Appendix G to Part 417 - Natural and Triggered Lightning Flight Commit Criteria
14:4.0.2.9.10.7.24.1.22 : Appendix G
Appendix G to Part 417 - Natural and Triggered Lightning Flight
Commit Criteria G417.1 General
This appendix provides flight commit criteria for mitigating
against natural lightning strikes and lightning triggered by the
flight of a launch vehicle through or near an electrified
environment. A launch operator may not initiate flight unless the
weather conditions at the time of launch satisfy all lightning
flight commit criteria of this appendix.
(a) In order to meet the lightning flight commit criteria, a
launch operator must employ any:
(1) Weather monitoring and measuring equipment needed, and
(2) Procedures needed to verify compliance.
(b) When equipment or procedures, such as a field mill or
calculation of the volume-averaged, height-integrated radar
reflectivity (VAHIRR) of clouds, are used with the lightning flight
commit criteria to increase launch opportunities, a launch operator
must evaluate all applicable measurements to determine whether the
measurements satisfy the criteria. A launch operator may not turn
off available instrumentation to create the appearance of meeting a
requirement and must use all radar reflectivity measurements within
a specified volume for a VAHIRR calculation.
(c) If a launch operator proposes any alternative lightning
flight commit criteria, the launch operator must clearly and
convincingly demonstrate that the alternative provides an
equivalent level of safety to that required by this appendix.
G417.3 Definitions
For the purpose of this appendix:
Anvil cloud means a stratiform or fibrous cloud formed by
the upper-level outflow or blow-off from a thunderstorm or
convective cloud.
Associated means two or more clouds are caused by the
same disturbed weather or are physically connected.
Bright band means an enhancement of radar reflectivity
caused by frozen hydrometeors falling and beginning to melt at any
altitude where the temperature is 0 degrees Celsius or warmer.
Cloud means a visible mass of suspended water droplets or
ice crystals, or a combination of water droplets and ice crystals.
The cloud is the entire volume containing such particles.
Cloud layer means a vertically continuous array of
clouds, not necessarily of the same type, whose bases are
approximately at the same altitude.
Cone of silence means the 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.
Debris cloud means any cloud, except an anvil cloud, that
has become detached from a parent cumulonimbus cloud or
thunderstorm, or that results from the decay of a parent
cumulonimbus cloud or thunderstorm.
Disturbed weather means a weather system where a
dynamical process destabilizes the air on a scale larger than the
individual clouds or cells. Examples of disturbed weather include
fronts, troughs, and squall lines.
Electric field means a vertical electric field (Ez) at
the surface of the Earth.
Field mill means an electric-field sensor that uses a
moving, grounded conductor to induce a time-varying electric charge
on one or more sensing elements in proportion to the ambient
electrostatic field.
Flight path means a launch vehicle's planned flight
trajectory, and includes the trajectory's vertical and horizontal
uncertainties resulting from all three-sigma guidance and
performance deviations.
Horizontal distance means 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.
Moderate precipitation means a precipitation rate of 0.1
inches/hr or a radar reflectivity of 30 dBZ.
Non-transparent means that one or more of the following
conditions apply:
(1) Objects above, including higher clouds, blue sky, and stars,
are blurred, indistinct, or obscured when viewed from below when
looking through a cloud at visible wavelengths; or objects below,
including terrain, buildings, and lights on the ground, are
blurred, indistinct, or obscured when viewed from above when
looking through a cloud at visible wavelengths;
(2) Objects above an observer are seen distinctly only through
breaks in a cloud; or
(3) The cloud has a radar reflectivity of 0 dBZ or greater.
Precipitation means detectable rain, snow, hail, graupel,
or sleet at the ground; virga; or a radar reflectivity greater than
18 dBZ.
Radar reflectivity means the radar reflectivity factor
due to hydrometeors, in dBZ.
Slant distance means the shortest distance between two
ports, whether horizontal, vertical, or inclined, in three
dimensional space.
Thick cloud layer means one or more cloud layers whose
combined vertical extent from the base of the bottom cloud layer to
the top of the uppermost cloud layer exceeds 4,500 feet. Cloud
layers are combined with neighboring layers for determining total
thickness only when they are physically connected by vertically
continuous clouds.
Thunderstorm means any convective cloud that produces
lightning.
