What is accelerate-stop distance in aviation?

It is the runway length required to accelerate to a decision speed (V1) and then bring the aircraft to a complete stop if takeoff is rejected.

How is accelerate-stop distance calculated?

It combines the distance to accelerate to V1, a 2-second allowance at V1, and the distance to decelerate to a stop, considering worst-case scenarios.

What factors increase accelerate-stop distance?

Higher aircraft mass, increased temperature, higher pressure altitude, tailwind, upsloping runway, and contaminated or wet surfaces all increase the required distance.

How does an error in V1 selection affect accelerate-stop distance?

Selecting a V1 that is too high increases the stopping distance required, potentially exceeding the available runway.

Can reverse thrust be used in accelerate-stop distance calculations?

Reverse thrust is only considered in wet runway calculations, not for dry runway accelerate-stop distances.

Accelerate-Stop Distance

Hard4 min readPerformance Aeroplanes

Moderately Examined

Why this matters

Understanding accelerate-stop distance is vital for safe takeoff planning, ensuring that the aircraft can always be stopped safely in the event of an emergency. It directly impacts operational decisions, runway selection, and weight limits, protecting both passengers and crew.

The accelerate-stop distance is the runway length required for an aircraft to accelerate to a decision speed (V1), experience an engine failure or choose to abort, and then safely come to a complete stop. This critical performance figure ensures that, in the event of a rejected takeoff at the last possible moment, there is enough runway available to halt the aircraft, accounting for real-world factors like reaction time and runway conditions.

Quick Check

Which of the following best describes the accelerate-stop distance on a dry runway for a multi-engine aeroplane?

AI Tutor

Go beyond the textbook.

Ask Avi AI about Accelerate-Stop Distance

In depth

Explanation

What Is Accelerate-Stop Distance?

Accelerate-stop distance (ASD) is the minimum runway length needed for an aircraft to accelerate from a standing start to V1 (the takeoff decision speed), and then, if takeoff is rejected at V1, decelerate to a complete stop. It is calculated for both the all-engines-operating and engine-failure scenarios, with the longer distance used for certification and operational planning.

How Is ASD Determined?

ASD calculations include:

Acceleration to V1 (with or without engine failure)
A reaction time buffer (typically 2 seconds at V1)
Deceleration using all available means (brakes, spoilers, reverse thrust if permitted)

On a wet or contaminated runway, the calculation uses reduced friction values and may allow for reverse thrust in the stopping phase. The certified ASD is always the greater of the dry or wet calculation.

Factors Affecting Accelerate-Stop Distance

Several variables can increase ASD:

Aircraft mass: Heavier aircraft need more distance to stop.
Temperature and pressure altitude: Both increase groundspeed at V1, lengthening stopping distance.
Wind: Headwinds reduce, tailwinds increase ASD.
Runway slope: Upslope increases, downslope decreases ASD.
Surface condition: Wet, icy, or soft surfaces reduce braking effectiveness and increase ASD.
Brakes, anti-skid, spoilers, and reverse thrust: Effective use of these systems reduces ASD, but their performance limits (like brake energy absorption and temperature) must be respected.

V1 Errors and Operational Considerations

Choosing an incorrect V1 can have serious consequences. If V1 is set too high, there may not be enough runway left to stop safely. Too low, and takeoff performance is unnecessarily limited. The use of a stopway (an area beyond the runway suitable for stopping) can increase the allowable takeoff mass by extending the ASDA (Accelerate-Stop Distance Available).

Practical Application

Pilots must compare the calculated ASD to the runway length available (ASDA) before every takeoff. If the calculated ASD exceeds the available distance, takeoff is not permitted at that mass or configuration. This ensures safety in the event of an aborted takeoff.

The essentials

Key Points

Accelerate-stop distance is the runway length needed to accelerate to V1 and then stop safely if takeoff is rejected.

ASD includes acceleration, a reaction time buffer, and full deceleration using all available means.

Wet or contaminated runways increase ASD due to reduced friction.

Heavier aircraft, higher temperatures, and higher pressure altitudes all increase ASD.

Headwinds decrease ASD; tailwinds and upsloping runways increase it.

Reverse thrust is only considered in ASD calculations for wet runways.

Incorrect V1 selection can make stopping within the available runway impossible.

Watch out

Exam Traps & Typical Mistakes

Confusing ASDA (available distance) with ASD (required distance) or TODA (takeoff distance available).

Assuming reverse thrust is always considered in ASD calculations (it's not for dry runways).

Overlooking the impact of runway slope or wind direction on ASD.

Forgetting to add the 2-second buffer at V1 in calculation scenarios.

Believing that surface contaminants only affect acceleration, not deceleration.

Test yourself

Example Exam Questions

Question 2Easy

How does a headwind affect the accelerate-stop distance required for takeoff?

Question 3Medium

What is the effect of using a stopway on the accelerate-stop distance available (ASDA)?

Still not fully confident?

Deepen your knowledge with an AI tutor built specifically for EASA ATPL students.

Built from thousands of ATPL knowledge references, real exam references and official learning objectives.

Open Avi AI Tutor

Keep going

Related Concepts

Still have questions?

Ask questions in plain English and get exam-focused explanations from an AI tutor built specifically for EASA ATPL students.

Open Avi AI