Tuesday, November 13, 2012

Cessna 172R ELT

     The ME406 is a type AF (automatic fixed) beacons. Inputs and outputs are protected against electrostatic discharge (ESD) and connections to +28V or ground. If a terminal is inadvertently misconnected or a wire shorted, the ME406 will operate normally after the condition has been corrected. The RF output is through a single BNC connector.
All functions of the ME406 is under microprocessor control. A self-test routine checks ELT operation and installation, then presents the results as visual and auditory ‘error codes’ to aid in troubleshooting and to indicate status.
The battery pack consists of two D-size, lithium cells mounted in a cover assembly and is field replaceable. Rated life is 6 years or one hour of use, whichever comes first.

                                The ME406 is pre-programmed at the factory using a short message format. The following User Protocols are supported:
• Serial Number
• Tail Number
• 24-Bit Aircraft Address
• Aircraft Operator Designator/Serial Number
                   In the event of a crash, the ME406 activates automatically (automatic fixed “AF” configuration), and transmits the standard swept tone on 121.5 MHz lasting until battery power is gone. This 121.5 MHz signal is mainly used to pinpoint the beacon during search and rescue operations.
Doppler positioning is employed using both 121.5 MHz and 406 MHz signals. Position accuracy of the 121.5 MHz signal is within an area of approximately 15-20 km radius about the transmitter. Due to the better signal integrity of the 406 MHz, its location accuracy is within a 3 km radius.
                                  Switch Operation
In a crash, an acceleration activated crash sensor (G-switch) turns the ELT ‘ON’ automatically when the ELT experiences a change in velocity (or deceleration) of 4.5 fps ±0.5 fps. Activation is also accomplished by means of the cockpit mounted remote switch or the switch on the ELT. To deactivate the ELT set either switch to the ‘ON’ position, then back to ‘ARM’.
The ELT does not have an ‘OFF’ position. Instead, a jumper between two pins on the front D-sub connector must be in place for the G-switch to activate the unit. The jumper is installed on the mating half of the connector so that when the connector is installed, the beacon is armed. This allows the beacon to be handled or shipped without ‘nuisance’ activation (front connector removed).
NOTE: The ELT can still be manually activated using the local switch on the front of the ELT. Care should be taken when transporting or shipping the ELT to not move the switch or allow packing material to become lodged such as to toggle the switch.
In the ME406HM, activation is also accomplished by any of the 5 auxiliary “G” switches at a nominal 12 “G” level
 Self-Test mode
Upon turn-off, the ELT automatically enters a self-test mode that transmits a 406 MHz test coded transmission that monitors certain system functions before returning to the ‘ARM’ mode. The transmission is ignored by any satellite that receives this signal, but the ELT requires it to check output power and correct frequency. If the ELT is left activated for approximately 50 seconds or greater, a distress signal is generated that is accepted by the satellites.
In addition to 121.5 and 406 MHz signal integrity, other operating parameters are checked during the self-test. Error codes are then generated if other problems are found. The error codes are displayed by a series of “blinks” of the ELT LED, remote LED and audio indicator.
NOTE: Any time the ELT is activated, it is transmitting a 121.5 MHz distress signal. Therefore, all activations of the ELT should be kept to a minimum. Local or national regulations may limit testing of the ELT or impose special requirements or conditions to perform testing. For the “Self-Test,” Artex recommends the ELT be “ON” for no more than 5 seconds. Testing should occur during the first 5 minutes after the hour.

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