Flight Management Systems

The term management takes on many forms. In fact the most basic definition “to control or direct” about says it all. When used in aviation we find structured organizations with employees having specific functions or specialties and it is up to the department manager to set the priorities in terms of which aircraft needs which specialist and the percentage of the work force to get the aircraft back on the line for a scheduled trip. Often the chief of maintenance has considerations including available manpower, schedules, and costs that all have to be weighed to set in motion the best possible plan to achieve the desired results.

In many modern aircraft, the cockpit crew are often referred to as “flight deck managers.” Piloting skills, although still important, are being supplemented with proficiency in varying kinds of computer technology.

It was not all that many years ago when methods of navigation were up to the discretion of the pilot. Do they tune an automatic direction finder (ADF) or set a frequency for a very high frequency omni directional range (VOR) station, perhaps look out the flight deck windows and follow familiar geography including highways and railroad tracks?

The point here is that a flight management system (FMS) is primarily a navigation system computer with some mind-boggling capabilities.

Computerized systems as a rule can be broken down into four main areas; the computer itself, inputs or sensors, programming or controls and the work performed otherwise known as outputs.

Functions performed by FMS can vary with both manufacturers and models; once again the primary function of a FMS is to facilitate navigation. In addition to information to the flight crew, data can also be sent via steering channels into the auto flight system. Many systems contain extensive memories that can be programmed with specific aircraft information including performance. This can enable sophisticated computations that can assist the pilots in knowing the range of the aircraft in varying conditions and if fuel starvation could occur prior to reaching the predicted destination.

When the FMS is initialized it first has to be made aware of its present position. In many cases the last known latitude and longitude coordinates are committed to memory at the time of system shutdown and are then recalled during the power up process. In other cases various navigation sensors such as global positioning systems (GPS) will automatically communicate with the FMS to provide position reference. Once initialization has been accomplished then the flight crew can establish a flight plan to the destination. This consists of establishing a set of waypoints accommodating standard instrument departures (SIDs), standard terminal arrival routes (STARs), and designated airways and allowing the system to calculate the best way to get from the point of departure to the destination.

The System

Typical flight management systems consist of a control display unit (CDU), flight management or navigation computer, global position sensor, and a data loader.

The flight management computer accepts information from numerous navigation sensors including VOR, distance measuring equipment (DME), and GPS. Data from each sensor is prioritized based on its known percentage of error and can be blended to provide the most accurate position information.

The computer has a programmable database containing known radio navigation stations along with their tunable frequencies, airports, SIDs, and STARs as well as approach data for runways. Due to frequent changes the database requires updating every 28 days. This is accomplished by loading electronic media files into some type of data loader which can vary from a floppy drive, zip, or even a compact disc. In some cases the data loader can be used to download diagnostic or fault data to the same type of electronic media. This information can then be interrogated to allow more accurate fault analysis. Some aircraft will have a multipurpose unit where in addition to using some form of electronic memory a laptop computer could also be connected allowing flight crews to create flight plans in their offices or at a hotel room and then when they get to the aircraft they can transfer data to the FMS.