[Federal Register Volume 66, Number 117 (Monday, June 18, 2001)]
[Rules and Regulations]
[Pages 32717-32728]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-15333]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM185; Special Conditions No. 25-180-SC]


Special Conditions: Enhanced Vision System (EVS) for Gulfstream 
Model G-V Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for Gulfstream Model G-V 
airplanes. These airplanes, as modified by Gulfstream Aerospace 
Corporation, will have novel or unusual design features associated with 
a head-up display (HUD) system modified to display forward-looking 
infrared (FLIR) imagery. The regulations applicable to pilot 
compartment view do not contain adequate or appropriate safety 
standards for this design feature. These special conditions contain the 
additional safety standards that the Administrator considers necessary 
to establish a level of safety equivalent to that provided by the 
existing airworthiness standards.

EFFECTIVE DATE: June 18, 2001.

FOR FURTHER INFORMATION CONTACT: Dale Dunford, FAA, Transport Standards

[[Page 32718]]

Staff, ANM-111, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue SW., Renton, Washington 98055-4056; telephone 
(425) 227-2239; fax (425) 227-1100; e-mail: <a href="/cdn-cgi/l/email-protection#583c39343d763c2d363e372a3c183e3939763f372e"><span class="__cf_email__" data-cfemail="debabfb2bbf0baabb0b8b1acba9eb8bfbff0b9b1a8">[email protected]</span></a>.

SUPPLEMENTARY INFORMATION

Background

    On February 13, 1998, Gulfstream Aerospace Corporation, 4150 Donald 
Douglas Drive, Long Beach, California 90808, applied for a supplemental 
type certificate (STC) to modify Gulfstream Model G-V airplanes. The 
Model G-V is a transport category to modify Gulfstream Model G-V 
airplanes. The Model G-V is a transport category airplane with a 
maximum takeoff weight of 90,500 pounds and powered by two BMW-Rolls 
Royce Mark BR700-710A1-10 engines. This airplane operates with a two-
pilot crew and can hold up to 19 passengers.
    The modification incorporates the installation of an Enhanced 
Vision System (EVS), consisting of a Honeywell 2020 head-up display 
(HUD) system modified to display forward-looking infrared (FLIR) 
imagery provided from a Kollsman FLIR assembly. The FAA has previously 
approved the Honeywell 2020 HUD.
    The FAA only considered natural pilot vision for the pilot 
compartment view when issuing Sec. 25.773. The electronic infrared 
image displayed between the pilot and the forward windshield represents 
a novel or unusual design feature in the context of Sec. 25.773. The 
projection of electronic imagery has the potential to enhance the 
pilot's situational awareness. The FAA needs to evaluate EVS to 
determine that the imagery does not adversely affect the pilot's 
outside compartment view.
    Although the FAA determined that the existing regulations are not 
adequate for certification of EVS, it believes that EVS could be 
certified through application of appropriate safety criteria. 
Therefore, the FAA has determined that special conditions should be 
issued for certification of EVS to establish an equivalent level of 
safety and effectiveness of the pilot compartment view as intended by 
the regulation.
    Gulfstream and the FAA conducted an extensive proof of concept 
flight demonstration program and concluded that the EVS could be 
certified to provide an image that would aid the pilot during an 
instrument approach for detecting and identifying the visual references 
listed in Title 14, Code of Federal Regulations (14 CFR 91.175(c)(3)) 
for descent below decision height to 100 feet above touchdown. 
Conditions permitting, EVS may yield safety and operational benefits by 
providing the pilot with enhanced situational awareness.

Type Certification Basis

    Under the provisions of Sec. 21.101 (``Designation of applicable 
regulations''), Gulfstream Aerospace Corporation must show that the 
Gulfstream Model G-V airplanes, as changed, comply with the regulations 
in the U.S. type certification basis established for the Model G-V 
airplane. The U.S. type certificate basis established for the Model G-V 
airplane is established in accordance with Sec. 21.21 (``Issue of type 
certificate * * *'') and Sec. 21.17 (``Designation of applicable 
regulations''), and the type certification application date. The U.S. 
type certification basis for this model airplane is listed in Type 
Certificate Data Sheet No. A12EA.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25, as amended) do not contain adequate or 
appropriate safety standards for the Gulfstream Model G-V airplanes 
modified by Gulfstream Aerospace Corporation because of a novel or 
unusual design feature, special conditions are prescribed under the 
provisions of Sec. 21.16 (``Special conditions'').
    In addition to the applicable airworthiness regulations and special 
conditions, these Gulfstream Model G-V airplanes must comply with the 
fuel vent and exhaust emission requirements of part 34 and the noise 
certification requirements of part 36.
    Special conditions, as appropriate, are issued in accordance with 
Sec. 11.19 (``What is a final rule?''), after public notice, as 
required by Sec. 11.38 (``What public comment procedures does FAA 
follow for Special Conditions?''), and become part of the type 
certification basis in accordance with Sec. 21.101(b)(2).
    Special conditions are initially applicable to the model for which 
they are issued. Should Gulfstream Aerospace Corporation apply at a 
later date for a supplemental type certificate to modify any other 
model included on the same type certificate to incorporate the same 
novel or unusual design feature, these special conditions would also 
apply to the other model under the provisions of Sec. 21.101(a)(1).

Novel or Unusual Design Features

    The Gulfstream EVS project is the first civil certification of 
infrared imagery displayed on a HUD. This EVS is novel or unusual 
technology because it places a raster* infrared image in the center of 
the pilot's regulated ``pilot compartment view,'' which must be free of 
interference, distortion, and glare that would adversely affect the 
performance of the pilot's normal duties. (*A ``raster'' image is 
comprised of a set of horizontal lines that continuously sweep across 
the display and form a picture on the display by modulating their 
intensity (luminance).) The EVS/HUD system projects a raster image 
derived from a forward-looking infrared (FLIR) camera onto the display 
of the Honeywell HUD 2020 system. The EVS image is displayed with HUD 
symbology and overlays the forward outside view.
    Operationally, during an instrument approach, the EVS image is 
intended to enhance the pilot's ability to detect and identify ``visual 
references for the intended runway'' (see Sec. 91.175(c)(3)), to 
continue the approach below decision height. Depending on atmospheric 
conditions and the strength of infrared energy emitted and/or reflected 
from the scene, the pilot can see these visual references in the image 
better than the pilot can see them through the window without EVS.
    Scene contrast detected by infrared sensors can be much different 
than that detected by natural pilot vision. On a dark night, thermal 
differences of objects, which are not detectable by the naked eye, will 
be easily detected by many imaging infrared systems. On the other hand, 
contrasting colors in visual wavelengths may be distinguished by the 
naked eye, but not by an imaging infrared system. Where thermal 
contrast in the scene is sufficiently detectable, shapes and patterns 
of certain visual references can be recognized in the infrared image by 
the pilot, but, depending on conditions, they can also appear 
significantly different to a pilot in the infrared image than they 
would with normal vision.
    There is the potential for the image to improve the pilot's ability 
to detect and identify items of interest. EVS needs to be evaluated to 
determine that the imagery does not adversely affect the pilot's 
ability to see outside the window through the image. Section 
25.773(a)(2) states:

    Each pilot compartment must be free of glare and reflection that 
could interfere with the normal duties of the minimum flight crew.

