DESCRIPTION
The ELT transmits the standard emergency swept tone on 121.5 and 243.0 MHz and the aircraft identification code or serial number of the transmitter, country code and the ID code on the 406.025 MHz.
The 406.025 MHz transmitter transmits for 24 hours every 50 seconds for 520 ms and then is automatically shut down and has an average error of 1 to 2 km.
The 121.5 MHz/243.0 MHz transmitter transmits continuously until the battery is drained which takes approximately 72 hours, and has an error of 15 to 20 km.
The information sent to the satellite is programmed at the factory and contains a unique number that can be used to identify the beacon. ELT/NAV (Navigation) Interface Unit (new)
When the ELT is coupled to an ELT/NAV interface unit, it also will transmit the position coordinates (longitude and latitude) of the aircraft in the encoded digital message, in the event of a crash. This results in a better accuracy of the position, which is approximately 100 m.
The ELT/NAV interface unit will also be able to automatically reprogram the ELT with the aircraft 24-bit address in the event of an ELT replacement. One of the connectors of the ELT/NAV interface unit is wired, according to the aircraft 24-bit address.
Upon power-up, the ELT/NAV interface unit reads the ELT's 24-bit address data and compares it to the 24-bit address data hardwired to the ELT/NAV interface unit. If there is a difference, the ELT/NAV interface unit reprograms the ELT according to the connector straps. If the two sets of data are identical, no action is taken.
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Emergency Equipment
ELT TRANSMITTER UNIT
The transmitter unit is housed in a high impact fire resistant polycarbonate plastic case, which is installed in the aft avionics compartment and it has the internal components that follow:
• G-Switch • Transmitter • Microprocessor • Miscellaneous components • “ON” light • Battery
The transmitter is an electronic circuit which transmits RF (Radio Frequency) signals on the frequencies of 121.5 MHz, 243.0 MHz and 406.025 MHz.
ELT SWITCH
The ELT unit has an ON/OFF switch which has the f unctions that follow: Emergency Locator Transmitter System-ELT-ON/OFF Switch
• ON – The transmitter starts its operation manually
• OFF - The unit is OFF but it can start operation automatically
through the G-Switch operation ELT REMOTE SWITCH PANEL
The ELT remote switch panel is located on the main instrument panel, in the cockpit. It has an ON/ARM switch and a red LED (Light-Emitting Diode) which indicates if the ELT is activated or not activated. The ON/ARM switch has the following functions:
• ON - The transmitter starts its operation manually • ARM - It is the normal position for an automatic operation
ELT ANTENNA
The ELT antenna is a blade antenna installed on the top of the center fuselage III.
ELT BATTERY
The battery pack for the ELT consist of 4 “D” size lithium manganese dioxide cells connected in series. The expiration date of the battery is printed on the label attached to the unit. T he battery pack expires 5 years from the date (month) it is shipped from ELTA. The battery pack must be replaced with a new one in the following cases:
• After use in an emergency.
• After an inadvertent activation of unknown duration.
• When the total of all known transmissions exceeds one hour. • On or before the battery replacement (expiration) date.
ELT BUZZER
The ELT buzzer is located next to the ELT unit, in the aft avionics compartment. It is fed by the ELT and therefore is not dependent upon the aircraft battery for operation. The ELT buzzer provides an aural sound to alert the pilot when the ELT has been activated and is transmitting. Its signal is loud enough to be heard outside the aircraft when the engines are off. It enables a search and rescue team to easily locate an aircraft with a transmitting ELT in a confined area with a large number of aircraft (i.e. such as an airport) so that they can disable the offending ELT without a great deal of effort.
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Emergency Equipment
The ELT/NAV interface unit is also installed next to the ELT unit, in the aft avionics compartment.
The ELT/NAV interface unit gives to the ELT the capability of interfacing with the aircraft navigation system.
It receives the position coordinates from the GPS (Global Positioning System) 1 receiver module through the generic I/O (Input/Output) module, both installed in the MAU (Modular Avionics Unit) 1, and send this information to the ELT.
In the event of a crash, the ELT will transmit the position information from the navigation system. The crash site is instantly known due to the aircraft navigation system position data communication with the ELT via ELT/NAV interface unit. Without this interface, in the worst case, the time to locate the aircraft could take until 3 or 4 hours. In addition, the accuracy of the position fix is better than a system which does not use this interface (i.e. 100 m versus 1 or 2 km).
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Emergency Equipment
OPERATION
The ELT signals transmitted on 121.5 and 243.0 MHz are modulated in AM. They are designated with the carrier amplitude modulated with an audio frequency sweeping downward over a range of not less than 700 Hz, within the range of 1600 to 300 Hz. The sweep repetition rate is between 2 and 4 Hz with a modulation factor of at least 0.85.
The ELT signal transmitted in 406.025 MHz is a digital information message. The modulation is phase modulated and classified as 16K0G1D.Every 47.5 to 52.5 seconds the 5 W transmitter is turned on for 440 ms (short message) or 520 ms (short message).
The transmitter has a G-Switch that senses the aircraft longitudinal deceleration. The G-Switch shall activate the ELT in accordance with the requirements as depicted in the response curve of the G-Switch.
Two criteria govern the performance of the G-Switch sensor:
• A threshold force level (G th) below which the G-Switch sensor
will not respond.
• A minimum velocity change (V min) before the G-Switch sensor
will activate.
The ELT can be operated either manually or automatically.
Under normal conditions, the ON/ARM switch of the ELT remote switch panel is in the ARM position and the ON/OFF switch of the ELT unit is in the OFF position. Upon impact (a change velocity of 4.5 +/- 0.5 ft/s or if subjected to 30 G’s of cross axis forces) the G-Switch will automatically activate, activating the ELT. The LED, in the ELT remote switch panel, will continuously flash and the swept tone will be audible.
For manual operation, the ON/OFF switch of the ELT unit or the ON/ARM switch of the ELT remote switch panel must be at the ON position. These switches can also be used to do the test of the ELT, which must be
performed within the first five minutes after the hour UTC (Universal Time Coordinated) and cannot exceed 30 seconds. After approximately 47 seconds the satellite system will consider the transmission as a valid distress signal. If the ELT is activated accidentally, it can be reset through the ON/ARM switch. The resetting is done when the switch is set to the ON position and then immediately set again to the ARM position. It is also possible to reset the ELT at the unit itself by positioning the ON/OFF switch on the ELT unit to ON position, then immediately back down to the OFF position. The ELT cannot be reset if either the ON/ARM switch of the ELT remote switch panel or the ON/OFF switch of the ELT unit is in the ON position.
The DC ESS BUS 2 supplies power for the LED of the ELT remote switch panel.
The status of the ELT, active or not active, is indicated on the ELT remote switch panel. When the ELT is active, a continuous flashing light will be present on the ELT remote switch panel. If a problem is detected, the light provides a coded signal following the initial 1-second pulse. The coded signal and related problems are as follows:
• 1 flash indicates a G-Switch loop open failure.
• 3 flashes indicates a 406.025 MHz transmitter problem. • 5 flashes indicates there is no navigation data present. • 7 flashes indicates a battery problem.