Home' RTCA Documents for Review : DO-204B, MOPS Aircraft ELT 406MHZ Contents © EUROCAE, 2018
ELT(AD) not in ADFR shall be buoyant and, when floating in fresh water or salt water,
shall be self-righting and sufficiently stable to maintain the antenna substantially in its
normal operating position.
For ELT(AD) in ADFR, this requirement is replaced by ED-112(), section 3-3.2.8.
An internal or integral antenna is required and may not be rigidly fixed to the aircraft
before a crash. If an external antenna is needed to transmit without deployment, it
shall be rigidly fixed to the aircraft.
Distress Tracking (DT) ELT
18.104.22.168 ELT(DT) functional specifications
The ELT(DT) shall be capable of being armed/disarmed upon reception of a signal
from an aircraft system (e.g. automatic triggering system). Once armed, it shall have
the means to automatically activate the ELT transmitter upon command from the
automatic triggering system or if the communication connections to the automatic
triggering system is lost and radiate a signal through an antenna. ELT(DT) shall stop
transmitting an alert signal and shall start transmitting a cancellation signal only when
the cancellation command is from the same means that activated it, as specified per
C/S T.018 and T.001 as applicable. Once disarmed, it will not begin transmitting
based on any command from the automatic triggering system nor will it begin
transmitting if the communication connections to the automatic triggering system is
Whatever its arming state, the ELT(DT) shall activate when manually triggered by the
crew or upon detection of post-crash conditions except in OFF mode.
An ELT(DT) with crash survivability shall continue 406 MHz satellite transmissions
upon crash condition detection. The required endurance time for 406 MHz satellite
transmission shall be 24 hours for the combined flight and post-crash time.
The ELT(DT) shall have an input disabling it and overriding the routine arming logic.
The intent is to avoid inadvertent activation of the ELT(DT) during maintenance or
flight tests, and also make the controls for the input inaccessible during routine flight
An ELT(DT) shall transmit an encoded location as defined in C/S T.018 or C/S T.001
The ELT system shall incorporate an external, integral or internal antenna. Means
shall be provided to prevent antennas from interfering with normal operation of the
aircraft or with its occupants. If the antenna is not attached directly to the ELT unit, it
shall be connected to the ELT unit by means of a suitable RF cable resistant to
disconnection during normal operations (see § 2.9.6), distress conditions, and, if the
ELT(DT) has the crash survivability capability, accident events.
If fitted with a homing capability, the homing signal shall be transmitted following the
ELT activation and detection of a post-crash condition. Acceptable means for
detection of a post-crash condition are for example: static GNSS position for more
than one minute (provided that the GNSS position is actually being updated at least
once every 5 seconds over this period of time), water-detection or crash-sensor
activation. If the ELT(DT) is automatically activated, homing signals shall not be
transmitted while the aircraft is still in flight.
22.214.171.124 Functional Interface(s)
An ELT(DT) shall incorporate one or more interfaces to aircraft systems and/or the
flight deck controls.
Required Interface Functions
An ELT(DT) shall have an interface(s) for the following functions (either as separate
electrical discrete or coded on a digital bus).
Receive a triggering command from the automatic triggering system.
Provide information that an automatic trigger was received.
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