- Lubitz was hospitalized for severe depression and "suicidal ideations"
- His German medical certificate would have been invalid if he had a relapse
- Germanwings Flight 9525 crashed last year, killing 150 people
- Investigators say Lubitz crashed the plane intentionally
(CNN)Relatives of victims killed in the Germanwings plane crash last year are suing a U.S. flight school, saying co-pilot Andreas Lubitz should never have been allowed to join its commercial training program because of his mental health history.