This was the last communication with the flight crew. Communication between the operations centre and flight crew ended at 06:20 h as the aircraft passes 28 900 ft. As the exchange continues, the passenger oxygen mask was automatically deployed as intended at 06:14 h at an altitude of 18 000ft. However, the captain, already experiencing the onset of hypoxia’s initial symptoms disregarded the question, and instead asked in reply, “Where are my equipment cooling circuit breakers?”. In one of the exchanges, the engineer asked the flight crew to confirm that the pressurization panel is set to AUTO. There was an exchange between an engineer and flight crew to try and rectify the issue.

Communication with Company Operations Centre As a result, the crew contacted the company operations centre at 06:14 h to report “take-off configuration warning on” and “cooling equipment normal and alternate off line”. However, the crew misunderstood the alarm and identified the alarm as a takeoff configuration warning. Just 5 minutes after take-off, as the aircraft continue ascending, the cabin altitude warning horn sounded at an altitude of 12 040ft. Helios Airways Boeing 737-31S – Image Courtesy of Alan Lebeda Warning Horn Helios flight 522 departed Larnaca International Airport at 06:07 h (UTC). The aircraft was signed off and sent into service for the next flight HCY522 which was scheduled to leave Larnaca International Airport for Prague, the Czech Republic with a stopover at Athens. Upon completion of the test, the pressurisation system was not reset to ‘auto’ To perform this task, the pressurisation system has to be set to ‘manual’. An engineer proceeded to carry out a pressurization leak check. Prior to the flight, an inspection was done due to an issue on the right aft service door that was reported during its previous flight. The flight path of Helios Airways Flight 522 on 14 August 2005 – Courtesy of Oona Räisänen Maintenance

Helios airways flight 522 video