    A raster image can be more difficult for the pilot to see through 
than stroke-written symbols also displayed on the HUD. Stroke symbology 
illuminates a small fraction of the total display area of the HUD, 
leaving much of that area free of reflected light that could interfere

[[Page 32719]]

with the pilot's view out the window through the display. However, 
unlike stroke symbology, the raster image illuminates, to some degree, 
most of the total display area of the HUD (approximately 30 degrees 
horizontally and 20 degrees vertically) with much greater potential 
interference with the pilot compartment view. The pilot cannot see 
around the raster image, but must see the outside scene through it.
    Unlike the pilot's external view, the EVS image is a monochrome, 
two-dimensional display. Some, but not all, of the depth cues found in 
the natural view are also found in the imagery. The quality of the EVS 
image and the level of EVS infrared sensor performance could depend 
significantly on the atmospheric and external light source conditions. 
Gain settings of the sensor, and brightness or contrast settings of the 
HUD, can significantly affect image quality. Certain system 
characteristics could create distracting and confusing display 
artifacts. Finally, because this is a sensor-based system that is 
intended to provide a conformal perspective corresponding with the 
outside scene, the potential for misalignment must be considered.
    Hence, safety standards for each of the following factors are 
needed:
    <bullet> An acceptable degree of interference of the window or 
``window and HUD'' view;
    <bullet> Potential image misalignment;
    <bullet> Distortion; and
    <bullet> The potential for pilot confusion or misleading 
information.
    The FAA did not anticipate the novel and unusual design features of 
the EVS when Sec. 25.773 was issued, and does not consider the current 
regulation to be adequate to address the specific issues related to an 
enhanced vision system. Therefore, the FAA has determined that, in 
addition to the requirements of 14 CFR part 25, special conditions are 
needed to address requirements particular to the installation of an 
EVS.

Discussion

    Gulfstream Aerospace Corporation intends for the EVS to function by 
presenting an enhanced view that would aid the pilot, during the 
approach:
    <bullet> To see and recognize external visual references that are 
required by Sec. 91.175(c), and
    <bullet> To visually monitor the integrity of the approach, as 
described in FAA Order 6750.24D (``Instrument Landing System and 
Ancillary electronic Component Configuration and Performance 
Requirements,'' dated March 1, 2000).
    Based on this functionality, users would seek to obtain operational 
approval to conduct approaches when the Runway Visual Range (RVR) is as 
low as 1,200 feet, including approaches to Type I runways. Gulfstream 
does not intend, and the FAA does not intend by these special 
conditions for the EVS imagery to be used either as a means of flight 
guidance, or as the substitution for the outside view while maneuvering 
the airplane during approach, landing, rollout, or takeoff.
    The criteria of these special conditions were developed to 
determine that this EVS is of the kind and design appropriate to the 
following functions:
    <bullet> Presenting an enhanced view that would aid the pilot 
during the approach.
    <bullet> Displaying an image that the pilot can use to detect and 
identify the ``visual references for the intended runway'' required by 
Sec. 91.175(c)(3) to continue the approach with vertical guidance to 
100 feet height above touchdown (HAT).
    Depending on the atmospheric conditions and the particular visual 
references that happen to be distinctly visible and detectable in the 
EVS image, these two functions would support its use by the pilot to 
visually monitor the integrity of the approach path.
    Compliance with these special conditions does not affect the 
applicability of any of the requirements in the operating regulations 
(e.g., parts 91, 121, and 135). The EVS does not change the approach 
minima prescribed in the standard instrument approach procedure being 
used; published minima still apply.
    The FAA certification of this EVS is limited as follows:
    <bullet> The infrared-based EVS image will not be certified as a 
means to satisfy the requirements for descent below 100 feet HAT.
    <bullet> The infrared-based EVS image will not be certified as a 
means to establish that flight visibility is consistent with the 
visibility condition prescribed in the standard instrument approach 
being used (see Sec. 91.175(c)(2)).
    <bullet> The EVS imagery, alone, will not be certified either as 
flight guidance, or as a substitution for the outside view for 
maneuvering the airplane during approach, landing, rollout, or takeoff.
    <bullet> The EVS may be used as a supplemental device to enhance 
the pilot's situational awareness during any phase of flight or 
operation in which its safe use has been established.
    An EVS image may provide an enhanced image of the scene that may 
compensate for any reduction in the clear outside view of the visual 
field framed by the HUD combiner. The pilot must be able to use this 
combination of information seen in the image, and the natural view of 
the outside scene seen through the image, as safely and effectively as 
the pilot would use a Sec. 25.773-compliant pilot compartment view 
without an EVS image. This is the fundamental objective of the special 
conditions.
    The FAA also intends to apply certification criteria, not as 
special conditions, for compliance with other Federal Aviation 
Regulations, including Sec. 25.1301 (``Equipment: Function and 
installation'') and Sec. 25.1309 (``Equipment, systems, and 
installations''). These criteria address certain image characteristics, 
installation, demonstration, and system safety.
    Image characteristics criteria include:

    <bullet> resolution,
    <bullet> luminance,
    <bullet> luminance uniformity,
    <bullet> low level luminance,
    <bullet> contrast variation,
    <bullet> display quality,
    <bullet> display dynamics (for example, jitter, flicker, update 
rate, and lag), and
    <bullet> brightness controls.

    Installation criteria address:

<bullet> visibility and access to EVS controls, and
<bullet> integration of EVS in the cockpit.

    The EVS demonstration criteria address the flight and environmental 
conditions that need to be covered.
    The FAA also intends to apply certification criteria relevant to 
high intensity radiated fields (HIRF) and lightning protection.

Discussion of Comments

    Notice of proposed special conditions No. 25-01-02-SC for 
Gulfstream Model G-V airplanes was published in the Federal Register on 
March 16, 2001 (66 FR 15203). Eighteen commenters, including the 
applicant, responded. A discussion of the comments follows, along with 
the FAA's disposition of those comments.

Special Conditions Paragraph 4. (Intended Function)

    Several commenters recommend withdrawal or revision of paragraph 4. 
and provide the following comments in support of this recommendation.
    Two commenters state that it is not clear why operational 
restrictions are specified within the special conditions, and recommend 
that all references and attempts at rulemaking and rule interpretations 
of parts 91 and 97 be withdrawn and removed.
    Another commenter states that paragraph 4. may not be accurate as a

[[Page 32720]]

