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Helicopter installations - special considerations, A. background, B. recommendations – ACR&Artex C406-N User Manual

Page 81: Figure 26. elt orthogonal axes

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25-62-13

Page 81 of 109

MAR 1/13

ACR ELECTRONICS, INC / ARTEX PRODUCTS

DESCRIPTION, OPERATION, INSTALLATION AND MAINTENANCE MANUAL

C406-N (453-5060), C406-N HM (453-5061)

TASK 25-62-13-410-803

9. Helicopter Installations - Special Considerations

SUBTASK 25-62-13-990-001

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)

ACR Electronics does not recommend installing ELTs designed with a single-axis G-switch in

helicopters due the limitations and issues cited above.

SUBTASK 25-62-13-990-002

B. Recommendations

(1)

ACR Electronics recommends installation of the C406-N HM ELT in helicopters. The C406-N

HM 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".

Figure 26. ELT Orthogonal Axes

(2)

The six-axis coverage of the C406-N HM design accommodates the flight characteristics of

helicopters, while allowing “normal” installation and eliminating or significantly reducing

“nuisance” ELT activations.

-X

+X

+Z

-Z

FWD

-Y

+Y

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