Low-altitude unstable approach (UA) is one of the crucial risks that threaten flight safety. In this study, we proposed a technical program for detecting low-altitude UA events. The detection logic was to optimize the step-wise regression model with iterative surveys with more than 20 experienced pilots. Accordingly, the frequencies of UA events occurring around each airport in January 2018 were calculated for all the airports within mainland China. Finally, the spatial distribution characteristics of UA events were analyzed via exploratory spatial data analysis. In addition, Pearson’s correlation coefficient and the geographically weighted correlation coefficient were used to explore the correlations between UA frequency and the altitude elevation, wind level, and bad weather. The experimental results revealed that the proposed method can accurately detect the occurrence of low-altitude UA and quantitatively characterize risks. It was found that UA exhibits obvious differences in spatial distribution. Moreover, significantly strong correlations were found between UA and altitude elevation, wind level, and bad weather, and correlation differences were also reflected in different regions in China.

![53ad0624-9d80-460d-a709-23bd319917da_TemporalHeatmap.png](/media/7475434a-573e-4d8d-a4a6-bf53098315b6_53ad0624-9d80-460d-a709-23bd319917da_TemporalHeatmap.png)

> Temporal heatmap of unstable approach (UA) events.

![f363204b-145f-4235-8e72-da1190ddf369_Correlation.png](/media/e58606a8-a4ee-410e-b1dd-a979ad6e9c0b_f363204b-145f-4235-8e72-da1190ddf369_Correlation.png)

> Correlation between UA triggering frequency (Boeing aircraft) and elevation.

![04374fac-fe39-448b-a98a-fd21e3a4c2e5_GWCCs.png](/media/afd8337a-814c-49f8-8e42-f604a32565bd_04374fac-fe39-448b-a98a-fd21e3a4c2e5_GWCCs.png)

> Geographically-weighted correlation coefficients (GWCCs) between UA triggering frequency and wind levels 5-6.