The weather conditions encountered in CAT III operations  range from an area where visual references are adequate for  manual rollout in CAT IIIa, to an area where visual references  are inadequate even for taxi operations in CAT IIIc. To  date, no U.S. operator has received approval for CAT IIIc  in OpSpecs. Depending on the auto-flight systems, some  aircraft require a DH to ensure that the aircraft is going to  land in the TDZ and some require an Alert Height as a final  cross-check of the performance of the auto-flight systems.  These heights are based on radio altitude (RA) and can be  found in the specific aircraft’s AFM. [Figure 4-42]  Both CAT II and III approaches require special ground and  airborne equipment to be installed and operational, as  well as special aircrew training and authorization. The  OpSpecs of individual air carriers detail the requirements  of these types of approaches, as well as their performance  criteria. Lists of locations where each operator is approved  to conduct CAT II and III approaches can also be found in  the OpSpecs.  Special Authorization approaches are designed to  take advantage of advances in flight deck avionics and  technologies like Head-Up Displays (HUD) and automatic  landings. There are extensive ground infrastructures and  lighting requirements for standard CAT II/III, and the  Special Authorization approaches mitigate the lack of some  lighting with the modern avionics found in many aircraft  today. Similar to standard CAT II/III, an air carrier must be  specifically authorized to conduct Special Authorization  CAT I/II in OpSpecs Part C.  Simultaneous Approaches To Parallel Runways  Simultaneous Dependent Approaches [Figure  4-46] NOTE:  Airports that have two or more parallel runways may be  authorized to use simultaneous parallel approaches to  maximize the capacity of the airport. Depending on the  runway centerline separation and ATC procedures, there are  three classifications of simultaneous parallel approaches:  Simultaneous dependent approaches, simultaneous  independent approaches and simultaneous independent  close parallel approaches. A simultaneous dependent  approach differs from a simultaneous independent  approach in that the minimum distance between parallel  runway centerlines may be less. A staggered separation of  aircraft on the adjacent final approach course is required;  but there is no requirement for a No Transgression Zone  (NTZ) or Final Monitor Controllers. An independent  approach eliminates the need for staggered approaches  and aircraft may be side by side or pass if speeds are  different.  may only be conducted when (GPS) appears in the  approach title or a chart note states that GPS is required.  See the “ILS Approaches” paragraph above for information  about pilot responsibilities when simultaneous approaches  are in use.  Where a simultaneous approach operation is approved,  sometimes each approach chart indicates the other  runway(s) with which simultaneous approaches can be  conducted. For example, “Simultaneous approaches  authorized with runway 12L”. As procedures are revised,  the chart note will be modified to indicate “Simultaneous  approach authorized” but will not list the other runways or  approach types as that detailed information will normally  be transmitted in the ATIS or by ATC. For example, pilots  flying into Sacramento, California, may encounter parallel  approach procedures. [Figure 4-44] When there is no  At some airports, simultaneous dependent instrument  approaches can be conducted with runways spaced less  than 2,500 feet with specific centerline separations and  threshold staggers. ATC is permitted to apply reduced  diagonal separation and special wake turbulence  procedures. The lead aircraft of the dependent pair is  restricted to being small or large aircraft weight type and is  cleared to the lower approach. The design of the approach,  aircraft weight type, and lateral separation between the two  approaches provide necessary wake turbulence avoidance  for this type of operation. An example of approach design  to help avoid wake turbulence is that some locations use  different glide slope angles on adjacent approaches; also,  if applicable, staggered thresholds help. An ATIS example  is: “Simultaneous ILS Runway 28 Left and ILS Runway 28  Right in use.” For further information, see FAA Orders JO  7110.65 and JO 7110.308.  When simultaneous dependent approaches are provided,  ATC applies specific minimum diagonal separation criteria,  depending on the runway separation, between aircraft on  adjacent final approach courses. Aircraft will be staggered  by a minimum of 1 NM diagonally on final, depending  on the distance between runway centerlines. Greater  separation standards are applied when the distance  between runway centerlines is greater. [Figure 4-43]  4-64 1. Simultaneous approaches involving an RNAV approach  2. Flight Director or Autopilot requirements for simultaneous  operations will be annotated on the approach chart. 3. Simultaneous approaches may only be conducted  where instrument approach charts specifically authorize  simultaneous approaches. 