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Gulfstream G450 Systems

[G450 AOM, §2A-23-10] The communications system provides audio links within the airplane, and radio communication with other airplanes and ground stations. Transmitter and audio reception selections are made using push buttons on audio panels installed at the pilot, copilot, and observer stations. The communications system is divided into the following subsystems:


Audio Control Panels


>You can get by with no training or advanced knowledge of the audio control panel whatsoever and survive. You will need to know a few things about the ACP above and beyond what appears in the operating manual to deal with a few avionics issues and to do more than just talk on the VHF and HF radios.

General Description

[G450 MM, §23-52-00 ¶1.A.] The audio source selection control system is an integrated system that provides the flight crew with selection and control of all cockpit related aircraft audio services at the pilot, copilot, and observer stations. The Audio Control Panel (ACP) controls the audio functions of the Navigation (NAV) and Communication (COM) radios, headphones / headsets, Microphones (MIC) and loudspeakers.

Controls and Indicators

[G450 AOM, §2A-23-20 ¶2.A.]

  • Transmit Buttons — The ten rectangular transmit buttons on the audio panel illuminate green when selected. Pushing in a transmit button will automatically select the corresponding audio reception. (1) COM 1, COM 2 and COM 3 selections transmit voice or data over the selected VDR / VHF radio, tuned with the MCDU. (2) HF 1 and HF 2 selections transmit voice over the selected HF radio, tuned with the MCDU. (3) SAT selection transmits voice or data over the SATCOM installation linked to the INMARSAT network. (4) PA selection transmits voice to the cabin speaker system. (5) CABIN selection allows communication over the cabin interphone system. (6) FONE selection allows MAGNASTAR telephone operation including call pick-up, hang-up, hold, transfer, and conference calls. (7) CONF selection is used to participate in conference calling.
  • Aircraft 4110 and later do not have MAGNASTAR, the FONE and CONF buttons do not work.

  • Reception Buttons — Reception buttons are provided for: identifying navigational radio sources, monitoring the cockpit voice recorder, receiving cabin calls, selecting the cockpit speakers on or off, turning headphones on or off, turning internal communications (ICS) on or off, communicating with the maintenance interphone panels (at the nose and tail of the aircraft), controlling the volume of transmitter sidetone, and selecting a voice-activated microphone feature. Audio volume of the selected source is controlled by rotating the button.
  • The reception buttons do not rotate to control volume. Pressing the button changes the LCD screen below to reflect the selected item for 15 seconds. During that time you can use the panels only volume button to vary that item's volume.

  • MIC — The boom mic is selected when the button is pushed in; the oxygen mask mic is selected with the button out. For either of these microphones, the pilot and copilot transmit using the yoke-mounted mic switches (forward for the audio panel selected transmitter or aft for aircraft interphone) or by using the voice activated mic function (VOX). The observer transmits with a similar forward and aft transmit select button at the observer station or uses the VOX option. The handheld microphones may be used at any time regardless of the MIC push-button selection.
  • EMER — The EMER button selects normal audio panel operation when pushed in, or emergency panel operation when selected out. The EMER button rotates to control volume. Emergency operation is necessary in the event of an aircraft electrical failure that places systems on battery power. If the main batteries are available, all three audio panels remain operative provided that the EMER button is selected out. If only the aircraft emergency batteries are available, only the audio panel at the pilot position is powered. Only the #1 VHF NAV and COM radios are available on emergency battery power. These radios are tuned using MCDU #3 that is powered by the emergency batteries and has a direct ARINC-429 connection to the #1 NAV / COM radios. Cockpit speakers are not available in emergency battery mode.
  • ID — ID turns on or off Morse code identifiers when monitoring the audio of navigational radios
  • MUTE — MUTE eliminates marker beacon audio, if selected on with the round audio reception button
  • SELCAL — SELCAL selects the automatic monitoring function, enabling communication radios to detect messages addressed to the aircraft using the unique aircraft selcal code embedded in the configuration module. Upon receipt of a selcal message, the selcal indicator light flashes and the light within the reception button of the radio detecting the message flashes, and a message annunciation will appear in the LCD window. Pressing the selcal selector or selecting and keying the transmitter of the radio carrying the incoming message—will cancel the selcal alert indications.
  • Side Tone Adjustment (ST) — The ST rotary button sets speaker sidetone level to eliminate feedback from the speaker to the headset. The sidetone level is indicated in the LED window. The ST button is illuminated and the LED indication active only for five (5) seconds after adjustment. The sidetone may be adjusted with or without speaker sound.
  • We have yet to get this thing to work and have resorted to setting it to 60 and not worrying about it.

