Federal investigators say an 86-year-old Ohio man at the controls of a plane that crashed last year, killing him and five passengers, had been warned not to drive by his eye doctor.

A report issued this week by the National Transportation Safety Board says Gene Damschroder Sr. had been in treatment for macular degeneration for two years.

But on the last airman medical certificate he filed, in 2007, he denied having any eye conditions.

Damschroder, a former state representative, was giving airplane rides in June 2008 at Fremont Airport in northwest Ohio, The Blade newspaper reported.

Damschroder's son, Rex Damschroder, says he thinks his aging father's slower reflexes may have been a key reason for the crash.

The NTSB expects to release a probable cause statement on the crash on Dec. 3.