Stay informed on COVID-19 updates from EASARead more

Runway Micro Texture (RWYMT)

The research objectives and expected outcome

According to EASA Annual Safety Review 2021, runway excursion is one of the main key safety risk areas for commercial air transport (CAT), business aviation and non-commercial operations with complex motor-powered aircraft (NCC).

Wet runways are a contributing factor in runway excursions. Good aeroplane tyre braking friction on wet runways is of essential importance for the safe stop of aircraft. The braking action generated by an aeroplane tyre depends on several factors, amongst which the macro- and micro-texture characteristics of the runway surface are very important. Macro-texture refers to visible roughness of the pavement surface. Micro-texture refers to the fine-scale roughness contributed by small individual aggregate particles on pavement surfaces, e.g., the roughness of the individual stones that form the macro-texture.

The macro-texture can be measured through simple methods such as the ‘sand and grease patch’. This method was used for the early research on which the current airworthiness requirements are based and which refer to a classification categorising macro-texture from A to E corresponding to certain texture depths. This classification was issued in 1971 by the Engineering Sciences Data Unit (ESDU) and can be found in EASA’s GM1 ADR-DSN.B.191 of CS-ADR-DSN.

For the micro-texture however, there are neither minimum requirements nor an established method for determining and monitoring micro-texture characteristics. Therefore, there is a need to establish minimum values for micro-texture characteristics and to develop a method which can be used to determine and monitor these characteristics.

The outcome of the research project will enable EASA to:

  • initiate rulemaking action to revise Regulation (EU) No 139/2014 as regards aerodromes in order to establish micro-texture threshold values, below which a runway would be considered as slippery wet and maintenance actions are required;
  • establish clear criteria for the development of a trend monitoring programme of runway surface; and
  • review the certification specifications regarding runway surface construction.

The requested output

The deliverables will include:

  • a correlation of measured micro-texture characteristics derived from high-resolution surface laser scanners with aircraft braking performance;
  • recommended  runway micro-texture threshold values, below which a runway becomes ‘slippery wet’;
  • a practical guide, which could be used by aerodrome operators, competent authorities and accident investigation bodies, on using surface laser scanners for assessing runway micro-texture.

The work break-down structure of this project is the following:

  • Task 1: Literature review
  • Task 2: Flight test plan
  • Task 3: Flight test campaign and data collection
  • Task 4: Analysis and recommendations
  • Task 5: Communication, dissemination, knowledge-sharing, stakeholder management
  • Task 6: Project management