categorical statement for the future. There could be other images 
developed in the future that may have greater capabilities than FLIR; 
hence, this statement could be mistakenly interpreted to rule out any 
chance of progress in this area.
    One commenter states that the proposed language is a precedent-
setting prohibition against the reduction of ceiling and visibility 
minimums through EVS usage.
    The same commenter also states that the extensive investments by 
NASA and industry to develop commercially viable and certifiable 
enhanced and synthetic vision products to increase the overall safety 
are viewed as jeopardized by the operational restrictions contained 
within the proposed special conditions.
    Two commenters contend that the use of EVS to lower landing 
minimums is not an issue that is historically addressed by FAA Aircraft 
Certification, but by FAA Flight Standards. Following some period of 
operational use, Flight Standards may or may not see fit to allow the 
use of an enhanced vision image to replace visual contact below the 
normal decision height.
    Several commenters state that paragraph 4. is beyond the scope of 
the rulemaking and outside the authority established by Sec. 21.16 in 
that it establishes interpretations of operating rules.
    One commenter objects to the use of the special conditions by the 
Aircraft Certification Service to prescribe operational limits. 
Approach limits are codified rather than allowing for growth of the 
system into one with reduced limits.
    Another commenter states that the proposed special conditions set 
the overall policy direction for all future HUD and EVS installations. 
The commenter goes on to say that even though the rule is written as a 
part 91 only concern, the philosophy will carry forward and affect part 
121 operators as well.
    Three commenters recommend the following revisions to paragraph 4.:
    <bullet> Delete the first sentence,
    <bullet> Replace the reference to ``100 ft. HAT'' with ``to an 
appropriate height above touchdown,''
    <bullet> Add a paragraph 4.c. that states, ``presenting an image 
that would act as an independent integrity monitor during the 
approach,'' and
    <bullet> Revise paragraph 4. to read, ``The use of EVS will not 
reduce the ceiling and visibility minima of the instrument approach 
procedure being used, unless an equivalent level of task performance 
and safety required for that reduced visibility minima can be 
achieved.''
    The FAA agrees that special conditions should not establish 
interpretations of the operating rules. The special conditions are not 
intended to create, change, restrict, or reinterpret provisions of the 
operational rules, including those related to ceiling and visibility 
minima. Special conditions paragraph 4. is meant to define the intended 
function for which this EVS would be certified, since installed 
equipment must be of a type and design appropriate to its intended 
function. If future applicants propose to expand the intended functions 
of this or similar equipment, different special conditions may be 
necessary to identify the appropriate certification criteria for those 
intended functions.
    The FAA does not agree that references to operational regulations 
should be deleted. Section 91.175(c)(3) is only mentioned to clarify a 
function of the EVS that the pilot may use to detect and identify 
``visual references.''
    The first sentence of special conditions paragraph 4. is not an 
operational restriction. Instead, the intent of that sentence was to 
clarify that the airworthiness approval of EVS does not reduce or 
override the established ceiling and visibility minima that are legally 
prescribed in the standard instrument approach procedure. In fact, 
airworthiness approval of any equipment, whether it uses a raster image 
or not, cannot take precedence over the established minima. The special 
condition does not impose this limitation; it acknowledges it. When the 
notice was issued, there were no published instrument procedures that 
prescribed different minima for operators of EVS-equipped airplanes.
    The FAA agrees that FAA Flight Standards is responsible for 
determining operational requirements. However, it is also true that the 
requirements of the existing operational regulations are mandatory. 
Flight Standards may choose to approve different minima for operators 
of EVS-equipped airplanes either by revising the operational rules or 
instrument approach procedures to specify minima for EVS-equipped 
airplanes. As needed, Flight Standards would also determine in the 
future whether different minima would be applied to operators of 
airplanes equipped with this or other EVS configurations. Therefore, 
the FAA does not agree that the first sentence of special conditions 
paragraph 4. should be revised to add the phrase ``unless an equivalent 
level of task performance and safety required for that reduced 
visibility minima can be achieved.''
    The FAA also does not agree that the first sentence of paragraph 4. 
should be deleted. However, to clarify the intent of the first 
sentence, it is changed to read: ``Compliance with these special 
conditions does not affect the applicability of any of the requirements 
in the operating regulations (e.g., parts 91, 121, 135).
    The FAA does not agree that the reference to ``100 feet HAT'' 
should be replaced with ``an appropriate height above touchdown.'' 
Section 91.175(c)(3) (as well as respective provisions in parts 121 and 
135) distinguishes between visual references required for descent below 
decision height and those required for descent below 100 feet HAT. The 
Gulfstream Proof of Concept (PoC) Flight Test Report recommended that 
descent below 100 feet HAT must not be predicated on EVS imagery alone. 
To make such a change as requested would require separate rulemaking to 
change the relevant regulations.
    The FAA does not agree that a new paragraph 4.c. needs to be added 
to address the use of the EVS as an independent monitor. The pilot may 
use the EVS image to identify certain visual references that serve as 
airplane position cues. The EVS sensor performance (i.e., what can be 
seen and at what distance) in the actual atmospheric conditions will 
affect the usefulness of the image for the purpose of verifying 
airplane position. Special conditions paragraph 4., with its 
subparagraphs, does not explicitly list the function of ``integrity 
monitor'' for the guidance, but this function is covered within the 
dual intended function of ``presenting an image that would aid the 
pilot during the approach'' and ``that the pilot can use to detect and 
identify the visual references'' [Sec. 91.175(c)(3)]. The EVS cannot be 
an independent monitor in the same sense as the term is normally used. 
Normal use of this term is automatic detection and annunciation of 
system performance deviations and failure conditions.

Clarification of Notice Preamble (Discussion) and Special Conditions 
Paragraph 4

    One commenter submitted the following questions to the FAA docket 
for these special conditions. Each question is followed by an FAA 
response which is based on the plain reading of the regulatory 
requirements; specifically, the applicability of the operational 
regulations (e.g., parts 91, 121, 135) is the same whether EVS is 
installed or not.
    Question: Paragraph 4. of the proposed special conditions states: 
``The

[[Page 32721]]

use of EVS will not reduce the ceiling and visibility minima of the 
instrument approach procedure being used.'' What is the purpose of this 
statement? Is this a reference to Sec. 91.175(c)(2), and would this 
preclude operation below DH or HAT if the requirements of 
Sec. 91.175(c)(3) were met with EVS alone but the flight visibility was 
less than the visibility prescribed in the approach being used?
    FAA Response: The first sentence of special conditions paragraph 4. 
is meant to clarify that the airworthiness approval of EVS under part 
25 does not reduce or override the established ceiling and visibility 
minima that are legally prescribed in the standard instrument approach 
procedure.
    To clarify the intent of the first sentence, it is changed to read: 
``Compliance with these special conditions does not affect the 
applicability of any of the requirements in the operating regulations 
(e.g., Parts 91, 121, 135).''
    Question: With respect to item 4(b); would the pilot be allowed to 
continue the approach below a 200 foot HAT to 100 feet, if the EVS 
detected the required ``visual references for the intended runway'' but 
the flight visibility was less than the visibility prescribed for the 
approach being used?
    FAA Response: As stated previously, the applicability of the 
operational regulations (e.g., parts 91, 121, 135) is the same whether 
EVS is installed or not. Descent and operation below decision height is 
not permitted by Sec. 91.175 and similar provisions of other 
operational parts, as applicable, when flight visibility is less than 
prescribed in the standard instrument approach procedure being used.
    Question: In paragraph eight of the ``Discussion'' the FAA states: 
``However, the FAA finds that it would not be appropriate to reduce the 
ceiling and visibility minima of the instrument approach procedure 
being used based on the use of EVS.'' Is this a reference to 
Sec. 91.175(c)(2) and would this preclude a descent below a 200 foot 
HAT minimum to 100 feet if the requirements of Sec. 91.175(c)(3) were 
met with the EVS?
    FAA Response: This sentence was not clearly stated. The intent was 
to say that compliance with the criteria of these special conditions 
does not affect the applicability of any of the requirements in the 
operating regulations (e.g., Parts 91, 121, 135). A descent would be 
permitted only if all requirements of Sec. 91.175 are met. The first 
sentence of special conditions paragraph 4. is revised accordingly.
    Question: Reference paragraph ten of the ``Discussion'' section: 
``The infrared-based EVS image will not be certified as a means to 
satisfy the requirements for descent below 100 feet HAT.'' Does this 
statement mean that, if the pilot meets the requirements of 
Sec. 91.175(c)(3) with EVS alone at a 200 foot HAT, then he may descend 
to a 100 foot HAT?
    FAA Response: No, this statement means that, in order for the pilot 
to descend below 100 feet HAT, the requirements of Secs. 91.175(c) and 
(d) must be met without the aid of EVS. The pilot may use EVS below 100 
feet HAT, but the visual references must be distinctly visible and 
identifiable with the naked eye.
    Question: If the flight visibility is less than the prescribed 
visibility for the approach being used, but the requirements of 
Sec. 91.175(c)(3) at 200 feet HAT are met, may the approach be 
continued to a 100 foot HAT on EVS alone?
    FAA Response: As stated previously, the applicability of the 
operational regulations (e.g., parts 91, 121, 135) is the same whether 
EVS is installed or not. Descent and operation below decision height is 
not permitted by Sec. 91.175 and similar provisions of other 
operational parts, as applicable, when flight visibility is less than 
prescribed in the standard instrument approach procedure being used.
    Descent below the 200 foot decision height cannot be based on EVS 
alone. To use EVS for the descent below decision height, precision 
approach guidance must also be provided on the HUD. With valid 
precision approach guidance provided on the HUD, EVS may be used to 
meet the requirements of Sec. 91.175(c)(3) from the decision height to 
100 feet HAT.
    Question: The following example is provided in an attempt to 
clarify to all parties the suggested operating rules.

Situation:
    --Part 91 Operator
    --Flight Visibility: 0/0
    --Published Minima: 200 feet/\1/2\ mile
    --EVS: Operational with ``Phase I'' certification

    Note: ``Phase I'' refers to this certification program.

