Last month the TSB published an investigation report that stated:
“Given that the captain rarely used continuous positive airway pressure therapy, he would have been at risk of experiencing fatigue related to chronic sleep disruption caused by obstructive sleep apnea. However, there was no indication that fatigue played a causal or contributory role in this occurrence.”
The report also indicated that TC Civil Aviation Medical Examiners may not be consistently following the TC “protocol for the assessment of aeromedical risk and ongoing surveillance in applicants who suffer from obstructive sleep apnea.”
There is a hint in the report about how communication between the Medical Examiner and the pilot may have played a role in allowing a person with an untreated sleep disorder to continue to operate. The report said that the pilot with obstructive sleep apnea (OSA) did not report any daytime sleepiness to the doctor. There are two reasons why the sleepiness may not have been reported.
First, if you are not extremely sleepy, it is difficult to recognize that you may still be too fatigued. Simply asking “Do you ever feel sleepy during the day?” isn’t enough. Low levels of fatigue can impair a pilot’s ability to fly safely. This means that just because your head isn’t bobbing around all day as you fight to stay awake, it doesn’t mean you are safe. Unsafe levels of fatigue can be unrecognizable by the fatigued person.
Second, most people in transportation know how to answer a doctor’s questions. They know the answers that will have them yanked off the job. This means that fatigue will often be unreported to doctors.
Without any symptoms reported, the doctor would have no reason to follow up; unless the doctor had been trained in sleep medicine, and most are not. This means that the people responsible for ensuring that transportation workers are medically fit may not know that asking a person if they are fatigued usually results in a wrong answer. It also means that they may not know that a Multiple Sleep Latency Test (MSLT) or a Maintenance of Wakefulness Test (MWT) can be used to objectively assess levels of fatigue.
For Safety Investigators, this TSB report highlights the need to go deeper, we have to do more that just ask people if they were fatigued. We need data from tests like the MSLT or the MWT, or we need to collect sleep-wake histories that can be used to determine levels of fatigue.
 Collision with terrain Air Canada Airbus Industrie A320-211, C-FTJP Halifax/Stanfield International Airport Halifax, Nova Scotia 29 March 2015, http://tsb.gc.ca/eng/rapports-reports/aviation/2015/a15h0002/a15h0002.pdf.