Enhanced Flight Vision System (EFVS)
Figure: Phases of an EFVS Approach, from Eddie's notes.
[AC 90-106 ¶5.] In 2004, 14 CFR 91.175. was revised to allow a pilot to descend below DA or MDA from a straight-in IAP other than CAT II or CAT III using an Enhanced Flight Vision System (EFVS) which uses imaging sensor technology to produce a real-time enhanced image of the external topography.
- To descend below DA or MDA using an EFVS, the enhanced flight visibility observed by the EFVS cannot be less than the visibility prescribed in the IAP being flown, and the visual references required by the regulations must be distinctly visible and identifiable to the pilot using the EFVS. This revision of the regulations permits a pilot to use an EFVS to do the following when the runway environment may not be visible to a pilot relying on natural vision alone:
- Determine that the enhanced flight visibility is not less than the visibility prescribed by the IAP being used,
- Identify the required visual references,
- Verify proper runway alignment, and
- Descend from DA or MDA down to 100 feet above the TDZE of the runway of intended landing.
[14 CFR 91.175. l.] Approach to straight-in landing operations below DH, or MDA using an enhanced flight vision system (EFVS). For straight-in instrument approach procedures other than Category II or Category III, no pilot operating under this section or §121.651, 125.381, and 135.225 of this chapter may operate an aircraft at any airport below the authorized MDA or continue an approach below the authorized DH and land unless—
- The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and, for operations conducted under part 121 or part 135 of this chapter, the descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;
- The pilot determines that the enhanced flight visibility observed by use of a certified enhanced flight vision system is not less than the visibility prescribed in the standard instrument approach procedure being used;
- The following visual references for the intended runway are distinctly visible and identifiable to the pilot using the enhanced flight vision system:
- The approach light system (if installed); or
- The following visual references in both paragraphs (l)(3)(ii)(A) and (B) of this section:
- The runway threshold, identified by at least one of the following:
- The beginning of the runway landing surface;
- The threshold lights; or
- The runway end identifier lights.
- The touchdown zone, identified by at least one of the following:
- The runway touchdown zone landing surface;
- The touchdown zone lights;
- The touchdown zone markings; or
- The runway lights.
- At 100 feet above the touchdown zone elevation of the runway of intended landing and below that altitude, the flight visibility must be sufficient for the following to be distinctly visible and identifiable to the pilot without reliance on the enhanced flight vision system to continue to a landing:
- The lights or markings of the threshold; or
- The lights or markings of the touchdown zone;
What's in a name? Why does it matter? Gulfstream was leading the pack on this and decided to call the Forward Looking Infrared Radar (FLIR) to Heads Up Display (HUD) interface an Enhanced Vision System (EVS). The FAA, years later, decided an EVS was the heads down portion and decided to call the heads up portion Enhanced Flight Vision System (EFVS). The Gulfstream system is certified to take advantage of 14 CFR 91.175, so where the regulation says EFVS, in the Gulfstream fleet that means EVS.
Figure: Approach utilising EVS RVR/CMV reduction v. normal RVR/CMV, from EU Ops 1, Subpart E, Section OPS 1.430, Appendix 1, Table 9.
[EU Ops 1, Subpart E, Section OPS 1.430, Appendix 1, ¶(h)]
1. A pilot using an enhanced vision system certificated for the purpose of this paragraph and used in accordance with the procedures and limitations of the approved flight manual, may:
(i) continue an approach below DH or MDH to 100 feet above the threshold elevation of the runway provided that at least one of the following visual references is displayed and identifiable on the enhanced vision system:
(A) elements of the approach lighting; or
(B) the runway threshold, identified by at least one of the following: the beginning of the runway landing surface, the threshold lights, the threshold identification lights; and the touchdown zone, identified by at least one of the following: the runway touchdown zone landing surface, the touchdown zone lights, the touchdown zone markings or the runway lights;
(ii) reduce the calculated RVR/CMV for the approach from the value in column 1 of Table 9 below to the value in column 2:
2. Paragraph (h)1. above may only be used for ILS, MLS, PAR, GLS and APV Operations with a DH no lower than 200 feet or an approach flown using approved vertical flight path guidance to a MDH or DH no lower than 250 feet.
3. A pilot may not continue an approach below 100 feet above runway threshold elevation for the intended runway, unless at least one of the visual references specified below is distinctly visible and identifiable to the pilot without reliance on the enhanced vision system:
(A) The lights or markings of the threshold; or
(B) The lights or markings of the touchdown zone.
The U.S. and EU regulations do not mention obstacles, but FAA GIV-X/GV/GV-SP FSB report does, allowing the use of the Gulfstream EVS "provided that vertical guidance with reference to an obstacle-free path is used." For a discussion of why this is indeed a factor, scroll down to "Obstacle Clearance."
In the United States and in EU countries, you can use a qualified EFVS to continue an approach below DH/DA or MDH/MDA under certain conditions. Outside of those areas you need to check country-specific AIPs.
