Federal Aviation Administration, DOT

Section 121.321

than one exit, provided the proximity
of the exits allows unassisted verbal
communication between seated flight
attendants;
(e) Is capable of operation within 10
seconds by a flight attendant at each of
those stations in the passenger compartment from which its use is accessible;
(f) Is audible at all passenger seats,
lavatories, and flight attendant seats
and work stations; and
(g) For transport category airplanes
manufactured on or after November 27,
1990, meets the requirements of Section 25.1423
of this chapter.
[Doc. No. 24995, 54 FR 43926, Oct. 27, 1989]

Section 121.319 Crewmember interphone system.
(a) No person may operate an airplane with a seating capacity of more
than 19 passengers unless the airplane
is equipped with a crewmember interphone system that:
(1) [Reserved]
(2) Is capable of operation independent of the public address system
required by Section 121.318(a) except for
handsets, headsets, microphones, selector switches, and signaling devices; and
(3) Meets the requirements of paragraph (b) of this section.
(b) The crewmember interphone system required by paragraph (a) of this
section must be approved in accordance
with Section 21.305 of this chapter and meet
the following requirements:
(1) It must provide a means of twoway communication between the pilot
compartment and - 
(i) Each passenger compartment; and
(ii) Each galley located on other than
the main passenger deck level.
(2) It must be accessible for immediate use from each of two flight crewmember stations in the pilot compartment;
(3) It must be accessible for use from
at least one normal flight attendant
station in each passenger compartment;
(4) It must be capable of operation
within 10 seconds by a flight attendant
at those stations in each passenger
compartment from which its use is accessible; and
(5) For large turbojet-powered airplanes:

(i) It must be accessible for use at
enough flight attendant stations so
that all floor-level emergency exits (or
entryways to those exits in the case of
exits located within galleys) in each
passenger compartment are observable
from one or more of those stations so
equipped;
(ii) It must have an alerting system
incorporating aural or visual signals
for use by flight crewmembers to alert
flight attendants and for use by flight
attendants to alert flight crewmembers;
(iii) The alerting system required by
paragraph (b)(5)(ii) of this section must
have a means for the recipient of a call
to determine whether it is a normal
call or an emergency call; and
(iv) When the airplane is on the
ground, it must provide a means of
two-way
communication
between
ground personnel and either of at least
two flight crewmembers in the pilot
compartment. The interphone system
station for use by ground personnel
must be so located that personnel
using the system may avoid visible detection from within the airplane.
[Doc. No. 10865, 38 FR 21494, Aug. 9, 1973, as
amended by Amdt. 121-121, 40 FR 42186, Sept.
11, 1975; Amdt. 121-149, 43 FR 50602, Oct. 30,
1978; Amdt. 121-178, 47 FR 13316, Mar. 29, 1982;
Amdt. 121-253, 61 FR 2611, Jan. 26, 1996]

Section 121.321 Operations in icing.
After October 21, 2013, no person may
operate an airplane with a certificated
maximum takeoff weight less than
60,000 pounds in conditions conducive
to airframe icing unless it complies
with this section. As used in this section, the phrase  - conditions conducive
to airframe icing -  means visible moisture at or below a static air temperature of 5 SectionC or a total air temperature
of 10 SectionC, unless the approved Airplane
Flight Manual provides another definition.
(a) When operating in conditions conducive to airframe icing, compliance
must be shown with paragraph (a)(1),
or (2), or (3) of this section.
(1) The airplane must be equipped
with a certificated primary airframe
ice detection system.
(i) The airframe ice protection system must be activated automatically,
or manually by the flightcrew, when

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