Write a lead that frames the incident as a case study in aviation safety, then explain what NOTAMs are and how pilots use them during flight planning. Highlight the specific slackline warning near Telegraph Canyon and how such temporary obstacles can pose risks to low-flying helicopters. Compare preflight planning practices with the realities pilots face in remote or rugged terrain, emphasizing situational awareness. Conclude with practical safety takeaways for pilots, regulators, and the general public, and suggest how technology and policy could reduce similar hazards in the future. Include at least one clear recommended action or policy implication.