Helicopter Installations - Special Considerations; Background; Recommendations; Figure 26. Elt Orthogonal Axes - ACR Electronics Cobham C406-1 Series Abbreviated Component Maintenance Manual

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9. Helicopter Installations - Special Considerations

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A.

Background

(1) There are few guidelines, aside from experience, regarding the best way to mount an ELT in
helicopters.
(2) Before the availability of multi-axis G-switch modules, manufacturers advised installing ELTs
with the sensitive axis pointing approximately 45° downward from the normal forward
direction of flight.
(a) This mounting attitude was adapted due to a combination of the directional sensing
limitations of a single-axis G-switch and the flight characteristics of helicopters.
(b) Mounting the ELT at this attitude and orientation is currently specified by CAR, Part 5,
Subpart 551.104.
(c) Experience has indicated this mounting angle tends to preload the G-switch and
"nuisance" activation can occur as a result of severe aircraft maneuvers, and abrupt
takeoffs and landings.
(3) Artex does not recommend installing ELTs designed with a single-axis G-switch in helicopters
due the limitations and issues cited above.
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B.

Recommendations

(1) Artex recommends installation of the C406-1HM ELT in helicopters. The C406-1HM ELT is
equipped with a 5-axis G-switch module in addition to the usual primary G-switch, which is
oriented to the direction of flight. See "Figure 26. ELT Orthogonal Axes".
(2) The six-axis coverage of the C406-1HM design accommodates the flight characteristics of
helicopters, while allowing "normal" installation and eliminating or significantly reducing
"nuisance" ELT activations.
COBHAM AVIONICS WULFSBERG ELECTRONICS
ABBREVIATED COMPONENT MAINTENANCE MANUAL
C406-1 (453-5002), C406-1HM (453-5003)
-X
-Y

Figure 26. ELT Orthogonal Axes

+Z
+Y
+X
-Z
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APR 06/10