What is Accelerate-Go Distance?
Accelerate-go distance is a critical performance metric for multi-engine aircraft—the total distance required to accelerate to decision speed (V1), experience an engine failure, continue the takeoff on remaining engine(s), and climb to a specified height (typically 35 or 50 feet) above the runway.
This metric forms an essential component of the takeoff performance calculations pilots must perform before departure. Single-engine aircraft are exempt from this calculation—they simply cannot continue takeoff following engine failure.
Key Components of Accelerate-Go Distance
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Initial Acceleration: The aircraft accelerates on the runway from a standstill to the critical decision speed (V1).
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Recognition and Continuation: The pilot identifies the engine failure and makes the decision to continue the takeoff.
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Continued Acceleration and Liftoff: Using reduced power, the aircraft continues to accelerate to rotation speed (VR) and then lifts off.
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Climb: The aircraft ascends to the standard obstacle clearance height (35 or 50 feet, depending on the regulatory framework).
These phases are influenced by variables such as aircraft weight, atmospheric conditions, and runway characteristics, requiring precise calculations to ensure obstacle clearance despite reduced power.
Calculating Accelerate-Go Distance
The calculation covers the total distance required for the aircraft to accelerate to V1 (assuming engine failure occurs at this critical moment), continue to liftoff, and climb to standard obstacle height at takeoff safety speed (V2).
Normal takeoff calculations incorporate a 15% safety margin for all-engines-operating scenarios. Accelerate-go distance calculations, however, do not include this safety buffer.
Performance Factors Influencing Takeoff
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Aircraft Weight: Higher weight requires extended acceleration and liftoff distances.
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Engine Power & Environment: Air density fluctuations—driven by temperature, humidity, and altitude—directly impact engine performance. Hot, humid, high-elevation conditions reduce power output.
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Runway Conditions: Contamination (water, snow, ice) or slope extends required distances. Headwinds provide assistance; tailwinds create penalties.
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Pilot Technique: Accurate, timely execution is critical—especially the V1 decision point and subsequent rotation during engine failure scenarios.
Implications of Engine Failure During Takeoff
Engine failure during takeoff represents one of aviation’s most critical emergency scenarios. The timing relative to V1 (decision speed) dictates the appropriate response.
If engine failure occurs after V1, the response is different. The pilot must continue takeoff—calculations have already confirmed the aircraft can safely become airborne and climb on remaining power.
This dual-scenario approach explains why accurate accelerate-go and accelerate-stop calculations are essential. They ensure a safe course of action exists—whether stopping or climbing.
Safety Margins in Aviation
Safety margins are fundamental to aviation operations, creating essential buffers for performance variables, environmental fluctuations, and human factors. Within takeoff performance, these margins ensure safe operation even when conditions deviate from calculated parameters.
Regulatory authorities mandate specific safety margins. Runway length must accommodate both accelerate-stop distance (for aborted takeoffs) and accelerate-go distance (for continued takeoffs following engine failure). The more restrictive distance, combined with additional required margins, determines minimum runway requirements for any given takeoff weight.
These buffers accommodate real-world variables—subtle pilot technique differences or runway condition variations—that theoretical models cannot perfectly predict.
Many operators exceed regulatory minimums with supplementary margins. Conservative weight limits are especially common in challenging operational environments.
Comparing Accelerate-Go and Accelerate-Stop Distances
Accelerate-go and accelerate-stop distances represent two critical performance parameters governing aircraft takeoff capability during engine failure scenarios. Though related, they serve distinct purposes and establish different operational limitations.
| Feature | Accelerate-Go Distance | Accelerate-Stop Distance |
| :— | :— | :— |
| Definition | Total distance to accelerate to V1, lose an engine, continue takeoff, and climb to a safe height (35 or 50 ft). | Total distance to accelerate to V1, lose an engine, recognize the failure, and bring the aircraft to a complete stop. |
| Pilot Action at V1 | Continue the takeoff. | Abort the takeoff. |
| Primary Concern | Clearing obstacles in the departure path with reduced engine power. | Having enough runway length to stop safely. |
| When Limiting | Often on runways with significant obstacles in the departure path. | Often on shorter runways where stopping distance is critical. |
