931
Federal Aviation Administration, DOT
Pt. 36, App. A
D
log
T
antilog
PNLT
10
t 1
=
⎛
⎝
⎞
⎠
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
−
( )
( )
∫
10
1
2
t
dt
PNLTM
where T is a normalizing time constant,
PNLTM is the maximum value of PNLT,
t(1) is the first point of time after which
PNLT becomes greater than PNLTM–10,
and t(2) is the point of time after which
PNLT remains constantly less than
PNLTM–10.
A36.4.5.2 Since PNLT is calculated from
measured values of sound pressure level
(SPL), there is no obvious equation for
PNLT as a function of time. Consequently,
the equation is to be rewritten with a sum-
mation sign instead of an integral sign as
follows:
D
10 log
1
T
t.antilog
PNLTM
d/ t
=
⎛
⎝
⎞
⎠
( )
⎡
⎣
⎢
⎤
⎦
⎥ −
=
∑
Δ
Δ
k
PNLT k
0
10
where
Dt is the length of the equal incre-
ments of time for which PNLT(k) is cal-
culated and d is the time interval to the
nearest 0.5s during which PNLT(k) re-
mains greater or equal to PNLTM–10.
A36.4.5.3 To obtain a satisfactory history of
the perceived noise level use one of the fol-
lowing:
(a) Half-Second time intervals for
Dt; or
(b) A shorter time interval with approved
limits and constants.
A36.4.5.4 The following values for T and
Dt
must be used in calculating D in the equa-
tion given in section A36.4.5.2:
T=10 s, and
Dt=0.5s (or the approved sampling time inter-
val).
Using these values, the equation for D be-
comes:
D = 10 log
antilog
PNLT k
10
PNLTM
2d
k
=
∑
( )
⎡
⎣
⎢
⎤
⎦
⎥ −
−
0
13
where d is the duration time defined by the
points corresponding to the values
PNLTM–10.
A36.4.5.5 If in using the procedures given in
section A36.4.5.2, the limits of PNLTM–10 fall
between the calculated PNLT(k) values (the
usual case), the PNLT(k) values defining the
limits of the duration interval must be cho-
sen from the PNLT(k) values closest to
PNLTM–10. For those cases with more than
one peak value of PNLT(k), the applicable
limits must be chosen to yield the largest
possible value for the duration time.
A36.4.6
Effective perceived noise level.
The total subjective effect of an airplane
noise event, designated effective perceived
noise level, EPNL, is equal to the algebraic
sum of the maximum value of the tone-cor-
rected perceived noise level, PNLTM, and
the duration correction D. That is:
EPNL=PNLTM+D
where PNLTM and D are calculated using
the procedures given in sections A36.4.2,
A36.4.3, A36.4.4. and A36.4.5.
A36.4.7
Mathematical formulation of noy ta-
bles.
A36.4.7.1 The relationship between sound
pressure level (SPL) and the logarithm of
perceived noisiness is illustrated in Figure
A36–3 and Table A36–3.
A36.4.7.2 The bases of the mathematical
formulation are:
(a) The slopes (M(b), M(c), M(d) and M(e))
of the straight lines;
(b) The intercepts (SPL(b) and SPL(c)) of
the lines on the SPL axis; and
(c) The coordinates of the discontinuities,
SPL(a) and log n(a); SPL(d) and log n=¥1.0;
and SPL(e) and log n=log (0.3).
A36.4.7.3 Calculate noy values using the
following equations:
(a)
SPL
≥
SPL (a)
n=antilog
{
(c)[SPL¥SPL(c)]
}
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