Launch Safety: Lightning Criteria for Expendable Launch Vehicles, 33139-33152 [2011-14146]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 76, Number 110 (Wednesday, June 8, 2011)]
[Rules and Regulations]
[Pages 33139-33152]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-14146]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 417

[Docket No. FAA-2011-0181; Amdt. No. 417-2]
RIN 2120-AJ84


Launch Safety: Lightning Criteria for Expendable Launch Vehicles

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Direct final rule; request for comments.

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SUMMARY: The FAA is amending its lightning commit criteria to account 
for new information about the risks of natural and triggered lightning. 
This action amends flight criteria for mitigating against naturally 
occurring lightning and lightning triggered by the flight of an 
expendable launch vehicle through or near an electrified environment in 
or near a cloud. These changes will increase launch availability and 
implement changes already adopted by the United States Air Force.

DATES: Effective July 25, 2011. Submit comments on or before July 8, 
2011.

ADDRESSES: You may send comments identified by Docket Number FAA-2011-
0181 using any of the following methods:
     Federal eRulemaking Portal: Go to https://www.regulations.gov and follow the instructions for sending your 
comments electronically.
     Mail: Send comments to Docket Operations, U.S. Department 
of Transportation, 1200 New Jersey Avenue, SE., West Building Ground 
Floor, Room W12-140, Washington, DC 20590.
     Fax: Fax comments to Docket Operations at 202-493-2251.
     Hand Delivery: Take comments to Docket Operations in Room 
W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue, 
SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays.
    For more information on the rulemaking process, see the 
SUPPLEMENTARY INFORMATION section of this document.
    Privacy: We will post all comments we receive, without change, to 
https://www.regulations.gov, including any personal information you 
provide. Using the search function of our docket web site, anyone can 
find and read the comments received into any of our dockets, including 
the name of the individual sending the comment (or signing the comment 
for an association, business, labor union, etc.). You may review DOT's 
complete Privacy Act Statement in the Federal Register published on 
April 11, 2000 (65 FR 19477-78) or you may visit https://DocketsInfo.dot.gov.
    Docket: To read background documents or comments received, go to 
https://www.regulations.gov at any time or to Docket Operations in Room 
W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue, 
SE., Washington, DC, between 9 a.m. and

[[Page 33140]]

5 p.m., Monday through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: For technical questions concerning 
this rule contact Karen Shelton-Mur, Office of Commercial Space 
Transportation, AST-300, Federal Aviation Administration, 800 
Independence Avenue, SW., Washington, DC 20591; telephone (202) 267-
7985; facsimile (202) 267-5463, e-mail Karen.Shelton-Mur@faa.gov.
    For legal questions concerning this rule contact Laura Montgomery, 
Senior Attorney for Commercial Space Transportation, Office of the 
Chief Counsel, Federal Aviation Administration, 800 Independence 
Avenue, SW., Washington, DC 20591; telephone (202) 267-3150; facsimile 
(202) 267-7971, e-mail laura.montgomery@faa.gov.

SUPPLEMENTARY INFORMATION: 

Authority for This Rulemaking

    The FAA's authority to issue rules on commercial space 
transportation safety is found in Title 49 of the United States Codes, 
section 322(a), which authorizes the Secretary of Transportation to 
carry out rulemakings. 51 U.S.C. subtitle V, chapter 509, 51 U.S.C. 
50901-50923 (Chapter 509) governs the FAA's regulation of the safety of 
commercial space transportation. This rulemaking is promulgated under 
the authority of section 322(a).

Direct Final Rule Procedure

    The FAA anticipates this regulation will not result in adverse or 
negative comment and therefore is issuing it as a direct final 
rulemaking. Because the changes to the lightning commit criteria will 
increase launch availability and are already implemented at Air Force 
launch ranges, the public interest is well served by this rulemaking.
    Unless a written adverse or negative comment or a written notice of 
intent to submit an adverse or negative comment is received within the 
comment period, the regulations will become effective on the date 
specified above. After the close of the comment period, the FAA will 
publish a document in the Federal Register indicating that no adverse 
or negative comments were received and confirming the date on which the 
final rule will become effective. If the FAA does receive, within the 
comment period, an adverse or negative comment, or written notice of 
intent to submit such a comment, the FAA will withdraw the direct final 
rule by publication in the Federal Register, and a notice of proposed 
rulemaking may be published with a new comment period.

Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking by submitting written comments, data, or views. The agency 
also invites comments relating to the economic, environmental, energy, 
or federalism impacts that might result from adopting the changes. The 
most helpful comments reference a specific portion of the proposal, 
explain the reason for any recommended change, and include supporting 
data. To ensure the docket does not contain duplicate comments, please 
send only one copy of written comments, or if you are filing comments 
electronically, please submit your comments only one time.
    The FAA will file in the docket all comments we receive, as well as 
a report summarizing each substantive public contact with FAA personnel 
concerning this rulemaking. Before acting on this proposal, the FAA 
will consider all comments received on or before the closing date for 
comments. The agency will consider comments filed after the comment 
period has closed if possible without incurring expense or delay. The 
FAA may make changes in light of the comments received.

Proprietary or Confidential Business Information

    Do not file in the docket information that you consider to be 
proprietary or confidential business information. Send or deliver this 
information directly to the person identified in the FOR FURTHER 
INFORMATION CONTACT section of this document. Mark the information that 
is considered proprietary or confidential. If the information is on a 
disk or CD-ROM, mark the outside of the disk or CD-ROM and also 
identify electronically within the disk or CD-ROM the specific 
information that is proprietary or confidential.
    Under 14 CFR 11.35(b), when the FAA is aware of proprietary 
information filed with a comment, the agency does not place it in the 
docket. The FAA holds it in a separate file to which the public does 
not have access, and the agency places a note in the docket that it has 
received it. If the FAA receives a request to examine or copy this 
information, the FAA treats it as any other request under the Freedom 
of Information Act, 5 U.S.C. 552. The FAA processes such a request 
under the DOT procedures found in 49 CFR part 7.

Availability of Rulemaking Documents

    You can get an electronic copy using the Internet by:
    (1) Searching the Federal eRulemaking portal at https://www.regulations.gov;
    (2) Visiting the FAA's Regulations and Policies web page at https://www.faa.gov/regulations_policies/; or
    (3) Accessing the Government Printing Office's web page at https://www.gpoaccess.gov/fr/.
    You can also get a copy by sending a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue, SW., Washington, DC 20591, or by calling (202) 267-9680. Make 
sure to identify the docket and amendment numbers of this rulemaking.

