<s>
Flight	B-Device
envelope	I-Device
protection	I-Device
is	O
a	O
human	B-Application
machine	I-Application
interface	I-Application
extension	O
of	O
an	O
aircraft	O
's	O
control	O
system	O
that	O
prevents	O
the	O
pilot	O
of	O
an	O
aircraft	O
from	O
making	O
control	O
commands	O
that	O
would	O
force	O
the	O
aircraft	O
to	O
exceed	O
its	O
structural	O
and	O
aerodynamic	O
operating	O
limits	O
.	O
</s>
<s>
The	O
professed	O
advantage	O
of	O
flight	B-Device
envelope	I-Device
protection	I-Device
systems	O
is	O
that	O
they	O
restrict	O
a	O
pilot	O
's	O
excessive	O
control	O
inputs	O
,	O
whether	O
in	O
surprise	O
reaction	O
to	O
emergencies	O
or	O
otherwise	O
,	O
from	O
translating	O
into	O
excessive	O
flight	O
control	O
surface	O
movements	O
.	O
</s>
<s>
Flight	B-Device
envelope	I-Device
protection	I-Device
calculates	O
that	O
flight	O
envelope	O
(	O
and	O
adds	O
a	O
margin	O
of	O
safety	O
)	O
and	O
uses	O
this	O
information	O
to	O
stop	O
pilots	O
from	O
making	O
control	O
inputs	O
that	O
would	O
put	O
the	O
aircraft	O
outside	O
that	O
flight	O
envelope	O
.	O
</s>
<s>
The	O
interference	O
of	O
the	O
flight	B-Device
envelope	I-Device
protection	I-Device
system	O
with	O
the	O
pilot	O
's	O
commands	O
can	O
happen	O
in	O
two	O
different	O
ways	O
(	O
which	O
can	O
also	O
be	O
combined	O
)	O
:	O
</s>
<s>
For	O
example	O
,	O
if	O
the	O
pilot	O
uses	O
the	O
rearward	O
side-stick	O
to	O
pitch	O
the	O
aircraft	O
nose	O
up	O
,	O
the	O
control	O
computers	O
creating	O
the	O
flight	B-Device
envelope	I-Device
protection	I-Device
can	O
prevent	O
the	O
pilot	O
pitching	O
the	O
aircraft	O
beyond	O
the	O
stalling	O
angle	O
of	O
attack	O
:	O
</s>
<s>
In	O
the	O
first	O
case	O
,	O
if	O
the	O
pilot	O
tries	O
to	O
apply	O
even	O
more	O
rearward	O
control	O
,	O
the	O
flight	B-Device
envelope	I-Device
protection	I-Device
would	O
cause	O
the	O
aircraft	O
to	O
ignore	O
this	O
command	O
.	O
</s>
<s>
Flight	B-Device
envelope	I-Device
protection	I-Device
can	O
in	O
this	O
way	O
increase	O
aircraft	O
safety	O
by	O
allowing	O
the	O
pilot	O
to	O
apply	O
maximum	O
control	O
forces	O
in	O
an	O
emergency	O
while	O
not	O
at	O
the	O
same	O
time	O
inadvertently	O
putting	O
the	O
aircraft	O
outside	O
the	O
margins	O
of	O
its	O
operational	O
safety	O
.	O
</s>
<s>
In	O
this	O
case	O
without	O
a	O
flight	B-Device
envelope	I-Device
protection	I-Device
system	O
,	O
"	O
you	O
would	O
probably	O
hold	O
back	O
from	O
maneuvering	O
as	O
hard	O
as	O
you	O
could	O
for	O
fear	O
of	O
tumbling	O
out	O
of	O
control	O
,	O
or	O
worse	O
.	O
</s>
<s>
when	O
using	O
a	O
force-feedback-system	O
to	O
communicate	O
with	O
the	O
pilot	O
,	O
if	O
the	O
pilot	O
tries	O
to	O
