On 14 August 2005, Helios Airways Flight 522, a Boeing 737-300 flying from Larnaca, Cyprus, to Prague via Athens, crashed near Grammatiko, Greece, killing all 121 passengers and crew—making it the deadliest aviation accident in Greek history. The tragedy began when a ground engineer set the cabin pressurization system to "manual" for a leak test and forgot to restore it to "auto," a critical error that the flight crew, led by Captain Hans-Jürgen Merten and First Officer Pampos Charalambous, missed during their pre-flight checks. As the aircraft climbed, the cabin gradually lost pressure, causing everyone on board to suffer from critical hypoxia, and the crew misidentified the identical-sounding cabin altitude warning horn as a takeoff configuration alert, which can only sound on the ground. The investigation by Greece's Air Accident Investigation and Aviation Safety Board (AAIASB) pinpointed this fatal chain of events, leading to lawsuits against both Helios Airways and Boeing. Ultimately, the Cypriot government shut down Helios Airways the following year due to the negligent nature of the accident.