For the owner of a Cessna Citation III, the Aero-M satellite communication (satcom) system proved to be an ideal choice. He flies his business aircraft regularly to the Caribbean, where the commonly used, air-to-ground Magnavox communication system is not supported, unless a satcom system also is utilized. He needs worldwide coverage and initially installed an Iridium satcom system, but after that service filed for bankruptcy, he decided to switch to an Aero-M system.
Aero-M is a smaller, more economical system compared to Aero-I, Aero-H, Aero-H+, all provided by long-time satcom provider Inmarsat. It is a single-channel system, allowing both voice and digital communication, but not both at once. However, since the owner of the Citation III is often the only passenger on board, the Aero-M system serves just fine. What’s more, it is smaller and lighter (only 13 pounds/5.9 kg) than the multichannel Aero-H system commonly found on air transport aircraft, and this makes it appropriate for the small to medium-size bizjets like the Citation.
The Citation III owner also does not need the four handsets and two fax ports and two modem ports provided by the Aero-I satcom, which often are installed in the larger bizjets: Gulfstreams and Bombardier Challengers. Both Aero-M and Aero-I receive spot-beam transmissions from the Inmarsat satellites, but the latter, larger system also offers multiple channels. The Citation owner needs no more than what Aero-M offers: two handsets, a single fax port and an internal modem with RS-232 interface for a personal computer.
However, if the owner chooses to upgrade to the triple-channel Aero-I system, he can do so without swapping antennas. He can use the same TT-5006A mechanically steered, intermediate gain satcom antenna and navigation reference system (NRS) that is part of his Aero-M system. (Alternatively, the Aero-I system can include an electronically steered, phased array antenna, which requires the addition of an inertial reference system.)
Like a Flashlight Beam
Aero-M has been providing worldwide public telephone/fax/data transmission since it was introduced in 1999 as an extension to Inmarsat’s land mobile Mini-M, which is commonly used for maritime purposes, on offshore rigs, and in remote land areas. Inmarsat decided that it needed to offer a small, economical system, so it included in each of its Inmarsat-3 satellites five spot-beam antennas. These more powerful satellites supercede the four Inmarsat-2 satellites, which have served the aviation community since 1990 (but now with secondary status), covering 3-MHz of the 10-MHz L-band spectrum.
Unlike the global beam that showers down to serve the larger Aero-H systems on air transport aircraft, the spot beam transmits from satellites much like a narrow flashlight beam. Although its global coverage does not match the breadth of the Aero-H system, these spot beams do cover every continent and all air routes, according to Paul de Herrera, Universal Avionics’ director-North American marketing.
The Inmarsat-3 satellites are cost-saving because they make more efficient use of the L-band spectrum. Specifically, they can re-use frequencies in non-adjacent beams without interference. Also, they allow each satellite’s RF power to be focused where communications traffic is generated and not dispersed over a larger portion of the Earth.
Tucson, Ariz.-based Universal is one of two Aero-M system providers, offering the Thrane & Thrane TT-3000. Meanwhile, Honeywell has teamed with Racal Avionics and OmniPless (Pty) Ltd., in South Africa, to offer its comparable SCS-1000 Mini-M satcom system. Both entities offer extra services with its satcom systems: Universal’s air-to-ground data link with graphical weather transmissions and the Honeywell OneLink communication service.
East Coast Aviation Inc., in Stuart, Fla., installed the Citation III owner’s TT-3000 Aero-M system. Installation required no Supplemental Type Certificate (STC); East Coast only had to secure field approval from the local FAA Flight Standards District Office (FSDO).
Outfitting an aircraft with satcom isn’t easy, however (although it is comparable in complexity to installing a ground-based telephony system). It involves virtually gutting the aircraft interior. So, wisely, the Citation III owner had his Aero-M system installed at the same time he incorporated a new cabin, new in-flight entertainment (IFE) system, and a traffic alert and collision avoidance system II (TCAS-II). The IFE system, incidentally, is a scaled down version of IEC International Ltd.’s package developed for the Canadair Challenger (see Avionics Magazine, June 2000).
"In some aircraft, you can install satcom by taking down the top and one side [of the cabin shell]," says Scott Edwards, East Coast’s project manager for completions and FAA certification, "but we take it all down."
Most critical is installing the TT-3000’s domed antenna, a three-to-five-day job, according to Edwards. Universal’s Aero-M antenna is 22 inches (55.9 cm) long, about 6 inches (15.2 cm) wide, and weighs 4.9 pounds (2.2 kg). It has to be positioned atop the aircraft about mid-way between the windscreen in front and the tail.
Positioning the Aero-M satcom antenna at least 18 inches (45.7 cm) from any source of magnetic interference is essential. (East Coast quite conservatively secures two feet [61 cm] of clearance, according to Edwards). That means the antenna cannot be near any speakers, high power electrical wires, or anything that could cause magnetic interference.