I. Background

    On August 25, 2006, the FAA issued requirements designed for an 
expendable launch vehicle (ELV) to avoid natural and triggered 
lightning during flight. Licensing and Safety Requirements for Launch, 
71 FR 50508 (Aug. 25, 2006). An ELV is an unmanned rocket that 
typically carries satellites to orbit. ELVs carry large amounts of fuel 
and, due to the explosive nature of the fuel, may not be permitted to 
reach populated areas in the event they go off course. In the United 
States, safety for ELVs is achieved by use of a flight termination 
system. A flight termination system prevents an errant launch vehicle 
from reaching a populated area by destroying the vehicle. A flight 
termination system consists of all components on board a launch vehicle 
that provide the ability to end its flight in a controlled manner. 
Without the restrictions mandated by appendix G of part 417, a 
lightning strike could disable a flight safety system yet allow 
continued flight of the launch vehicle without a launch operator being 
able to stop its flight.
    By codifying appendix G, the FAA implemented criteria developed by 
a Lightning Advisory Panel (LAP) to the National Aeronautics and Space 
Administration (NASA) and the U.S. Air Force. See Merceret et al., ed., 
A History of the Lightning Launch Commit Criteria and the Lightning 
Advisory Panel for America's Space Program, NASA/SP-2010-216283, 124, 
par. 25 (Aug. 2010) (A History of the Lightning Criteria) and 
Rationales for the Lightning Flight-Commit Criteria, NASA/TP-2010-
216291, (Oct. 7, 2010)(Rationales for Lightning Criteria). Appendix G's 
flight commit criteria impose time and distance restrictions on launch, 
requiring a launch operator to wait to initiate flight for specified 
amounts of time after a lightning strike or when launch would take a 
flight path too close to an electrified cloud.

[[Page 33141]]

    In this direct final rule, the FAA is permitting greater launch 
availability. In brief, the FAA is reducing requirements that a launch 
operator wait to launch by expanding the applicability of certain 
exceptions and recognizing that the risk of triggering lightning is 
less than previously understood at distances closer than previously 
believed. The FAA is also codifying criteria for obtaining accurate 
radar reflectivity measurements to ensure calculation of the volume-
averaged, height-integrated radar reflectivity (VAHIRR) and other 
measurements, such as the vertical extent of a cloud top, are 
representative of actual conditions at the time of launch, because 
these calculations are instrumental in determining the presence of and 
risk posed by electrified clouds.

II. New Requirements

A. General Applicability

    The FAA is revising the general description of appendix G to 
clarify that the flight commit criteria are to mitigate lightning 
strikes and avoid initiation of lightning when a launch vehicle flies 
near or through a highly electrified environment in or near a cloud. 
The FAA is also clarifying that, when a launch operator uses optional 
equipment, such as a field mill, to increase launch availability, an 
operator may not ignore data that does not satisfy the requirement. 
This addition, particularly when read in conjunction with 14 CFR 
417.113(c)(1)(ii), should ensure that a launch takes place only when it 
is clear that all the criteria are satisfied. Section 417.113(c)(1)(ii) 
states that a launch operator's launch safety rules \1\ must ensure 
there is clear and convincing evidence that the criteria of appendix G, 
which apply to the conditions present at the time of lift-off, are not 
violated. Section G417.1 states that all lightning flight commit 
criteria of Appendix G must be satisfied. In other words, each 
paragraph of each section must be individually satisfied at the time of 
launch. In short, the burden is on the launch operator to ensure that 
conditions are safe for launch.
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    \1\ A launch operator must follow its safety rules. 14 CFR 
417.113(a)(3).
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    A launch operator must understand that each of the sections of 
appendix G deliberately prohibits launch under certain conditions. 
Since all of the criteria must be satisfied, appendix G must be read in 
its entirety to determine whether or not launch is prohibited. Thus, 
the satisfaction of any particular paragraph or section cannot be 
considered to permit launch. Even the simultaneous satisfaction of all 
sections means only that there are no known natural- or triggered-
lightning threats that prohibit launch. According to Sec.  
417.113(c)(1)(ii), it is still necessary for the launch weather team to 
report any other hazardous conditions to the person with authority for 
deciding whether or not to launch.

B. New Definitions and Clarifications of Existing Definitions

    Section G.417.3 of appendix G defines terms if they would not be 
familiar to a trained meteorological observer, such as ``field mill,'' 
or if they constitute non-standard usage of an otherwise familiar term, 
such as ``associated.'' The FAA is adding new definitions, clarifying 
existing ones, and making minor editorial changes to others. For terms 
not defined in this section, a useful reference is the AMS Glossary of 
Meteorology, American Meteorological Society, 2000: Glossary of 
Meteorology, 2nd ed., American Meteorological Society, Boston, MA, 850; 
also available on line at https://amsglossary.allenpress.com/glossary.
    New definitions to appendix G include definitions of Cone of 
silence, Electric field, Horizontal distance, Radar reflectivity, and 
Slant distance.
    A cone of silence is a volume within which a radar cannot detect 
any object and is an inverted circular cone centered on the radar 
antenna. A cone of silence consists of all elevation angles greater 
than the maximum elevation angle reached by the radar. The cone of 
silence is a volume that the radar beam cannot access because of a 
radar's maximum tilt elevation. Radar echoes close to and directly 
above the radar cannot be detected. The methodology of section 
G417.25(b) provides that the specified volume for the VAHIRR 
calculation must not contain any portion of the cone of silence. Note 
as well that, for any given search pattern, certain sectors may be 
blocked out for reasons of payload safety, and the specified volume 
also may not contain any portion of a sector blocked out for these 
reasons. The methodology of section G417.25(a) also provides that no 
other radar reflectivity measurements, such as those used to delineate 
a cloud, may be affected by any volume that is inaccessible to the 
radar.
    An electric field is a vertical electric field (Ez) at the surface 
of the Earth. This definition differentiates the surface electric field 
from those measured aloft.
    A horizontal distance is a distance that is measured horizontally 
between a field mill or electric-field-measurement point and the 
nearest part of the vertical projection of an object or flight path 
onto the surface of the Earth. The FAA is defining horizontal distance 
in order to distinguish between the measurement of this two-dimensional 
distance and the three-dimensional ``slant distance.''
    Radar reflectivity means the radar reflectivity factor due to 
hydrometeors, in dBZ. This is non-standard usage of a term that is 
defined in the Glossary of Meteorology. Radar reflectivity measurements 
in units of dBZ (as defined in the Glossary and not further discussed 
herein) are further specified in section G417.25(a) and are used 
throughout this appendix, including for the calculation of VAHIRR.
    A slant distance means the shortest distance between two points, 
whether horizontal, vertical, or inclined in three dimensional space. A 
slant distance is used in measuring the distance between a radar 
reflectivity or VAHIRR measurement point and either a flight path or an 
object such as a cloud.
    The FAA is also clarifying the definitions of Associated, Cloud, 
Disturbed weather, Flight path, Transparent, and Volume-averaged 
height-integrated radar reflectivity (VAHIRR). The following paragraphs 
describe the changes made to these definitions and the reasons for 
those changes.
    Associated means two or more clouds are caused by the same 
disturbed weather or are physically connected. The FAA is deleting the 
discussion contained in the current definition. Discussion is better 
placed in explanatory material like this preamble, and is unnecessary 
in regulatory text. Accordingly, it is still the case that 
``associated'' does not have to mean occurring at the same time. It is 
also still the case that a cumulus cloud formed locally and a cirrus 
layer physically separated from that cumulus cloud and generated by a 
distant source are not associated, even if they occur over or near the 
launch point at the same time.
    A cloud is a visible mass of suspended water droplets, ice 
crystals, or a combination of water droplets and ice crystals. A 
``cloud'' includes the entire volume containing such particles. This 
clarification omits an unnecessary reference to the particles being 
produced by condensation of water vapor in the atmosphere. Note that 
this definition works together with that of ``slant distance'' to 
specify that standoff distances from a cloud be measured from the 
nearest edge of that cloud.
    Disturbed weather is a weather system where a dynamical process 
destabilizes the air on a scale larger than individual clouds or cells. 
Disturbed weather specifically includes, but is not limited to, fronts, 
troughs, and squall lines. (In

