The calculated distance (air line) between Chlumec nad Cidlinou and Třinec is approximately 147 miles respectively 236 kilometers.
By car or train, the actual journey to Třinec is certainly longer, as only the direct route (as the crow flies) between Chlumec nad Cidlinou and Třinec has been calculated here.
Air line (approximately)
236 kilometers
127 nautical miles