Transparent means that any of the following conditions
apply:
(1) Objects above, including higher clouds, blue sky, and stars,
are not blurred, are distinct and are not obscured when viewed at
visible wavelengths; or objects below, including terrain,
buildings, and lights on the ground, are clear, distinct, and not
obscured when viewed at visible wavelengths; (2) Objects identified
in paragraph (1) of this definition are seen distinctly not only
through breaks in a cloud; and (3) The cloud has a radar
reflectivity of less than 0 dBZ.
Triboelectrification means the transfer of electrical
charge between ice particles and a launch vehicle when the ice
particles collide with the vehicle during flight.
Volume-averaged, height integrated radar reflectivity
(VAHIRR) means the product, expressed in units of dBZ-km or
dBZ-kft, of a volume-averaged radar reflectivity and an average
cloud thickness in a specified volume corresponding to a point.
G417.5 Lightning
(a) A launch operator must wait 30 minutes to initiate flight
after any type of lightning occurs in a thunderstorm if the flight
path will carry the launch vehicle at a slant distance of less than
or equal to 10 nautical miles from that thunderstorm. This
paragraph does not apply to an anvil cloud that is attached to a
parent thunderstorm.
(b) A launch operator must wait 30 minutes to initiate flight
after any type of lightning occurs at a slant distance of less than
or equal to 10 nautical miles from the flight path, unless:
(1) The non-transparent part of the cloud that produced the
lightning is at a slant distance of greater than 10 nautical miles
from the flight path;
(2) There is at least one working field mill at a horizontal
distance of less than or equal to 5 nautical miles from each such
lightning discharge; and
(3) The absolute values of all electric field measurements at a
horizontal distance of less than or equal to 5 nautical miles from
the flight path and at each field mill specified in paragraph
(b)(2) of this section have been less than 1000 volts/meter for at
least 15 minutes.
G417.7 Cumulus Clouds
(a) This section applies to non-transparent cumulus clouds,
except for cirrocumulus, altocumulus, or stratocumulus clouds. This
section does not apply to an anvil cloud that is attached to a
parent cumulus cloud.
(b) A launch operator may not initiate flight if the slant
distance to the flight path is less than or equal to 10 nautical
miles from any cumulus cloud that has a top at an altitude where
the temperature is colder than or equal to −20 degrees Celsius.
(c) A launch operator may not initiate flight if the slant
distance to the flight path is less than or equal to 5 nautical
miles from any cumulus cloud that has a top at an altitude where
the temperature is colder than or equal to −10 degrees Celsius.
(d) A launch operator may not initiate flight if the flight path
will carry the launch vehicle through any cumulus cloud with its
top at an altitude where the temperature is colder than or equal to
−5 degrees Celsius.
(e) A launch operator may not initiate flight if the flight path
will carry the launch vehicle through any cumulus cloud that has a
top at an altitude where the temperature is colder than or equal to
+ 5, and warmer than −5 degrees Celsius unless:
(1) The cloud is not producing precipitation;
(2) The horizontal distance from the center of the cloud top to
at least one working field mill is less than 2 nautical miles;
and
(3) All electric field measurements at a horizontal distance of
less than or equal to 5 nautical miles of the flight path and at
each field mill specified in paragraph (e)(2) of this section have
been between −100 volts/meter and + 500 volts/meter for at least 15
minutes.
G417.9 Attached Anvil Clouds
(a) This section applies to any non-transparent anvil cloud
formed from a parent cloud that has a top at an altitude where the
temperature is colder than or equal to −10 degrees Celsius.
(b) Flight path through cloud: If a flight path will carry a
launch vehicle through any attached anvil cloud, the launch
operator may not initiate flight unless:
(1) 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; and
(2) The volume-averaged, height-integrated radar reflectivity is
less than + 10 dBZ-km (+33 dBZ-kft) at every point at a slant
distance of less than or equal to 1 nautical mile from the flight
path.
(c) Flight path between 0 and 3 nautical miles from cloud: If a
flight path will carry a launch vehicle at a slant distance of
greater than 0, but less than or equal to 3, nautical miles from
any attached anvil cloud, a launch operator must wait 3 hours to
initiate flight after a lightning discharge in or from the parent
cloud or anvil cloud, unless:
(1) 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; and
(2) The volume-averaged, height-integrated radar reflectivity is
less than + 10 dBZ-km (+33 dBZ-kft) at every point at a slant
distance of less than or equal to 1 nautical mile from the flight
path.
