The Incident Overview
- Helios Airways Flight 522 was a passenger flight from Larnaca, Cyprus to Prague, with a stop in Athens, that crashed on August 14, 2005, killing all 121 on board.
- The incident remains the deadliest aviation accident in Greek history.
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Investigators revealed that prior tests left the cabin pressurization switch set to manual instead of automatic.
One of the pivotal findings in the investigation of Helios Airways Flight 522 was the discovery that the cabin pressurization system, a critical component in ensuring passenger and crew safety, had been left in the manual setting during prior maintenance tests. This occurred when ground engineers conducted a routine leak check but failed to reset the switch to “automatic” before the aircraft was cleared for flight. In manual mode, the system relies entirely on human intervention to maintain proper cabin pressure, which, in this case, was not adjusted during flight operations.
The oversight was compounded further by the flight crew’s failure to identify the incorrect switch position during their pre-flight checks or throughout the flight. This technical error, rooted in miscommunication and lax procedural adherence, initiated a cascade of events that ultimately led to cabin depressurization. The absence of automatic cabin pressurization caused oxygen levels to plummet, rendering the pilots and nearly all passengers unconscious due to hypoxia, and underscored the need for stricter adherence to maintenance protocols and crew training regarding safety-critical systems.
- The airplane eventually ran out of fuel and lost power, crashing into a hillside near Grammatiko, Greece.
Pressurization System and Crew Errors
- A ground engineer set the pressurization system to manual to perform a leak check and failed to revert it.
- The flight crew overlooked the pressurization system settings during key pre-flight checks.
- The warning horn, indicating cabin pressure issues, was misidentified as a takeoff configuration warning.
- Both pilots and nearly all passengers lost consciousness due to hypoxia induced by gradual depressurization.
Impact of Hypoxia
- Hypoxia occurred due to insufficient oxygen, incapacitating crew and passengers, essentially turning it into a ‘ghost flight’.
- Autopsies revealed some passengers might have been alive but unconscious upon impact.
- One flight attendant with a pilot’s license tried to save the aircraft using a portable oxygen bottle but was unable to regain control.
Design Flaws and Company Responsibility
- Boeing had been previously informed of the ambiguous nature of warning alarms in the cockpit.
- The aircraft manufacturer stated human error as the cause but faced criticism for cockpit design issues.
- Boeing’s yet unresolved issues surrounding the alert system of the Boeing 737 had been highlighted by NASA.
- Families involved in the crash settled out of court with Boeing for an undisclosed sum.
Legal Outcomes and Accountability
- Investigations resulted in multiple lawsuits citing negligence against Helios Airways and Boeing.
- The engineer at the center faced a lengthy legal battle but was ultimately found not guilty on appeal.
- Other Helios management faced convictions and were held liable for negligence.
- Greek and Cypriot authorities investigated Helios for past operational issues.
Improvements in Aerospace Safety Protocols
- Boeing later added training for discerning alert system differences in the cockpit.
- Pressurization systems in Boeing 737s were later altered to include more redundant alerts.
- Airlines received increased scrutiny over maintenance check protocols.
- The aviation industry mandated better checks on crew awareness for cabin depressurization scenarios.
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