A Comparison Of Flight Management Systems Engineering Essay

Published: 2021-07-01 01:30:06
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Looking at many aircraft of the 80’s and before, we often wonder why there is a provision for a third person, viz., the Flight Engineer in the cockpit. If such a person is truly required, why don’t we have one in modern aircraft? The answer is simple. As in other fields, a computer has replaced such a person in modern aircraft. No more do we need a flight engineer to constantly check for path correction, communication, faults, etc. The different onboard computers can do all this, and more. These computer systems, sensors and navigational aids are called the Flight Management Systems. This article also includes a brief description of some common flight navigation and control systems as well.
The Flight Management System (FMS) is a fundamental part of a modern aircraft's avionics. Avionics refers to the electronic systems on aircraft and spacecraft that provide communications, navigation and guidance, display systems, flight management systems, sensors and indicators, weather radars, electrical systems, and various computers onboard modern aircraft and spacecraft. It includes hundreds of systems installed in an aircraft or spacecraft to meet specific roles. These can be simple systems like a search light for a police helicopter or complicated systems such as the tactical system for an airborne early warning platform. The word avionics is a combination of aviation and electronics.
A FMS is an integrated computer system in an aircraft that automates many in-flight tasks that have to be performed either by the pilots or a flight engineer, thereby reducing the workload on the flight crew to such an extent that modern aircraft no longer carry flight engineers or navigators. A primary function is the in-flight management of the flight plan. Using various modules (such as GPS and INS) to determine the aircraft's position, the FMS can guide the aircraft's autopilot along the flight plan. From the cockpit, the FMS is normally controlled through a Control Display Unit (CDU) which comprises of a small screen and a keyboard. The FMS displays the flight plan on the EFIS, Navigation Display (ND) or a Multifunction Display (MFD).
The modern FMS was introduced on the Boeing 767, though earlier navigation computers did exist. Now, FMS exist on almost all aircraft, right from the Cessna 172 to the Airbus 380. In its evolution the FMS had provided many different sizes, capabilities and controls. However certain characteristics are common to all FMS.
All FMS contain a navigation database. The navigation database contains the elements from which the flight plan is constructed. These are defined via the ARINC 424 standard. The navigation database is normally updated every 28 days, in order to ensure that its contents are current. Each FMS contains only a subset of the ARINC data, relevant to the capabilities of the FMS.
The FMS contains all of the information and systems required for building a flight plan, navigating the plane using autopilot and perform course corrections. These include
Airways (highways in the sky)
Radio navigation aids including distance measuring equipment (DME), VHF omnidirectional range (VOR), and non-directional beacons (NDBs)
Instrument Landing System (ILS)
Standard instrument departure (SID)
Standard terminal arrival (STAR)
Holding patterns
And a variety of related and often installation-specific information
VHF omnidirectional range (VOR)
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for guiding aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice (if equipped), and a navigation signal. The identifier is in Morse code. The voice signal is usually a station name, in-flight recorded advisories, or live flight service broadcasts. The navigation signal allows the airborne receiving equipment to determine a magnetic bearing from the station to the aircraft (direction from the VOR station in relation to the Earth's magnetic North at the time of installation). VOR stations in areas of magnetic compass unreliability are oriented with respect to True North. This line of position is called the "radial" from the VOR. The "intersection" of two radials from different VOR stations on a chart provides an approximate position of the aircraft.
Distance measuring equipment (DME)
Distance measuring equipment (DME) is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals. Aircraft use DME to determine their distance from a land-based transponder by sending and receiving pulse pairs - two pulses of fixed duration and separation. The ground stations are typically co-located with VORs. A typical DME ground transponder system for en-route or terminal navigation will have a 1 kW peak pulse output on the assigned UHF channel. A low-power DME can also be co-located with an ILS glide slope or localizer where it provides an accurate distance function, similar to that otherwise provided by ILS Marker Beacons.
Instrument Landing System (ILS)
An instrument landing system (ILS) is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or blowing snow.
Instrument approach procedure charts (or approach plates) are published for each ILS approach, providing pilots with the needed information to fly an ILS approach during instrument flight rules (IFR) operations, including the radio frequencies used by the ILS components or navaids and the minimum visibility requirements prescribed for the specific approach.
Radio-navigation aids must keep a certain degree of accuracy (set by international standards of CAST/ICAO); to assure this is the case, flight inspection organizations periodically check critical parameters with properly equipped aircraft to calibrate and certify ILS precision.
A glass cockpit is an aircraft cockpit that features electronic instrument displays. Whereas a traditional cockpit relies on numerous mechanical gauges to display information, a glass cockpit uses several displays driven by flight management systems that can be adjusted to display flight information as needed. This simplifies aircraft operation and navigation and allows pilots to focus only on the most pertinent information. They are also popular with airline companies as they usually eliminate the need for a flight engineer. In recent years the technology has become widely available in small aircraft.
