725 

Federal Aviation Administration, DOT 

§ 91.219 

operating automatic pressure altitude 
reporting equipment having a Mode C 
capability, the request may be made at 
any time. 

(2) For operation of an aircraft with 

an inoperative transponder to the air-
port of ultimate destination, including 
any intermediate stops, or to proceed 
to a place where suitable repairs can be 
made or both, the request may be made 
at any time. 

(3) For operation of an aircraft that 

is not equipped with a transponder, the 
request must be made at least one hour 
before the proposed operation. 

(e) 

Unmanned aircraft. (1) The require-

ments of paragraph (b) of this section 
do not apply to a person operating an 
unmanned aircraft under this part un-
less the operation is conducted under a 
flight plan and the person operating 
the unmanned aircraft maintains two- 
way communication with ATC. 

(2) No person may operate an un-

manned aircraft under this part with a 
transponder on unless: 

(i) The operation is conducted under 

a flight plan and the person operating 
the unmanned aircraft maintains two- 
way communication with ATC; or 

(ii) The use of a transponder is other-

wise authorized by the Administrator. 

(Approved by the Office of Management and 
Budget under control number 2120–0005) 

[Doc. No. 18334, 54 FR 34304, Aug. 18, 1989, as 
amended by Amdt. 91–221, 56 FR 469, Jan. 4, 
1991; Amdt. 91–227, 56 FR 65660, Dec. 17, 1991; 
Amdt. 91–227, 7 FR 328, Jan. 3, 1992; Amdt. 91– 
229, 57 FR 34618, Aug. 5, 1992; Amdt. 91–267, 66 
FR 21066, Apr. 27, 2001; Amdt. 91–355, 84 FR 
34287, July 18, 2019; Amdt. No. 91–361, 86 FR 
4512, Jan. 15, 2021; Docket No. FAA–2023–1836; 
Amdt. No. 91–371, 88 FR 71476, Oct. 17, 2023] 

§ 91.217

Data correspondence between 

automatically reported pressure al-
titude data and the pilot’s altitude 
reference. 

(a) No person may operate any auto-

matic pressure altitude reporting 
equipment associated with a radar bea-
con transponder— 

(1) When deactivation of that equip-

ment is directed by ATC; 

(2) Unless, as installed, that equip-

ment was tested and calibrated to 
transmit altitude data corresponding 
within 125 feet (on a 95 percent prob-
ability basis) of the indicated or cali-
brated datum of the altimeter nor-

mally used to maintain flight altitude, 
with that altimeter referenced to 29.92 
inches of mercury for altitudes from 
sea level to the maximum operating al-
titude of the aircraft; or 

(3) Unless the altimeters and 

digitizers in that equipment meet the 
standards of TSO-C10b and TSO-C88, re-
spectively. 

(b) No person may operate any auto-

matic pressure altitude reporting 
equipment associated with a radar bea-
con transponder or with ADS–B Out 
equipment unless the pressure altitude 
reported for ADS–B Out and Mode C/S 
is derived from the same source for air-
craft equipped with both a transponder 
and ADS–B Out. 

[Doc. No. 18334, 54 FR 34304, Aug. 18, 1989, as 
amended by Amdt. 91–314, 75 FR 30193, May 
28, 2010] 

§ 91.219

Altitude alerting system or de-

vice: Turbojet-powered civil air-
planes. 

(a) Except as provided in paragraph 

(d) of this section, no person may oper-
ate a turbojet-powered U.S.-registered 
civil airplane unless that airplane is 
equipped with an approved altitude 
alerting system or device that is in op-
erable condition and meets the require-
ments of paragraph (b) of this section. 

(b) Each altitude alerting system or 

device required by paragraph (a) of this 
section must be able to— 

(1) Alert the pilot— 
(i) Upon approaching a preselected 

altitude in either ascent or descent, by 
a sequence of both aural and visual sig-
nals in sufficient time to establish 
level flight at that preselected alti-
tude; or 

(ii) Upon approaching a preselected 

altitude in either ascent or descent, by 
a sequence of visual signals in suffi-
cient time to establish level flight at 
that preselected altitude, and when de-
viating above and below that 
preselected altitude, by an aural sig-
nal; 

(2) Provide the required signals from 

sea level to the highest operating alti-
tude approved for the airplane in which 
it is installed; 

(3) Preselect altitudes in increments 

that are commensurate with the alti-
tudes at which the aircraft is operated; 

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