- Landing charts — ground roll and total distance over a 50 ft obstacle.
- Crosswind and headwind component chart — resolves reported wind into runway components.
- Stall speed chart — stall speeds at various bank angles, weights, and configurations.
Chart Formats
The FAA recognizes three main formats:
- Tables — Data are arranged in rows and columns. The pilot enters the table with known conditions (pressure altitude, temperature, weight) and reads out performance values. Interpolation between published values is required when conditions fall between table entries.
- Graphs — A continuous chart with multiple reference lines. The pilot enters at a known value, projects up or across to a reference line, then follows the line to the next variable, repeating until the answer is read.
- Combined graph/table — Hybrid presentations common in modern POHs.
Conditions Required Before Use
Before consulting any performance chart, the pilot must determine:
- Pressure altitude — set the altimeter to 29.92 in Hg and read the indicated altitude.
- Outside air temperature (OAT) — used with pressure altitude to determine density altitude.
- Aircraft gross weight — actual takeoff or landing weight.
- Wind component — headwind or tailwind on the runway.
- Runway surface and slope — dry/wet, paved/turf, level/upslope.
- Configuration — flap setting, power setting, and technique (short field, soft field, etc.).
Interpolation
When the actual condition lies between two charted values, linear interpolation is used. For example, if takeoff distance at 2,000 ft pressure altitude is 1,000 ft and at 3,000 ft is 1,150 ft, the value at 2,500 ft is:
1,000 + (0.5 × (1,150 − 1,000)) = 1,075 ft
Never extrapolate beyond the published range — the data may be invalid or unsafe outside tested conditions.
Example: Takeoff Distance Chart
A Cessna 172 takeoff chart at 2,400 lb gross weight, with the following conditions:
- Pressure altitude: 2,000 ft
- Temperature: 20 °C
- Wind: 9 kt headwind
- Paved, level, dry runway
- Short-field technique, flaps 10°
From the chart, the ground roll might read 860 ft and the total distance over a 50 ft obstacle 1,570 ft. Each 9 kt of headwind allows a 10% reduction; each 2 kt of tailwind (up to 10 kt) requires a 10% increase. For a dry grass runway, add 15% to the ground roll. After applying corrections, the corrected total distance might be approximately 1,400 ft.
Crosswind Component Chart
Given a reported wind of 250° at 20 kt and runway 30, the angle between wind and runway is 50°. Entering the chart at 50° and following the 20 kt arc, the pilot reads:
- Headwind component: ≈ 13 kt
- Crosswind component: ≈ 15 kt
The pilot then compares the crosswind component to the airplane's maximum demonstrated crosswind (a not-limiting but advisory value) before proceeding.
Density Altitude Chart
Density altitude is found by entering the chart with OAT on the bottom and pressure altitude on the diagonal lines, then reading density altitude on the left scale. High density altitude reduces engine power, propeller efficiency, and aerodynamic lift, lengthening takeoff and landing distances and decreasing climb rate.
Practical Considerations
- Always use the chart that matches the specific airplane model and serial number range.
- Apply a personal safety factor (commonly 50% added to takeoff and landing distances).
- Account for non-standard conditions not modeled in the chart, such as gusty winds, contaminated runways, or worn brakes.
- For Part 91 operations, performance computation is required by 14 CFR 91.103 as part of preflight action whenever a flight is not in the vicinity of an airport.
Properly using performance charts is a hallmark of professional airmanship. The numbers themselves are only as good as the inputs and the pilot's willingness to add conservative margins.