    In this situation, may the pilot commence the approach?
    FAA Response: Based on the situation described in the commenter's 
question above, the Part 91 operator can commence the approach. 
However, Part 121 and Part 135 operators may not.
    Question: At 200 feet the pilot meets the requirements of 
Sec. 91.175(c)(3) with EVS alone, may he continue to 100 feet?
    FAA Response: This response is based on the situation described 
above by the commenter. As stated previously, the applicability of the 
operational regulations (e.g., parts 91, 121, 135) is the same whether 
EVS is installed or not. Descent and operation below decision height is 
not permitted by Sec. 91.175 and similar provisions of other 
operational parts, as applicable, when flight visibility is less than 
prescribed in the standard instrument approach procedure being used.
    Descent below the 200-foot decision height cannot be based on EVS 
alone. To use EVS for the descent below decision height, precision 
approach guidance must also be provided on the HUD. With valid 
precision approach guidance provided on the HUD, EVS may be used to 
meet the requirements of Sec. 91.175(c)(3) from the decision height to 
100 feet HAT.
    Question: At 100 feet the pilot meets the requirements of 
Sec. 91.175(c)(3) without the aid of EVS, may he continue to land?
    FAA Response: This response is based on the situation described 
above by the commenter. As stated previously, the applicability of the 
operational regulations (e.g., parts 91, 121, 135) is the same whether 
EVS is installed or not. Operation below decision height is not 
permitted by Sec. 91.175 and similar provisions of other operational 
parts, as applicable, when flight visibility is less than prescribed in 
the standard instrument approach procedure being used.

Need for Special Conditions

Part 21 and FAA Order 8110.4B

    Several commenters state that the FAA has failed, in accordance 
with Sec. 21.16 and FAA Handbook 8110.4B, to justify the need for 
special conditions. The commenters state that the existing regulations 
(Secs. 25.773, 25.1301, and 25.1309) contain the necessary 
requirements, and the proposed special conditions serve no additional 
purpose. Two of these commenters recommend that the special conditions 
be withdrawn and paragraphs 1., 2., and 3. be developed in a method of 
compliance issue paper. One of these commenters states that even if the 
raster display of an FLIR image on the HUD is deemed novel or unusual, 
regulations are in place to assure safety.
    The FAA disagrees. The legal basis for the special conditions was 
carefully reviewed by the FAA and deemed appropriate. As discussed in 
the preamble of the notice, and these final special conditions, the FAA 
issues special conditions when it determines that the existing 
airworthiness standards do not contain adequate or appropriate

[[Page 32722]]

safety standards for a novel or unusual design feature. The regulatory 
process for issuing special conditions provides for public notification 
and opportunity for comment on the proposed certification criteria, and 
promotes standardization of new FAA certification requirements.
    The FAA does not agree that Sec. 25.773 is adequate for 
certification of the EVS. When the FAA issued Sec. 25.773, it did not 
anticipate the display of an electronic image in the regulated field of 
view, and did not account for the potential of the EVS imagery to help 
achieve the safety objectives of the pilot compartment view. As 
discussed in the notice, the EVS image is different from the natural 
pilot vision that was assumed when Sec. 25.773 was issued. The 
differences include:
    <bullet> Image resolution compared to a pilot's vision,
    <bullet> Monochrome image compared to color vision,
    <bullet> Fewer cues for depth perception, and
    <bullet> The thermal response characteristics of an infrared sensor 
compared to the color discrimination of pilot vision.
    Additionally, the EVS raster image could potentially interfere with 
the pilot view. The raster image covers most of the combiner at one 
time, unlike stroke-written HUD symbology, which covers much less 
combiner area. Because none of the regulations referenced by the 
commenters contain criteria for evaluating these issues, the FAA has 
determined that those regulations are inadequate for certification of 
the EVS. For these reasons, the FAA determined that the EVS is novel 
and unusual with respect to current airworthiness regulations, and 
special conditions are needed.
    One commenter states that the FAA has failed to provide an adequate 
explanation for the basis of the ``novel and unusual design feature.''
    The special conditions are not merely a new means of compliance 
with Sec. 25.773, rather they provide a new requirement and a 
regulatory path to certify the EVS and achieve an equivalent level of 
safety. The fundamental requirement contained in the special 
conditions, not found in Sec. 25.773, is that the combination of what 
the pilot sees in the EVS image and what the pilot sees through and 
around the image must be as safe and effective as the view without the 
image. The FAA considers that the level of safety provided by the 
special conditions is equivalent to the level of safety intended by 
Sec. 25.773.

Aerospace Standard AS8055

    Two commenters state that Aerospace Standard AS8055 already 
establishes standards for EVS and therefore the special conditions are 
unnecessary. One of the commenters states that the FAA requested 
industry to recommend standards for head up displays, which resulted in 
the SAE Aerospace Standard AS8055 that recommends standards for HUD's, 
including raster displays.
    The second commenter states that the basis for the special 
conditions is inadequate, and the rationale is one of opinion. This 
commenter goes on to say that the special conditions make no mention of 
certain documents (AC 25.773-1, AC 120-28D, SAE AS8055). The commenter 
contends that these documents adequately describe HUD and EVS design 
for certification purposes, without the need for special conditions.
    The FAA does not agree. While the FAA did request that SAE develop 
standards for head up displays, they do not take the place of 
airworthiness regulations or special conditions. Industry standards, 
alone, are not mandatory. The FAA request that SAE develop these 
standards does not contradict the need for special conditions.
    Nevertheless, AS8055 contains extremely useful industry developed 
standards, particularly regarding raster display quality, that have 
been adapted to the fullest possible extent in a separate means of 
compliance issue paper for EVS certification. The current AS8055 
addresses head up displays and the information presented on them, 
including raster imagery, but not imaging sensors, such as the infrared 
camera used in the Gulfstream EVS.
    Advisory Circular (AC) 25.773-1 provides criteria for an acceptable 
means of compliance with Sec. 25.773, but does not address the display 
of electronic imagery in the regulated pilot compartment view. The FAA 
therefore found no reason to refer to this document in the notice.
    Advisory Circular (AC) 120-28D provides a means of compliance for 
Category III low visibility operations and certification of equipment 
designed for that purpose. The Phase I Gulfstream EVS is not intended 
for Category III operations, and therefore the FAA did not find a 
reason to refer to this AC in the notice.

HUD vs. Raster Imagery

    One commenter contends that the FAA's main argument revolves around 
Sec. 25.773(a)(2), which states, ``Each pilot compartment must be free 
of glare and reflection that could interfere with the normal duties of 
the minimum flight crew.'' The commenter further states that this could 
equally apply to stroke-only HUD's which are currently certified.
    Another commenter states that the notice is in error, since 
Sec. 25.773 has been cited and accepted as a means of compliance for 
many HUD programs.
    A third commenter states that although Sec. 25.773 does not 
directly mention an EVS imagery display, this regulation, in 
combination with other pertinent regulations, contains the necessary 
and sufficient requirements for determining an acceptable pilot 
compartment view. The commenter asserts that these same existing 
regulations have been successfully applied to HUD's for several years.
    The FAA does not agree. Stroke-written HUD symbology and raster 
imagery have significantly different characteristics. As explained in 
the notice, stroke-written HUD symbology illuminates a small fraction 
of the HUD combiner area (approximately 20 by 30 degrees) at any one 
time. The imagery, on the other hand, can illuminate almost all of the 
HUD at one time. The pilot can see through the relatively large ``unlit 
spaces'' between HUD symbols with very little visual interference, but 
the EVS design provides no such spaces in the raster imagery. 
Consequently, depending on the content at any time, the EVS image might 
interfere with much more of the pilot's view.
    Unlike Sec. 25.773, the special conditions account for this 
potential interference by also considering that the EVS image may also 
provide useful information which, in combination with what the pilot 
can see through the image, is as safe and effective as the pilot's view 
without the image.