[[Page 33142]]

this case, the examples are retained as a critical part of the 
definition.) The body of the definition remains unchanged, but the FAA 
is now adding a squall line as an important example of disturbed 
weather because, along with fronts and troughs, it is frequently 
related to electrification of the associated clouds.
    Flight path means a launch vehicle's planned flight trajectory, 
including the trajectory's vertical and horizontal uncertainties 
resulting from all three-sigma guidance and performance deviations. The 
FAA is no longer referencing wind effects because three-sigma 
dispersions already take wind effects into account.
    The definition of transparent is clarified to mean any of the 
following conditions apply:
    [rtarr9] Objects above, including higher clouds, blue sky, and 
stars are not blurred, are distinct, and are not obscured when viewed 
at visible wavelengths;
    [rtarr9] Objects below, including terrain, buildings, and lights on 
the ground, are clear, distinct, and not obscured when viewed at 
visible wavelengths;
    [rtarr9] Objects above or below are seen distinctly not only 
through breaks in a cloud;
    [rtarr9] The cloud has a radar reflectivity of less than 0 dBZ.

Historically, transparency has been determined by a person watching the 
sky. The weather experts at the Federal launch ranges prefer 
observations undertaken by a person. Rather than limiting visual 
observations to those made by a person standing outdoors, this 
definition reflects the fact that transparency may be determined by 
satellite or camera as well. A person may also look at images of the 
conditions outside to ascertain transparency. For these reasons, the 
phrase ``at visible wavelengths'' has been retained; clouds that look 
transparent to a human observer may not look transparent to an imaging 
sensor operating at another wavelength, and vice versa.
    Volume-averaged height-integrated radar reflectivity means the 
product, expressed in units of dBZ-km, of the volume-averaged radar 
reflectivity (in dBZ) and the average cloud thickness (in kilometers) 
in the specified volume determined by a VAHIRR-measurement point. The 
old definition states that the calculation applies to ``a specified 
volume relative to a point along the flight track.'' The change 
clarifies that VAHIRR may be computed at points other than along a 
flight path. New section G417.25(b) describes in detail how VAHIRR is 
calculated.
    Additionally, the FAA is making minor editorial changes to the 
following definitions: Anvil cloud, Precipitation, Moderate 
precipitation, Thick cloud layer, Triboelectrification, and Volume-
averaged height-integrated radar reflectivity.
    The FAA is also deleting several definitions.
    Cloud edge is being deleted because it is now part of the 
definition of a cloud. Electric field measurement at the surface of the 
Earth is being deleted. The criteria this term contained are more 
accurately characterized as requirements, and, therefore, now appear in 
new section G417.25(c) Electric field measurement, which governs how to 
measure electric fields. Electric field measurement aloft is removed 
because Appendix G contains no criteria for electric field measurement 
aloft in the regulations. Although the FAA initially considered 
criteria for electric fields aloft, in the end, it did not promulgate 
requirements when it issued part 417. The definition was inadvertently 
left in the final rule. The definition of Ohms/square is removed 
because the term is a standard unit of measurement. The definition of 
Specified volume is no longer necessary because the term contained 
requirements now located in section G417.25. Treated is being deleted 
because it contained requirements now located in section G417.23(b). 
Within is being deleted because more precise language regarding the 
distance between a flight path and a cloud should prevent any 
misunderstanding regarding the distance for which a launch operator 
must account.

III. Changes to Temperature, Time, and Distance Restrictions for Anvil 
and Debris Clouds

    In this direct final rule, the FAA is permitting greater launch 
availability. In brief, the FAA is reducing requirements that a launch 
operator wait to launch by expanding the applicability of certain 
exceptions and decreasing waiting time requirements because of 
recognition that the risk of triggering lightning is less than 
previously understood at distances closer than previously believed. In 
order to ensure satisfaction of minimum standards of measurement and 
uniformity across launch sites, the FAA is codifying in new section 
G417.25 the measurement criteria used during a second airborne field 
mill campaign (ABFM-II) conducted during 2000 and 2001. A lightning 
advisory panel that provides expertise to the Air Force and NASA 
recommended this approach to the ranges. The FAA also accepts the more 
simple approach that the ranges currently use to calculate volume-
averaged, height-integrated radar reflectivity because it is more 
conservative than the codified approach. Acceptable techniques to 
calculate VAHIRR are further discussed in Section III.C.3 below.

A. Structural Changes

    At the outset, the FAA must note that the order of the new 
requirements for anvil and debris clouds is reversed from the old 
requirements. These new rules have also been written so that only one 
set of restrictions applies at a time. For example, for attached anvil 
clouds, in old section G417.9.
     Paragraph (a) contains requirements for flight paths 
through or within 10 nautical miles of the cloud,
     Paragraph (b) contains requirements for flight paths 
through or within 5 nautical miles of the cloud, and
     Paragraph (c) contains requirements for flight paths 
through a cloud.

This organization is potentially confusing, since all three paragraphs 
apply to flight through, and both paragraphs (a) and (b) apply to 
flight within 5 nautical miles of, the cloud. The application has been 
simplified in the new G417.9, where--
     Paragraph (b) contains all requirements for flight paths 
through a cloud,
     Paragraph (c) contains all requirements for flight paths 
greater than 0 and less than or equal to 3 nautical miles from the 
cloud,
     Paragraph (d) contains all requirements for flight paths 
greater than 3 and less than or equal to 5 nautical miles from the 
cloud, and finally,
     Paragraph (e) contains all requirements for flight paths 
greater than 5 and less than or equal to 10 nautical miles from a 
cloud.
    Whereas more than one paragraph could apply under the old rule, the 
end result of this restructuring is that, for any given slant distance 
from a cloud, at most, one paragraph will apply in the new rule. For 
example, suppose a launch vehicle's flight path would place the closest 
approach of the vehicle 2 nautical miles from an attached anvil cloud. 
Under the old rule, the operator would need to satisfy the requirements 
of both sections G417.9(a), because 2 nautical miles is less than 10 
nautical miles, and G417.9(b), because 2 nautical miles is less than 5 
nautical miles. Under the new rule, the operator only needs to satisfy 
the requirements of G417.9(c) because 2 nautical miles is between zero 
and 3 nautical miles. This change should make the rules easier to 
follow. However, because of this

[[Page 33143]]

restructuring, there is not a one-to-one correspondence between the 
paragraphs of the old and new rules.
    Even in the rules that have been structurally rearranged, it must 
be remembered that slant distance from a cloud refers only to the 
closest approach of the vehicle. Otherwise multiple paragraphs may 
still be taken to apply. An operator must always take care that all 
paragraphs are satisfied.

