Appendix D
SECTION I 2D RNAV CONSIDERATIONS
2. ENROUTE CRITERIA. Enroute procedures shall be evaluated using existing flight inspection facility performance data, or by flight inspection of the procedure when facility data is lacking.
a. RNAV Routes Protected Areas. The area to be protected is shown in Figure 1, the Area Navigation Route Width Summary, and is described as follows:
(1) Four miles each side of routes in which the tangent point distance of the route centerline is within 102 miles of the ground station.
The route boundaries splay at 3.25° beginning at the point where the route centerline exits the eight-mile zone.
When the tangent point distance is beyond the 102 mile limit, the minimum width of the protected area each side of the route at the tangent point distance is increased at the rate of 0.25 miles for each 10 miles increase in distance from the ground station.
The route boundaries splay 3.25° from this minimum width at the tangent point distance.
Parallel offset routes are not charted in flight information publications. When a pilot is cleared to fly a parallel offset route, he is expected to fly it in precisely the same fashion as the parent route. Parallel offsets will be used to separate overtaking traffic and other similar applications.
Enroute, it will not always be possible to'develop a parallel offset route on both sides of the parent route due to signal loss on the side of the parent route farthest from the reference station. When developing parallel offset routes consideration must be given to MOCA and MRA on both sides of the parent route.
In the event that the MEA is higher than the parent route, offset parallel operations will normally not be authorized on the side to which the higher MEA applies.
(4) Enroute vertical separation will be provided as prescribed in Air Traffic Control procedures handbooks where climb or descent is made using 3-D RNAV airborne equipment.
When using reference facilities not on the route the track angle must be computed relative to the reference facility being used. These track angles may change when using different reference facilities due to meridian divergence/convergence.
Page 4 Par 2
Appendix D
b. Obstacle Clearance Requirements. Obstacle clearance will be provided as described in Advisory Circular 95-1, paragraphs 4, 5, and 7, except that the primary obstacle clearance areas will be as specified in paragraphs 2.a. (1) and 2.a. (2) above.
(1) Secondary obstacle clearance areas extend laterally 2 miles on each side of the primary area and splay at 4.9° where the primary area splays at 3.25°.
(2) Obstacle clearance areas are expanded as specified in paragraph 3.c of AC 95-1 and as illustrated in Figure 3 to accommodate turns of more than 15 degrees.
Enroute Waypoint Displacement Area. The enroute waypoint displacement area is a rectangular or square area formed around the plotted position of the waypoint. The dimensions of this area are derived from the appropriate along-track and cross-track error values.
Table 2, Appendix D. The enroute waypoint displacement area shall be considered for each waypoint when developing RNAV enroute procedures.
3. INTA FOr it at dear 190% TERMINAL CRITERIA. Terminal routes provide access to the enroute structure for aircraft departing an airport and routing to enter an instrument approach procedure for arriving aircraft. Parallel offset terminal routes will be used where practical for spacing and to separate overtaking aircraft. Terminal routes shall be evaluated by flight inspection concurrently with associated instrument approach and departure procedures.
Terminal arrival routes will be designed for efficient traffic flow to the final approach aid - normally ILS. To the extent possible the altitudes specified on the arrival routes will provide for a 300' per mile rate of descent from the enroute environment to the runway or the point where the final approach aid is intercepted. To facilitate the transition and to standardize the terminal route structure, the last waypoint on the arrival route will be established approximately 8 miles from the runway at the intermediate fix. The altitude at the eight mile waypoint should agree with the glide slope or provide an approximate 300'/mile gradient to the runway as appropriate to the type of final approach utilized.
Terminal departure routes will be designed from the departure end of the runway to the enroute structure. The first waypoint will be shown at the departure end of the runway. Immediate turns at the end of the runway are discouraged. Insofar as possible from the standpoint of airspace management the second waypoint will be established on the runway centerline extended.
Par 2 Page 5
Appendix D
AREA NAVIGATION Route Width Summary Distance along-track from Tangent Point 4 NM ZONE Terminal Procedures 8 NM ZONE ZONE of 3.25° SPLAY 'angent Point Distance MINIMUM WIDTH at Tangent Point Distance 110 (8.5 NM) -2 beyond 8 NM ZONE 220 19:0 NT Route width splays 3.25° from Tangent Point 30 [9.5 NM] TO 1IO.O MMS 150 110.5 MMS FIGURE 1 Page 6 Par 3
Appendix D FIGURE 2. TYPICAL RNAV ARRIVAL AND DEPARTURE ROUTE CONFIGURATION Par 3 Page 7
AC 90-45A CHG 2 Appendix D 7/22/76
FIX AREAS DETERMINED BY CROSS-TRACK AND ALONG-TRACK ERRORS AREA EXPANDED IAW AC 95-1 ABOVE 10,000 30 NM
• Earliest point for waypoint passage
•2 N 70 NM
ENROUTE
TURNING AREA
1. Expansion for "corner cutter" begins at a distance prior to the earliest point the waypoint can be received:
3 NM below 8000' - 7 NM 8000-18000' - 12 NM above FL 180.
Angle of splay for expanding area is 1/2 the amount of the course change.
