During a particularly windy day in Lancashire, England, a pilot of a four-person prop plane requested that a flying instructor join him in the air just be on the safe side. Shortly after take-off, the instructor's head tilted back and he closed his eyes. The pilot thought the instructor was "just pretending to take a nap" during the short flight. He wasn't. From CNN:
When the plane turned around, the instructor slumped over so that his head rested on the co-pilot's shoulder, but again the pilot still thought a joke was being played on him.
After landing safely with the instructor still resting on his shoulder and not responding, the pilot realized something was wrong and alerted airport emergency services who were unable to revive the instructor[…]
The medical department of the UK Civil Aviation Authority reviewed the incident and the instructor's medical history and concluded that, "From the evidence provided, it is likely the individual suffered a cardiac arrest as the aircraft took off."
