The August 2005 Helios Airways plane crash north of Athens, Greece, killing 121 passengers and crew, was a direct result of the pilots experiencing hypoxia, a lack of oxygen resulting in loss of consciousness . The pilots ignored the warning system in the Boeing 737-31S of cockpit pressure failure and the tragic results followed.
Pilots are trained and understand the dangers of hypoxia which makes one curious to understand why a highly trained, capable pilot responsible for human lives would chose to ignore a basic safety system. The first reason is that the popular passenger 737 aircraft warning horn is confusing to pilots. The warning system serves two purposes. It warns the pilots that there is a problem with the configuration of the aircraft before the take off. After the pilot trouble shoots the pre- takeoff problem, they assume there are no more issues and dismiss the warnings, when in reality, potential problems of pressurization can occur in flight.
Other problems that pilots deal with are false alarms. Faulty pressurization equipment cause alarms to sound when they shouldn't be. A publication sited that 25% of the 100 warning horns cited in the Aviation Safety Reporting System over the past 10 years were either alarms sounding when they shouldn't be or visa versa. Because of the false positive altitude and pressure warnings, pilots have been known to ignore the safety signals.
The FAA has been investigating numerous reports of pressurized problems in the aircrafts. They have recommended a warning light to accompany the warning horn, and have also focused on after take-off procedures to include safety checks of the pressurization switches. The latest safety action happened last month when the agency mandated that briefings to instruct pilots to heed the altitude horns be implemented.
Boeing, the manufacturing of the aircrafts, have built a new and improved altitude warning system in their new aircrafts and are retrofitting older crafts with a improved safety altitude warning systems. More effective warning systems of pressure problems in flight may lead to less pilot hypoxia-related aircraft accidents.
The documented pilot errors and dismissal of warning systems have led to investigations and litigation. In the case of the August 2005 Helios Airways plane crash north of Athens, Greece, Helios executives were charged with man-slaughter. In additions, U.S. and Cyprus attorneys filed lawsuits in 2006 on behalf of the crash victims.
The FAA acknowledged the problems of the warning horn problems and issued an airworthiness directive July 2006. Even so, there has been at least 3 more reports of horn confusion. The most recent FAA directive comes in March of this year that requires before the first flight of the day and following any change is flight crew members, Being 737 crews must be reminded to acknowledge the safety horns and take appropriate actions.