B. Clarification of Applicability of Restrictions to Anvil Clouds 
Formed From Parents at Altitudes below -10 Degrees Celsius

    Under new paragraphs (a) of sections G417.9 and G417.11, for both 
attached and detached anvil clouds, the requirements to wait before 
initiating flight apply only when an anvil cloud forms from a parent 
cloud that has a top at an altitude where the temperature is -10 
degrees Celsius or colder. Even though anvil clouds can form in 
temperatures slightly above freezing, only anvil clouds with parents 
whose tops are at altitudes with temperatures at or below -10 degrees 
Celsius pose a real possibility of containing high electric fields.\2\ 
When a convective cloud grows through different altitudes, it may reach 
altitudes with freezing or colder temperatures. At these altitudes the 
cloud may acquire ice particles, ice crystals, super-cooled water 
droplets or a combination thereof. It is primarily this mixture of 
phases that can produce a strong electrical generator within the cloud. 
When the cloud top has become colder than -10 degrees Celsius, the 
cloud is likely to be electrified, and when its top has become colder 
than -20 degrees Celsius, strong electrification is likely.\3\
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    \2\ Willett, ed., Rationales for Lightning Criteria, at 9, 45, 
61, and 108.
    \3\ Id. at 45.
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    The temperature criterion in paragraphs (a) applies to the parent 
cloud. Anvil clouds are limited to outflow from convective clouds at 
altitudes with temperatures at or colder than --10 degrees Celsius. 
According to studies, anvil clouds that develop from cumulus clouds 
with cloud top temperatures warmer than -10 degrees Celsius rarely 
develop electric fields with the strength of a thunderstorm.\4\
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    \4\ Dye, J.E., W.P. Winn, J.J. Jones, and D.W. Breed, 1989: The 
electrification of New Mexico Thunderstorms. 1. Relationship between 
precipitation development and the onset of electrification, J. 
Geophys. Res., 94, 8643-8656. Breed, D.W., and J.E. Dye, 1989: The 
electrification of New Mexico Thunderstorms Part 2. Electric field 
growth during initial electrification. J. Geophys. Res, 94, 14, 841-
14, 854.
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    In practice, this limitation of the flight commit criteria to anvil 
clouds formed from parents at sufficiently cold altitudes is not new. 
Although not clearly expressed in the old appendix G, the Federal 
ranges have historically limited their restrictions on flight to non-
transparent anvil clouds formed from parents at altitudes where the 
temperatures are -10 degrees Celsius or colder.

C. Exceptions to the Requirement To Wait To Initiate Flight

    This rulemaking increases the availability of exceptions to certain 
prohibitions on initiating flight under circumstances posing a risk of 
natural or triggered lightning. Specifically, although an FAA licensee 
must wait specified amounts of time after the last lightning discharge 
to initiate flight through a non-transparent attached or detached anvil 
cloud or a non-transparent debris cloud, the licensee need not wait, 
under the new versions of the anvil and debris-cloud rules, if all of 
the non-transparent anvil or debris clouds within 3 nautical miles of a 
flight path are located at altitudes where the temperature is colder 
than 0 degrees Celsius and if the volume-averaged, height-integrated 
radar reflectivity (VAHIRR) is less than +10 dBZ-km. For the longer 
standoff distances, anvil clouds must be cold within 10 nautical miles, 
but there is no requirement to calculate VAHIRR.
    The launch operator must always remember, however, that all 
sections of Appendix G must be satisfied simultaneously. In particular, 
section G417.5, requires standoff distances of 10 nautical miles from a 
parent thunderstorm and from the lightning itself, so there will 
usually be portions of a non-transparent anvil or debris cloud through 
which flight is prohibited by the lightning provision even though it 
may not be prohibited by the anvil or debris cloud requirements 
themselves.
1. Reduced Restrictions on Launches With a Flight Path Greater Than 3 
Nautical Miles From an Anvil or Debris Cloud
    The first change reduces some restrictions on launches with a 
flight path greater than 3 nautical miles from a non-transparent anvil 
or debris cloud. For flight paths more than 3 nautical miles from a 
non-transparent anvil cloud, rather than requiring that a launch 
operator always wait after a lightning discharge, the FAA now requires 
only that the altitude of the portion of the cloud within a specified 
distance of the flight path be at temperatures less than 0 degrees 
Celsius to permit flight. For non-transparent debris clouds with flight 
paths greater than 3 nautical miles from the cloud, the FAA will no 
longer require any waiting after a lightning discharge or detachment.
    For non-transparent anvil clouds, the requirements for a waiting 
period for flight paths more than 3 nautical miles from a cloud are not 
being dropped entirely. However, the requirements for anvil clouds will 
be more flexible beyond 3 nautical miles than they are under the 
current rules. For anvil clouds more than 3 nautical miles from a 
flight path, the FAA will require, unless the operator waits 3 hours 
after the last lightning discharge, that the altitudes at which the 
flight path passes within a specified distance of the cloud have 
temperatures of less than 0 degrees Celsius. This restriction was based 
on the first Airborne Field Mill campaign (ABFM-II) which showed that 
clouds at altitudes with temperatures of less than 0 degrees Celsius do 
not contain electric field magnitudes of greater than 3 kV/m. Merceret 
et al., supra, 242. The specific rule changes for attached and detached 
anvil clouds are explained in turn below. The reasons for the changes 
follow these descriptions.
i. Attached Anvil Clouds (G417.9)
    A launch operator using flight paths of greater than 3 and less 
than or equal to 5 nautical miles from an attached non-transparent 
anvil cloud will no longer always need to wait 30 minutes after a 
lightning discharge, and will no longer need to show that the VAHIRR is 
less than 33 dBZ-kft within 3 hours of a lightning discharge. The old 
requirement is contained in both section G417.9(a), which requires 
waiting for 30 minutes after a lightning discharge regardless of 
distance, and in section G417.9(b), which only allows passage between 
30 minutes and 3 hours after a lightning discharge, if the VAHIRR 
measurement is under +33 dBZ-kft and the altitudes at which the flight 
path passes within 5 nautical miles of the cloud have temperatures of 
less than 0 degrees Celsius.
    Under the new requirements, the restriction applicable to flight 
paths between 3 and 5 nautical miles will be contained in section 
G417.9(d) and will require waiting for 3 hours after a lighting 
discharge unless, as with the old rule, the portion of the attached 
anvil cloud at a slant distance of less than or equal to 5 nautical 
miles from the flight path is located entirely at altitudes where the 
temperature is colder than 0 degrees Celsius. A launch operator will no 
longer be required to wait for 30 minutes after a lightning discharge 
and will not need to calculate VAHIRR to be able to launch within 3

