In order to investigate the structural dynamic response of amphibious aircraft during wave planing in irregular waves, a 1∶10 geometrically scaled full-aircraft model was fabricated in adherence to Froude similarity criteria. This model was then tested in a towing tank under controlled wave conditions, covering a Froude number range of Fr=0.31~1.52. Dynamic responses including trim angle, bow vertical overload, and vertical overload increment at the center of gravity (CG) were measured and statistically characterized. Results demonstrate that the Weibull distribution effectively captures extreme-value statistics for all three responses (goodness-of-fit R²> 0.95). As the Froude number (Fr=0.31~1.52, wave height=0.15 m) increases, the characteristic extreme values of the trim angle grow by 283%, CG vertical overload increment shows a 383% rise in characteristic amplitude. Bow acceleration distribution develops significantly thicker tails at high Fr, indicating a sharp escalation in extreme load occurrence probability. Based on these findings, a statistically-derived load spectrum is developed using Weibull parameters via multi-condition weighting, providing essential input for fatigue life prediction of amphibious aircraft, and is validated through comparison with full-scale fatigue test data, confirming its engineering reliability.