282 

14 CFR Ch. I (1–1–19 Edition) 

§ 25.783 

(2) Each door that could be a hazard 

if it unlatches must be designed so that 
unlatching during pressurized and un-
pressurized flight from the fully closed, 
latched, and locked condition is ex-
tremely improbable. This must be 
shown by safety analysis. 

(3) Each element of each door oper-

ating system must be designed or, 
where impracticable, distinctively and 
permanently marked, to minimize the 
probability of incorrect assembly and 
adjustment that could result in a mal-
function. 

(4) All sources of power that could 

initiate unlocking or unlatching of any 
door must be automatically isolated 
from the latching and locking systems 
prior to flight and it must not be pos-
sible to restore power to the door dur-
ing flight. 

(5) Each removable bolt, screw, nut, 

pin, or other removable fastener must 
meet the locking requirements of 
§ 25.607. 

(6) Certain doors, as specified by 

§ 25.807(h), must also meet the applica-
ble requirements of §§ 25.809 through 
25.812 for emergency exits. 

(b) 

Opening by persons. 

There must be 

a means to safeguard each door against 
opening during flight due to inad-
vertent action by persons. In addition, 
design precautions must be taken to 
minimize the possibility for a person to 
open a door intentionally during flight. 
If these precautions include the use of 
auxiliary devices, those devices and 
their controlling systems must be de-
signed so that— 

(1) No single failure will prevent 

more than one exit from being opened; 
and 

(2) Failures that would prevent open-

ing of the exit after landing are im-
probable. 

(c) 

Pressurization prevention means. 

There must be a provision to prevent 
pressurization of the airplane to an un-
safe level if any door subject to pres-
surization is not fully closed, latched, 
and locked. 

(1) The provision must be designed to 

function after any single failure, or 
after any combination of failures not 
shown to be extremely improbable. 

(2) Doors that meet the conditions 

described in paragraph (h) of this sec-
tion are not required to have a dedi-

cated pressurization prevention means 
if, from every possible position of the 
door, it will remain open to the extent 
that it prevents pressurization or safe-
ly close and latch as pressurization 
takes place. This must also be shown 
with any single failure and malfunc-
tion, except that— 

(i) With failures or malfunctions in 

the latching mechanism, it need not 
latch after closing; and 

(ii) With jamming as a result of me-

chanical failure or blocking debris, the 
door need not close and latch if it can 
be shown that the pressurization loads 
on the jammed door or mechanism 
would not result in an unsafe condi-
tion. 

(d) 

Latching and locking. 

The latching 

and locking mechanisms must be de-
signed as follows: 

(1) There must be a provision to latch 

each door. 

(2) The latches and their operating 

mechanism must be designed so that, 
under all airplane flight and ground 
loading conditions, with the door 
latched, there is no force or torque 
tending to unlatch the latches. In addi-
tion, the latching system must include 
a means to secure the latches in the 
latched position. This means must be 
independent of the locking system. 

(3) Each door subject to pressuriza-

tion, and for which the initial opening 
movement is not inward, must— 

(i) Have an individual lock for each 

latch; 

(ii) Have the lock located as close as 

practicable to the latch; and 

(iii) Be designed so that, during pres-

surized flight, no single failure in the 
locking system would prevent the 
locks from restraining the latches nec-
essary to secure the door. 

(4) Each door for which the initial 

opening movement is inward, and 
unlatching of the door could result in a 
hazard, must have a locking means to 
prevent the latches from becoming dis-
engaged. The locking means must en-
sure sufficient latching to prevent 
opening of the door even with a single 
failure of the latching mechanism. 

(5) It must not be possible to position 

the lock in the locked position if the 
latch and the latching mechanism are 
not in the latched position. 

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