[[Page 33144]]

hours of a lightning discharge. However, a launch operator will still 
need to show satisfaction of the temperature at altitude restriction in 
order to launch within 3 hours of a lightning discharge.
    Launch operators with flight paths of greater than 5 and less than 
or equal to 10 nautical miles from an attached non-transparent anvil 
cloud will no longer always need to wait 30 minutes after a lightning 
discharge as required by old section G417.9(a). Section G417.9(e) will 
now require waiting 30 minutes unless the portion of the attached anvil 
cloud at a slant distance of less than or equal to 10 nautical miles 
from the flight path is located entirely at altitudes where the 
temperature is colder than 0 degrees Celsius.
ii. Detached Anvil Clouds (G417.11)
    Launch operators with flight paths between 3 and 10 nautical miles 
from a detached non-transparent anvil cloud will no longer always need 
to wait 30 minutes after a lightning discharge and will no longer need 
to meet any requirements once 30 minutes have passed since the last 
lightning discharge. The new G417.11(d) will require that the launch 
operator wait 30 minutes after a lightning discharge from the cloud 
unless the portion of the detached anvil cloud at a slant distance of 
less than or equal to 10 nautical miles from the flight path is located 
entirely at altitudes where the temperature is colder than 0 degrees 
Celsius. Section G417.11(a) currently requires that a launch operator 
wait 30 minutes after a lightning discharge, without the benefit of any 
exceptions. Additionally, current G417.11(b) does not allow a launch 
operator to pass between 3 and 5 nautical miles from a cloud between 30 
minutes and 3 hours after a lightning discharge unless one of two sets 
of conditions are met. The new requirements are more flexible because 
they allow an exception to the requirement that the launch operator 
wait 30 minutes after a lightning discharge and because they do not 
require any conditions to be met after 30 minutes, even between 3 and 5 
nautical miles.
iii. Rationale
    The reduced restrictions on a flight path in excess of 3 nautical 
miles of a cold \5\ anvil or debris cloud arise out of experimental and 
statistical work performed by the LAP, which recommends lightning 
requirements for launches at Federal launch ranges. The LAP has 
performed statistical analyses of data collected during ABFM-II. The 
goal of ABFM-II was to characterize the electric fields of anvil and 
debris clouds by flying an aircraft into these types of clouds while 
taking measurements at various distances from the clouds using electric 
field mills. The ABFM II campaign used aircraft carrying airborne field 
mills to measure the electric fields of clouds of interest. The 
campaign used ground-based radar to measure the reflectivity of the 
same clouds so that it would be possible to correlate the radar 
reflectivity of the clouds with the electric field measurements of the 
airborne field mills. Francis J. Merceret, et al., On the Magnitude of 
the Electric Field near Thunderstorm-Associated Clouds, 47 Journal of 
Applied Meteorology and Climatology 240, 243 (2008). These data were 
used to develop the VAHIRR parameter associated with cloud 
electrification. Both the temperature and VAHIRR criteria are 
correlated with mixed-phase precipitation, namely, the presence of 
water in both solid and liquid phases.
---------------------------------------------------------------------------

    \5\ For the sake of brevity, the references to ``cold'' anvil 
clouds in this discussion refer to those whose parent clouds have 
tops at an altitude where the temperature is equal to or colder than 
-10 degrees Celsius.
---------------------------------------------------------------------------

    When a cloud spans the freezing level, the cloud can acquire a 
charge due to processes involving the mixing of liquid water droplets 
and ice crystals. A build up of electric charge in a cloud can lead to 
natural or triggered lightning. When the VAHIRR is less than 10 dBZ-km, 
it means that any mixed phase processes are unable to produce 
significant charging.
    Like the Air Force and NASA before it, the FAA's existing triggered 
lightning criteria are based on the determination that a launch vehicle 
will not trigger lightning in an electric field with a magnitude of 
less than 3 kilovolts per meter (kV/m). The following discussion of 
each of the changes to the FAA's lightning commit criteria will, 
therefore, focus on showing how the FAA's new requirements ensure that 
the electric field magnitude along the flight path will be less than 3 
kV/m, so that the new requirements will be essentially as safe as the 
current requirements.
    Therefore, the FAA is able to follow the Federal launch range's 
lead in making the rules less restrictive because of new analyses of 
the ABFM-II data. T.P. O'Brien & R. Walterscheid, Supplemental 
Statistical Analysis of ABFM-II Data for Lightning Launch Commit 
Criteria, Aerospace Report No. TOR-2007(1494)-6, 3 (2007).
    As a purely qualitative matter, out of 158 flights through non-
transparent debris or anvil clouds during ABFM-II, the field mills 
detected no electric field with a magnitude of greater than 3 kV/m 
outside of a cloud. This was so even though the sample contained 30 
flights through clouds with an electric field magnitude of more than 3 
kV/m somewhere inside the cloud. Id.
    Based on the data obtained, a qualitative analysis shows that 
flying more than 3 nautical miles from a non-transparent anvil cloud is 
as safe as the FAA's current requirements. The LAP also used this data 
to demonstrate statistically in two ways that it is extremely unlikely 
that the electric field magnitude will be more than 3 kV/m at distances 
greater than 3 nautical miles from the clouds.
    A launch operator may calculate VAHIRR to help determine whether it 
is safe to fly, even if there has been a relatively recent lightning 
discharge. If the VAHIRR is less than 10 dBZ-km (about 33 dBZ-kft), the 
probability of an electric field of greater than 3 kV/m occurring is 
less than 1 in 10,000. Dye et al., supra, 14.
    Calculating VAHIRR consists of multiplying the average cloud 
thickness and the average radar reflectivity found in a column with an 
11 kilometer by 11 kilometer cross-section centered on a point of 
interest, where the two sides are oriented north-south and east-west. 
Because 3 nautical miles is 5.52 kilometers, a VAHIRR box centered on a 
flight path more than 3 nautical miles from the anvil cloud's edge will 
not contain the anvil cloud and will, therefore, have a radar 
reflectivity of zero, meaning that the VAHIRR will be zero. Because 
zero is clearly less than +33 dBZ-kft, flight at more than 3 nautical 
miles from the cloud will be at least as safe as the current 
requirements of G417.9(b)(2) and G417.11(b)(2)(ii), which only require 
a VAHIRR of less than +33 dBZ-kft. James E. Dye, et al., Analysis of 
Proposed 2007-2008 Revisions to the Lightning Launch Commit Criteria 
for United States Space Launches, 13th Conference on Aviation, Range 
and Aerospace Meteorology 8.2, 2-3 (available at https://ams.confex.com/ams/88Annual/techprogram/programexpanded_474.htm) (2008); Francis J. 
Merceret, Risk Analysis of Proposed Reduction of Anvil and Debris Cloud 
LLCC Standoff Distances from Five to Three Miles, 1-2 (2007) (internal 
LAP memorandum).
    The LAP also performed a Gaussian statistical analysis on the 
electric field data collected between 6 kilometers (3.2 nautical miles) 
and 12 kilometers (6.5 nautical miles) from anvil and debris clouds in 
an attempt to determine the likelihood of various electric field 
magnitudes occurring at those distances from the clouds. The LAP found 
that an electric field of significance was highly unlikely.