In the design of the cockpit in a military fast jet, the traditional "knobs and dials" associated with the cockpit are mainly absent. Instrument panels are now almost wholly replaced by electronic displays which are often re-configurable to save space. While some hard-wired dedicated switches must still be used for reasons of integrity and safety, many traditional controls are replaced by multi-function re-configurable controls or so-called "soft keys". Controls are incorporated onto the stick and throttle to enable the pilot to maintain a head-up and eyes-out position – the so-called Hands on Throttle and Stick or HOTAS concept. These controls may be then further augmented by new control media such as head pointing with a Helmet Mounted Sighting System or Direct Voice Input (DVI). New advances in auditory displays even allow for Direct Voice Output of aircraft status information and for the spatial localisation of warning sounds for improved monitoring of aircraft systems. A central concept in the design of the cockpit is the Design Eye Position or "DEP".
The layout of control panels in modern airliners has become largely unified across the industry. The majority of the systems-related controls (such as electrical, fuel, hydraulics and pressurization) for example, are usually located in the ceiling on an overhead panel. Radios are generally placed on a panel between the pilot's seats known as the pedestal. Automatic flight controls such as the autopilot are usually placed just below the windscreen and above the main instrument panel on the glare shield.
Most modern cockpit will also include some kind of integrated warning systems.
Flight Instruments
Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with information about the flight situation of that aircraft, such as height, speed and altitude. The flight instruments are of particular use in conditions of poor visibility, such as in cloud, when such information is not available from visual reference outside the aircraft.
Traditional Instruments :
The altimeter shows the aircraft's altitude above sea-level by measuring the difference between the pressure in a stack of aneroid capsules inside the altimeter and the atmospheric pressure obtained through the static system. It is adjustable for local barometric pressure which must be set correctly to obtain accurate altitude readings. As the aircraft ascends, the capsules expand as the static pressure drops therefore causing the altimeter to indicate a higher altitude. The opposite occurs when descending.
Attitude indicator
The attitude indicator (also known as an artificial horizon) shows the aircraft's attitude relative to the horizon. From this the pilot can tell whether the wings are level and if the aircraft nose is pointing above or below the horizon. This is a primary instrument for instrument flight and is also useful in conditions of poor visibility. Pilots are trained to use other instruments in combination should this instrument or its power fail.
Airspeed indicator
The airspeed indicator shows the aircraft's speed (usually in knots) relative to the surrounding air. It works by measuring the ram-air pressure in the aircraft's Pitot tube. The indicated airspeed must be corrected for air density (which varies with altitude, temperature and humidity) in order to obtain the true airspeed, and for wind conditions in order to obtain the speed over the ground.
Magnetic compass
The compass shows the aircraft's heading relative to magnetic north. While reliable in steady level flight it can give confusing indications when turning, climbing, descending, or accelerating due to the inclination of the Earth's magnetic field. For this reason, the heading indicator is also used for aircraft operation. For purposes of navigation it may be necessary to correct the direction indicated (which points to a magnetic pole) in order to obtain direction of true north or south (which points to the Earth's axis of rotation).
Heading indicator
The heading indicator (also known as the directional gyro, or DG; sometimes also called the gyrocompass, though usually not in aviation applications) displays the aircraft's heading with respect to geographical north. Principle of operation is a spinning gyroscope, and is therefore subject to drift errors (called precession) which must be periodically corrected by calibrating the instrument to the magnetic compass. In many advanced aircraft (including almost all jet aircraft), the heading indicator is replaced by a Horizontal Situation Indicator (HSI) which provides the same heading information, but also assists with navigation.
Turn Indicator
The turn indicator displays direction of turn and rate of turn. Internally mounted inclinometer displays 'quality' of turn, i.e. whether the turn is correctly coordinated, as opposed to an uncoordinated turn, wherein the aircraft would be in either a slip or a skid. The original turn and bank indicator was replaced in the late 1960s and early '70s by the newer turn coordinator, which is responsive to roll as well as rate of turn, the turn and bank is typically only seen in aircraft manufactured prior to that time, or in gliders manufactured in Europe.
Vertical speed indicator
The VSI (also sometimes called a variometer). It senses changing air pressure, and displays that information to the pilot as a rate of climb or descent in feet per minute, meters per second or knots.