  • Voice Activated Microphone (VOX) — Selecting the VOX feature enables transmissions (both radio and ICS or Cabin) to be made without using the press-to-talk switches on the yoke or hand microphones.
  • At some point this button was replaced with one marked H'MIC which functions as written here except only for the intercom system.



Photo: Audio Control Panel, (Eddie's aircraft)

You should start with the ST (Side Tone), ICS (Intercom System), HDPH (Headphone), and H'MIC (Hot Microphone) selected. Then you select the top row MIC button to the radio you wish to transmit and what ever other audio sources you would like to listen to. As you press an audio source you will be given an opportunity to select its volume. Start with 60 and see how it goes.

Voice and Data Communication Systems


The voice and data communications system on this airplane is one of those things that works well and hardly ever goes wrong. But when it does go wrong, there is a fair amount of redundancy if you know how to get at it.

Radio Tuning


[G450 AOM], §2B-11-10] Radio tuning in the PLANEVIEW system is done through the MCDU, or CCD manipulating radio data on the PFD. When the aircraft is operating on emergency batteries the MCDU provides radio tuning for the VOR/ILS datalink (VIDL), VHF data radio (VDR), and transponder (XPDR). Back-up radio tuning is accomplished through MCDU 3 only.

Radio tuning can be done, in a very limited fashion, on the MAP display, not the PFD.

[G450 AOM], §2B-11-20]


When you can't seem to get the radio you want, when the volume control no longer works the way it used to, or if your SELCAL has an identity crisis, you can fix all that with a few pages from the G-450 AMM, 23-50-00. Those pages are not a bad thing to keep with you on the road, a copy available: right here.

VHF Voice Communications


[G450 MM], §23-12-00 ¶1.A.] The VHF voice communications system is a part of the modular radio system. The VHF voice communications system supplies the following:

  • Conventional voice data
  • Conventional low-speed minimum shift keying ACARS data
  • High-speed data modes related to Differential 8 Phase Shift Keying (D8PSK) modulation techniques

The system operates in the frequency range of 118 - 137 MHz with channel separations of 8.33 kHz or 25 kHz. The pilot or copilot makes a selection of the channel separation. The system automatically transmits a time-out signal to prevent blockage of a communication channel in the event that a MIC / Boom push to talk switch is stuck active for two minutes.

[G450 AOM], §2A-23-30 ¶2.A.] Each COM radio is connected to a dedicated blade-type antenna via RF coaxial cable. COM 1 antenna is located on the center line of the airplane’s lower fuselage just forward of the leading edge of the wing. COM 2 antenna is located on the center line of the top of the airplane aft of the first passenger compartment window. COM 3 antenna is located on the underside of the aft part of the airplane adjacent to the drain mast. COM 2 is most effective for ground communications because of the location of the antenna.

In actual practice, COM 1 doesn't seem to have a problem for ground or air communications and has the advantage of remaining powered down to the batteries.

HF Voice Communications


[G450 MM], §23-13-00 ¶1.A.] The High Frequency (HF) voice communication system provides long range voice communication capabilities to and from the aircraft. The HF Receiver / Transmitters (R/T) operate in either simplex or half duplex mode including Upper Side Band (USB) voice, Lower Side Band (LSB) voice, amplitude modulation equivalent and Continuous Wave (CW). The USB data and LSB data modes are available options. The HF voice communication system consists of 2 R/Ts and 2 antenna couplers. A dual coupler mount connects both antenna couplers to a HF shunt antenna. The HF shunt antenna connects to the HF dual coupler mount by a copper bus bar via the HF antenna adapter.