apply	O
even	O
more	O
rearward	O
control	O
,	O
the	O
flight	B-Device
envelope	I-Device
protection	I-Device
would	O
present	O
increasing	O
counterforces	O
on	O
the	O
controls	O
so	O
that	O
the	O
pilot	O
has	O
to	O
apply	O
increasing	O
force	O
in	O
order	O
to	O
continue	O
the	O
control	O
input	O
that	O
is	O
perceived	O
as	O
dangerous	O
by	O
the	O
flight	B-Device
envelope	I-Device
protection	I-Device
.	O
</s>
<s>
While	O
most	O
designers	O
of	O
modern	O
fly-by-wire	O
aircraft	O
stick	O
to	O
either	O
one	O
of	O
these	O
two	O
solutions	O
( 	O
 '	O
sidestick-control	O
&	O
no	O
feedback	O
 '	O
or	O
'	O
conventional	O
control	O
&	O
feedback	O
 '	O
,	O
see	O
also	O
below	O
)	O
,	O
there	O
are	O
also	O
approaches	O
in	O
science	O
to	O
combine	O
both	O
of	O
them	O
:	O
As	O
a	O
study	O
demonstrated	O
,	O
force-feedback	B-Device
applied	O
to	O
the	O
side-stick	O
of	O
an	O
aircraft	O
controlled	O
via	O
roll	O
rate	O
and	O
g-load	O
(	O
as	O
e.g.	O
</s>
<s>
In	O
the	O
Airbus	O
,	O
the	O
flight	B-Device
envelope	I-Device
protection	I-Device
cannot	O
be	O
overridden	O
completely	O
,	O
although	O
the	O
crew	O
can	O
fly	O
beyond	O
flight	O
envelope	O
limits	O
by	O
selecting	O
an	O
alternate	O
"	O
control	O
law	O
"	O
.	O
</s>
<s>
One	O
objection	O
raised	O
against	O
flight	B-Device
envelope	I-Device
protection	I-Device
is	O
the	O
incident	O
that	O
happened	O
to	O
China	O
Airlines	O
Flight	O
006	O
,	O
a	O
Boeing	O
747SP-09	O
,	O
northwest	O
of	O
San	O
Francisco	O
in	O
1985	O
.	O
</s>
<s>
incorporated	O
a	O
flight	B-Device
envelope	I-Device
protection	I-Device
system	O
,	O
this	O
excessive	O
manoeuvre	O
could	O
not	O
have	O
been	O
performed	O
,	O
greatly	O
reducing	O
chances	O
of	O
recovery	O
.	O
</s>
<s>
The	O
NTSB	O
accident	O
report	O
mentions	O
the	O
effect	O
of	O
flight	B-Device
envelope	I-Device
protection	I-Device
:	O
"	O
The	O
airplane	O
’s	O
airspeed	O
in	O
the	O
last	O
150	O
feet	O
of	O
the	O
descent	O
was	O
low	O
enough	O
to	O
activate	O
the	O
alpha-protection	O
mode	O
of	O
the	O
airplane	O
’s	O
fly-by-wire	O
envelope	O
protection	O
features	O
...	O
Because	O
of	O
these	O
features	O
,	O
the	O
airplane	O
could	O
not	O
reach	O
the	O
maximum	O
angle	O
of	O
attack	O
(	O
AoA	O
)	O
attainable	O
in	O
pitch	O
normal	O
law	O
for	O
the	O
airplane	O
weight	O
and	O
configuration	O
;	O
however	O
,	O
the	O
airplane	O
did	O
provide	O
maximum	O
performance	O
for	O
the	O
weight	O
and	O
configuration	O
at	O
that	O
time	O
...	O
</s>
<s>
The	O
flight	B-Device
envelope	I-Device
protections	I-Device
allowed	O
the	O
captain	O
to	O
pull	O
full	O
aft	O
on	O
the	O
sidestick	O
without	O
the	O
risk	O
of	O
stalling	O
the	O
airplane.	O
"	O
</s>
