# BVLOS Unmanned Aircraft Operations in Forest Environments
## 5 Taking a Risk-Based Approach to BVLOS Operations in Forest Environments
### Other Considerations
#### 5.3.2 Fatigue Risk Management  
BVLOS operations take place over larger operational areas, where the ability to perform BVLOS is advantageous, which also means that operations are typically longer endurance than conventional operations. In such instances, it is important to consider duty limits for pilots and visual observers to avoid the negative consequences of fatigue. Fatigue is a state of deep tiredness that impairs performance, particularly motor skills, situational awareness, vision, and personal standards [88]. There are a number of ways to manage fatigue. Primarily, these centre on schedule optimisation, rest breaks and naps, fatigue aids (e.g., caffeine), and ensuring that crew are practicing good sleep hygiene [89]. The schedule optimisation is aimed at avoiding duty periods that are excessive and ensuring sufficient rest periods between duties. Rules and guidelines vary internationally for manned aviation. However, differences exist based upon whether the operation is a single crew operation or multi-crew operation and whether the flight is done under Visual Flight Rules (VFR) or Instrument Flight Rules (IFR). To generalise those requirements, a single duty period should not exceed 8-11 h, a pilot should not be scheduled for more than 30-35 h in 7 consecutive days, 90-100 h in 28 consecutive days, or 250-300 h in 90 consecutive days [90]. In addition to this, employees need to ensure they get at least 8 h of sleep per night, plan sleep ahead of time, and report fatigue [91]. During multi-crew operations, it may also be possible for an individual crew member to take a short break, which sees some short-term improvement in alertness, or even to take a nap (10-30 min), allowing 30 min post-nap to prevent sleep inertia [89]. Caffeine is also a useful fatigue countermeasure that increases alertness. However, it does take about 30-50 min to act, its effects wear off after about 4-5 h, and high caffeine intake can have an adverse effect [89]. Personal sleep practices are also critical, with crew needing to ensure that they get enough rest (most people need between 6-10 h sleep), that they try to avoid sleeping at unusual times (sleep at night to align with circadian rhythms), ensure that their sleeping environment is dark and cool, keep their sleep environments as safe sleep zones (e.g., never use the same area for sleep and work), and avoid detrimental sleep aids such as alcohol, among other things [92]. As can be seen thus far, fatigue management is both a crew responsibility and an organisational responsibility. If conducting BVLOS operations, which tend to be more complex, it is critical that flight crew do not have their performance impaired due to fatigue. Despite the importance of this topic area within manned aviation, research into pilot fatigue for long-endurance unmanned aircraft has primarily been within military applications [93; 94; 95] and often calls for further research due to the lack of data on this issue. This presents a potentially useful area for future research, given the likely increase in long-range BVLOS operations in coming years.