Transmission lines (TL) are the arteries of the power infrastructure, responsible of delivering electricity over long distances. Extreme wind events have shown the vulnerability of transmission lines to wind loads through several tower failure incidents consistently happening around the globe. End towers serve as containment failure elements to stop the progression of failure of tangent towers. Downbursts are one of the windstorm phenomena that has led to many failures of TLs. The objective of this study is to assess through an aero-elastic test the adequacy of using the design loads for synoptic wind to design end towers to resist downbursts. The wind test is conducted at the Wind Engineering, Energy and Environment (WindEEE) Dome, which is capable of simulating downbursts. The downburst wind field and the shear forces at the base of the end tower are obtained from the test. Finite element analysis of the tested line is then carried out under both the downburst wind field measured experimentally and the synoptic wind load cases described in the ASCE guidelines. The straining actions produced by the downburst wind field measured in the test and the synoptic load cases are compared.