Managing Change In FMS

By Frank Alexander | March 1, 2007
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New types of aircraft operating procedures and concepts are influencing the development of flight management systems (FMS). As those technology-driven procedures evolve, avionics and airframe manufacturers say they are improving their products and adding new capabilities.

The term FMS refers not only to flight management computer (FMC) avionics, but in some instances it includes the aircraft’s flight control systems, horizontal situation indicators and primary flight displays.

Each segment of the industry — air carrier, business aviation and general aviation — has similar factors but differing priorities that drive technology changes. The common drivers are cost and operational capability. These will vary in priority but are constant throughout the industry. There are also other considerations that guide avionics vendors in developing and introducing improvements.

For the air carrier industry, standardization is very important in terms of cost to an operator for training system differences or in some cases having to split a fleet, using different flight crews for the same airplane with different FMSs.

Both Airbus and Boeing say they are cognizant of this fact and work to insure the man-machine interfaces of their FMSs are similar across their respective fleets. This does not preclude the addition of new technology (processors, larger navigation databases and operation features), but the emphasis remains on standardization.

The business aviation industry is not as sensitive to the standardization issue because aircraft are typically purchased as a single unit and fleet standardization is less of an issue. This also allows avionics and airframe manufacturers greater latitude in introducing advanced technologies, such as enhanced vision head-up guidance displays.

The general aviation industry is starting to undergo changes and is likely to be mixed between single aircraft sales and fleet sales with the introduction of Very Light Jets.

RNP capability

The two main areas where advanced concepts and technology are influencing change are Required Navigation Performance (RNP) and augmented satellite based navigation.

The air carrier industry expressed a strong desire for greater operational capability using RNP-based procedures; in particular, RNP procedures that necessitate special aircraft and aircrew authorization required (SAAAR).

RNP requires the aircraft maintain the specified level of accuracy (e.g., RNP 0.3 is ±3/10ths of a nautical mile with a 95 percent confidence rate) and also specifies a level of integrity through performance monitoring, alerting and enhanced functionality.

SAAAR requirements are based on the aircraft system including FMC, navigation sensors (e.g. GPS), displays and documentation stating the autopilot, flight director and flight control systems meet the required levels of performance and integrity.

SAAAR procedures include arrival, departure and instrument approach procedures and are typically based on RNP values of less than 0.3.

Both Boeing and Airbus have or will have their aircraft approved for SAAAR procedures, and there is a growing interest in the business aviation community for this capability as well.

The first SAAAR procedure developed by FAA and Alaska Airlines was an instrument approach to runway 19 at Reagan National Airport in Washington, D.C.

Late last year, Horizon Airlines, working with Universal Avionics Systems, Tucson, Ariz., and Bombardier received the first SAAAR approval for a regional airline for operations at Portland, Ore.

In 2006, FAA published 28 RNP SAAAR procedures at 14 airports. FAA said it plans to publish at least 25 more RNP approach procedures in fiscal year 2007.

Augmented GPS is rapidly evolving as a replacement for many ILS instrument approach procedures. There are two concepts in play. FAA’s Wide Area Augmentation System (WAAS) currently provides precision instrument approach capability for WAAS-equipped aircraft.

Vendors including Rockwell Collins, Universal Avionics and Garmin have in service or are developing avionics systems that support WAAS procedures.

Last September, Rockwell Collins introduced its WAAS-capable GPS-4000S sensor, integrated with the FMS in its Pro Line 4 and 21 avionics systems.

Garmin has 17,000 orders for WAAS upgrades to its existing GPS navigation systems that will provide three-dimensional guidance for a precision approach.

Universal Avionics is developing an FMS that will integrate an internal WAAS receiver and be capable of both WAAS localizer performance with vertical guidance and RNP procedures.

Universal Avionics officials say they expect to be able to achieve RNP values of less than 0.3 for their FMS.

The Ground Based Augmentation System (GBAS — also known as Local Area Augmentation System), while not getting strong support from FAA, is being developed and used in other parts of the world. Qantas Airlines’ Boeing 737-800s are flying a GBAS approach on a trial basis in Sydney, Australia.

Boeing also is working to develop GBAS approaches in Germany and Micronesia.

Universal Avionics developed and certified a GBAS approach system in use in Norway. Honeywell is supporting prototype GBAS installations in Australia, Germany and Spain, and at cargo carrier FedEx’s hub in Memphis, Tenn.

Major air carriers tend to favor the implementation of RNP procedures over WAAS, and this is supported by both Boeing and Airbus.

The regional airline market is mixed, due in part to the fact that a large percentage of regional jets do not have inertial reference units, an integral component for RNP approach procedures. General aviation is a strong supporter of WAAS.

One advantage of the RNP concept is to be able to define different levels of navigation performance to meet airspace and instrument approach requirements.

An RNP approach procedure may use two or more RNP values from the initial approach fix through the final approach to the missed approach.

This creates difficulties with respect to providing the pilot with deviation information both laterally and vertically.

Boeing developed performance scales for its navigation displays that will display both lateral navigation and vertical navigation path deviation for precise RNP operations as well as real time display of the lateral and vertical path locations and position update sensor performance. This is operational on the B737NG and B777 and is planned for the B747-800.

Universal Avionics is developing flexible scaling as a function of the RNP value taken from the FMC navigation database as opposed to the current method based on phase of flight.

The pace toward new technologies will increase with the evolution of the operations concepts being produced for the Next-Generation Air Transportation System and the European Commission’s Single European Sky ATM Research, or SESAR. (See story p. 10).

These efforts will describe the necessary capabilities and functions that will be required to manage the capacity increases and operating efficiency improvements envisaged in the 2020 to 2025 time frame.

Much of what is being discussed now will drive evolutionary and in some cases revolutionary changes to existing flight management systems.

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