Home' RTCA Documents for Review : DO-204B, MOPS Aircraft ELT 406MHZ Contents © EUROCAE, 2018
1) testing to ensure that the ELT system will survive the crash environment
and will function properly (including automatic activation, if provided)
during and after a crash, and,
2) testing to ensure that during a crash sequence, the ELT system
components will remain safely in their mounting and, if appropriate, be
activated by any associated crash sensor(s).
220.127.116.11 Shock – Crash Acceleration Sensors
18.104.22.168.1.1 When testing the crash sensor system, include all circuitry related to the sensor, including
the transmitter power switching device. Testing should include all components of the ELT
system, as mounted in their production configuration. If the sensor is internal to the ELT,
then the entire ELT unit shall be tested.
22.214.171.124.1.2 The test procedure described in § 126.96.36.199.3 applies to the forward direction of the
airframe only. Test procedures for other directions are described in § 188.8.131.52.7.
The crash sensor response curves for fixed wing aircraft (FIGURE 5-4)
and helicopters (FIGURE 5-6) are with respect to the forward direction of
184.108.40.206.1.3 A technique to determine the crash acceleration sensor threshold acceleration level (Gth)
and the minimum velocity change (ΔVmin) required to cause the sensor to activate is
Threshold Acceleration Level
Establish the threshold acceleration level (Gth) for the crash activation sensor,
b. Minimum Velocity Change
Establish the minimum velocity change (ΔVmin) at which the crash acceleration
sensor activates (§ 220.127.116.11.4).
18.104.22.168.1.4 During § 22.214.171.124.1.3.3.a. above, the crash acceleration sensor is subjected to various
constant g pulses. The duration of the g pulse should be selected to ensure that the
velocity change which the crash acceleration sensor experience is well above the
minimum required for activation.
126.96.36.199.1.5 During § 188.8.131.52.1.3.b. above, tests are conducted at g levels above the threshold level
determined during § 184.108.40.206.1.3.a., above, but at varying velocity changes until the
minimum velocity change, (ΔVmin), is found.
220.127.116.11.1.6 Automatic crash activation test procedures are simplified if a square shock wave pulse is
used. For other than square pulse shapes, the peak magnitude shall be greater than that
for a square wave to obtain the same velocity change (ΔV) during the same time period.
It is recognised that crash pulses generated during impact are of varied shapes and not
necessarily square. However, the square pulse shape is considered adequate for
evaluating sensor activation.
18.104.22.168.2 Measurement Method
22.214.171.124.2.1 The threshold acceleration level may be determined by use of a suitable item of test
equipment e.g.: shock tester, electrodynamic shaker or centrifuge.
126.96.36.199.2.2 The crash acceleration sensor is mounted on a shock tester. A shock pulse is applied
and the response of the table and sensor are measured and recorded as acceleration, (in
g), versus time. Sensor activation is monitored and recorded. Data on average
acceleration g., pulse duration (TP) and velocity change (ΔV) are derived.
188.8.131.52.2.3 Data Specifications
The following data are required.
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