Military Use of EVS

    One commenter states that the EVS application may be novel and 
unusual (that is, for commercial aircraft); however the technology is 
not. This technology, including raster images on a HUD, has been in use 
by the military. The commenter states that special conditions are 
premature and the issue should be studied.
    The FAA disagrees. The phrase ``novel or unusual'' is used in 
Sec. 21.16 in the context of existing regulations. Under the provisions 
of Sec. 21.16, the FAA issues special conditions when it determines 
existing airworthiness regulations do not contain adequate safety 
standards for a novel or unusual design feature. The special conditions 
are issued to establish a level of safety

[[Page 32723]]

equivalent to that established in the existing regulations.
    Granted, elements of the EVS have been in use in the military, even 
to the extent of displaying infrared imagery on a HUD. However, 
military use of this technology differs from this civil application, 
and the level of safety required of military systems used in combat 
operations differs from what is required for civil transport airplane 
airworthiness. As previously stated in this document in response to 
other comments, certain design features of the EVS are considered novel 
or unusual with respect to the current airworthiness standards, and the 
FAA has determined that special conditions are needed.

Not Based on Real Data or Analysis

    One commenter suggests that the special conditions be deferred and 
modified as necessary so that they are supported by data and analysis. 
The commenter suggests that until that time, the FAA could make a 
determination regarding certification of EVS systems on a case by case 
basis.
    Another commenter considers the special conditions to be premature 
in that they are based on ``findings'' that are not supported by real 
data or analysis, and therefore are actually based on opinions. The 
commenter states they participated in the Synthetic Vision System (SVS) 
program and that most of the key elements of the proposed special 
conditions are not supported by the FAA SVS database.
    The FAA does not agree that the special conditions are premature, 
or that the criteria for applying the special conditions for the EVS is 
not supported by data and analysis.
    The FAA did, in fact, consider the reported findings of the FAA 
Synthetic Vision System Technology Demonstration program, and the 
Gulfstream proof of concept (PoC) flight test. The large FAA SVS 
database is primarily measured sensor performance with measured 
atmospheric and scene conditions. Many of the issues raised and 
considered in the FAA SVS program are addressed in these special 
conditions and in a means of compliance issue paper. As explained in 
the notice, and earlier in these final special conditions in response 
to other comments, the electronic EVS image is different from the 
pilot's natural vision and was not anticipated when Sec. 25.773 was 
issued, so the FAA determined that special conditions are needed.
    While the FAA believes, based on the PoC results, that the 
Gulfstream EVS can be safely certified, that does not mean safety 
standards are unnecessary. The safety standards covered by the special 
conditions are based on issues investigated during the PoC of the 
Gulfstream EVS and the earlier FAA SVS program.
    These special conditions are specific to the Gulfstream 
certification project. If appropriate, different special conditions may 
be adopted for future programs involving similar equipment. The FAA is 
making these certification determinations on a case-by-case basis.

Proof of Concept (PoC) Test Results

    One commenter states that the FAA failed to properly take into 
account the results of the FAA proof of concept program. The test 
program required two years and over 200 approaches flown by FAA 
selected pilots and specialists, and the report states that the HUD and 
the EVS did not obscure the pilot's forward field of view and did not 
interfere with the pilot's view of the runway during the landing 
approach.
    Another commenter is of the opinion that the FAA completely ignored 
the PoC tests. The commenter states that the FAA is not justified in 
issuing the proposed special conditions since the results of extensive 
evaluations during FAA-mandated PoC flight tests concluded that the EVS 
could be certified and safely used in transport category operations 
under existing airworthiness certification standards.
    Another commenter states that the FAA failed to recognize test 
results that show the good faith effort in addressing the concerns 
related to safe and effective use of the EVS. The commenter contends 
that the EVS proof-of-concept tests concluded that the EVS provided 
situational awareness, did not obscure the pilot's view, and did not 
interfere with the pilot's view of the runway. As such, it is compliant 
with the intent of Sec. 25.773.
    A fourth commenter states that it is surprising that the notice, 
which lists the criteria for issues that must be addressed for the EVS, 
makes no reference to the findings of the PoC flight test results that 
conclude these issues are not a concern.
    The FAA does not agree with the commenters that the PoC test 
results were not considered in determining the need for special 
conditions. The purpose of the PoC is to determine what would be 
operationally acceptable and what standards or criteria are needed for 
airworthiness approval. It is not the purpose of the PoC to determine 
whether or not the safety standards must be contained in special 
conditions.
    While the FAA concluded, based on the PoC results, that the 
Gulfstream EVS could be safely certified, it did not conclude that 
safety standards were unnecessary. The safety standards covered by the 
special conditions are not based on deficiencies of the Gulfstream EVS, 
but rather on issues that were investigated during the PoC and the 
earlier FAA SVS program. While the PoC test results show that the EVS 
image does not obscure the pilot's view, there must be appropriate 
safety standards for the impact of the EVS image on the pilot's view.
    The FAA actions have been consistent with the PoC process as 
outlined in paragraph 10.18 of Advisory Circular 120-28D. As stated 
earlier, the special conditions provide a legal avenue to certify this 
system.

EVS Enhances Safety and Should Not Be Delayed

    One commenter states that reduced visibility is a major or 
contributing factor in many civil aircraft accidents. If the pilot 
could have had the real-time information provided by EVS, a significant 
number of these accidents could have been avoided. The commenter 
asserts that the EVS can save lives now, and recommends that the FAA 
continue to understand and not delay the benefits of EVS to the air 
transportation system.
    Another commenter states that new technology that provides enhanced 
aircraft safety should be certified and deployed in a quick and orderly 
fashion, rather than through a long series of disjointed special 
conditions. It is the commenter's opinion that this is detrimental both 
to the FAA and airlines through unnecessary delays, and to the 
traveling public who deserve improved safety of flight.
    A third commenter believes that the EVS will provide operational 
safety improvement. The commenter states that EVS technology is 
specifically aimed at eliminating low-visibility conditions as a causal 
factor in civil aircraft accidents, and that if installed, the EVS will 
provide operational benefits approaching those found in clear daytime 
operations, regardless of weather conditions.
    The FAA agrees in part with the commenters. Indeed, EVS may be able 
to improve safety in certain conditions and phases of flight. The FAA 
acknowledges that the EVS image may improve the pilot's ability to 
detect and identify items of interest. The application of safety 
standards through special conditions does not prevent the use of EVS in 
ways that would enhance safety. The EVS may be used for any operation 
or phase of flight where it is shown to be safe.

[[Page 32724]]

    It has not yet been demonstrated that the Gulfstream EVS can 
actually provide benefits equivalent to conventional clear daytime 
operations in all low visibility conditions. The infrared sensor is 
affected by the same visible moisture that is often the cause of low 
visibility conditions. Nevertheless, the actual operational benefits 
that the EVS can provide will be shown in due time with the 
accumulation of service experience.
    The FAA has not delayed the certification project, or the safety or 
operational benefits that the EVS might provide. Publication of these 
final special conditions has not adversely impacted the overall 
certification program schedule.

Use of Infrared (IR) Imagery To Establish Visibility

    One commenter states that the notice raises concern that the 
reported visibility (visible spectrum) would not be consistent with the 
IR visibility ``seen'' by the EVS, and that this is a valid operational 
concern, but not a certification issue.
    The same commenter also states that the current regulations do not 
permit any operator to descend below the published approach minimums, 
unless the visibility is at least that prescribed in the instrument 
approach procedure being used. The commenter says that the current 
regulations do not address electronic aiding, and recommends that the 
following statement be added to the AFM limitations: ``Installation of 
the EVS does not constitute approval to continue an approach below 
decision height.''
    The FAA disagrees. The notice addressed ``flight visibility,'' not 
reported visibility. The two terms are distinctly different. For 
descent below decision height, Sec. 91.175(c)(2) requires that ``flight 
visibility,'' which is the forward horizontal distance that unlighted 
objects can be seen from the cockpit by day, and lighted objects by 
night, be no less than the visibility prescribed in the standard 
instrument approach procedure being used.
    The FAA agrees that the requirements for approach, including flight 
visibility, are established by operational regulations, particularly 
parts 91, 121, and 135, and are therefore operational concerns. 
However, the requirement that installed equipment must be of a type and 
design to perform its intended function, defined in special conditions 
paragraph 4. for certification purposes, is a valid airworthiness 
certification concern.
    The FAA agrees that current regulations do not address electronic 
images in the pilot compartment view regulated by Sec. 25.773. As 
stated earlier, the special conditions are considered necessary because 
Sec. 25.773 is not adequate for the novel or unusual design features of 
the EVS. However, the special conditions do not address whether 
operational regulations adequately address the use of the EVS and do 
not create, change, restrict, or reinterpret the operational 
requirements.
    The FAA does not agree with the recommended change to the AFM 
limitations, because it appears more conservative than the FAA 
concluded is necessary. One conclusion drawn from the PoC testing was 
that the visual references listed in Sec. 91.175(c)(3) could be 
detected and identified in the EVS image, and that the ability to do 
this could be evaluated. The FAA has revised the first sentence of 
paragraph 4. to clarify that the use of EVS does not affect the 
applicability of the operational requirements.

