Home' RTCA Documents for Review : DO-204B, MOPS Aircraft ELT 406MHZ Contents © EUROCAE, 2018
Shock acceleration in g versus time.
b. Start of shock event.
Crash sensor activation in the form of ON or OFF signal.
The basic data will be used to derive velocity change, mean acceleration levels and
22.214.171.124.2.4 Equipment and Instrumentation
In addition to a shock tester or centrifuge, the following equipment is required:
Accelerometer, for shock or centrifuge measurements, having an accuracy of
+1% and a minimum frequency response range of 0 to 750 Hz.
b. Dual trace storage oscilloscope with scope-mounted camera or equivalent
Signal conditioning equipment appropriate to equipment used.
d. Event switch to establish start time for shock.
126.96.36.199.3 Procedure – Airframe forward direction
188.8.131.52.3.1 The following procedure uses a square wave shock pulse with the threshold level
184.108.40.206.3.2 Use of a centrifuge can simplify the procedure by determining the threshold g level in
essentially one test, followed by a repetitive test, as necessary, to verify results.
220.127.116.11.3.3 Threshold Level Determination
Mount the crash acceleration sensor rigidly on the shock tester with the active
axis pointed in the direction of the applied shock force.
b. The monitoring accelerometer shall be rigidly mounted on the shock tester, and
in close proximity to the crash acceleration sensor, to ensure valid
measurement of the crash sensor shock.
Subject the sensor to a constant acceleration test of sufficient duration to
exceed the velocity change which is required to activate the sensor. During the
shock, monitor and record the activation status of the sensor.
d. Conduct a sufficient number of tests at various constant acceleration levels, as
described in the preceding paragraph, until sensor activation threshold is noted.
18.104.22.168.4 Velocity Change Determination
Mount the crash acceleration sensor rigidly on the shock table with the active
axis pointed in the direction of the applied shock force. If the crash acceleration
sensor is internal to the ELT, then the applied shock force shall be directed
along the airframe forward direction in accordance with the manufacturer’s
b. The monitoring accelerometer shall be rigidly mounted to the shock tester and
in close proximity to the sensor to ensure valid measurements of the crash
Subject the sensor to a shock pulse having an average acceleration greater
than the threshold acceleration determined from (§ 22.214.171.124.3.3), above. Monitor
and record the activation status of the sensor. Calculate the velocity change
experienced by the sensor during the shock test using a procedure similar to
that outlined in FIGURE 4-1 for a square wave, (trapezoid).
d. Conduct a sufficient number of tests in accordance with the preceding
paragraph at various velocity change levels. Record the activation status of the
sensor. Reduce the data in accordance with the procedures outlined in FIGURE
4-1. As a minimum, an activation and a non-activation pulse shall be applied at
each of the following g levels, (+/-1 g):
Fixed-wing aircraft: 3 g, 6 g, 9 g, 12 g;
Helicopters: 7 g, 9 g, 12 g.
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