First, neither your question nor your code makes it clear (to me, anyway; YMMV) precisely what you're trying to do; what the result of all this processing is supposed to provide, other than "values in @powers."

But, in hopes your answers may shed some light on the matter:
In your line 7, did you intend for $i < @in; to be $i < $#in; ?
... or, maybe $i < ( $#in + 1 );?
@in is the entire array; not a count of elements See replies :-(

And does this -- in any way -- resemble what you want?

#!/usr/bin/perl
use Modern::Perl;
use Data::Dumper;

# 942489

my @in= qw/1 2 3 4 5 6 7 8 9 10 11 1.155031267e-5 13 14
           101 102 103 104 105 106 107 108 109 110 111 1.13 113 114
           181 182 183 184 185 186 187 188 189 190 191 0.192 193 194/;

my $MaxAgc0 = "1.15503129132678e-005";           # MaxAgc0 is a consta
+nt
my @Attn; 
my @powers;

for ( my $i = 0; $i < $#in; $i += 14  ) {
    for ( my $j = 1; $j <= $in[$i]; $j++ ){       # $j is *WHAT ?*
        my $num = ( $in[$i+12]*$MaxAgc0  );
        push @Attn, $num / $in[$i + 10];
    }
}

for (my $i = 0; $i < $#in; $i += 14) {
    push @powers, ( $in[$i + $_] - $Attn[$i] ) / 100 for (2..9); 
}

say "\@Attn next" . "-" x20;
print Dumper @Attn;
say "\@powers next" . "~" x20;
print Dumper @powers;
[download]

Output

@Attn next--------------------
$VAR1 = '1.36503698065892e-005';
$VAR2 = '1.17584266594528e-005';
$VAR3 = '1.17584266594528e-005';
$VAR4 = '1.17584266594528e-005';
$VAR5 = '1.17584266594528e-005';
$VAR6 = '1.17584266594528e-005';
$VAR7 = '1.17584266594528e-005';
...
$VAR101 = '1.17584266594528e-005';
$VAR102 = '1.17584266594528e-005';
$VAR103 = '1.16712585982235e-005';  # value changes
$VAR104 = '1.16712585982235e-005';
$VAR105 = '1.16712585982235e-005';
...
$VAR282 = '1.16712585982235e-005';
$VAR283 = '1.16712585982235e-005';
@powers next~~~~~~~~~~~~~~~~~~~~
$VAR1 = '0.0299998634963019';
$VAR2 = '0.0399998634963019';
$VAR3 = '0.0499998634963019';
$VAR4 = '0.0599998634963019';
$VAR5 = '0.0699998634963019';
$VAR6 = '0.0799998634963019';
$VAR7 = '0.0899998634963019';
$VAR8 = '0.0999998634963019';
$VAR9 = '1.02999988241573';
$VAR10 = '1.03999988241573';
$VAR11 = '1.04999988241573';
$VAR12 = '1.05999988241573';
$VAR13 = '1.06999988241573';
$VAR14 = '1.07999988241573';
$VAR15 = '1.08999988241573';
$VAR16 = '1.09999988241573';
$VAR17 = '1.82999988241573';
$VAR18 = '1.83999988241573';
$VAR19 = '1.84999988241573';
$VAR20 = '1.85999988241573';
$VAR21 = '1.86999988241573';
$VAR22 = '1.87999988241573';
$VAR23 = '1.88999988241573';
$VAR24 = '1.89999988241573';
[download]

WAG: Given your reference to a "set", could it be that @in is supposed to be an AoA?

And, given the recommendation that SOPW include a minimal sample of code and data which reproduce the problem, why bother with the else clause when @in is (pseudo-)instantiated at your line 2?