Special Conditions Were Identified Late in the Program

    Two commenters state that the FAA needs to review processes that 
were followed to ensure that FAA personnel are fully aware of their 
responsibilities to raise such concerns early in a program.
    The commenters express the opinion that the FAA did not follow the 
principles of the certification process improvement effort. The 
principles include surfacing issues early in the program so that they 
can be resolved before they have an adverse effect on the ability of 
the applicant to certify the product in accordance with the program 
schedule.
    The FAA disagrees. Although the need for special conditions was not 
known in the beginning of the program, the need for special conditions 
was identified early enough in the program to not impact the 
certification schedule.

The Language in the Notice Is Damaging to the Development and Use 
of EVS

    Two commenters express the opinion that the language and 
limitations contained in the notice are prejudicial against EVS and HUD 
developments. One has concerns about the future FAA response to new 
safety technologies and many other proposed safety systems to meet the 
goals of the Safer Skies program.
    Another commenter states that the proposed special conditions do 
not accurately represent the Gulfstream EVS program. The commenter 
asserts that the EVS would enhance the ability of the pilot to see and 
identify visual references to continue an approach to a decision point 
of 100 feet for Phase I and 50 feet for Phase II. It is the commenter's 
opinion that the special conditions create a negative impression of EVS 
technology, which further reflects a biased judgment against EVS and is 
contrary to the conclusions reached under the controlled evaluations.
    The FAA disagrees. The special conditions are not intended to be a 
reference to the product or a commentary on the product's success. 
Differences between EVS infrared imagery and natural pilot vision were 
described in the preamble of the notice for the purpose of addressing 
the uniqueness of the EVS and the need for safety standards to address 
the differences. That an EVS image has the potential to interfere or 
obscure the pilot's view does not mean that an EVS is unacceptable, but 
that the product needs to be evaluated with these potential 
characteristics in mind to maintain the level of safety established by 
the current airworthiness standards.
    The special conditions are not intended to characterize the 
Gulfstream EVS project. The requirements in the proposed special 
conditions, and adopted in these final special conditions, are intended 
to provide safety standards for this EVS to meet, and to ensure that 
such a determination is made during certification, not to imply that 
this EVS is unacceptable. The special conditions address Phase I of the 
Gulfstream project, and anything beyond Phase I will be addressed 
outside this rulemaking activity.

The Proposed Special Conditions Are Too Restrictive on the Use of 
EVS

    One commenter states that the notice denies the following uses of 
the EVS:
    <bullet> As a substitution for the real-world view,
    <bullet> As a means to establish that flight visibility is 
consistent with the visibility condition prescribed in the standard 
instrument approach being used,
    <bullet> As a means to reduce the ceiling and visibility minima of 
the instrument approach procedure being used, and
    <bullet> As a means to satisfy the requirements for descent below 
100 feet HAT.
    Another commenter states that there could be other images developed 
in the future that may have greater capabilities than FLIR. Paragraph 
4. of the proposed special conditions could be mistakenly interpreted 
to rule out any chance of progress in this area.
    The FAA disagrees. The special conditions do not deny or restrict 
the use of EVS. Rather, the language

[[Page 32725]]

referred to in the comment (and discussed in the preamble to the 
notice) defines what intended functions it is being certified for and 
the limits of that airworthiness certification approval. Unless found 
unsafe during any operation or phase of flight, this would not limit 
the use of EVS as a supplemental device, nor would it restrict the role 
of Flight Standards to authorize the use of EVS.
    The first sentence of special conditions paragraph 4. is not an 
operational restriction; instead, it is meant to clarify that the 
airworthiness approval of EVS, itself, does not reduce or override the 
established ceiling and visibility minima prescribed in the standard 
instrument approach procedure. In fact, airworthiness approval of any 
equipment, whether it uses a raster image or not, cannot take 
precedence over the established minima. These special conditions do not 
impose this limitation; they acknowledge it. When the notice was 
issued, there were no published instrument procedures that prescribed 
different minima for operators of EVS-equipped airplanes.
    To clarify the intent of the first sentence of special conditions 
paragraph 4., it is changed to read: ``Compliance with these special 
conditions does not affect the applicability of any of the requirements 
in the operating regulations (e.g., parts 91, 121, 135).''
    FAA Flight Standards has the authority to determine operational 
requirements. However, it is also true that the requirements of the 
existing operational regulations are mandatory. Flight Standards may 
choose to approve different minima for operators of EVS-equipped 
airplanes. As needed, Flight Standards would also determine in the 
future whether different minima would be applied to operators of 
airplanes equipped with this or other EVS configurations.

Clarification Issues

Special Conditions Paragraph 2.a.

    One commenter provided the following comments relative to paragraph 
2.a.:
    <bullet> ``Burlap overlay'' is not defined in the examples provided 
in paragraph 2.a.
    <bullet> Use of FLIR, under some circumstances, may not be 
desirable or an improvement over the pilot's vision, and may not be 
appropriate.
    <bullet> The ability to easily dim and/or clear the image on the 
HUD should be incorporated to permit removal of the image quickly, if 
conditions are not favorable.
    FAA clarification of each issue is as follows:
    ``Burlap overlay'' is one example of a display artifact that has a 
burlap-like appearance and was observed during the PoC flight testing. 
It could be distracting to the pilot, make the image difficult to use, 
and potentially interfere with the pilot's outside view.
    The FAA agrees with the commenter that in some circumstances the 
EVS image may not be desirable, and that is why paragraph 2.c. of the 
special conditions requires that a readily accessible control be 
provided for the pilot to immediately deactivate and reactivate display 
of the image on demand.
    The FAA agrees with the commenter that the ability to dim or clear 
the image on the HUD should be incorporated, and that is why paragraph 
2.b. of the special conditions requires effective control of image 
brightness, and paragraph 2.c. requires that a readily accessible 
control be provided for the pilot to immediately deactivate and 
reactivate display of the image on demand.

Special Conditions Paragraph 2.f.

    One commenter interprets special conditions paragraph 2.f. to mean 
that the EVS image must not affect the performance of the pilot in the 
use of the HUD for previously approved operations. The commenter 
assumes that the EVS image may be removed during those operations (or 
phases) which could be impacted, and states that the EVS image may need 
to be automatically deactivated during certain phases of flight, 
perhaps at or prior to decision height during a low visibility 
approach.
    The objective of paragraph 2.f. is that the EVS installation would 
not adversely affect the ability of the HUD to meet any requirement to 
which it was originally certified. Whether or not the EVS image must be 
removed for some phases of flight to comply with this paragraph must be 
determined on a case-by-case basis. If there are cases where removal of 
the image is required, automatic means to deactivate the image would 
not be required, unless it is shown that manual procedures to 
deactivate the image are inadequate.

Special Conditions Paragraph 3.