Modern Improvisations of Aircraft Instruments :
A Mode Control Panel (or MCP), usually a long narrow panel located centrally in front of the pilot, may be used to control Heading(HDG), Speed(SPD), Altitude(ALT), Vertical Speed(V/S), Vertical Navigation(VNAV) and Lateral Navigation(LNAV). It is also used to engage or disengage both the autopilot and the autothrottle. The panel as an area is usually referred to as the "glare shield panel". MCP is a Boeing designation (that has been informally adopted as a generic name for the unit/panel) for a unit that allows for the selection and parameter setting of the different Autoflight functions, the same unit on an Airbus aircraft is referred to as the FCU (Flight Control unit).
A primary flight display or PFD is a modern aircraft instrument dedicated to flight information. Much like multi-function displays, primary flight displays are built around an LCD or CRT display device. Representations of older six pack or "steam gauge" instruments are combined on one compact display, simplifying pilot workflow and streamlining cockpit layouts.
Most airliners built since the 1980s — as well as many business jets and an increasing number of newer general aviation aircraft — have glass cockpits equipped with primary flight and multi-function displays.
Mechanical gauges have not been completely eliminated from the cockpit with the onset of the PFD; they are retained for backup purposes in the event of total electrical failure.
A head-up display or heads-up display (HUD) is any transparent display that presents data without requiring users to look away from their usual viewpoints. The origin of the name stems from the pilots being able to view information with heads "up" and looking forward, instead of angled down looking at lower instruments.
Although they were initially developed for military aviation, HUDs are now used in commercial aircraft, automobiles, and other applications.
There are two types of HUD:-
A fixed HUD requires users to look through a display element attached to the airframe or vehicle chassis. The system determines the image to be presented depending solely on the orientation of the vehicle. Most aircraft HUDs are of this type.
Helmet mounted displays (HMD) are technically a form of HUD, the distinction being that they feature a display element that moves with the orientation of the users' heads relative the airframe.
Future Developments :
Unlike the previous era of glass cockpits—where designers merely copied the look and feel of conventional electromechanical instruments onto cathode ray tubes—the new displays represent a true departure. They look and behave very similarly to other computers, with windows and data that can be manipulated with point-and-click devices. They also add terrain, approach charts, weather, vertical displays, and 3D navigation images.
The improved concepts enable aircraft makers to customize cockpits to a greater degree than previously. All of the manufacturers involved have chosen to do so in one way or another—such as using a trackball, thumb pad or joystick as a pilot-input device in a computer-style environment. Many of the modifications offered by the aircraft manufacturers improve situational awareness and customize the human-machine interface to increase safety.
As aircraft displays have modernized, the sensors that feed them have modernized as well. Traditional gyroscopic flight instruments have been replaced by Attitude and Heading Reference Systems (AHRS) and Air Data Computers (ADCs), improving reliability and reducing cost and maintenance. GPS receivers are frequently integrated into glass cockpits.
Modern glass cockpits might include Synthetic Vision (SVS) or Enhanced Vision systems (EVS). Synthetic Vision systems display a realistic 3D depiction of the outside world (similar to a flight simulator), based on a database of terrain and geophysical features in conjunction with the attitude and position information gathered from the aircraft navigational systems. Enhanced Vision systems add realtime information from external sensors, such as an infrared camera.
Sophisticated aircraft have full performance VNAV or Vertical Navigation. The purpose of VNAV is to predict and optimize the vertical path. Guidance includes control of the pitch axis and control of the throttle. In order to have the information necessary to accomplish this, the FMS must have a detailed flight and engine model. With this information, the function can build a predicted vertical path along the lateral flight plan. This detailed flight model is generally only available from the aircraft manufacturer.
During pre-flight, the FMS builds the vertical profile. It uses the initial aircraft empty weight, fuel weight, centre of gravity and initial cruise altitude, plus the lateral flight plan. A vertical path starts with a climb to cruise altitude. As an aircraft burns fuel it gets lighter and can cruise higher where it is generally more efficient. Step climbs or cruise climbs facilitate this. VNAV can determine where the step or cruise climbs (where the aircraft drifts up) should occur to minimize fuel consumption.
Performance optimization allows the FMS to determine the best or most economical speed to fly in level flight. This is often called the ECON speed. This is based on the cost index, which is entered to give a weighting between speed and fuel efficiency. Generally a cost index of 999 gives ECON speeds as fast as possible without consideration of fuel and a cost index of Zero gives maximum efficiency. ECON mode is the VNAV speed used by most airliners in cruise.
An ideal idle descent, also known as a "green descent" uses the minimum fuel, minimizes pollution (both at high altitude and local to the airport) and minimizes local noise. While most modern FMS of large airliners are capable of idle descents, most air traffic control systems cannot handle multiple aircraft each using its own optimum descent path to the airport, at this time. Thus the use of idle descents is minimized by Air Traffic Control.

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