[[Page 33145]]

    The LAP used a Gaussian distribution to perform a conservative 
three-sigma worst-case risk analysis by using an assumed mean of three 
times the measured mean and an assumed error estimate of three times 
the calculated error. The LAP concluded that, even with these 
conservative assumptions, the probability that an electric field with a 
magnitude of 3 kV/m would occur within 3.2 to 6.5 nautical miles of a 
non-transparent anvil or debris cloud was negligible; the probability 
of a field of even 2 kV/m was on the order of 10-7. Dye et 
al., supra, at 3-4. These probabilities were obtained by only analyzing 
non-transparent clouds that typically contain elevated electric fields, 
namely, those that somewhere contained electric fields greater than 3 
kV/m. Merceret, supra, at 2-6. The FAA concludes from this analysis 
that launches more than 3 nautical miles from anvil and debris clouds 
are unlikely to trigger lightning because it is extremely remote for 
the electric field to reach a magnitude of 3 kV/m at distances more 
than 3 nautical miles from these clouds.
    However, this analysis uses an unconventional technique for extreme 
value analysis. Gaussian analysis is not typically used to determine 
the likelihood of a quantity that is relatively far from any of the 
observed quantities. Therefore, the LAP also performed a second 
statistical analysis. Dye et al., supra, at 4-5.
    The LAP used a second statistical method to determine the 
probability of the electric field magnitude exceeding 3 kV/m at various 
distances from the anvil and debris clouds in increments of 0.6 
kilometers (0.32 nautical miles) and again found it extremely unlikely. 
O'Brien & Walterscheid, supra, at 7. Gaussian distributions are not 
necessarily well suited to extrapolating fits to the wings of a 
frequency distribution where the event frequency (in this case the 
frequency of fields exceeding 3 kV/m) is very small. A widely used 
function for extreme value estimation is the Weibull function. For each 
distance increment from the clouds, a 2-parameter Weibull distribution 
was a good statistical fit for the data. Extrapolating the tail of the 
Weibull shows how likely it would be at each increment to encounter an 
electric field with a magnitude greater than 3 kV/m. Even at 0.6 
kilometers (0.32 nautical miles) from the cloud's edge, the probability 
of exceeding 3 kV/m was on the order of 10-9. If only clouds 
containing an electric field of over 3 kV/m were considered, the 
calculated probability was somewhat lower, but this is most likely a 
statistical artifact relating to sample size. At 5.4 kilometers (2.9 
nautical miles), the probability was under 10-16 even if 
only clouds containing an electric field of over 3 kV/m were 
considered. O'Brien & Walterscheid, supra, at 7.
    Therefore, the FAA concludes that the risk of encountering electric 
field magnitudes greater than 3 kV/m is very small if the flight path 
is more than 3 nautical miles from the edge of an anvil or debris 
cloud. In fact, the Weibull fit analysis indicates that a launch would 
not likely encounter a field of 3 kV/m even if the flight path was at 
0.32 nautical miles from the cloud's edge, so the requirements to wait 
or satisfy the VAHIRR criteria on launches with flight paths more than 
3 nautical miles from a cloud's edge are not necessary.
iv. Reduced Restrictions on Launches With a Flight Path Within 3 
Nautical Miles of a Debris Cloud
    Analysis of the ABFM-II data has also demonstrated that satisfying 
the VAHIRR criteria can allow greater launch opportunities near a non-
transparent debris cloud that has discharged lightning. This change 
expands launch availability because at any distance from a cloud the 
regulations permit flight if the conditions satisfy the VAHIRR and 
temperature restrictions. For a flight path through a non-transparent 
debris cloud under old section G417.13(a), a launch operator must wait 
3 hours after detachment or a lightning discharge without exception. 
New section G417.13(a) requires a launch operator to wait 3 hours only 
if the operator cannot demonstrate that the VAHIRR is below 10 dBZ-km 
(+33 dBZ-kft) and that every portion of the non-transparent debris 
cloud at a slant distance within 5 nautical miles of the flight path is 
at altitudes where the cloud has temperatures of less than 0 degrees 
Celsius.
    For flight paths between 0 and 3 nautical miles from the debris 
cloud, the current section G417.13(b) requires waiting 3 hours unless 
the launch meets three conditions:
    1. There is at least one working field mill within 5 nautical miles 
of the cloud,
    2. The magnitude of the electric field measurements has been less 
than 1 kV/m for 15 minutes within 5 nautical miles of the cloud, and
    3. The maximum radar reflectivity has been less than 10 dBZ for 15 
minutes within 5 nautical miles of the cloud.
    The new requirements still allow the fulfillment of these three 
conditions as a method to avoid waiting the 3-hour period, but will 
also allow earlier flight if the operator meets the VAHIRR exception, 
and if every portion of the debris cloud at a slant distance within 5 
nautical miles of the flight path is at altitudes where the cloud has 
temperatures of less than 0 degrees Celsius.
    A VAHIRR measurement of less than 10 dBZ-km (or approximately 33 
dBZ-kft), along with satisfactory field mill measurements and 
temperatures, means that a debris cloud does not contain an elevated 
electric field, even if portions of it are located at an altitude 
conducive to the creation of an electric charge. In fact, the VAHIRR 
method may be even more reliable when applied to non-transparent debris 
clouds than to anvil clouds. To demonstrate this, the LAP used a 
Weibull distribution to show that the upper bound of the 95-percent-
confidence-interval for the probability of the electric field exceeding 
3 kV/m if the VAHIRR measurement is between 5 and 15 dBZ-km is on the 
order of 10-5 for debris clouds, as opposed to 
10-2 for anvil clouds. The expected value of the probability 
of exceeding 3 kV/m is much less. A more detailed examination 
demonstrated that the expected value of the probability of exceeding 3 
kV/m for anvil clouds is 10-4 if the VAHIRR is less than 10 
dBZ-km, so the probability of exceeding 3 kV/m for debris clouds is 
probably even lower than 10-5 if the VAHIRR is less than 10 
dBZ-km. Dye et al., supra, 4-5. Therefore, the FAA has concluded that 
it is appropriate to extend the availability of the VAHIRR exception to 
waiting to launch to debris clouds.
2. Changes for Launches With a Flight Path Within Three Nautical Miles 
of an Attached Anvil Cloud
    For flight paths within 3 nautical miles of a cold, non-transparent 
anvil cloud, the FAA will now permit flight within 30 minutes of a 
lightning discharge when temperature and VAHIRR readings satisfy the 
regulatory criteria. Therefore, for flight paths between 0 and 3 
nautical miles from a cloud, the new section G417.9(c) allows launch at 
any time if the VAHIRR is below 10 dBZ-km and every portion of the 
anvil cloud at a slant distance within 5 nautical miles of the flight 
path is at altitudes where the non-transparent cloud has temperatures 
of less than 0 degrees Celsius. The old rule requires waiting for 30 
minutes after lightning discharge if not passing through the non-
transparent cloud (current G417.9(a) and (b)) or 3 hours after 
lightning discharge if passing through the non-transparent cloud 
(current G417.9(c)) unless VAHIRR and temperature at altitude 
conditions are