This HF is very reliable and effective.

There is more information on HF available here: HF Radios.

Satellite Communications


[G450 AOM], §2A-23-30 ¶2.C.] The satellite communications system allows the exchange of voice or data, including Datalink communications, between airplane peripherals (telephone handsets, PC modems or FAX machines) and any operating telephone or data unit within the coverage of the International Maritime Satellite Organization (INMARSAT). Coverage is provided by four (4) or more geostationary satellites operating in the L band of the radio spectrum, providing global communications linkage except in the polar regions (north or south of seventy-five degrees latitude). Equipment aboard the airplane transmits voice or data in a digital signal to the best positioned satellite that in turn relays the signal to a ground station linked to telephone networks. Ground stations (as of this writing) are located in England (UK), France, Norway, Italy, Singapore, Japan, Australia, Thailand and the USA.

Data Communications


[G450 AOM], §2B-31-40 ¶1.B.] By default, the PLANEVIEW CMF communicates by way of the land-based ACARS VHF network, which includes the Aeronautical Radio, Inc. (ARINC) and SITA subnetworks. Based on position information provided by the aircraft FMSs, the CMF automatically tunes to the appropriate subnetwork. In areas where VHF coverage is unavailable, the CMF may use the InmarsatAero-H,Aero-H+, or Aero-I satellite UHF networks. This provides both packet mode (datalink) and circuit mode (voice and data) capabilities to the aircraft. The CMF switches to and from the satellite UHF network based on the availability of land-based VHF network coverage.

[G450 AOM], §2B-31-40 ¶1.D.] All PLANEVIEW CMF transmissions, whether VHF or satellite, require line of sight to a VHF ground station or Inmarsat satellite, respectively. Establishing and maintaining line of sight is most often a concern when transmitting VHF on the ground due to the curvature of the Earth, high surrounding terrain, and man-made structures. VHF transmissions from many airports are simply not possible because the nearest VHF ground station is below the horizon or blocked by surrounding terrain. Even at airports with on-airport VHF ground stations, VHF transmissions from certain areas of the airport may not be successful due to man-made structures obstructing line of sight. In flight, VHF coverage is normally excellent, although coverage limitations may exist in remote areas of the world or at low altitudes. Transmitting by way of satellite while on the ground is generally reliable. Although, line of sight issues may still arise due to surrounding terrain and man-made structures because the Inmarsat satellites are in an equatorial geostationary orbit. In flight, the curvature of the Earth is a concern only at latitudes greater than 70° North or South. Except at these high latitudes, satellite coverage while in flight is seamless.


There isn't much in the AOM or AMM about data but you can piece together what you need to know. Just the important bits:

  • "Data" usually refers to ACARS which used to be the "Airline Communications Addressing and Reporting System," but now is called the "Aircraft Communications Addressing and Reporting System." In our FMS, the "AOC" you see on the DLK page is "Aeronautical Operational Communications," which is ACARS.
  • Your data usually comes from Comm/Nav 3, provided it is set to receive data. You can also use Comm/Nav 1 or Comm/Nav 2. If the VHF mode cannot make the connection, the system automatically goes to satellite.
  • If, for some reason, Comm/Nav 3 is not set to data, you need to Configure Comm/Nav 3.

  • Every time you download a flight plan, get your PDC, or access any of the data features of the DLK page, you are accessing ACARS.
  • Controller Pilot Data Link Communications obviously make intensive use of the data system.

Radio Tuning System


Radio Tuning Using the MCDU


[G450 AOM], §2A-23-40 ¶2.A.] Any of the three MCDUs installed on the cockpit pedestal may be used to tune the COM and NAV radios. Tuning is accessed by selecting the RADIO function key on the MCDU and toggling between the RADIO 1/2 and RADIO 2/2 pages with the NEXT or PREV function keys. The RADIO 1/2 page contains the tuning information for COM 1 and COM 2, NAV 1 and NAV 2, DME 1 and DME 2, and XPDR code. The RADIO 2/2 page contains tuning information for HF 1 and HF 2, ADF 1 and ADF 2, and COM/NAV 3. The current active frequency is displayed in green.

