CLEAR LAKE — The National Transportation Safety Board has declined a request to reopen the investigation of the Iowa plane crash that killed musicians Buddy Holly, Ritchie Valens and J.P. “The Big Bopper” Richardson. The Civil Aeronautics Board ruled in 1959 that the most likely cause of the crash was pilot error. Snow was listed as a secondary caused. In a letter dated April 21, the agency said the evidence presented in a request from pilot L.J. Coon wasn’t sufficient to merit the reconsideration of the findings of the original investigation. Coon had contended that there were other issues involving weight and balance calculations, fuel-gauge readings and more that contributed to the crash.