Tail-End Fatigue and Why Part 135 Needs Enforceable Rest & Duty Regulations

In September of 2020, the NTSB published a Final Report with a very simple determination of probable cause: “The pilot’s loss of helicopter control as a result of fatigue during cruise flight at night.”

The flight was a “tail-end ferry flight.” Unlike FAR Part 121 operations, charter operators under FAR Part 135 have no rest requirements for a Part 91 repositioning flight at the end of the day. Part 91 flights at the beginning of the day or between Part 135 flights are counted, but the tail-end ferry flight home can extend a pilot’s flight and duty. It can’t be counted as “rest,” so the pilot would need the required rest before starting the next Part 135 day.

Tail-end ferry flights have been a part of the charter world since the original charter rest & duty rules were written. It[DG3]  has been confirmed by numerous FAA Legal Interpretations.  In 2003, I served on an Aviation Rulemaking Committee (ARC) that sought to eliminate tail-end ferry flights as part of a comprehensive overhaul of outdated rest & duty regulations.  The ARC’s recommendations never made it to the Notice of Proposed Rulemaking (NPRM) stage.  Now I serve on another ARC with the same goal of drafting enforceable, science-based rest & duty regulations that fit the on-demand nature of the charter world.

So what does that tail-end ferry accident tell us?  Would new regulations have prevented this accident?  

The Facts

• It was an air ambulance helicopter with one pilot and two emergency medical service crew members. 
• They took off about 2107 on their final flight.
• It was night, but VMC.  Before the final flight, they had flown three flights, for a total of 94 minutes flight time over 2.5 hours.
• Shortly after takeoff, the pilot asked the crewmembers whether they were “alright.” One crewmember responded “yup” and then asked the pilot, “question is are you alright up there?” The pilot responded, “uhhh think so.  Good enough to get us home at least.” There was no further discussion related to fatigue.
• During the flight, the pilot adjusted his seat position and flexed his legs, which were actions consistent with signs of fatigue. Also, although the pilot participated in the medical crewmembers’ conversations in the middle of the flight, he did not participate in their conversations near the end of the flight.
• During the last portion of the flight, the helicopter entered a progressively steepening right bank, and the pilot did not respond as the medical crewmembers shouted his name.
• The helicopter descended and became inverted, and the pilot continued not to respond as the medical crewmembers’ shouted his name.
• After the helicopter began to roll to the right, the pilot slumped to the left, appearing incapacitated.  The crash occurred at approximately 2250. The pilot and two medical crewmembers were killed.
• On the day of the accident, cellular telephone activity revealed two possible opportunities for the pilot to sleep before going on duty but it is not known if the pilot rested during those times. Thus, the pilot could have been awake for about 15.5 hours at the time of the accident (based on telephone records showing activity at 0725 on the morning of the accident) if he did not take advantage of the sleep opportunities.

The NTSB stated: “Although this time since awakening would not be considered excessive, this accident shift was the pilot’s first after returning from a week-long vacation during which his circadian rhythm would have had him sleeping. Further, the environment created by the helicopter vibration, darkness of night, and few operational demands during the cruise phase of flight would have increased the pilot’s fatigue and the body’s biological desire to sleep.”

There is little doubt that this experienced pilot simply fell asleep.  But why?  This accident didn’t happen simply because the current regulations allow tail-end ferry flights.  The cruel irony of this accident is that the pilot was coming off a week of vacation.  The NTSB mentions time zone change, but the pilot, who was based in Wisconsin, simply took a week in Florida. 

A one-hour time zone change was not a major factor.  A bigger factor: circadian rhythms.  Pilots were talking about the dangers of flying “on the back side of the clock” long before scientists coined the term “Window of Circadian Low” (WOCL). 

This pilot switched to sleeping nights for a week.  Then he gave himself a day to switch to being a night pilot.  But, the crash occurred before 11:00 PM.  He didn’t make it to the backside of the clock.  The WOCL for people adapted to a usual day-wake/night-sleep schedule begins around 2:00 AM.

The Conclusion

Part 135 needs enforceable, science-based rest & duty regulations that fit the on-demand nature of the charter world.  These rules do need to address the dangers of tail-end ferry flights, but more importantly, these rules need to introduce SMS-based fatigue management principles so that pilots and operators better understand the risks of quickly changing their days to nights.

This article appeared in the November, 2020 issue of Business & Commercial Aviation as a Point of Law article.