FIX AREAS DETERMINED BY CROSS-TRACK AND ALONG-TRACK ERRORS AREA EXPANDED IAW AC 95-1 - 20 NM - ABOVE 10,000 Earliest point for waypoint passage TERMINAL FIGURE 3. TYPICAL TURNING AREAS 20 NM TURNING * AREA Page 8 Par 3.
Appendix D RNAV Routes Protected Areas. The area to be protected is as shown in Figure 1 and is described as follows:
(1) Primary obstacle clearance areas extend laterally two miles each side of routes in which the tangent point distance of the route centerline is within 53 miles of the ground station. The route boundaries splay 3.25 beginning at the point where the * route centerline exits the four-mile zone.
Secondary obstacle clearance areas extend laterally 1 mile each side of the primary area and splay 4.9° where the primary area splays at 3.25°. * Obstacle clearance areas are expanded as specified in paragraph
3.e in AC 95-1 and as illustrated in Figure 3 to accommodate turns of more than 15 degrees.
(4) Paragraphs 2.a(3) and 2.b(2) above which concern parallel offsets and turning areas also apply.
b. Obstacle Clearance Requirements. Obstacle clearance will be provided as described in FAA Handbook 8260.3A (TERPS), paragraph 232.c.
Terminal Waypoint Displacement Area. The terminal waypoint displacement area is a rectangular or square area formed around the plotted position of the waypoint. The dimensions of this area are derived from the appropriate along-track and cross-track error values. See Table 3, Appendix D. The terminal waypoint displacement error shall be considered for each waypoint when used in RNAV departures and arrivals, including initial and intermediate approach waypoints.
Holding Pattern Area Determination. The holding pattern is a racetrack pattern flown at a waypoint or an ATD fix and at an IAS appropriate to the aircraft and altitude. The holding IAS for helicopters is 90 knots. The RNAV holding area will have the outbound leg length specified in nautical miles. Minimum leg length for helicopters is 2 NM. Determination of required area is made using Table 2 or Table 3, Appendix D, appropriate IAS, an omnidirectional wind of 50 knots increasing 3 knots per 2000' above 4000 AGL, pattern turn or a 2505 seconds. Turning radi1 are based on a standard rate entry direction, ICAO standard atmosphere plus 15°C and fix passage tolerance of angle of bank whichever is less. The following example is for helicopters holding at a sea level terminal area, but the method applies to all aircraft by using the appropriate IAS, altiterminal (Table 3). tude, and table for the mode of flight; i.e., enroute (Table 2) or * Par 3 Page 8-1
Appendix D * Example: IAS = 90 KTS ATD = 30 NM Alt = 6000' MSL & AGL TPD = 30 NM OAT = 3° + 15° = 18°C xwind = 50 + 3 = 53 KTS From Table 3, Appendix D; cross-track error (x trk) = 2.4 NM, alongtrack error (alg trk) = 2.2 NM.
(1) The cross-track area is determined as follows.
Holding side. The area on the holding side is determined by the cross-track navigation system errors, the effect of wind and the area required for a standard rate turn (max 25°) from entries along-track or the reciprocal and including all directions from the nonholding side.
The contribution due to winds will be .88 NM during the 180° turn outbound (assume crosswind for worst case).
The cross-track error value and the wind contribution are root-sun-squared, yielding:
RSS = V2.4 + .88' = 2.55 NM The angle of bank at 90 KTS (95 KTS, TAS) for a standard rate turn is determined by the following:
tan @ = .00275V, V = KTS, IAS = .00275(95) = ,26125 then Ø = 14.64° = 15° The turning radius (r) at TAS = 95 KTS and bank angle (ø) of 15° is determined by the following:
r = 1.4589 × 10-5 tan Ø V, where V - KIS, TAS r = 1.4589 × 10-5 (95) ₴
• 2679 · = .49 NM The cross-track contribution due to the turn is:
2x = .98 NM.