    The commenter interprets paragraph 3. as follows: ``The EVS image 
must not interfere in the pilot's detection of traffic, terrain, 
obstacles, and other hazards of flight. The assumption is that objects 
are recognizable within the EVS image, or visual objects are still 
recognizable through the EVS image.''
    The commenter's interpretation with respect to the ability of the 
pilot to ``see'' discrete visual items is correct. For completeness, 
though, one must also determine if there are characteristics that 
adversely affect the pilot's ability to maneuver the airplane to avoid 
flight hazards. Excessive image latency or lag, for example, might have 
an adverse effect.

Special Conditions Paragraph 4.a.

    One commenter provided the following comments:
    <bullet> It is not clear if this rules out the use of the EVS for 
taxi and/or takeoff.
    <bullet> The words seem to indicate that the evaluation has already 
been completed and the special conditions authorize use during the 
approach.
    <bullet> Other potential uses should be considered (that is, 
takeoff, taxi, seeing threatening cloud formations at night).
    Special conditions paragraph 4. is meant to clarify the intended 
function of EVS, not to impose operational limitations. A requirement 
for airworthiness certification is that the system must be of a type 
and design to perform its intended function.
    The FAA and the applicant agree that the intended functions listed 
in paragraphs 4.a. and 4.b., associated with approach operations, are 
the primary focus of the certification, and for which the FAA will 
certify the EVS. However, there is no intent to restrict use of the EVS 
to approach and landing operations only. The EVS may be used as a 
supplemental system for any phase of flight, including taxi and take-
off, when it is shown to be safe.
    A PoC flight test program was conducted to evaluate what the EVS 
was capable of, how it should be used, and what certification criteria 
would be needed. Demonstrations for showing compliance with the 
airworthiness certification requirements will be accomplished after 
issuance of the final special conditions.

Proof of Concept Test

    One commenter states that it is unclear whether a proof of concept 
demonstration was conducted and if so, no results were revealed.
    As stated earlier, a PoC demonstration has already been conducted. 
The PoC test report, itself, is proprietary to the applicant, so the 
FAA did not provide it to the public.

Additional Requirements to Proposed Special Conditions

    One commenter states that consideration should be given to the 
following areas in the proposed special conditions:

[[Page 32726]]

    <bullet> Ensure acceptable characteristics when transitioning from 
EVS ON to OFF and vice versa, particularly the ability to reacquire 
outside visual references when EVS is selected OFF during an instrument 
approach.
    <bullet> Evaluate the perception of actual colors as viewed through 
the HUD with the EVS ON.
    <bullet> Address the effects of power transients or temporary 
interruptions.
    <bullet> Address pilot fatigue or eye strain while using the EVS.
    <bullet> Consider EVS dispatch requirements.
    <bullet> Paragraph 2.d. should be expanded to state that the 
initial certification should include sufficient testing to cover the 
normal range of expected flight maneuvers for all of the phases of 
flight to be certified with the EVS active.
    Another commenter states that it may be desirable to provide the 
option of a head down FLIR display when operations are conducted with a 
single HUD.
    The FAA agrees, in part, with the issues raised by the first 
commenter. The FAA plans to evaluate these issues during the 
certification program, but does not see the need to revise the language 
of the special conditions. FAA responses to the issues are provided in 
the order presented by the commenter.
    <bullet> Specific standards for acceptable EVS on/off transitions 
and color perception need not be stated. These factors can be evaluated 
in the context of special conditions paragraphs 1. and 2. (including 
sub-paragraphs).
    <bullet> The HUD was already certified to have acceptable responses 
to power transients and interruptions. The FAA does not consider this 
EVS image, itself, critical. Based on special conditions paragraph 
2.f., with the EVS modification, the HUD must continue to meet the 
requirements of its original approval.
    <bullet> Per special conditions paragraph 2.f., the HUD with the 
EVS modification must continue to meet the requirements of its original 
approval, including the eye strain and fatigue criteria of the HUD 
issue paper.
    <bullet> Dispatch requirements are determined by the FAA Aircraft 
Evaluation Group and will not be specified in the special conditions.
    <bullet> Software requirements are addressed, separately, in a 
means of compliance issue paper and will not be addressed in the 
special conditions.
    In response to the second commenter, the FAA considers that the 
desirability of an option to display the EVS image head down is a 
matter for the customer to decide, but is not a safety issue that would 
justify a mandatory standard.

Recognize EVS as an Avionics System With a Broad Base of Experience

    The commenter states that the EVS should be recognized as a system 
with an extremely long and broad base of experience. Many of the issues 
raised in the notice are old concerns resolved by the military in great 
detail, and at great cost, including:
    <bullet> Issues of visual acuity and cognizant processing.
    <bullet> Perception of the 3rd dimension is accomplished through a 
combination of relative intensity (brightness), apparent movement, and 
size growth with decreasing distance to items of interest.
    <bullet> In spite of technical limitations of older military 
systems, they were whole-heartedly embraced as beneficial, even a poor 
image is better than no image. The present technology is better since 
it has a larger, more sensitive detector array.
    The FAA did not discount the military experience when proposing 
these special conditions. The ``old concerns'' may have been resolved 
by the military for the sake of weapon system design and operational 
use. The notice (preamble and special conditions) raised the issues 
that distinguish the EVS image from natural pilot vision because there 
are novel or unusual design features which the existing rule, 
Sec. 25.773, does not adequately address, and to provide safety 
standards that can be used to certify the EVS to the level of safety 
required for civil transport category airplanes.
    While acknowledging that there are some differences between the EVS 
image and natural vision, special conditions provide a way to certify 
EVS and maintain the level of safety, based on the premise that the 
combination of what the pilot can see in the image and what can be seen 
naturally, while the image is displayed, must be as safe and effective 
as the view without the image (in the same conditions).
    The special conditions were proposed because of the need for 
appropriate safety standards for such systems that perform required 
functions previously done only by natural pilot vision. The FAA does 
not suggest, and has no reason to believe, that that the Gulfstream EVS 
is unsafe and cannot comply with the requirements of the special 
conditions.
    The special conditions acknowledge enhanced situational awareness 
as an intended function of EVS, where its safety benefits might be best 
realized. Use of the EVS may also be beneficial during Category I 
approaches, when the ceiling and visibility are as prescribed in the 
standard instrument approach procedure. However, its safety benefit, 
when used for a Category I approach in less than prescribed flight 
visibility, has yet to be evaluated.
    The FAA accepts that the EVS image can provide some depth cues; 
however, unlike EVS, the natural view provides actual stereoscopic and 
accommodation (focus) cues, in addition to depth perception cues which 
may be found in the EVS image. The airworthiness standard, Sec. 25.773, 
and the operational rules, including Sec. 91.175, were written with 
natural vision in mind.
    The visual acuity (resolution) of the raster EVS image display also 
differs from natural pilot vision. This does not mean that EVS is 
unacceptable, only that it does not match natural vision, and that 
safety standards are needed for the image resolution to be satisfactory 
for its intended function, and that it does not unacceptably interfere 
with the pilot's natural vision.

Notice Implies that Existing Regulations Do Not Permit the Use of a 
``Sensor Based'' System

    One commenter states that the notice asserts that the existing 
regulations do not permit the use of a ``sensor based'' system for 
independent verification that the primary guidance is accurate. Another 
commenter states that there is no reference in the notice to the PoC 
test results that found the EVS suitable for acting as an independent 
integrity monitor for ILS approaches.
    The FAA did not say in the notice that sensor based systems cannot 
be used for independent verification of the primary guidance. Paragraph 
4. of the special conditions does not explicitly list the function of 
``integrity monitor'' for the guidance, but this function is covered 
within the dual intended function of ``presenting an image that would 
aid the pilot during the approach'' and ``that the pilot can use to 
detect and identify the visual references'' (Sec. 91.175(c)(3)).
    The EVS cannot be an independent monitor in the same sense as the 
term is normally used. Normally, use of this term refers to automatic 
detection and annunciation of system performance deviations and failure 
conditions. The pilot may be able to use the EVS image to identify 
certain visual references that serve as airplane position cues. The EVS 
sensor performance (i.e., what can be seen and at what distance) in the 
actual atmospheric conditions will affect the usefulness of the image 
for the purpose of verifying airplane position.