[G450 AOM], §2A-23-40 ¶2.A.] In the event of ASCB-D tuning path failure, the MCDU tuning commands are communicated directly to the MRCs over a secondary ARINC-429 bus. During electrical system malfunctions / emergencies, the aircraft can operate on emergency batteries. In that case, a backup tuning path (using a dedicated ARINC-429 bus linking MCDU #3 and MRC #1) allows the crew to tune only the #1 radios using functions of the MCDU #3 RADIO pages.

[G450 AOM], §2B-11-20] Each MCDU page is arranged with a centered title at the top and a page number in the upper-right corner. Page numbers are formatted as the current page number (among those with the same page title), a slash ( / ), and the number of pages with the same title. For example, there are two pages entitled RADIO , the first is labeled RADIO 1/2 and the second is labeled RADIO 2/2. The bottom line on each page displays the characters entered on the MCDU keypad and is called the scratchpad. The scratchpad is shared across all MCDU client functions, and is not under the control of the radio tuning function.

Radio Tuning Using the CCD


[G450 AOM], §2A-23-40 ¶2.A.] Tuning procedures using CCD commands have not been finalized as of this writing. Information regarding CCD radio tuning will be included when it becomes available.

There isn't much available on this subject, but there isn't much capability either. You can click on the map display and see a list of ARTCC frequencies, line select a frequency and it will tune. The list of frequencies, however, is incomplete.

Selective Calling System (SELCAL)

There isn't much to this, other than knowing it works for VHF as well as HF radios and how to restore the SELCAL code if it gets lost.

Selective Calling System (SELCAL)

[G450 MM, §23-20-00 ¶1.A.] The Selective Calling (SELCAL) system provides visual and audio alerts that indicate a request to communicate has been made. These requests are made via the Very High Frequency (VHF) or High Frequency (HF) Receiver / Transmitters (R/Ts). The SELCAL outputs of these R/Ts are routed to the Network Interface Module (NIM).

[G450 MM, §4.A.] A ground operator who wishes to contact a particular aircraft selects the four tone code that has been assigned to the aircraft. Each code consists of a four letter alphabetical group (e.g., AB-CD). Each letter represents a specific frequency ranging from 312.6 - 1479.1 Hz. The is transmitted via a VHF or HF Radio Frequency (RF) signal. The RF signal can be picked up by all receivers tuned to the transmitted frequency. However, only the receiver that is configured for the specific four tone code can respond to the RF signal and produce the appropriate crew alert signals. The SELCAL codes consist of two sequential tone pulses, each pulse containing two simultaneously transmitted tones. These four tones are transmitted on the selected radiotelephone voice channel. The four tones are generated in a station coder and are received by a decoder that is connected to the audio output of the transceiver. If the assigned aircraft code is detected, a blue message is displayed on the CAS and an aural tone is heard. The message informs the crew that there is a request to communicate on a specific radio. The crew then establishes communication with the caller by selecting the appropriate button / indicator on the audio control panel.

Restore Lost SELCAL Code


Photo: G450 Audio Control Panel SELCAL Setting, (Eddie's aircraft)

If your SELCAL has an identity crisis, you can fix all that with a few pages from G450 Maintenance Manual, §23-50-00. You can only do this on the ground, however, so if you discover blank SELCAL letters on your audio control panel in flight, you are out of luck until the next flight. Those pages are not a bad thing to keep with you on the road, a copy available: right here.

Cockpit Voice Recorder System


The cockpit voice recorder is one of those things you have to test on a daily basis but then you never think about it. If you have an NTSB 830 qualified event, however, things change. (More on that below.)