[G450 Aircraft Operating Manual §01-34-80]
- Pilot’s Manuals: The HUD section of the G450 Operating Manual (Chapter 2B: PlaneView System, Basic Issue or later approved revision) must be immediately available to the flight crew whenever use of the EVS system is contemplated.
- Presence of Visual Cues: At 100 feet HAT, visual cues must be seen without the aid of EVS to continue descent to landing.
- Qualifications For Use: EVS may be used only by qualified pilots who have been trained in accordance with requirements listed in the FAA GIV-X/GV/GV-SP FSB report.
- Vertical Guidance Requirements For IMC EVS Approaches: Flight Director or autopilot with vertical guidance, either ILS glideslope or FMS vertical path, is required for all IMC EVS approaches.
- Requirements: EVS as installed meets the requirements of EFVS (Enhanced Flight Vision System) as defined in FAR 91.175.
[AC 90-106 8.b.] Except for part 91K operators, part 91 operators are not required to be issued an LOA to conduct EFVS operations.
[AC 90-106 9.a.(1)] An EFVS may be used to descend below DA or MDA from any straight-in instrument approach procedure, other than CAT II or CAT III approaches, provided all of the requirements of §91.175(l) are met. This includes:
- straight-in precision approaches,
- approaches with vertical guidance (e.g., lateral approach procedures with vertical guidance (LPV) or lateral navigation (LNAV)/vertical navigation (VNAV)), and
- non-precision approaches (e.g., VHF omni-directional range station (VOR), non-directional radio beacon (NDB), LOC, Area Navigation (RNAV), global positioning system (GPS), localizer-type directional aid (LDA), Simplified Directional Facility (SDF), etc.).
While the Advisory Circular does not prohibit the use of EFVS for offset approaches, it does caution that pilots must be aware of runway alignment prior to descending.
[AC 90-106 9.a.(2)] An instrument approach with a circle-to-land maneuver or circle-to-land minimums does not meet criteria for straight-in landing minimums.
Parallel Decision Making: When to Go Around.
[AC 90-106 9.a.(4)] Any pilot operating an aircraft with an EFVS installed should be aware that the requirements of §91.175(c), using natural vision, and §91.175(l), using EFVS, are different. A pilot would, therefore, first have to determine whether an approach will be commenced using natural vision in accordance with §91.175(c) or using EFVS in accordance with §91.175(l). While these two sets of requirements provide a parallel decision making process, the requirements for when a missed approach must be executed differ.
Using EFVS, a missed approach must be initiated at or below DA or MDA down to 100 feet above TDZE whenever the pilot determines that:
- The enhanced flight visibility is less than the visibility minima prescribed for the IAP being used;
- The required visual references for the runway of intended landing are no longer distinctly visible and identifiable to the pilot using the EFVS imagery (§91.175(l)(3));
- The aircraft is not continuously in a position from which a descent to a landing can be made on the intended runway, at a normal rate of descent, using normal maneuvers; or
- For parts 121 and 135 operators, the descent rate of the aircraft would not allow touchdown to occur within the TDZ of the runway of intended landing.
Missed Approach Below the DA or after passing the MAP
Figure: Missed approach below published DA, from Eddie's notes.
[AC 90-106 9.a.(5)] Missed Approach Considerations. It should be noted that a missed approach after passing the DA, or beyond the missed approach point (MAP) involves additional risk until established on the published missed approach segment. Missed approach obstacle clearance is predicated on beginning the missed approach procedure at the DA or MAP and then climbing 200 feet/nm or greater. Initiating a go-around after passing the published MAP may result in loss of obstacle clearance. As with any approach, pilot planning should include contingencies between the published MAP and touchdown with reference to obstacle clearance, aircraft performance, and alternate escape plans. Paragraphs 9(e)(2) and (3) contain additional information about obstacle clearance as does the Aeronautical Information Manual (AIM) and the Instrument Procedures Handbook.
Figure: Eagle County RNAV (GPS)-D, from FAA AL-6403.
If the runway in use has a VASI, PAPI, RNAV(GPS), or ILS glide path, it has been surveyed to assure obstacle clearance so long as you stay at or above the indicated glide path. Obstacles will rarely have an IR signature, they are often invisible to EFVS.
If the runway in use does not have a VASI, PAPI, RNAV(GPS), or ILS glide path, it may be okay (it just hasn't been surveyed) but it may be that there is an obstacle issue to consider. Take the obvious example of the RNAV(GPS)-D to Eagle County Regional. Unless the mountains to the east are radiating residual heat from the day, they will be invisible to EFVS. Flying a 3° glide path will put you 2,000 feet below the 9,860 minimum altitude 3 nm from NEPRY.
14 CFR 91, Title 14: Aeronautics and Space, General Operating and Flight Rules, Federal Aviation Administration, Department of Transportation
Advisory Circular 90-106, Enhanced Flight Vision Systems, 6/2/10, U.S. Department of Transportation
European Union Regulation No 859/2008, Technical requirements and administrative procedures applicable to commercial transportation by aeroplane, 20 August 2008
Flight Standardization Board (FSB) Report, Gulfstream GIV-X, GV, GV-AP, Revision 8, 08/01/2012
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.