9.1 Takeoff Performance Speeds & Balanced Field Concept

Takeoff Speeds and Runway Analysis

Transport-category takeoff planning uses approved AFM data to demonstrate both stopping and continuing capability under the applicable certification assumptions. The dispatcher compares the computed performance with runway declared distances, obstacles, weather, airplane configuration, and maintenance restrictions. A mnemonic such as “balanced field” describes one calculation concept; it does not replace the approved analysis or the crew's aircraft-specific rejected-takeoff procedure.

Define the speeds before using them

VEF is the speed at which the critical engine is assumed to fail for the performance calculation. V1 is the maximum speed by which the first action to stop must begin within accelerate-stop distance, and also relates to the minimum continuation speed after the assumed engine failure. VR is rotation speed. V2 is takeoff safety speed. VMCG and VMCA are minimum-control speeds on the ground and in the air. VMBE represents the brake-energy limitation used in applicable approved performance analysis.

Section 25.107(a) requires VEF not less than VMCG, and V1 not less than VEF plus the speed gained during the demonstrated interval between engine failure and the pilot's first stopping action. Thus the familiar VMCG ≤ V1 relationship is not a complete description of the lower bound. Section 25.107(e) makes VR no lower than V1 or 1.05 VMC, with further liftoff and screen-height requirements. Use the applicable AFM's speeds rather than calculating an operational V1 from only these two inequalities.

Section 25.107(b) sets different V2min stall-speed factors for specified aircraft configurations, including 1.13 VSR in some cases and 1.08 VSR in others, together with the 1.10 VMC requirement and other constraints. Neither V2 = 1.13 VSR nor V2 = maximum L/D is a universal dispatch formula. Certification basis and aircraft design matter.

Engine failure and rejected takeoff

The certification model includes an assumed engine failure before V1 and the recognition/action interval. Consequently, “every failure before V1 means abort” is an inadequate training rule. Crews apply their approved rejected-takeoff policy, including whether the airplane can safely fly and whether a stop can be completed. A failure exactly at a particular displayed speed does not guarantee either an overrun or safe continuation regardless of other circumstances.

The dispatcher's task is to supply correct, applicable data and restrictions, not improvise cockpit memory actions. If the approved analysis cannot satisfy the applicable stopping, continuing, obstacle, or brake-energy requirements, change weight, runway, configuration, or the plan before departure. Do not infer that adding thrust alone cures every limiting condition.

Declared distances and screen height

TORA is takeoff run available. TODA adds the available clearway to TORA. ASDA adds a stopway to TORA. LDA is landing distance available. They may differ from the physical pavement length. A clearway is not stopping pavement; a stopway is not automatically landing runway. Check current airport data and NOTAMs before assigning credit.

Approved dry-runway takeoff-distance data generally include engine-inoperative distance to 35 feet and the applicable all-engine factor. Wet-runway data can use a 15-foot engine-inoperative screen-height provision with its associated requirements, including the required V2 achievement and subsequent obstacle analysis. This is not permission to discard the net takeoff flight path's obstacle clearance. Reverse-thrust credit also depends on the certification condition and approved data; do not import wet-runway credit into a dry-runway chart.

A clearway's usable credit is limited by the applicable operational rule and AFM analysis. The definition in § 1.1 describes its dimensions and obstacle plane; the statement that § 1.1 itself universally caps its usable length at 50 percent of TORA is incorrect. Identify the actual operational limit when applying clearway credit.

Balanced and unbalanced fields

A balanced field uses a decision speed for which the limiting accelerate-stop and engine-inoperative accelerate-go requirements are equal under the stated assumptions. Raising V1 generally increases the stopping distance and reduces the continuing distance; lowering it does the reverse. The optimum for a runway with unequal declared distances or significant obstacles may be unbalanced.

For an illustrative analysis, suppose approved data at a proposed weight give 7,000 feet accelerate-stop and 7,400 feet takeoff distance, while ASDA is 7,200 and TODA 7,300 feet. The stop requirement fits, but the takeoff-distance requirement does not. The flight is not acceptable merely because one comparison passes. A permitted V1 adjustment, weight reduction, or another runway must satisfy all applicable limits, including TORA and obstacles.

Reduced thrust and fixed derates

The assumed-temperature method selects thrust appropriate to an assumed temperature higher than actual temperature, within approved limitations. FAA AC 25-13 supplies certification guidance, including a maximum 25 percent reduction for reduced thrust relative to the approved takeoff thrust basis. A fixed derate is an approved lower rating with its own performance and control-speed data. The two methods are distinct and may be combined only as authorized.

Do not universalize airline-specific prohibitions about anti-skid, contamination, or windshear without consulting the AFM and approved procedures. These conditions can make reduced thrust unavailable or inappropriate; the controlling restriction is the approved aircraft/operation data. A fixed derate does not mean the crew is physically incapable of selecting higher thrust. Higher thrust can invalidate the lower control-speed assumptions, so follow the approved limitation and emergency procedures.

Practical verification

Before accepting a runway-analysis result, verify the airplane variant and engine rating, weight, pressure altitude, temperature, wind and gust treatment, runway slope and condition, flap setting, bleed/anti-ice configuration, inoperative equipment, and obstacle procedure. Confirm the output speed units and whether the data are dry, wet, or contaminated. A correct arithmetic result using the wrong configuration remains an incorrect dispatch decision.

Official References

Source check: 2026-10-12. Transport performance certification; Part 121 performance rules. For operational use, apply current issued authorizations and the assigned aircraft’s approved data.