(d) Flight path between 3 and 5 nautical miles from cloud: If a
flight path will carry a launch vehicle at a slant distance of
greater than 3 and less than or equal to 5 nautical miles from any
attached anvil cloud, a launch operator must wait 3 hours to
initiate flight after every lightning discharge in or from the
parent cloud or anvil cloud, unless 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.
(e) Flight path between 5 and 10 nautical miles from cloud: If
the flight path will carry the launch vehicle at a slant distance
of greater than 5 and less than or equal to 10 nautical miles from
any attached anvil cloud, the launch operator must wait to initiate
flight for 30 minutes after every lightning discharge in or from
the parent cloud or anvil cloud, 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.
G417.11 Detached Anvil Clouds
(a) This section applies to any non-transparent anvil cloud
formed from a parent cloud that had a top at an altitude where the
temperature was colder than or equal to −10 degrees Celsius.
(b) Flight path through cloud: If the flight path will carry the
launch vehicle through a detached anvil cloud, the launch operator
may not initiate flight unless:
(1) The launch operator waits 4 hours after every lightning
discharge in or from the detached anvil cloud; and observation
shows that 3 hours have passed since the anvil cloud detached from
the parent cloud; or
(2) Each of the following conditions exists:
(i) Any portion of the detached 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; and
(ii) The VAHIRR is less than +10 dBZ-km (+33 dBZ-kft) everywhere
in the flight path.
(c) Flight path between 0 and 3 nautical miles from cloud: If a
flight path will carry a launch vehicle at a slant distance of
greater than 0 and less than or equal to 3 nautical miles from a
detached anvil cloud, the launch operator must accomplish both of
the following:
(1) Wait 30 minutes to initiate flight after every lightning
discharge in or from the parent cloud or anvil cloud before
detachment of the anvil cloud, and after every lightning discharge
in or from the detached anvil cloud after detachment, unless:
(i) The portion of the detached anvil cloud 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;
and
(ii) The VAHIRR is less than + 10 dBZ-km (+33 dBZ-kft) at every
point at a slant distance of less than or equal to 1 nautical mile
from the flight path; and
(2) If a launch operator is unable to initiate flight in the
first 30 minutes under paragraph (c)(1) of this section, the launch
operator must wait to initiate flight for 3 hours after every
lightning discharge in or from the parent cloud or anvil cloud
before detachment of the anvil cloud, and after every lightning
discharge in or from the detached anvil cloud after detachment,
unless:
(i) All of the following are true:
(A) There is at least one working field mill at a horizontal
distance of less than or equal to 5 nautical miles from the
detached anvil cloud;
(B) The absolute values of all electric field measurements at a
horizontal distance of less than or equal to 5 nautical miles from
the flight path and at each field mill specified in paragraph
(c)(2)(i)(A) of this section have been less than 1000 V/m for at
least 15 minutes; and
(C) The maximum radar reflectivity from any part of the detached
anvil cloud at a slant distance of less than or equal to 5 nautical
miles from the flight path has been less than +10 dBZ for at least
15 minutes; or
(ii) Both of the following are true:
(A) The portion of the detached 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; and
(B) The volume-averaged, height-integrated radar reflectivity is
less than +10 dBZ-km (+33 dBZ-kft) at every point at a slant
distance of less than or equal to 1 nautical mile from the flight
path.
(d) Flight path between 3 and 10 nautical miles from cloud: If a
flight path will carry a launch vehicle at a slant distance of
greater than 3 and less than or equal to 10 nautical miles from a
detached anvil cloud, the launch operator must wait 30 minutes to
initiate flight after every lightning discharge in or from the
parent cloud or anvil cloud before detachment, and after every
lightning discharge in or from the detached anvil cloud after
detachment, 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.
G417.13 Debris Clouds
(a) This section applies to any non-transparent debris cloud
whose parent cumuliform cloud has had any part at an altitude where
the temperature was colder than −20 degrees Celsius or to any
debris cloud formed by a thunderstorm. This section does not apply
to a detached anvil cloud.
(b) A launch operator must calculate a “3-hour period” as
starting at the latest of the following times:
(1) The debris cloud is observed to be detached from the parent
cloud;
(2) The debris cloud is observed to have formed by the collapse
of the parent cloud top to an altitude where the temperature is
warmer than −10 degrees Celsius; or
(3) Any lightning discharge occurs in or from the debris
cloud.
(c) Flight path through cloud: If a flight path will carry a
launch vehicle through a debris cloud, the launch operator may not
initiate flight during the “3-hour period,” of paragraph (b) of
this section, unless:
(1) The portion of the debris 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; and
(2) The VAHIRR is less than +10 dBZ-km (+33 dBZ-kft) everywhere
in the flight path.