[[Page 32727]]

Lack of Understanding of the Technology and Underlying Physics

    One commenter states that the special conditions delve into the 
technical ``nitty-gritty'' of infrared and display performance with 
little understanding of the technology and underlying physics. The 
commenter further states that:
    <bullet> Infrared sensors are not limited to the mere sensing of 
``heat.'' The EVS sensor has been tailored to detect electromagnetic 
radiation from the near-IR out to the long-wavelength. This is 
technically interesting but not relevant to the issue at hand.
    <bullet> Most important is what the system provides, not the 
theoretical basis for infrared operation. With EVS, the pilot sees the 
same visual cues, in the same way, as presented on the HUD in a form 
that promotes outside/far-field vision and facilitates a transition 
from the IR image to the real scene.
    The FAA agrees, in part, with the commenter. While the infrared 
energy detected by these sensors is primarily due to ``thermal'' 
contrast in the scene, it is also true that reflected and emitted 
infrared energy might be detected. Because of their spectral response, 
the infrared sensors detect contrast in the scene differently from 
natural pilot vision. A scene that shows significant contrast in the 
infrared wavelengths may have less contrast in the visual wavelengths, 
and vice versa.
    The FAA agrees that the pilot may see many of the same visual cues 
with the EVS that might be seen naturally, but they are not seen in 
exactly the same way. As stated earlier, the cause and degree of scene 
contrast can vary between the infrared image and the natural view. 
However, the FAA acknowledges that the size and spatial relationships 
of certain visual references, particularly lighted objects such as 
those listed in Sec. 91.175(c)(3), may be similar in the image and in 
the natural view and therefore may be identifiable to the pilot.
    This is not to say that the EVS infrared imagery is unacceptable, 
only that it is not the same as natural vision, in a variety of ways. 
Natural vision was originally assumed when Secs. 25.773 and 91.175 were 
issued, which, as discussed earlier, is one basis for the special 
conditions. So far, the FAA has not certified the use of any electronic 
imagery displayed in the windshield's field of view or imagery 
generated from a different part of the electromagnetic spectrum.

Operational Benefits of EVS

    One commenter states that the EVS could be used at many runway ends 
closed for critical take-off and landing operations due to limited 
visibility. The EVS could restore the pilot's vision and increase 
airport capacity.
    The full potential for operational benefits of the EVS will be 
demonstrated by the accumulation of service experience, and will depend 
on the FAA Flight Standards' determination of what operational uses 
will be authorized.
    That EVS may provide significant operational benefits is not a 
factor when determining the need for safety standards or special 
conditions. The special conditions, alone, will not restrict the use of 
EVS for operationally beneficial purposes.

Requests To Extend Comment Period

    One commenter, representing the interests of airlines and 
manufacturers, requests that the comment period be extended for 30 
days. The commenter states that airlines and manufacturers must be able 
to understand the implications and future impact of the proposed 
special conditions and need the additional time to provide responsive 
and constructive comments.
    The FAA has decided not to extend the public comment period. 
Eighteen commenters, including this commenter, were able to provide 
extensive comments to the proposed special conditions during the 
allotted time. These special conditions are specific to the Gulfstream 
Model G-V EVS project, and any extension to the public comment period 
would adversely delay certification. There will be additional 
opportunities to comment on other special conditions and rulemaking 
related to future EVS certification projects as they arise.

Request for a Public Meeting

    One commenter expresses concern about the effect this special 
condition action will have on the industry-wide joint effort to improve 
the certification process through the use of strong and trustworthy 
partnerships, and requests that the FAA conduct a public hearing into 
the process of handling such further industry developments.
    A second commenter requests that the FAA hold a public hearing to 
discuss the special conditions and the rationale for broader 
application to products developed as part of the Safer Skies program.
    The FAA does not agree. The process of holding a public meeting and 
dealing with the result of such a meeting would unduly delay completion 
of this rulemaking and could adversely affect the applicant's 
certification schedule.
    The FAA does not believe that such a meeting would materially serve 
the purposes of this rulemaking. A significant amount of substantive 
public comments have already been submitted that sufficiently 
characterize objections and concerns with the special conditions.

Applicability

    As discussed above, these special conditions are applicable to 
Gulfstream Model G-V airplanes modified by Gulfstream Aerospace. Should 
Gulfstream Aerospace apply at a later date for a supplemental type 
certificate to modify any other model included on the same type 
certificate to incorporate the same novel or unusual design feature, 
these special conditions would apply to that model as well under the 
provisions of Sec. 21.101(a)(1).

Conclusion

    This action affects only certain novel or unusual design features 
on the Gulfstream Model G-V airplanes modified by Gulfstream Aerospace. 
It is not a rule of general applicability and affects only the 
applicant who applied to the FAA for approval of these features on the 
airplane.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.
    The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special conditions are issued as part of 
the supplemental type certification basis for Gulfstream Model G-V 
airplanes modified by Gulfstream Aerospace:
    1. The EVS imagery on the HUD must not degrade the safety of 
flight, nor interfere with the effective use of outside visual 
references for required pilot tasks, during any phase of flight in 
which it is to be used.
    2. To avoid unacceptable interference with the safe and effective 
use of the pilot compartment view, the EVS device must meet the 
following requirements:
    2.a. The EVS design must minimize unacceptable display 
characteristics or artifacts (for example, noise, ``burlap'' overlay, 
running water droplets) that obscure the desired image of the scene, 
impair the pilot's ability to detect and identify visual references, 
mask flight hazards, distract the pilot, or otherwise degrade task 
performance or safety.

[[Page 32728]]

    2.b. Control of EVS display brightness must be sufficiently 
effective, in dynamically changing background (ambient) lighting 
conditions, to prevent full or partial blooming of the display that 
would distract the pilot, impair the pilot's ability to detect and 
identify visual references, mask flight hazards, or otherwise degrade 
task performance or safety. If automatic control for image brightness 
is not provided, it must be shown that a single manual setting is 
satisfactory.
    2.c. A readily accessible control must be provided that permits the 
pilot to immediately deactivate and reactivate display of the EVS image 
on demand.
    2.d. The EVS image on the HUD must not impair the pilot's use of 
guidance information nor degrade the presentation and pilot awareness 
of essential flight information displayed on the HUD, such as alerts, 
airspeed, attitude, altitude and direction, approach guidance, 
windshear guidance, TCAS resolution advisories, and unusual attitude 
recovery cues.
    2.e. The EVS image must be sufficiently aligned and conformal to 
both the external scene and conformal HUD symbology so as not to be 
misleading, cause pilot confusion, or increase workload.
    2.f. A HUD system modified to display EVS images must continue to 
meet all the requirements of the original approval.
    3. The safety and performance of the pilot tasks associated with 
the use of the pilot compartment view must be not be degraded by the 
display of the EVS image. Pilot tasks that must not be degraded by the 
EVS image include:
    3.a. Detection, accurate identification, and maneuvering, as 
necessary, to avoid traffic, terrain, obstacles, and other hazards of 
flight.
    3.b. Accurate identification and use of visual references required 
for every task relevant to the phase of flight.
    4. Compliance with these special conditions does not affect the 
applicability of any of the requirements in the operating regulations 
(e.g., parts 91, 121, 135). The criteria in special conditions 
paragraphs 1., 2., and 3. were developed to determine that this EVS is 
of a kind and design appropriate to the following functions:
    4.a. Presenting an image that would aid the pilot during the 
approach.
    4.b. Displaying an image that the pilot can use to detect and 
identify the ``visual references for the intended runway'' required by 
Sec. 91.175(c)(3) to continue the approach with vertical guidance to 
100 feet height above touchdown (HAT). Appropriate limitations must be 
included in the Operating Limitations section of the Airplane Flight 
Manual to prohibit the use of the EVS for functions not found to be 
acceptable.

    Issued in Renton, Washington, on June 8, 2001.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-15333 Filed 6-15-01; 8:45 am]
BILLING CODE 4910-13-U


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