Wiring, too, is critical. Because the antenna’s coaxes are subject to interference, Edwards claims that it is best to "run the antenna wires by themselves and not bundle them" with other wiring. He adds that East Coast technicians can make the satcom antenna harness in about a day; harness installation then takes about three days.
Strict physical size and attenuation requirements must be observed when selecting the low-loss wiring for satcom. Three different types of coax wires are used for Aero-M; the choice depends on the length of cabling required.
The Aero-M’s two unbundled wires link the antenna with the high-power/low-noise amplifier (HPA/LNA), which gains 28 volts DC power from the satellite data unit (SDU). The small HPA/LNA (weighing 2.2 pounds [1.0 kg]) provides a maximum 1.5 dB noise figure and minimum 34 dB LNA gain. Edwards says the unit "should be mounted flush in a panel in a pressure vessel due to temperature restrictions; it can’t be in colder than -25ï¿½ C conditions."
The link between the HPA/LNA and SDU also should not be bundled with other wiring. The latter box can fit into a standard 2MCU ARINC 404a tray and must be in the pressurized cabin avionics area. The SDU, powered by 18 to 32 volts DC non-floating, 40-watts maximum, includes for antenna steering a 12-channel Global Positioning System engine with 3-dimensional magnetometer and level sensors.
East Coast installed two handsets in the Citation III, one in the cabin and one in the cockpit for the pilot. TT-3000 users have an option of handsets:
One with keypad and liquid crystal display (LCD) that can show up to 24 characters and has a four-wire interface.
And a less expensive alternative with a keypad, but no display, and a two-wire tip/ring, voice-only interface.
The Citation III has one of each handset type. The one with an LCD will display in four-digit codes any errors in an attempted communication: a busy channel, invalid country code, invalid phone number, etc. These coded messages are recorded, so maintenance personnel can determine if the on-board satcom system has any problems.
Finally, after the Aero-M satcom system is installed, a comprehensive checkout procedure is required, according to Edwards. The following steps must be taken:
First the aircraft’s takeoff speed is entered into the system, using the keypad, to ensure optimum tracking algorithms for the antenna.
Second, the aircraft must be pulled away from buildings and anything that could create magnetic interference, then turned on a smooth, level surface 360ï¿½ while calibrations are made of the magnetometers in the antenna.
And finally, the system is verified by checking the satellite signal, using the handset; an error code will inform the installers as to whether the calibration score is good, acceptable, marginal, unacceptable, or a complete failure.
The Citation III owner is now ready for his regular business travel to the Caribbean, while still maintaining phone, fax, and data communications all the way.
For additional information, see www.inmarsat.com, www.uasc.com, www.honeywell.com and www.eastcoast-avionics.com.
Inmarsat’s Services for Bizjets
–by Jim Jensen
In recent months, Inmarsat has introduced Aero H+, Aero I, and Aero Mini-M services to business and commercial aviation. These new services are in addition to the well-established Aero H systems already used by many airlines and business aviation flight departments for global satcom telephone, fax and personal computer (PC) data communications.
Below is a quick summary of each Inmarsat Service:
Aero H–The first global voice, fax, and PC data service offered to business and commercial aviation, Aero H (high gain antenna) Inmarsat "global beam" systems are installed on "heavy iron" business aviation aircraft and support multiple channels for satcom communications. The present Inmarsat Aero H data rate is 2.4K baud for PC data and will be able to support 64K baud data by mid-2001. The 64K baud version is called Aero M4 (for Multi Media Mini M), and both existing and new aeronautical Aero H systems will need to be upgraded to support Aero M4.
Aero H+–This is a new service provided by Inmarsat for business aviation. Presently, only four Inmarsat ground stations support Aero H+, and they are located in France and Australia. By mid-2001 additional Inmarsat ground stations will be able to support Aero H+. These systems support multiple channels and require the same antenna (high gain) used by an Aero H system. Aero H+ systems work in both "global beam and spot beam" Inmarsat coverage areas and will be able to support Aero M4 (64K baud data). When in spot beam coverage, all aircraft Aero H+ satcom channels will be able to act simultaneously at any given moment. When in global beam coverage, only two or three channels will be able to function simultaneously. This is because Aero H+ systems have a maximum transmit power of less than 20 watts.
Aero Mini-M–Most major Inmarsat ground stations presently support Aero Mini-M, a single-channel satcom system. The single channel can be used for voice, fax or PC data. The maximum PC data rate for Mini-M is 2.4K baud, and it is not clear at this time if it will be able to support 64 K M4 data. Aero Mini-M was intended to compete with Iridium. It is lightweight and inexpensive when compared to the other Inmarsat Aero systems. Universal Avionics introduced a Mini-M system, the TT-3000, to the business jet market in late 1999.
Aero M4–This Inmarsat service is not scheduled to be available to aviation until mid-2001. It will provide 64K baud PC data for Internet connection. Inmarsat land mobile systems presently support M4.
Jim Jensen is president and chief executive officer of Satcom Direct Inc., and no relation to David Jensen, Avionics Magazine’s editor-in-chief. For more information about his company, see www.satcomdirect.com.