The ACK E-04 406 mhz unit I installed specified a maximum amount of deflection when a given load is placed on the mounting member.
RTCA document DO-204 paragraph 3.1.8. prescribes the mounting requirements which
must be met when installing this ELT, these requirements are as follows:
The ELT shall be mounted to primary load-carrying structures such as trusses, bulkheads,
longerons, spars, or floor beams. (not aircraft skin.) The mounts shall have a maximum
static local deflection no greater than 2.5mm (0.1 inch) when a force of 450 newtons (100
lbs) is applied to the mount in the most flexible direction. Deflection measurements shall
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be made with reference to another part of the airframe not less than 0.3 meter (1 foot) nor
more than 1.0 meter (3 feet) from the mounting location. After selecting a suitable location
meeting all of the above requirements. Drill and mount the ELT tray assembly as shown in
Fig 3. A doubler plate may be required. Secure latches with tie wrap as shown.