The heads of Lufthansa and its low-cost airline Germanwings are visiting the site of a crash that killed 150 people amid mounting questions about the co-pilot and how much his employers knew about his mental health.

Lufthansa CEO Carsten Spohr and Germanwings CEO Thomas Winkelmann touched down Wednesday by helicopter in Seyne-les-Alpes, near the ravine where the A320 jet shattered into thousands of pieces March 24.

Investigators believe co-pilot Andreas Lubitz intentionally crashed the plane. Lufthansa said Tuesday that it knew he had suffered from an episode of "severe depression" before he finished his flight training.

German prosecutors say Lubitz's medical records from before he received his pilot's license referred to "suicidal tendencies," but visits to doctors since then showed no record of any suicidal tendencies or aggression against others.