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

010-09-02Pablo Asensio Martínez2026-03-272 min

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 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.