[[Page 33146]]

met. The new requirements will allow VAHIRR and the temperature at 
altitude conditions to always be an alternative to having to wait after 
a lightning discharge. For detached non-transparent anvil clouds, the 
requirements remain the same for flight paths less than or equal to 3 
nautical miles except that now a launch operator can pass within 3 
nautical miles of the non-transparent cloud within 30 minutes of a 
lightning discharge if the VAHIRR is below 10 dBZ-km and every portion 
of the non-transparent cloud at a slant distance within 5 nautical 
miles of the flight path is at altitudes where the cloud has 
temperatures of less than 0 degrees Celsius. This change is contained 
in G417.11(c)(1). This change is possible because the studies of the 
ABFM-II campaign show, as discussed above, that electric fields greater 
than 3 kv/m do not extend as far and the decay rate is much more rapid 
near the anvil edge \6\ than previously believed. Cloud charges decay 
in time in the absence of active charge generation and, real-time radar 
reflectivity readings and calculations may be used to confirm that the 
electric field has, in fact, subsided to acceptable levels.
---------------------------------------------------------------------------

    \6\ Dye, J. E., et al. (2007), Electric fields, cloud 
microphysics, and reflectivity in anvils of Florida thunderstorms. 
J. Geophys. Res., 112, D11215, doi:10.1029/2006JD007550.
---------------------------------------------------------------------------

    The FAA will not require a launch operator to wait 30 minutes when 
temperature and VAHIRR readings satisfy the criteria for attached and 
detached non-transparent anvil clouds when the flight path is between 0 
and 3 nautical miles. As described above, statistical analysis of the 
ABFM II measurements for all anvils shows that, even for highly 
electrified anvils with electric fields much greater than 3 kV/m inside 
the cloud, the electric field outside of the anvil cloud falls off very 
rapidly and once falling to low levels remains small at greater 
distances. O'Brien. et. al. at 9. For attached and detached non-
transparent anvil clouds and debris clouds, when the electric field is 
strong, namely, when it exceeds 3 kV/m, the radar reflectivity in the 
same location over the ABFM II data set is invariably greater than 
approximately 10 dBZ. As noted, the Weibull distribution and extreme 
value analysis for anvil and debris clouds showed that, when VAHIRR is 
<= 10 dBZ-km, the probability of having electric fields in excess of 3 
Kv/m is very small (on the order of 10-4 or lower). Based on 
these results, the FAA finds that a launch that meets the VAHIRR 
criterion obviates concerns regarding electric fields in excess of 3 
kV/m. Strong electric fields are known to occur in the melting zone of 
many precipitating layer clouds.\7\ Satisfaction of the temperature 
requirement ensures that this type of electric charging within the 
melting zone will not occur.
---------------------------------------------------------------------------

    \7\ Rationales for Lightning Criteria, at 123.
---------------------------------------------------------------------------

3. Codification of Measurement Criteria
    New section G417.25 represents a codification of three different 
sets of measurement specifications. Section G417.25(a) contains 
requirements for accurate and reliable radar reflectivity measurements 
that qualify for use throughout the other sections of this appendix. In 
addition to VAHIRR calculations, such uses include all radar 
measurements of the location, spatial extent, and intensity of clouds 
and precipitation. Such specifications are currently applied by the 
U.S. Air Force and NASA at the Federal ranges and can also be met by 
correct application of data from the national Next-Generation Radar 
(NEXRAD) network.\8\ If the available radar does not meet these 
requirements, a launch operator must fall back on visual and other 
observations to convincingly demonstrate that the rules are not 
violated.
---------------------------------------------------------------------------

    \8\ NEXRAD is a network of 159 high-resolution Doppler weather 
radars operated by the National Weather Service, an agency of the 
National Oceanic and Atmospheric Administration (NOAA) within the 
United States Department of Commerce.
---------------------------------------------------------------------------

    Section G417.25(b) applies specifically to VAHIRR calculations and 
explains how valid VAHIRR measurements must be made. These 
specifications are the same as those used during the ABFM II of 2000 
and 2001 from which a safe VAHIRR threshold of <=10 dBZ-km was 
statistically determined for anvil and debris clouds. Because there is 
no guarantee that this threshold would be safe if VAHIRR were 
calculated operationally in a different way, the FAA is codifying these 
specifications here. See below, however, for an alternative calculation 
that is currently in use by the U.S. Air Force and NASA at the Eastern 
Range and that satisfies section G417.1(c) by being at least as safe as 
the FAA's requirements.
    Finally, section G417.25(c) specifies the measurement techniques 
for electric fields to qualify for use in this appendix. Again, these 
are the specifications currently used by the federal launch ranges.
    Section G417.25(a) requires that a licensee who relies on radar 
reflectivity measurements, including the calculation of VAHIRR, to 
increase launch availability must satisfy a number of requirements. The 
Federal launch ranges satisfy the requirements of paragraph (a) of this 
section because they employ meteorological radar,\9\ and they ensure 
that--
---------------------------------------------------------------------------

    \9\ The Federal launch ranges employ meteorological radars 
because other radars do not provide sufficient granularity in 
depicting reflectivity on a gridded representation.
---------------------------------------------------------------------------

    (1) The radar wavelength is greater than or equal to 5 centimeters 
in order that attenuation by intervening clouds and/or precipitation 
not be significant; \10\
---------------------------------------------------------------------------

    \10\ The radar used at the Eastern and Western Ranges is WSR-88D 
and WSR-74C. They meet this criterion.
---------------------------------------------------------------------------

    (2) Any reflectivity measurement is of a meteorological target, 
such as a cloud or precipitation, and not of some other objects, such 
as birds or insects, nor due to ``anomalous propagation''; \11\
---------------------------------------------------------------------------

    \11\ 45th Weather Squadron, Steps for Evaluating VAHIRR, par. 6 
(March 2005.
---------------------------------------------------------------------------

    (3) The spatial accuracy and resolution of a reflectivity 
measurement is one kilometer or better in order that the locations and 
spatial extent of clouds--especially their critical altitudes and 
thicknesses--and of precipitation can be determined with sufficient 
accuracy for use in this appendix; \12\
---------------------------------------------------------------------------

