FAA Federal Aviation Regulations (FARS, 14 CFR)

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Symbol                   Unit                    Meaning
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antilog...............  ......................  Antilogarithm to the
base 10.
C(k)..................  dB....................  Tone correction factor.
The factor to be added
to PNL(k) to account
for the presence of
spectral irregularities
such as tones at the k-
th increment of time.
d.....................  s.....................  Duration time. The time
interval between the
limits of t(1) and t(2)
to the nearest 0.5
second.
D.....................  dB....................  Duration correction. The
factor to be added to
PNLTM to account for
the duration of the
noise.
EPNL..................  EPNdB.................  Effective perceived
noise level. The value
of PNL adjusted for
both spectral
irregularities and
duration of the noise.
(The unit EPNdB is used
instead of the unit
dB).
EPNL[INF]r[/INF]......  EPNdB.................  Effective perceived
noise level adjusted
for reference
conditions.
f(i)..................  Hz....................  Frequency. The
geometrical mean
frequency for the i-th
one-third octave band.
F (i, k)..............  dB....................  Delta-dB. The difference
between the original
sound pressure level
and the final
background sound
pressure level in the i-
th one-third octave
band at the k-th
interval of time. In
this case, background
sound pressure level
means the broadband
noise level that would
be present in the one-
third octave band in
the absence of the
tone.
h.....................  dB....................  dB-down. The value to be
subtracted from PNLTM
that defines the
duration of the noise.
H.....................  Percent...............  Relative humidity. The
ambient atmospheric
relative humidity.
i.....................  ......................  Frequency band index.
The numerical indicator
that denotes any one of
the 24 one-third octave
bands with geometrical
mean frequencies from
50 to 10,000 Hz.
k.....................  ......................  Time increment index.
The numerical indicator
that denotes the number
of equal time
increments that have
elapsed from a
reference zero.
Log...................  ......................  Logarithm to the base
10.
log n(a)..............  ......................  Noy discontinuity
coordinate. The log n
value of the
intersection point of
the straight lines
representing the
variation of SPL with
log n.
M(b), M(c), etc.......  ......................  Noy inverse slope. The
reciprocals of the
slopes of straight
lines representing the
variation of SPL with
log n.
n.....................  noy...................  The perceived noisiness
at any instant of time
that occurs in a
specified frequency.
n(i,k)................  noy...................  The percieved noisiness
at the k-th instant of
time that occurs in the
i-th one-third octave
band.
n(k)..................  noy...................  Maximum perceived
noisiness. The maximum
value of all of the 24
values of n(i) that
occurs at the k-th
instant of time.
N(k)..................  noy...................  Total perceived
noisiness. The total
perceived noisiness at
the k-th instant of
time calculated from
the 24-instantaneous
values of n (i, k).
p(b), p(c), etc.......  ......................  Noy slope. The slopes of
straight lines
representing the
variation of SPL with
log n.
PNL...................  PNdB..................  The perceived noise
level at any instant of
time. (The unit PNdB is
used instead of the
unit dB).
PNL(k)................  PNdB..................  The perceived noise
level calculated from
the 24 values of SPL
(i, k), at the k-th
increment of time. (The
unit PNdB is used
instead of the unit
dB).
PNLM..................  PNdB..................  Maximum perceived noise
level. The maximum
value of PNL(k). (The
unit PNdB is used
instead of the unit
dB).
PNLT..................  TPNdB.................  Tone-corrected perceived
noise level. The value
of PNL adjusted for the
spectral irregularities
that occur at any
instant of time. (The
unit TPNdB is used
instead of the unit
dB).
PNLT(k)...............  TPNdB.................  The tone-corrected
perceived noise level
that occurs at the k-th
increment of time.
PNLT(k) is obtained by
adjusting the value of
PNL(k) for the spectral
irregularities that
occur at the k-th
increment of time. (The
unit TPNdB is used
instead of the unit
dB).
PNLTM.................  TPNdB.................  Maximum tone-corrected
perceived noise level.
The maximum value of
PNLT(k). (The unit
TPNdB is used instead
of the unit dB).
PNLT[INF]r[/INF]......  TPNdB.................  Tone-corrected perceived
noise level adjusted
for reference
conditions.
s (i, k)..............  dB....................  Slope of sound pressure
level. The change in
level between adjacent
one-third octave band
sound pressure levels
at the i-th band for
the k-th instant of
time.
[Delta]s (i, k).......  dB....................  Change in slope of sound
pressure level.
s[prime] (i, k).......  dB....................  Adjusted slope of sound
pressure level. The
change in level between
adjacent adjusted one-
third octave band sound
pressure levels at the
i-th band for the k-th
instant of time.
s (i, k)..............  dB....................  Average slope of sound
pressure level.
