<s>
Avionics	B-Application
software	I-Application
is	O
embedded	B-Architecture
software	I-Architecture
with	O
legally	O
mandated	O
safety	O
and	O
reliability	O
concerns	O
used	O
in	O
avionics	O
.	O
</s>
<s>
The	O
main	O
difference	O
between	O
avionic	O
software	B-Application
and	O
conventional	O
embedded	B-Architecture
software	I-Architecture
is	O
that	O
the	O
development	O
process	O
is	O
required	O
by	O
law	O
and	O
is	O
optimized	O
for	O
safety	O
.	O
</s>
<s>
It	O
is	O
claimed	O
that	O
the	O
process	O
described	O
below	O
is	O
only	O
slightly	O
slower	O
and	O
more	O
costly	O
(	O
perhaps	O
15	O
percent	O
)	O
than	O
the	O
normal	O
ad	O
hoc	O
processes	O
used	O
for	O
commercial	O
software	B-Application
.	I-Application
</s>
<s>
Since	O
most	O
software	B-Application
fails	O
because	O
of	O
mistakes	O
,	O
eliminating	O
the	O
mistakes	O
at	O
the	O
earliest	O
possible	O
step	O
is	O
also	O
a	O
relatively	O
inexpensive	O
and	O
reliable	O
way	O
to	O
produce	O
software	B-Application
.	I-Application
</s>
<s>
The	O
basic	O
idea	O
of	O
any	O
software	B-Application
development	O
model	O
is	O
that	O
each	O
step	O
of	O
the	O
design	O
process	O
has	O
outputs	O
called	O
"	O
deliverables.	O
"	O
</s>
<s>
For	O
an	O
overview	O
of	O
embedded	B-Architecture
software	I-Architecture
see	O
embedded	B-Architecture
system	I-Architecture
and	O
software	B-Application
development	O
models	O
.	O
</s>
<s>
The	O
rest	O
of	O
this	O
article	O
assumes	O
familiarity	O
with	O
that	O
information	O
,	O
and	O
discusses	O
differences	O
between	O
commercial	O
embedded	B-Architecture
systems	I-Architecture
and	O
commercial	O
development	O
models	O
.	O
</s>
<s>
Since	O
most	O
avionics	O
manufacturers	O
see	O
software	B-Application
as	O
a	O
way	O
to	O
add	O
value	O
without	O
adding	O
weight	O
,	O
the	O
importance	O
of	O
embedded	B-Architecture
software	I-Architecture
in	O
avionic	O
systems	O
is	O
increasing	O
.	O
</s>
<s>
The	O
reliability	O
of	O
the	B-Application
software	I-Application
running	O
in	O
airborne	O
vehicles	O
(	O
civil	O
or	O
military	O
)	O
is	O
shown	O
by	O
the	O
fact	O
that	O
most	O
airborne	O
accidents	O
occur	O
due	O
to	O
manual	O
errors	O
.	O
</s>
<s>
Unfortunately	O
reliable	O
software	B-Application
is	O
not	O
necessarily	O
easy	O
to	O
use	O
or	O
intuitive	O
,	O
poor	O
user	O
interface	O
design	O
has	O
been	O
a	O
contributing	O
cause	O
of	O
many	O
aerospace	O
accidents	O
and	O
deaths	O
.	O
</s>
<s>
the	O
FAA	O
,	O
CAA	O
,	O
or	O
DOD	O
)	O
require	O
software	B-Application
development	O
standards	O
.	O
</s>
<s>
The	O
regulatory	O
requirements	O
for	O
this	O
software	B-Application
can	O
be	O
expensive	O
compared	O
to	O
other	O
software	B-Application
,	O
but	O
they	O
are	O
usually	O
the	O
minimum	O
that	O
is	O
required	O
to	O
produce	O
the	O
necessary	O
safety	O
.	O
</s>
<s>
The	O
main	O
difference	O
between	O
avionics	B-Application
software	I-Application
and	O
other	O
embedded	B-Architecture
systems	I-Architecture
is	O
that	O
the	O
actual	O
standards	O
are	O
often	O
far	O
more	O
detailed	O
and	O
rigorous	O
than	O
commercial	O
standards	O
,	O
usually	O
described	O
by	O
documents	O
with	O
hundreds	O
of	O
pages	O
.	O
</s>
<s>
Since	O
the	O
process	O
is	O
legally	O
required	O
,	O
most	O
processes	O
have	O
documents	O
or	O
software	B-Application
to	O
trace	O
requirements	O
from	O
numbered	O
paragraphs	O
in	O
the	O
specifications	O
and	O
designs	O
to	O
exact	O
pieces	O
of	O
code	O
,	O
with	O
exact	O
tests	O
for	O
each	O
,	O
and	O
a	O
box	O
on	O
the	O
final	O
certification	O
checklist	O
.	O
</s>
<s>
Almost	O
all	O
software	B-Application
development	O
standards	O
describe	O
how	O
to	O
perform	O
and	O
improve	O
specifications	O
,	O
designs	O
,	O
coding	O
,	O
and	O
testing	O
(	O
See	O
software	B-Application
development	O
model	O
)	O
.	O
</s>
<s>
However	O