    \12\ Blakeslee, R.J., H.J. Christian, and B. Vonnegut (1989), 
Electrical measurements over thunderstorms, J. Geophys. Res., 94, 
135-140.
---------------------------------------------------------------------------

    (4) Any attenuation caused by precipitation or an accumulation of 
water or ice on the radome that protects the radar antenna is less than 
or equal to 1 dBZ because the requirements in this appendix can be met 
only with that degree of accuracy; \13\ and
---------------------------------------------------------------------------

    \13\ 45th Weather Squadron, Steps for Evaluating VAHIRR, Par. 2, 
(March 2005).
---------------------------------------------------------------------------

    (5) A reflectivity measurement contains no portion of the cone of 
silence or other blocked out portion so that it is not giving a bogus 
indication.\14\
---------------------------------------------------------------------------

    \14\ A History of the Lightning Criteria, 124, par. 25.
---------------------------------------------------------------------------

    A launch operator who relies on VAHIRR to increase launch 
availability under this appendix must satisfy the requirements of both 
sections G417.25(a) and (b), or must otherwise ensure that its 
estimates of VAHIRR are at least as large as those that would result 
from section G417.25(b) to ensure that its invocation of any VAHIRR 
exceptions to these rules are at least as safe. The current 
requirements for calculating VAHIRR at the Federal launch ranges 
satisfy section G417.1(c) because they are more conservative, even 
though there are certain requirements of section G417.25(b) that they 
do not satisfy. The Federal launch ranges do not, as required by 
paragraph (b)(1), ensure that a digital signal processor provide radar 
reflectivity measurements on a three-dimensional

[[Page 33147]]

Cartesian grid having a maximum grid-point-to-grid-point spacing of one 
kilometer in each of the three dimensions. The ranges do, as required 
by paragraph (b)(2), ensure that the specified volume is bounded in the 
horizontal by vertical plane, perpendicular sides located 5.5 
kilometers (3 nautical miles) north, east, south, and west of the point 
where VAHIRR is to be evaluated; on the bottom by the 0 degree Celsius 
level; and on the top by an altitude of 18 kilometers.\15\ Note that 
the specified volume need not contain the VAHIRR evaluation point, 
which may be either below the lower boundary of that volume (as when 
the vehicle is on the launch pad) or above the upper boundary (as when 
the vehicle is flying high above an anvil cloud) of the specified 
volume.
---------------------------------------------------------------------------

    \15\ Id.
---------------------------------------------------------------------------

    To calculate VAHIRR a launch operator must compute both a volume 
averaged radar reflectivity and an average cloud thickness in a 
specified volume before multiplying them to obtain a value for VAHIRR. 
Neither of these quantities is available yet as an output product of 
the WSR-88D.\16\ or WSR-74C radar systems that the Federal ranges use 
to support commercial launches.\17\ Instead, the Federal ranges and 
NASA rely on Interim Instructions \18\ for computing these quantities, 
which are more conservative and, thus, afford less launch availability 
than allowed by section G417.25(b).
---------------------------------------------------------------------------

    \16\ Technical name for NEXRAD is WSR-88D, which stands for 
Weather Surveillance Radar, 1988, Doppler.
    \17\ A History of the Lightning Criteria, 124, par. J.
    \18\ Id. (describing the interim methodology).
---------------------------------------------------------------------------

    Paragraph (c) of section G417.25 requires a launch operator who 
measures an electric field to comply with this appendix to--
     Employ a ground-based field mill in order to obtain a 
reliable and easily calibrated measurement with a relatively low-
maintenance instrument;
     Use only the one-minute arithmetic average of the 
instantaneous readings from that field mill to minimize the effects of 
local space charge and lightning field changes;
     Ensure that all field mills are calibrated so that the 
polarity of the electric field measurements is the same as the polarity 
of a voltage placed on a test plate above the sensor as discussed in 
more detail below;
     Ensure that the altitude of the flight path of the launch 
vehicle is equal to or less than 20 kilometers (66 thousand feet) 
everywhere above a horizontal circle of 5 nautical miles centered on 
the field mill being used as discussed further below, and
     Use only direct measurements from a field mill. A launch 
operator may not interpolate based on electric-field contours because 
interpolation schemes are highly variable and can give unexpected 
results.
    The Federal launch ranges use electric field mills that satisfy 
each of the requirements of paragraph (c) of section G417.25. 
Accordingly, no new methodology is being codified here.
    Regarding the polarity of an electric field measurement, note that 
the required polarity is the opposite of the so-called ``physics sign 
convention'' that is now used almost exclusively in the atmospheric 
electricity literature. This older sign convention is retained here, 
however, because it has been in exclusive use at the Kennedy Space 
Center and the Eastern Range since the early days of the Launch Pad 
Lightning Warning System and it remains in use today.
    The FAA is relaxing the requirements for field measurement by 
limiting the altitude of the flight path of the launch vehicle to less 
than 20 kilometers (66 thousand feet) everywhere above a horizontal 
circle of 5 nautical miles centered on the field mill. Electric field 
measurements above 20 kilometers are to be ignored.

Small Business Regulatory Enforcement Fairness Act

    The Small Business Regulatory Enforcement Fairness Act (SBREFA) of 
1996 requires the FAA to comply with small entity requests for 
information or advice about compliance with statutes and regulations 
within its jurisdiction. Therefore, any small entity that has a 
question regarding this document may contact their local FAA official, 
or the person listed under FOR FURTHER INFORMATION CONTACT. You can 
find out more about SBREFA on the Internet at https://www.faa.gov/regulations_policies/rulemaking/sbre_act/.

IV. Regulatory Analyses

Paperwork Reduction Act

    The Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) requires 
that the FAA consider the impact of paperwork and other information 
collection burdens imposed on the public. The FAA has determined that 
this final rule has no new additional burden to respondents over and 
above that which the Office of Management and Budget already approved 
under the existing rule titled, ``Commercial Space Transportation 
Licensing Regulations'' (OMB 2120-0608).

International Compatibility

    The FAA has determined that a review of the Convention on 
International Civil Aviation Standards and Recommended Practices is not 
warranted because there is not a comparable rule under ICAO standards.

Regulatory Evaluation, Regulatory Flexibility Determination, 
International Trade Regulatory Flexibility Determination

    Changes to Federal regulations must undergo several economic 
analyses. First, Executive Order 12866 directs that each Federal agency 
may propose or adopt a regulation only upon a reasoned determination 
that the benefits of the intended regulation justify its costs. Second, 
the Regulatory Flexibility Act of 1980 (Pub. L. 96-354) requires 
agencies to analyze the economic impact of regulatory changes on small 
entities. Third, the Trade Agreements Act (Pub. L. 96-39) prohibits 
agencies from setting standards that create unnecessary obstacles to 
the foreign commerce of the United States. In developing U.S. 
standards, the Trade Act requires agencies developing standards to 
consider international standards and, where appropriate, that they be 
the basis of U.S. standards. Fourth, the Unfu