Imagine piloting a high-performance aircraft at 25,000 feet, cruising at speeds exceeding Mach 0.75, experiencing unparalleled velocity and exhilaration. Yet behind this aerial achievement lie significant challenges that demand careful consideration. The Federal Aviation Administration (FAA) recently released Advisory Circular AC 61-107B, providing pilots with enhanced guidance to navigate these challenges and ensure safety during high-altitude, high-speed operations.

Issued on March 29, 2023, AC 61-107B replaces the 2003 AC 61-107A, offering updated operational guidance for flights above 25,000 feet at speeds greater than Mach 0.75. This advisory serves as a crucial resource for pilots transitioning from lower-performance aircraft to complex, high-performance models, addressing physiological, equipment, and aerodynamic factors unique to these flight conditions.

Operating at extreme altitudes presents multiple challenges. Thin air reduces oxygen availability, potentially causing hypoxia, while low temperatures and increased radiation exposure create additional physiological stressors. Aerodynamically, aircraft behavior changes significantly, with phenomena like transonic flutter and shock waves affecting controllability. Pilots require comprehensive theoretical knowledge and practical experience to safely navigate these conditions.

The advisory circular addresses three critical aspects of high-altitude operations:

• Hypoxia: The document emphasizes supplemental oxygen requirements above 25,000 feet and recommends regular medical evaluations to assess altitude tolerance.
• Decompression sickness: Guidelines cover risk factors, symptoms, and preventive measures for rapid pressure changes.
• Additional effects: The circular addresses visual impairment, fatigue, and other altitude-related impacts, advising proper rest and dietary precautions.

• Pressurization systems: Stresses the importance of regular maintenance and checks for cabin pressure systems.
• Oxygen systems: Details different system types, operational procedures, and pre-flight verification requirements.
• Advanced avionics: Recommends thorough training for navigation, autopilot, and weather systems common in high-performance aircraft.

• Mach number effects: Explains critical concepts including critical Mach number (Mcr) and maximum operating Mach number (MMO).
• Shock waves: Describes formation mechanisms and operational impacts, with guidance on speed adjustments and attitude changes.
• Flutter: Details this self-exciting vibration phenomenon and emphasizes avoidance of critical speed ranges.

• 14 CFR Part 61.31(g) - High-altitude training requirements
• 14 CFR Part 91.211 - Supplemental oxygen regulations
• 14 CFR Part 91.215 - ATC transponder requirements
• Various altitude assignment and airspace operation rules

• Aspect ratio: Wing geometry relationship affecting performance
• Mach tuck: Nose-down pitching moment at high speeds
• Drag divergence: Rapid resistance increase near transonic speeds
• Cabin altitude: Pressure equivalent measurement
• Various Mach-related phenomena: Including buffet, buzz, and control surface oscillations

The FAA emphasizes that AC 61-107B represents foundational knowledge, recommending continuous study through technical references to master high-altitude operations. This advisory serves as both guidance and reminder of the significant responsibility inherent in high-performance flight operations.