Final answer:
To determine which TAA sector an aircraft is entering during an RNAV approach, the Initial Approach Fix (IAF) must be used. This is critical for maintaining adequate terrain clearance and proper approach procedures, as the TAA provides altitude guidance for specific sectors, rather than using a traditional Minimum Sector Altitude (MSA).
Step-by-step explanation:
Terminal Arrival Areas (TAAs) are designed to make the transition from the enroute structure to a final approach easier in RNAV (Area Navigation) approaches. Unlike conventional approaches which use a Minimum Sector Altitude (MSA), a TAA provides altitude guidance that is specific to the sector, based on the direction of the aircraft as it arrives at the terminal area.
To determine which area of the TAA an aircraft is entering, the Initial Approach Fix (IAF) associated with that particular sector should be used. This is critical because the TAA's altitude requirements are based on the sector the aircraft enters. Failure to correctly identify the appropriate sector could lead to inadequate terrain clearance or incorrect approach sequencing.
Each sector of a TAA has a minimum altitude that provides obstacle clearance which is usually higher than the MSA, but covers a smaller geographical area tailored to the approach path. Therefore, while RNAV approaches with TAAs do not have a traditional MSA, their segmented altitude clearances offer a comparable level of safety with greater efficiency.