General Description

[G450 AOM], §2A-23-60 ¶1.] The cockpit voice recorder (CVR) system records the most recent 120 minutes of all cockpit spoken conversation and ambient noise, communication radio traffic, and audio signals received by aircraft crew members. The recorded data is stored within a crash-resistant casing to preserve the data for investigation.

CVR Unit

[G450 AOM], §2A-23-60 ¶2.A.] The CVR is a solid-state unit, powered by 28v DC from the Right Essential DC bus. The recorder is mounted in the tail compartment and continuously records four channels: pilot audio panel, copilot audio panel, observer audio panel, and cockpit area audio. Voice recording is time synchronized with aircraft systems through an interface with the Flight Management System (FMS) provided by Modular Avionics Unit #3. The recorder medium is contained within a protective enclosure to guard against potential damage resulting from an aircraft accident. An underwater acoustic beacon is physically attached to CVR unit to aid in retrieving the unit. The beacon is triggered automatically upon contact with water. It operates from internal battery power.

Impact Switch


[G450 AOM], §2A-23-60 ¶2.E.] The CVR impact switch is located in the tail compartment adjacent to the CVR. If the switch is subjected to a force of approximately 2.5 G the switch activates to stop CVR recording, saving the previously-recorded data. If the impact switch is activated for any reason, an indicator light illuminates until an adjacent reset switch is reset.

The impact switch was in the nose of the GIV and we would have to reset it if someone slammed the nose on landing. I've never seen that needed in the G-450, but if you do, here is where it is. The maintenance manual, G-450 AMM 23-72-07 ¶1.B., says just press and hold the RESET switch until the light goes out.

Preservation of Data

[14 CFR 91, §91.609(g)] In the event of an accident or occurrence requiring immediate notification to the National Transportation Safety Board under part 830 of its regulations that results in the termination of the flight, any operator who has installed approved flight recorders and approved cockpit voice recorders shall keep the recorded information for at least 60 days or, if requested by the Administrator or the Board, for a longer period. Information obtained from the record is used to assist in determining the cause of accidents or occurrences in connection with the investigation under part 830. The Administrator does not use the cockpit voice recorder record in any civil penalty or certificate action.

The list of things requiring immediate notification of the NTSB is listed in 49 CFR 830.5 and for the most part is pretty serious stuff. One strange item is a TCAS resolution advisory issued "when an aircraft is being operated on an instrument flight rules flight plan and compliance with the advisory is necessary to avert a substantial risk of collision between two or more aircraft." In any case, if you have to notify the NTSB you will have to ask them about your cockpit voice recorder. If they want it, you are done flying until they come and pick it up. You cannot simply replace it and mail it to them, there are custody rules.

Emergency Locator Transmitter


You can fly an entire career and never have to know a thing about your ELT, in fact, that would be ideal. Unfortunately, you do take checkrides and you do meet a ramp inspector now and then, so pay attention.

Installation / Frequencies

[G450 AOM], §2A-23-70:] A battery powered Emergency Locator Transmitter (ELT) unit is installed in the upper shelf of the Electronic Equipment Rack in the baggage compartment. The unit is activated either in automatic mode by a G-force switch on the unit set at a velocity change of 4.5 fps or manually by a switch installed on the copilot instrument panel below the clock. Once activated, the ELT emits a loud aural siren-type sound that is audible outside the aircraft and transmits radio signals over a dedicated antenna on the upper fuselage just forward of the APU air intake scoop. The ELT uses three radio frequencies to facilitate locating the aircraft:

  • 121.5 MHz - standard civil emergency frequency
  • 243.0 MHz - military emergency frequency
  • 406.028 MHz - emergency satellite locating frequency

A "velocity change of 4.5 fps" is meaningless without a time reference and comes to a change of less than 3 knots. If they had meant 4.5 ft/sec2 that would be 0.14 G's and that can't be right either. The G-450 AMM doesn't include the ELT for some reason but has the Cockpit Voice Recorder G switch set at 2.5 G's which seems reasonable to me.