Hence, the total cross-track displacement on the HOLDING side is:
cross-track RSS + 2r: 2.55 + .98 = 3.53 NM. * Page 8-2 Par 3
Appendix D * (b) Nonholding side. The cross-track displacement on the NONHOLDING side is either one-half of the route width at the ATD fix, as discussed below, or the area required to make an entry from the holding side, whichever is greater.
One-half of the route width in the terminal area (50 NM or less) is 2.0 NM. In the enroute area (more than 50 NM but less than 102 NM) one-half of the route width is 4 NM. At distances greater than 102 NM, one-half of the route is 4 NM plus a 3.25° splay. (See Figure 1). For parallel entry at the 70° sector line (worst case), cross-track displacement is determined as follows (see Figure 3-1):
G M
PRIMARY AREA
EXPANDED PRIMARY AREA L_ FIGURE 3-1. HOLDING AREA DETERMINATION A - DME leg distance H - Fix passage tolerance (sin 9) B - Turn radius I - Nonholding side entry RSS C - Fix passage tolerance J - Turn radius (1 + cos 9) D - Direct entry RSS K - Fix passage tolerance (cos 0) E - 2 (Turn radius) L - Holding side entry RSS F - Cross-track RSS M - 1/2 Route width G - Turn radius (1 + sin 0) * Par 3 Page 8-3
Appendix D * The wind contribution during the 110° turn to parallel the outbound is .54 NM.
When RSS'd with the cross-track error:
RSS = V(2.4)½ + (.54)% = 2.46 NM The turn contribution is r(1 + sin 0): (here 0 = 20°) .49(1.3420) = .66 NM The fix passage tolerance is:
(5 secs @ 95 KTAS) sin 20° = .05 NM The cross-track displacement on the NONHOLDING side is then:
parallel entry RSS + r(1 + sin 0) + fix passage tolerance (sin 0) :
2.46 + .66 + .05 = 3.17 NM Since this exceeds 2.0 NM half route width, it is the width to be protected.
(2) The along-track area for a direct (or reciprocal) entry or an entry from the nonholding side is determined as follows.
The contribution due to winds during the 180° turn outbound is .44 NM (assume direct entry and tailwind for worst case).
When RSS'd with the along-track error:
RSS = V(2.2)? + (.44)% = 2.24 NM fix passage tolerance (5 secs) @ 95 KTAS = .13 NM.
The total along-track displacement is:
2 (nonholding side entry RSS) + 2(r) + 2 fix passage tolerance + DME leg 2(2.24) + 2(.49) + 2(.13) + 2 = 7.72 NM * Page 8-4 Par 3
Appendix D * (3) The along-track error for an entry from the holding side (70° sector line for worst case) will elongate the entry end and is determined as follows.
The wind contribution during the 160° turn to fly the pattern is .79 NM.
When RSS'd with the along-track error:
RSS = V(2.2) 2 + (.79) 2 = 2.33 NM The turn contribution is r(1 + cos 0): (here 0 = 20°) .49(1.9397) = .95 NM The fix passage tolerance is:
(5 secs @ 95 KTAS) cos 20° = .12 NM The total along-track displacement is the sum of the entry, leg distance and inbound turn displacements:
holding side entry RSS + r(1 + cos 0) + fix passage tolerance (cos 0) + DME leg + direct entry RSS + r + fix passage tolerance:
2.33 + .95 + •12 + 2.0 + 2.24 + .49 + .13 = 8.26 NM A secondary area of one-half of the cross-track error or 2 NM, whichever is greater, is added to the perimeter of the pattern for obstacle clearance. *
4. INSTRUMENT APPROACH PROCEDURE CRITERIA. FAA Handbook 8260.3A, The United States Standard for Terminal Instrument Procedures (TERPS), prescribes criteria for the design of instrument approach procedures.
Although it does not at the present time contain special criteria for the design of RNAV procedures, most of the TERPS criteria are applicable to RNAV procedures with minor modifications. This appendix will therefore provide only the criteria necessary to modify TERPS for RNAV procedure application. "fix" is equivalent to "waypoint," thus, In applying TERPS to RNAV procedures, the term "Final Approach Fix (FAF)" becomes "Final Approach Waypoint (FAWP)."
Procedures Construction. An RNAV instrument approach procedure may have four separate segments. They are the initial, the intermediate, the final and the missed approach segments. In addition, an area for circling the airport under visual conditions shall be considered. The approach segments begin and end at waypoints or Par 3 Page 9
Appendix D along-track distance (ATD) fixes which are identified to coincide with the associated segment. For example, the intermediate segment begins at the intermediate waypoint (INWP) and ends at the Final Approach Waypoint (FAWP) or ATD fix.
