# Aerodrome Data (AD): Pavement Strength, Declared Distances, and Friction Codes

> Review aerodrome data for pavement strength using ACN-PCN, declared distances TORA/TODA/ASDA/LDA, and runway friction coding principles.

- **Subject:** 010 — Air Law
- **Section:** 010-09 — Aerodromes
- **Topic code:** 010-09-02
- **Last reviewed:** 2026-03-27
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/air-law/aerodromes/aerodrome-ad-data/

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## Pavement Strength
The strength of pavements for aircraft over 5,700 kg is reported using the **ACN-PCN** (Aircraft Classification Number - Pavement Classification Number) method.
*   **ACN (Aircraft Classification Number):** Expresses the relative effect of an aircraft on a pavement.
*   **PCN (Pavement Classification Number):** Expresses the bearing strength of a pavement for unrestricted operations.

**General Rule:**
*   If **ACN ≤ PCN**, the aircraft can operate without restriction.
*   The PCN reports the pavement capability under maximum operational loads (not current load).
*   For aircraft of **5,700 kg or less**, the maximum allowable mass and maximum tire pressure are reported.

> **Update:** ICAO is transitioning to the **ACR-PCR** (Aircraft Classification Rating - Pavement Classification Rating) method, although ACN-PCN remains in use in many regions.

## Declared Distances
They are fundamental for performance calculations:

![Declared Distances: TORA, TODA, ASDA, LDA](https://upload.wikimedia.org/wikipedia/commons/7/7b/Aim_fig_4-3-5_Declared_Distances_with_Full-Standard_Runway_Safety_Areas%2C_Runway_Object_Free_areas%2C_and_Runway_Protection_Zones.jpg)
*Illustrative diagram of TORA, TODA, ASDA, and LDA.*

1.  **TORA (Take-off Run Available):** The length of runway declared available and suitable for the ground run of an aeroplane taking off.
2.  **TODA (Take-off Distance Available):** TORA + **Clearway**.
3.  **ASDA (Accelerate-Stop Distance Available):** TORA + **Stopway**.
4.  **LDA (Landing Distance Available):** The length of runway declared available and suitable for the ground run of an aeroplane landing.
    *   Affected by the **displaced threshold**.

**Relationships:**
*   If no Clearway or Stopway exists: **TORA = TODA = ASDA**.
*   A **Stopway** increases only the **ASDA** (distance to abort takeoff). It does not affect TORA or LDA.
*   A **displaced threshold** reduces the **LDA**, but does not necessarily affect the TORA (takeoff can start from the physical beginning of the runway).

## Surface Condition and Friction Coefficient
The measured friction coefficient correlates with a code and braking estimate:
*   **0.40 and above:** Good (Code 5).
*   **0.39 to 0.36:** Medium to good (Code 4).
*   **0.35 to 0.30:** Medium (Code 3).
*   **0.29 to 0.26:** Medium to poor (Code 2).
*   **0.25 and below:** Poor (Code 1).

**Contaminated Runway:** When more than **25%** of the surface is covered by water (>3mm), snow, slush, or ice.

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