(d) Flight path between 0 and 3 nautical miles from cloud: If
the flight path will carry the launch vehicle at a slant distance
of greater than or equal to 0 and less than or equal to 3 nautical
miles from the debris cloud, the launch operator may not initiate
flight during the “3-hour period,” unless one of the following
applies:
(1) A launch operator may initiate flight during the “3-hour
period,” of paragraph (b) of this section if:
(i) There is at least one working field mill at a horizontal
distance of less than or equal to 5 nautical miles from the debris
cloud;
(ii) The absolute values of all electric field measurements at a
horizontal distance of less than or equal to 5 nautical miles from
the flight path and at each field mill specified in paragraph
(d)(1)(i) of this section have been less than 1000 volts/meter for
at least 15 minutes; and
(ii) The maximum radar reflectivity from any part of the debris
cloud less than or equal to a slant distance of 5 nautical miles
from the flight path has been less than + 10 dBZ for at least 15
minutes; or
(2) A launch operator may initiate flight during the “3-hour
period,” of paragraph (b) of this section if:
(i) The portion of the debris 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; and
(ii) The VAHIRR is less than +10 dBZ-km (+33 dBZ-kft) at every
point at a slant distance of less than or equal to 1 nautical mile
from the flight path.
G417.15 Disturbed Weather
A launch operator may not initiate flight if the flight path
will carry the launch vehicle through a non-transparent cloud
associated with disturbed weather that has clouds with tops at
altitudes where the temperature is colder than 0 degrees Celsius
and that contains, at a slant distance of less than or equal to 5
nautical miles from the flight path, either:
(a) Moderate or greater precipitation; or
(b) Evidence of melting precipitation such as a radar bright
band.
G417.17 Thick Cloud Layers
(a) This section does not apply to either attached or detached
anvil clouds.
(b) A launch operator may not initiate flight if the flight path
will carry the launch vehicle through a non-transparent cloud layer
that is:
(1) Greater than or equal to 4,500 feet thick and any part of
the cloud layer in the flight path is located at an altitude where
the temperature is between 0 degrees Celsius and −20 degrees
Celsius, inclusive; or
(2) Connected to a thick cloud layer that, at a slant distance
of less than or equal to 5 nautical miles from the flight path, is
greater than or equal to 4,500 feet thick and has any part located
at any altitude where the temperature is between 0 degrees Celsius
and −20 degrees Celsius, inclusive.
(c) A launch operator may initiate flight despite paragraphs
(a)(1) and (a)(2) of this section if the thick cloud layer:
(1) Is a cirriform cloud layer that has never been associated
with convective clouds,
(2) Is located entirely at altitudes where the temperature is
colder than or equal to −15 degrees Celsius, and
(3) Shows no evidence of containing liquid water.
G417.19 Smoke Plumes
(a) A launch operator may not initiate flight if the flight path
will carry the launch vehicle through any non-transparent cumulus
cloud that has developed from a smoke plume while the cloud is
attached to the smoke plume, or for the first 60 minutes after the
cumulus cloud is observed to be detached from the smoke plume.
(b) This section does not apply to non-transparent cumulus
clouds that have formed above a fire but have been detached from
the smoke plume for more than 60 minutes. Section G417.7
applies.
G417.21 Surface Electric Fields
(a) A launch operator must wait 15 minutes to initiate flight
after the absolute value of any electric field measurement at a
horizontal distance of less than or equal to 5 nautical miles from
the flight path has been greater than or equal to 1500
volts/meter.
(b) A launch operator must wait 15 minutes to initiate flight
after the absolute value of any electric field measurement at a
horizontal distance of less than or equal to 5 nautical miles from
the flight path has been greater than or equal to 1000 volts/meter,
unless:
(1) All clouds at a slant distance of less than or equal to 10
nautical miles from the flight path are transparent; or
(2) All non-transparent clouds at a slant distance less than or
equal to 10 nautical miles from the flight path:
(i) Have tops at altitudes where the temperature is warmer than
or equal to + 5 degrees Celsius, and
(ii) Have not been part of convective clouds with cloud tops at
altitudes where the temperature was colder than or equal to −10
degrees Celsius for 3 hours.