Descent Gradients. TERPS descent gradients will apply to all RNAV procedures except where an uninterrupted descent gradient of 300 feet per mile (+20', -50') can be established from the initial approach through the final approach. It shall be done to provide stabilized descent throughout the arrival procedures.
Runway Waypoint and Flight Path Angle. Both standard and simplified procedures should incorporate a waypoint at the runway threshold. This waypoint will be used as the point from which the Flight Path Angle is computed. On ILS runways, the Flight Path Angle shall be computed using the runway waypoint elevation equal to the ILS threshold crossing height. Where no ILS glide path is present, the Flight Path Angle shall be computed from the runway waypoint elevation 50 feet higher than the runway threshold elevation for runways 4,000 feet and longer.
It may be established as low as 37 feet for runways less than 4,000 feet in length. The procedure shall specify the runway waypoint elevation under additional flight data. Example:
W/P elevation 1827'.
Transition Routes. When transition routes are required from the en route structure to the initial approach waypoint, they should be designed to coincide with the local air traffic flow. En route RNAV obstacle clearance criteria (paragraph 2.b. above) shall apply to transition routes in which the tangent point distance (TPD) of the route centerline is more than 53 miles from the ground station. When the TPD is within 53 miles of the ground station, RNAV terminal route obstacle clearance criteria (paragraph 3.b. above) shall apply.
Initial Approach Segment. The RNAV instrument approach procedure commences at the Initial Approach Waypoint (IAWP). In the initial approach, the aircraft has departed the en route phase of flight and is maneuvering to enter the intermediate segment. Standard RNAV procedures -- as opposed to simplified procedures -- may utilize several initial approach segments to accommodate the traffic flow requirements. En route RNAV obstacle clearance criteria (paragraph
2.b. above) shall apply to initial approaches in which the TPD of the initial approach course is more than 53 miles from the ground station. When the TPD is within 53 miles of the ground station, RNAV terminal route obstacle clearance criteria (paragraph 3.b. above) shall apply.
(1) Initial approach segments based on a procedure turn shall not be established. Where course reversal is required, a holding pattern shall be established in lieu of a procedure turn.
Standard holding pattern obstacle clearance shall apply.
Page 10 Par 4
Appendix D Intermediate Approach Segment. The purpose of the intermediate segment is to blend the initial approach into the final approach and provide an area in which aircraft configuration, speed and positioning adjustments are made for entry into the final approach segment. The intermediate segment begins at the Intermediate Waypoint (INWP) and ends at the FAWP or ATD fix.
Alignment. The course to be flown in the intermediate segment should be the same as the final approach course whenever possible. When it is not practical for the courses to be identical, the intermediate course may not differ from the final approach course by more than 60 degrees.
Distance from runway. For Standard procedures the intermediate waypoint shall be established approximately 8 miles from the runway. For the Simplified procedure the intermediate fix will be established as necessary to accommodate a procedure which utilizes only two waypoints. See paragraph 1.h.
(3) Length. The minimum length is 3 miles with standard procedures.
Final Approach Segment. This is the segment in which alignment and final descent for landing are accomplished. The final approach segment begins at the final approach waypoint or Along-Track Distance (ATD) fix and ends at the missed approach point, normally the runway threshold waypoint. When it is not at the runway threshold, it is an ATD fix based on a distance to the runway waypoint. Final approach may be made to a runway for straight-in landing, or to an airport for a circling approach. Only one final approach shall be specified for a procedure.
(1) Alignment. Whenever possible, the final approach course shall e aligned with the straight-in Landing runway. when the alignment exceeds 15 , straight-in minimums are not authorized.
(2) Final Approach Area. The area considered for obstacle clearance starts at the earliest point the Final Approach Waypoint (FAWP) or ATD fix can be received and ends at the latest point the Missed Approach Waypoint (MAWP) can be received or at the runway threshold whichever occurs last. See Table 4, Appendix D, for fix errors. When the final approach course is a continuation of the intermediate course, an ATD fix shall be used instead of a FAWP. Additional ATD fixes may be established as step-down fixes.
(a) Length. The OPTIMUM length of the final approach segment is 5 miles. The MAXIMUM length is 10 miles. The MINIMUM length of the final approach segment shall provide adequate distance for an aircraft to make the required descent, and Par 4 Page 11