Aeronautical Information Manual (AIM), page 347
12/10/15 AIM either case, the pilot should proceed direct to the IAF authorize a pilot to descend to a lower TAA altitude. or to the IF/IAF associated with the sector that the If a pilot desires a lower altitude without an approach aircraft will enter the TAA and join the approach clearance, request the lower TAA altitude from ATC. course from that point and if required by that sector Pilots not sure of the clearance should confirm their (i.e., sector is not labeled "NoPT), complete the clearance with ATC or request a specific clearance. HILPT course reversal. Pilots entering the TAA with two-way radio commu- NOTE- nications failure (14 CFR Section 91.185, IFR If approaching with a TO bearing that is on a sector bound- Operations: Two-way Radio Communications Fail- ary, the pilot is expected to proceed in accordance with a ure), must maintain the highest altitude prescribed by "NoPT" routing unless otherwise instructed by ATC. Section 91.185(c)(2) until arriving at the appropriate IAF. 5. Altitudes published within the TAA replace the MSA altitude. However, unlike MSA altitudes the (b) Once cleared for the approach, pilots may TAA altitudes are operationally usable altitudes. descend in the TAA sector to the minimum altitude These altitudes provide at least 1,000 feet of obstacle depicted within the defined area/subdivision, unless clearance, more in mountainous areas. It is important instructed otherwise by air traffic control. Pilots that the pilot knows which area of the TAA the aircraft should plan their descent within the TAA to permit a will enter in order to comply with the minimum alti- normal descent from the IF/IAF to the FAF. In tude requirements. The pilot can determine which FIG 5-4-4, pilots within the left or right-base areas area of the TAA the aircraft will enter by determining are expected to maintain a minimum altitude of 6,000 the magnetic bearing of the aircraft TO the fix labeled feet until within 17 NM of the associated IAF. After IF/IAF. The bearing should then be compared to the crossing the 17 NM arc, descent is authorized to the published lateral boundary bearings that define the lower charted altitudes. Pilots approaching from the TAA areas. Do not use magnetic bearing to the northwest are expected to maintain a minimum alti- right-base or left-base IAFs to determine position. tude of 6,000 feet, and when within 22 NM of the (a) An ATC clearance direct to an IAF or to IF/IAF, descend to a minimum altitude of 2,000 feet the IF/IAF without an approach clearance does not MSL until crossing the IF/IAF. FIG 5-4-4 Sectored TAA Areas Arrival Procedures 5-4-11
Page 347 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures