er altitude without an approach clearance, request the lower TAA altitude from ATC. Pilots not sure of the clear­ ance should confirm their clearance with ATC or request a specific clearance. Pilots entering the TAA with two−way radio communications failure (14 CFR § 91.185, IFR Op­ erations: Two−way Radio Communications Failure), must maintain the highest altitude prescribed by 14 CFR § 91.185(c)(2) until arriving at the appropriate IAF. 

Once cleared for the approach, pilots may descend in the TAA sector to the minimum altitude depicted within the defined area/subdivision, unless instructed otherwise by air traffic control. Pilots should plan their descent within the TAA to permit a normal descent from the IF/IAF to the FAF. 

U.S. Government charts depict TAAs using icons located in the plan view outside the depiction of the actual ap­ proach procedure. Use of icons is necessary to avoid ob­ scuring any portion of the “T” procedure (altitudes, cours­ es, minimum altitudes, etc.). The icon for each TAA area will be located and oriented on the plan view with respect to the direction of arrival to the approach procedure, and will show all TAA minimum altitudes and sector/radius subdivisions. The IAF for each area of the TAA is included on the icon where it appears on the approach to help the pilot orient the icon to the approach procedure. The IAF name and the distance of the TAA area boundary from the IAF are included on the outside arc of the TAA area icon. 

TAAs may be modified from the standard size and shape to accommodate operational or ATC requirements. Some areas may be eliminated, while the other areas are ex­ panded. The “T” design may be modified by the proce­ dure designers where required by terrain or ATC consider­ ations. For instance, the “T” design may appear more like a regularly or irregularly shaped “Y,” an upside down “L,” or an “I.” 

When an airway does not cross the lateral TAA boundar­ ies, a feeder route will be established from an airway fix or NAVAID to the TAA boundary to provide a transition from the en route structure to the appropriate IAF. Each feeder route will terminate at the TAA boundary and will be aligned along a path pointing to the associated IAF. Pilots should descend to the TAA altitude after crossing the TAA boundary and cleared for the approach by ATC. 

Each waypoint on the “T” is assigned a pronounceable 5− letter name, except the missed approach waypoint. These names are used for ATC communications, RNAV data­ bases, and aeronautical navigation products. The missed approach waypoint is assigned a pronounceable name 

when it is not located at the runway threshold. 

## RNAV Approach Types 

RNAV encompasses a variety of underlying navigation systems and, therefore, approach criteria. This results in different sets of criteria for the final approach segment of various RNAV approaches. RNAV instrument approach criteria address the following procedures: 

• GPS overlay of pre-existing nonprecision approaches. 

• VOR/DME based RNAV approaches. 

• Stand-alone RNAV (GPS) approaches. 

• RNAV (GPS) approaches with vertical guidance (APV). 

• RNAV (GPS) precision approaches (WAAS and LAAS). 

## GPS Overlay of Nonprecision Approach 

The original GPS approach procedures provided authorization to fly non-precision approaches based on conventional, ground-based NAVAIDs. Many of these approaches have been converted to stand-alone approaches, and the few that remain are identified by the name of the procedure and “or GPS.” These GPS non- precision approaches are predicated upon the design criteria of the ground-based NAVAID used as the basis of the approach. As such, they do not adhere to the RNAV design criteria for stand-alone GPS approaches, and are not considered part of the RNAV (GPS) approach classification for determining design criteria. [Figure 4-38] 

## GPS Stand-Alone/RNAV (GPS) Approach 

The number of GPS stand-alone approaches continues to decrease as they are replaced by RNAV approaches. RNAV (GPS) approaches are named so that airborne navigation databases can use either GPS or RNAV as the title of the approach. This is required for non-GPS approach systems, such as VOR/DME based RNAV systems. In the past, these approaches were often referred to as "stand-alone GPS" approaches. They are considered non-precision approaches, offering only LNAV and circling minimums. Precision minimums are not authorized, although LNAV/ VNAV minimums may be published and used as long as the on-board system is capable of providing approach approved VNAV. The RNAV (GPS) Runway 14 approach for Lincoln, Nebraska, incorporates only LNAV and circling minimums. [Figure 4-39] 

For a non-vertically guided straight-in RNAV (GPS) approach, the final approach course must be aligned within 15° of the extended runway centerline. The final approach segment should not exceed 10 NM, and when it exceeds 6 NM, a stepdown fix is typically incorporated. A minimum 