SPL...................  dB re.................  Sound pressure level.
20 μPa.............   The sound pressure
level that occurs in a
specified frequency
range at any instant of
time.
SPL(a)................  dB re.................  Noy discontinuity
20 μPa.............   coordinate. The SPL
value of the
intersection point of
the straight lines
representing the
variation of SPL with
log n.
SPL(b)................  dB re.................  Noy intercept. The
SPL (c)...............  20 μPa.............   intercepts on the SPL-
axis of the straight
lines representing the
variation of SPL with
log n.
SPL (i, k)............  dB re.................  The sound pressure level
20 μPa.............   at the k-th instant of
time that occurs in the
i-th one-third octave
band.
SPL[prime] (i, k).....  dB re.................  Adjusted sound pressure
20 μPa.............   level. The first
approximation to
background sound
pressure level in the i-
th one-third octave
band for the k-th
instant of time.
SPL(i)................  dB re.................  Maximum sound pressure
20 μPa.............   level. The sound
pressure level that
occurs in the i-th one-
third octave band of
the spectrum for PNLTM.
SPL(i)[INF]r[/INF]....  dB re.................  Corrected maximum sound
20 μPa.............   pressure level. The
sound pressure level
that occurs in the i-th
one-third octave band
of the spectrum for
PNLTM corrected for
atmospheric sound
absorption.
SPL[prime] (i, k).....  dB re.................  Final background sound
20 μPa.............   pressure level. The
second and final
approximation to
background sound
pressure level in the i-
th one-third octave
band for the k-th
instant of time.
t.....................  s.....................  Elapsed time. The length
of time measured from a
reference zero.
t(1), t(2)............  s.....................  Time limit. The
beginning and end,
respectively, of the
noise time history
defined by h.
[Delta]t..............  s.....................  Time increment. The
equal increments of
time for which PNL(k)
and PNLT(k) are
calculated.
T.....................  s.....................  Normalizing time
constant. The length of
time used as a
reference in the
integration method for
computing duration
corrections, where
T=10s.
t( °F) ( °C)   °F, °C.....  Temperature. The ambient
air temperature.
[alpha](i)............  dB/1000ft db/100m.....  Test atmospheric
absorption. The
atmospheric attenuation
of sound that occurs in
the i-th one-third
octave band at the
measured air
temperature and
relative humidity.
[alpha](i)[INF]o[/INF]  dB/1000ft db/100m.....  Reference atmospheric
absorption. The
atmospheric attenuation
of sound that occurs in
the i-th one-third
octave band at a
reference air
temperature and
relative humidity.
A[INF]1[/INF].........  Degrees...............  First constant climb
angle (Gear up, speed
of at least V[INF]2[/
INF]+10 kt (V[INF]2[/
INF]+19 km/h), takeoff
thrust).
A[INF]2[/INF].........  Degrees...............  Second constant climb
angle (Gear up, speed
of at least V[INF]2[/
INF]+10 kt (V[INF]2[/
INF]+19 km/h), after
cut-back).
[delta]...............  Degrees...............  Thrust cutback angles.
[egr].................                           The angles defining the
points on the takeoff
flight path at which
thrust reduction is
started and ended
respectively.
[eta].................  Degrees...............  Approach angle.
[eta][INF]r[/INF].....  Degrees...............  Reference approach
angle.
[thetas]..............  Degrees...............  Noise angle (relative to
flight path). The angle
between the flight path
and noise path. It is
identical for both
measured and corrected
flight paths.
[psi].................  Degrees...............  Noise angle (relative to
ground). The angle
between the noise path
and the ground. It is
identical for both
measured and corrected
flight paths.
μ..................  ......................  Engine noise emission
parameter.
μ[INF]r[/INF]......  ......................  Reference engine noise
emission parameter.
[Delta][INF]1[/INF]...  EPNdB.................  PNLT correction. The
correction to be added
to the EPNL calculated
from measured data to
account for noise level
changes due to
differences in
atmospheric absorption
and noise path length
between reference and
test conditions.
[Delta][INF]2[/INF]...  EPNdB.................  Adjustment to duration
correction. The
adjustment to be made
to the EPNL calculated
from measured data to
account for noise level
changes due to the
noise duration between
reference and test
conditions.
[Delta][INF]3[/INF]...  EPNdB.................  Source noise adjustment.
The adjustment to be
made to the EPNL
calculated from
measured data to
account for noise level
changes due to
differences between
reference and test
engine operating
conditions.
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