G417.23 Triboelectrification
(a) A launch operator may not initiate flight if the flight path
will carry the launch vehicle through any part of a cloud at any
altitude where:
(1) The temperature is colder than or equal to −10 degrees
Celsius; and
(2) The launch vehicle's velocity is less than or equal to 3000
feet/second,
(b) Paragraph (a) of this section does not apply if either:
(1) The launch vehicle is treated for surface electrification so
that:
(i) All surfaces of the launch vehicle susceptible to ice
particle impact are such that the surface resistivity is less than
10 9 Ohms per square; and
(ii) All conductors on surfaces, including dielectric surfaces
that have been coated with conductive materials, are bonded to the
launch vehicle by a resistance that is less than 10 5 ohms; or
(2) A launch operator demonstrates by test or analysis that
electrostatic discharges on the surface of the launch vehicle
caused by triboelectrification will not be hazardous to the launch
vehicle or the spacecraft.
G417.25 Measurement of Cloud Radar Reflectivity, Computation of
VAHIRR, and Measurement of Electric Field
(a) Radar reflectivity measurement. A launch operator who
measures radar reflectivity to comply with this appendix must
employ a meteorological radar and ensure that -
(1) The radar wavelength is greater than or equal to 5 cm;
(2) A reflectivity measurement is due to a meteorological
target;
(3) The spatial accuracy and resolution of a reflectivity
measurement is 1 kilometer or better;
(4) Any attenuation caused by intervening precipitation or by an
accumulation of water or ice on the radome is less than or equal to
1 dBZ; and
(5) A reflectivity measurement contains no portion of the cone
of silence above the radar antenna, nor any portion of any sector
that is blocked out for payload safety reasons.
(b) Computation of VAHIRR. A launch operator who measures
VAHIRR to comply with this appendix must ensure that -
(1) A digital signal processor provides radar reflectivity
measurements on a three-dimensional Cartesian grid having a maximum
grid-point-to-grid-point spacing of one kilometer in each of the
three dimensions;
(2) The specified volume is the volume 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 20 kilometers;
(3) Volume-averaged radar reflectivity is the arithmetic average
of the radar reflectivity measurements in dBZ at grid points within
the specified volume. A launch operator must include each grid
point within the specified volume in the average if and only if
that grid point has a radar reflectivity measurement equal to or
greater than 0 dBZ. If fewer than 10% of the grid points in the
specified volume have radar reflectivity measurements equal to or
greater than 0 dBZ, then the volume-averaged radar reflectivity is
either the maximum radar reflectivity measurement in the specified
volume, or 0 dBZ, whichever is greater.
(4) Average cloud thickness is the difference in kilometers or
thousands of feet between an average top and an average base of all
clouds in the specified volume, computed as follows:
(i) The cloud base to be averaged is the higher, at each
horizontal position, of either
(A) The 0 degree Celsius altitude, or
(B) The lowest altitude of all radar reflectivity measurements
of 0 dBZ or greater.
(ii) The cloud top to be averaged is the highest altitude of all
radar reflectivity measurements of 0 dBZ or greater at each
horizontal position.
(iii) A launch operator must -
(A) Take the cloud base at any horizontal position as the
altitude of the corresponding base grid point minus half of the
grid-point vertical separation;
(B) Take the cloud top at that horizontal position as the
altitude of the corresponding top grid point plus half of this
vertical separation.
(5) All VAHIRR-evaluation points in the flight path itself
are:
(i) Greater than a slant distance of 10 nautical miles from any
radar reflectivity of 35 dBZ or greater at altitudes of 4
kilometers or greater above mean sea level; and
(ii) Greater than a slant distance of 10 nautical miles from any
type of lightning that has occurred in the previous 5 minutes.
(iii) A launch operator need not apply paragraph (b)(5) of this
section to VAHIRR evaluation points outside the flight path but
within one nautical mile of the flight path.
(6) VAHIRR is the product, expressed in units of dBZ-km or
dBZ-kft, of the volume-averaged radar reflectivity defined in
paragraph (b)(3) of this section and the average cloud thickness
defined in paragraph (b)(4) of this section in the specified volume
defined in paragraph (b)(2) of this section.
(c) Electric field measurement. A launch operator who
measures an electric field to comply with this appendix must -
(1) Employ a ground-based field mill,
(2) Use only the one-minute arithmetic average of the
instantaneous readings from that field mill,
(3) 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,
(4) 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,
(5) Use only direct measurements from a field mill, and
(6) Not interpolate based on electric-field contours.
[Amdt. 417-2, 76 FR 33149, June 8, 2011]