an EFVS cannot be used to satisfy the requirement that an  identifiable part of the airport be distinctly visible to the  pilot during a circling maneuver at or above MDA or while  descending below MDA from a circling maneuver.  the flight information, navigation guidance, and sensor  imagery on a HUD or equivalent display allows the pilot to  continue looking forward along the flightpath throughout  the entire approach, landing, and rollout.  Sections 91.175(c) and 91.176 specify two means of operating  visually below DA/DH or MDA in the visual segment of an  IAP. One means is by using natural vision under § 91.175(c),  and the other is by using enhanced vision provided by an  EFVS under § 91.176. When the runway environment cannot  be visually acquired using natural vision, a pilot may use an  EFVS to continue descending below DA/DH or MDA under §  91.176. An EFVS operation is an operation in which visibility  conditions require an EFVS to be used in lieu of natural vision  to perform an approach or landing, determine enhanced  flight visibility, identify required visual references, or conduct  a rollout. There are two types of EFVS operations – EFVS  operations to touchdown and rollout and EFVS operations  to 100 feet above the touchdown zone elevation (TDZE). An  EFVS operation to touchdown and rollout is an operation in  which a pilot uses the enhanced vision imagery provided by  an EFVS in lieu of natural vision to descend below DA or DH to  touchdown and rollout [Figure 4-10B]. These operations may  be conducted on standard instrument approach procedures  (SIAPs) or special instrument approach procedures (IAPs) that  have a DA or DH (e.g., Precision or APV approach).  The visual information provided by an EFVS serves as  independent verification of the position information  provided by the aircraft’s displays and systems. An EFVS  also enables a pilot to assess the enhanced flight visibility  and identify required visual references, helps a pilot align  the aircraft with the runway, and provides position, roll, rate  of closure, and distance remaining information. Sections  91.176(a) and 91.176(b) permit a pilot to use an EFVS to  identify the required visual references and to determine  that the enhanced flight visibility provided by the EFVS is  not less than the visibility prescribed in the IAP to be flown.  Both the visual reference and enhanced flight visibility  requirements of the regulations must be met before the  pilot can descend below DA/DH during an EFVS operation  to touchdown and rollout or below DA/DH or MDA during  an EFVS operation to 100 feet above the TDZE. The aircraft  also must continuously be in a position from which a  descent to landing can be made on the intended runway at  a normal rate of descent using normal maneuvers. For EFVS  operations to touchdown, § 91.176(a)(2)(vi) requires that  the descent rate must allow touchdown to occur within the  touchdown zone of the runway of intended landing for all  operations. Section 91.176(b)(2)(v), operations conducted  to 100 feet above the TDZE, requires the descent rate to  allow touchdown to occur within the touchdown zone of  the runway of intended landing for operations conducted  under 14 CFR Parts 121 and 135.  An EFVS operation to 100 feet above the TDZE is an  operation in which the pilot uses the EFVS in lieu of natural  vision to descend below DA/DH or MDA down to 100 feet  above the TDZE [Figure 4-10C]. To descend below 100 feet  above the TDZE, however, natural vision must be used. EFVS  operations to 100 feet above the TDZE may be conducted  on SIAPs or special IAPs that have a DA/DH or MDA.  While the regulations do not prohibit EFVS from being used  during any phase of flight for situational awareness, EFVS  displays are not designed, installed, certified, or intended  as a sufficient visual system to conduct circling maneuvers.  EFVS may only be used during a circle-to-land maneuver  provided the visual references required throughout the  circling maneuver are distinctly visible to the pilot using  natural vision throughout the circling maneuver. Therefore,  It is important to understand that using an EFVS does not  result in obtaining lower minima with respect to the visibility  or the DA/DH or MDA specified in the IAP. For example, a  pilot who is using an EFVS on a Category I ILS approach that  specifies a DA of 200 feet and a required visibility of RVR 2400  feet must comply with a 200-foot DA and an enhanced flight  visibility of 2400 feet, even though the pilot may not have  2400 feet of flight visibility using natural vision or a reported  Figure 4-10 C . EFVS Operations to 100 Feet Above the TDZE.  Figure 4-10B. EFVS Operation to Touchdown and Rollout.  4-21