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122 

14 CFR Ch. I (1–1–18 Edition) 

§ 121.331 

a flight altitude that will allow suc-
cessful termination of the flight. 

(4) Following the failure, the cabin 

pressure altitude is considered to be 
the same as the flight altitude unless it 
is shown that no probable failure of the 
cabin or pressurization equipment will 
result in a cabin pressure altitude 
equal to the flight altitude. Under 
those circumstances, the maximum 
cabin pressure altitude attained may 
be used as a basis for certification or 
determination of oxygen supply, or 
both. 

(b)  Crewmembers.  Each certificate 

holder shall provide a supply of oxygen 
for crewmembers in accordance with 
the following: 

(1) At cabin pressure altitudes above 

10,000 feet, up to and including 12,000 
feet, oxygen must be provided for and 
used by each member of the flight crew 
on flight deck duty and must be pro-
vided for other crewmembers for that 
part of the flight at those altitudes 
that is of more than 30 minutes dura-
tion. 

(2) At cabin pressure altitudes above 

12,000 feet, oxygen must be provided 
for, and used by, each member of the 
flight crew on flight deck duty, and 
must be provided for other crew-
members during the entire flight at 
those altitudes. 

(3) When a flight crewmember is re-

quired to use oxygen, he must use it 
continuously except when necessary to 
remove the oxygen mask or other dis-
penser in connection with his regular 
duties. Standby crewmembers who are 
on call or are definitely going to have 
flight deck duty before completing the 
flight must be provided with an 
amount of supplemental oxygen equal 
to that provided for crewmembers on 
duty other than on flight duty. If a 
standby crewmember is not on call and 
will not be on flight deck duty during 
the remainder of the flight, he is con-
sidered to be a passenger for the pur-
poses of supplemental oxygen require-
ments. 

(c) Passengers. Each certificate holder 

shall provide a supply of oxygen for 
passengers in accordance with the fol-
lowing: 

(1) For flights at cabin pressure alti-

tudes above 10,000 feet, up to and in-
cluding 14,000 feet, enough oxygen for 

that part of the flight at those alti-
tudes that is of more than 30 minutes 
duration, for 10 percent of the pas-
sengers. 

(2) For flights at cabin pressure alti-

tudes above 14,000 feet, up to and in-
cluding 15,000 feet, enough oxygen for 
that part of the flight at those alti-
tudes for 30 percent of the passengers. 

(3) For flights at cabin pressure alti-

tudes above 15,000 feet, enough oxygen 
for each passenger carried during the 
entire flight at those altitudes. 

§ 121.331

Supplemental oxygen re-

quirements for pressurized cabin 
airplanes: Reciprocating engine 
powered airplanes. 

(a) When operating a reciprocating 

engine powered airplane pressurized 
cabin, each certificate holder shall 
equip the airplane to comply with 
paragraphs (b) through (d) of this sec-
tion in the event of cabin pressuriza-
tion failure. 

(b)  For crewmembers. When operating 

at flight altitudes above 10,000 feet, the 
certificate holder shall provide enough 
oxygen for each crewmember for the 
entire flight at those altitudes and not 
less than a two-hour supply for each 
flight crewmember on flight deck duty. 
The required two hours supply is that 
quantity of oxygen necessary for a con-
stant rate of descent from the air-
plane’s maximum certificated oper-
ating altitude to 10,000 feet in ten min-
utes and followed by 110 minutes at 
10,000 feet. The oxygen required by 
§ 121.337 may be considered in deter-
mining the supplemental breathing 
supply required for flight crewmembers 
on flight deck duty in the event of 
cabin pressurization failure. 

(c)  For passengers. When operating at 

flight altitudes above 8,000 feet, the 
certificate holder shall provide oxygen 
as follows: 

(1) When an airplane is not flown at 

a flight altitude above flight level 250, 
enough oxygen for 30 minutes for 10 
percent of the passengers, if at any 
point along the route to be flown the 
airplane can safely descend to a flight 
altitude of 14,000 feet or less within 
four minutes. 

(2) If the airplane cannot descend to 

a flight altitude of 14,000 feet or less 

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