## 3 Review of Friction Related Accidents on a Runway
### National Transportation Safety Board (USA)  
Aircraft accident data from the United States were also analyzed, based on the investigation reports provided by the National Transportation Safety Board (NTSB) [55]. All report runway excursions within the USA from 2014 to 2024 were considered. At least 75 out of 1800 (4.2%) runway excursions happened because of insufficient braking during landing or take-off (Table A2). This number is lower than the numbers obtained by other researchers [50; 51; 52] and the number of occurrences based on the data provided by ATSB. However, in this study, the number of occurrences related to insufficient braking was likely underestimated due to the character of the NTSB reports, where information about braking efficiency during the landing and contamination is not provided in all reports. Thus, this analysis does not provide information about the occurrence frequency. Rather, it provides information about the causes of poor braking action. At the same time, it is impossible to provide any recommendations related to runway maintenance and runway friction control, since the reports provided by NTSB do not include such adequate information, like the details provided by ATSB. Most of the occurrences reported for the United States (Table A2) had more than one contributing factor (Figure 10). Only 20% of all runway excursions due to poor braking had no other contributing factor(s). One of the most common contributing factors was a mistake during the approach and landing, which included excessive speed, long landings and unstable approaches to the runway. According to the study [56], pilot mistakes during approach and landing was the largest contributing factor to all runway excursion events in general. The second contributing factor was a lack of awareness of the prevailing runway conditions, which included either failure to update or provide a runway condition report, or ignoring the condition report by pilots. This also included an underestimation in the amount of contamination reported to the pilots. Wind-related problems included landing with a tailwind and gusting crosswind, with 15% of all runway excursion events due to poor braking being affected by wind conditions. In 11% of cases, the other contributing factors included incorrect brake application. In most of the cases, it was emergency brake application or the anti-skid braking system turning off that caused hydroplaning and the subsequent loss of directional control (cases 9, 19, 54, 58, 68, and 73 in Table A2). Figure 10: Other contributing factors to runway excursions according to NTSB investigations between 2014 and 2024. Most of the occurrences in USA between 2014 and 2024 that related to insufficient braking happened during landing. Overall, at least 4.9% of runway excursions during landing were related to poor braking, and at least 1.3% of runway excursions during take-off were related to poor braking (Table 1). Therefore, the landing phase is considered to be the most critical in regard to the risk of runway excursion events. This analysis provides useful information to pilots and airport operators and allows them to minimize the risk of runway excursion by consistently avoiding the identified contributing factors in poor runway conditions with reduced friction. It is also reasonable to take measures to inform pilots about the risks related to poor braking. This analysis, however, does not allow for the calculation of the influence of poor braking on the risk of runway excursion, since it is impossible to obtain data about all of the runways with poor braking. That is because, in most cases, the poor braking condition was only reported after the incident, which does not allow comparison of the risk of runway excursion on runways with poor braking due to contamination or poor friction maintenance, to runways with good braking on a large sample. Perhaps it is possible that reported poor braking improves pilot awareness and decreases the risk of a runway excursion.