Scenario Based Physiological Training

The current training standards for rapid or explosive cabin depressurization have served the commercial aviation industry well. Over the last 15 years there have been numerous high altitude rapid decompression events that have all resulted in safe landings without associated fatalities. This success is attributed to the extensive training resources available to the commercial pilot during initial and recurrent training.  These include:

1. Ground school curriculum requirements set forth by FAR 61.31g which emphasizes the physiology of hypoxia.

2. The high altitude endorsement which requires an FAA approved class D simulator demonstrating proficiency of the oxygen mask and emergency descent procedures.

3. The availability to attend high altitude chamber programs provided by the FAA and military as well as reduced oxygen breathing programs where pilots can experience the signs and symptoms of hypoxia. Collectively, these programs have successfully accomplished their training objectives given the absence of fatalities associated with explosive or rapid decompression.

However, there is a weak link when it comes to slow onset hypoxia associated with the failure of pressurization on ascent.  Since 1999, there have been over 150 fatalities related to this scenario involving commercial, corporate, and pressurized technically advanced aircraft.

This emphasizes the danger of slow onset hypoxia which is defined as a cabin ascent rate of 1500ft/min over a 10-15 minute period of time. In this slow onset model the signs and symptoms of hypoxia are subtle and if the crew is attentive to ascent related procedures it is very easy to become fixated resulting in loss of consciousness. This being the case, there is a need to address this scenario specifically and add it to the existing training standards.

Training for the slow onset scenario is best accomplished by the fusion of a simulator representative of the aircraft within a high altitude chamber so that the pilot or crew can relate their hypoxia experience directly to the flight deck. This training session requires 1 hour of simulator time that can be added to the existing requirements.

Simulators representative of the aircraft is the industry training standard. The training is rigorous requiring extensive knowledge of the aircraft and the ability to multi-task to maintain situational awareness.  It also requires the ability to problem solve sudden malfunctions that can occur unexpectedly. Slow onset hypoxia disrupts this complex requirement leading to fixation and subsequent incapacitation. This is due to the fact that neurocognitive impairment is already present when these subtle signs begin to occur and as such can easily be ignored. Standard altitude chamber programs emphasize rapid onset hypoxia by requiring the trainees to perform simple tasks. While effective in demonstrating the dangers of rapid or explosive cabin depressurization it is not representative of the aircraft in the “slow onset model”.  By providing a simulator based physiological experience further enhances the pilot’s “index of suspicion” to identify such potential hazards.