avionics	B-Application
software	I-Application
development	O
standards	O
add	O
some	O
steps	O
to	O
the	O
development	O
for	O
safety	O
and	O
certification	O
:	O
</s>
<s>
Safety-critical	O
avionics	O
usually	O
have	O
a	O
hazard	B-Device
analysis	I-Device
.	O
</s>
<s>
Projects	O
involving	O
military	O
cryptographic	O
security	O
usually	O
include	O
a	O
security	O
analysis	O
,	O
using	O
methods	O
very	O
like	O
the	O
hazard	B-Device
analysis	I-Device
.	O
</s>
<s>
These	O
are	O
usually	O
much	O
like	O
those	O
in	O
other	O
software	B-Application
development	O
models	O
.	O
</s>
<s>
The	O
code	O
is	O
also	O
often	O
examined	O
by	O
special	O
programs	O
that	O
analyze	O
correctness	O
(	O
Static	O
code	O
analysis	O
)	O
,	O
such	O
as	O
SPARK	B-Language
examiner	I-Language
for	O
the	O
SPARK	B-Language
(	O
a	O
subset	O
of	O
the	O
Ada	O
programming	O
language	O
)	O
or	O
lint	B-Device
for	O
the	O
C-family	O
of	O
programming	O
languages	O
(	O
primarily	O
C	O
,	O
though	O
)	O
.	O
</s>
<s>
The	O
compilers	B-Language
or	O
special	O
checking	O
programs	O
like	O
"	O
lint	B-Device
"	O
check	O
to	O
see	O
if	O
types	O
of	O
data	O
are	O
compatible	O
with	O
the	O
operations	O
on	O
them	O
,	O
also	O
such	O
tools	O
are	O
regularly	O
used	O
to	O
enforce	O
strict	O
usage	O
of	O
valid	O
programming	O
language	O
subsets	O
and	O
programming	O
styles	O
.	O
</s>
<s>
Another	O
set	O
of	O
programs	O
measure	O
software	B-Application
metrics	O
,	O
to	O
look	O
for	O
parts	O
of	O
the	O
code	O
that	O
are	O
likely	O
to	O
have	O
mistakes	O
.	O
</s>
<s>
Some	O
code	O
,	O
such	O
as	O
digital	O
filters	O
,	O
graphical	B-Application
user	I-Application
interfaces	I-Application
and	O
inertial	O
navigation	O
systems	O
,	O
are	O
so	O
well	O
understood	O
that	O
software	B-Application
tools	O
have	O
been	O
developed	O
to	O
write	O
the	B-Application
software	I-Application
.	O
</s>
<s>
In	O
these	O
cases	O
,	O
specifications	O
are	O
developed	O
and	O
reliable	O
software	B-Application
is	O
produced	O
automatically	O
.	O
</s>
<s>
"	O
Unit	O
test	O
"	O
code	O
is	O
written	O
to	O
exercise	O
every	O
instruction	O
of	O
the	O
code	O
at	O
least	O
once	O
to	O
get	O
100%	O
code	B-Application
coverage	I-Application
.	O
</s>
<s>
It	O
forces	O
detailed	O
review	O
of	O
the	O
program	O
logic	O
,	O
and	O
detects	O
most	O
coding	O
,	O
compiler	B-Language
and	O
some	O
design	O
errors	O
.	O
</s>
<s>
Some	O
organizations	O
write	O
the	O
unit	O
tests	O
before	O
writing	O
the	O
code	O
,	O
using	O
the	B-Application
software	I-Application
design	O
as	O
a	O
module	O
specification	O
.	O
</s>
<s>
Next	O
,	O
the	O
most	O
valuable	O
features	O
of	O
the	B-Application
software	I-Application
are	O
integrated	O
.	O
</s>
<s>
Meanwhile	O
,	O
the	O
test	O
engineers	O
usually	O
begin	O
assembling	O
a	O
test	O
rig	O
,	O
and	O
releasing	O
preliminary	O
tests	O
for	O
use	O
by	O
the	B-Application
software	I-Application
engineers	O
.	O
</s>
<s>
The	O
first	O
test	O
of	O
the	B-Application
software	I-Application
,	O
and	O
one	O
of	O
the	O
most	O
difficult	O
to	O
meet	O
in	O
a	O
tight	O
schedule	O
,	O
is	O
a	O
realistic	O
test	O
of	O
the	O
unit	O
's	O
radio	O
emissions	O
.	O
</s>
<s>
The	B-Application
software	I-Application
is	O
also	O
subjected	O
to	O
a	O
structural	B-Application
coverage	I-Application
analysis	O
,	O
where	O
test	O
's	O
are	O
run	O
and	O
code	B-Application
coverage	I-Application
is	O
collected	O
and	O
analysed	O
.	O
</s>
<s>
When	O
the	B-Application
software	I-Application
passes	O
all	O
of	O
its	O
tests	O
(	O
or	O
enough	O
to	O
be	O
sold	O
safely	O
)	O
,	O
these	O
are	O
bound	O
into	O
a	O
certification	O
report	O
,	O
that	O
can	O
literally	O
have	O
thousands	O
of	O
pages	O
.	O
</s>
<s>
If	O
it	O
is	O
,	O
he	O
signs	O
it	O
,	O
and	O
the	O
avionic	O
software	B-Application
is	O
certified	O
.	O
</s>