The transmission over the emergency satellite frequency (406.028 MHz) consists of a digital data block that includes the aircraft identification (tail number or a coded 24 bit address), country of registration, Search and Rescue Satellite (sarsat) identification code, and position coordinates. (The aircraft specific digital data is strapped into the ELT unit upon initial installation.) Position data is continually furnished to the ELT over a ARINC-429 link with IRU #1. Upon receipt of the data block by the emergency satellite, information particular to the aircraft is activated in the emergency satellite network database. The satellite frequency data transmission occurs every 50 seconds for 520 milliseconds, with the transmissions continuing for the first 24 hours after the ELT is activated. After 24 hours, the satellite transmission ceases to preserve battery power for the other two frequency transmissions that will continue to broadcast a pulsing audio tone signal until the unit batteries are exhausted, normally at least 50 hours after activation.

Electrical Power

The ELT is normally powered by the emergency DC bus to provide continuous IRU position information to the unit, but the ELT has four internal “D” size lithium / manganese dioxide batteries enabling the ELT to transmit independent of aircraft power.) The system is designed to immediately provide the satellite network with the aircraft position in order to initiate a search and rescue effort and subsequently provide a homing signal over standard emergency frequencies for as long as battery power is available. Using location data from IRU #1, the aircraft / ELT position broadcast over the sarsat frequency is able to achieve an accuracy approximating 100 meters. The ELT is housed within a polycarbonate plastic casing that will withstand 500 g’s, a 1,000 lb crush weight, and a temperature range of -20°C to +55°C.

Test Procedure

  1. Any ELT test should only be performed within the first 5 minutes of the hour.
  2. Notify any control tower or ATC facility within reception range of the intention to test the ELT and the time of the test.
  3. No test should exceed 5 seconds in duration.
  4. Provide aircraft power to the ELT unit for a least 30 seconds prior to testing in order for the position reporting system to be validated.
  5. Tune a communications receiver to 121.5 MHz to monitor the locator beacon.
  6. Turn either the cockpit or baggage compartment switch ON, monitoring the emergency frequency for 3 audio tone pulses that should be completed within approximately 1 second and verifying illumination of the adjacent red indicator light, then select the switch back to the ARM or OFF position. If the ELT is operating normally, the red indicator light should remain illuminated for one second and then extinguish. This test procedure verifies the G-force switch, the satellite transmitter integrity and validity of the IRU position information. (Locator beacon radio transmission is verified by monitoring the 121.5 radio frequency.)
  7. If a malfunction is revealed during the test, the indicator light(s) will flash a coded signal to identify the problem:
    • One flash indicates a G-force switch failure
    • Three flashes indicate a satellite frequency (408.028 MHz) transmitter problem
    • Five flashes indicate a lack of position information from the IRU
    • Seven flashes indicate an internal battery malfunction




The MMEL lists none installed, none required. Most U.S. based MELs list one installed, none required with the caveat shown.


An ELT is required by 14 CFR 91.207.

ICAO Annex 6, Part 2

[§6.12.3] From 1 January 2005, all aeroplanes operated on extended flights over water as described in 6.3.3 b) and when operated on flights over designated land areas as described in 6.4 shall be equipped with one automatic ELT.

[§6.3.3 b)] When over water away from land suitable for making an emergency landing at a distance of more than 185 km (100 NM), in the case of a single-engine aeroplanes, and more than 370 km (200 NM), in the case of multi-engined aeroplanes capable of continuing flight with one engine inoperative.

[§6.4] Aeroplanes when operated across land areas which have been designated by the State concerned as areas in which search and rescue would be especially difficult.


14 CFR 91, Title 14: Aeronautics and Space, General Operating and Flight Rules, Federal Aviation Administration, Department of Transportation

Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013

Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.

Gulfstream GV Master Minimum Equipment List (MMEL), GV GV-SP (G550), GV-SP (G500), GIV-X (G450), GIV-X (G350), Revision 8, 11/07/2014

ICAO Annex 6 - Operation of Aircraft - Part 2 General Aviation, International Standards and Recommended Practices, Annex 6 to the Convention on International Civil Aviation, Part II, 8th edition, July 2014

Revision: 20140209