Course deviation indicator. A course deviation indicator (CDI) is an avionics instrument used in aircraft navigation to determine an aircraft's lateral position in relation to a course to or from a radio navigation beacon.
An HSI, or Horizontal Situation Indicator, is a combination of two familiar cockpit instruments: the directional gyro with a heading bug and a VOR/ILS indicator. WHAT DOES AN HSI DO FOR THE PILOT?
When this indicator points to the head of the course arrow, it indicates that the course selected, if properly intercepted and flown, will take the aircraft TO the selected facility, and vice versa. The glide slope deviation pointer indicates the relationship of the aircraft to the glide slope.
Next determine where the head of the needle points and the status of the CDI (either deflected or centered). Each dot on the deflection scale represents 2° of deviation.
4:0812:30Notice the green course selector arrow it's pointed at 0 9 0.. Also notice the white triangleMoreNotice the green course selector arrow it's pointed at 0 9 0.. Also notice the white triangle pointed the same direction as the green arrow marking the two indication.
The CDI acts somewhat like a course line, showing the pilot the relationship of the airplane to the selected course. If you're flying westbound, for example, and the OBS is properly tuned and the CDI is to the left (or south), you know the airplane is north of the desired course.
The horizontal situation indicator (commonly called the HSI) is an aircraft flight instrument normally mounted below the artificial horizon in place of a conventional heading indicator. It shows the heading, course, bearings and the lateral deviation of an aircraft.
Each division (dot) represents 1.25 degrees deviation from the ideal ILS flightpath approach.
So the term 3/4 scale deflection for an ILS means that at all times during the approach procedure, the needles must not exceed 3.75 dots (or 75% of the available space) on both lateral and vertical guidance needles.
sixty milesIt's used in aviation and is based on the fact that for every one degree you travel off course for sixty miles, you will land one mile from where you had intended. If you are traveling across our country, one degree off course will land you about 50 miles from your destination.
The course deviation bar operates with a VOR/Localizer (VOR/LOC) or GPS navigation receiver to indicate left or right deviations from the course selected with the course select pointer; operating in the same manner, the angular movement of a conventional VOR/LOC needle indicates deviation from course.
WHAT'S AN HSI? An HSI, or Horizontal Situation Indicator, is a combination of two familiar cockpit instruments: the directional gyro with a heading bug and a VOR/ILS indicator.
The HSI has a fixed aircraft symbol and the course deviation bar displays the aircraft's position relative to the selected course. The TO/FROM indicator is a triangular pointer: When the indicator points to the head of the course select pointer, the arrow shows the course selected.
2°Deflection is 10° deviation at full scale (each side), with each dot on the CDI representing 2°. (See Using a VOR for usage during flight.)
ILS/VOR CDI Deviation RNAV There are two types of CDI display: 2 dot and 5 dot. The key to this question is to remember what full scale deflection means for both of these displays.
Each dot on the deflection scale represents 2° of deviation. Thus, a full-scale lateral deflection represents a deviation of 10° or greater. In cases where an ILS is installed, a back course may be available in conjunction with the localizer.
The indicator shows the direction to steer to correct for course deviations. Correction is made until the vertical needle centres, meaning the aircraft has intercepted the given courseline. The pilot then steers to stay on that line. Only the receiver's current position determines the reading: the aircraft's heading, orientation, and track are not indicated.
From Wikipedia, the free encyclopedia. Jump to navigation Jump to search. A course deviation indicator ( CDI) is an avionics instrument used in aircraft navigation to determine an aircraft's lateral position in relation to a course to or from a radio navigation beacon.
A CDI might incorporate a horizontal needle to provide vertical guidance when used with a precision ILS approach where the glideslope is broadcast by another transmitter located on the ground. A CDI is not used with an automatic direction finder (ADF), which receives information from a normal AM radio station or an NDB .
It consists of an omnibearing selector (OBS) sometimes referred to as the course selector, a CDI needle (left-right needle), and a TO/ FROM indicator. ^ Radio Navigation & Instrument Flying. Air Pilot Publishing Ltd. 2008. ISBN 1-84336-069-1.
Sensitivity is usually programmable or automatically switched, but 5 nautical miles (9.3 km) deviation at full scale is typical for en route operations. Approach and terminal operations have a higher sensitivity up to frequently 0.3 nautical miles (0.56 km) at full scale.
The deflection of the needle is proportional to the course deviation, but sensitivity and deflection vary depending on the system being used:
An "on course" condition is indicated when the course pointer, the course deviation bar, and the course reciprocal are all "in line."
RNAV. The legend "RNAV" will appear in the lower right corner of the instrument face when the HSI is part of an area navigation system and that mode is engaged. Slaving Meter. A slaving meter is located in the upper right hand corner of the instrument face on slaved models.
The HSI provides a basic horizontal view of the aircraft's navigation picture. In the F-15E, it can provide navigation data to selected ground navigation facilities (TACAN or Instrument Landing System (ILS)) or to onboard navigation systems like the Inertial Navigation System (INS). Instrument flying without an HSI requires a fair amount ...
This red warning flag indicates inadequate VOR or LOC signal, or loss of power to meter circuits. Under these conditions, course information is unusable, however, all heading information remains valid.
This orange line, located at the top of the display, indicates the aircraft's magnetic heading on the compass card. The lubber line is "in line" with the reference symbol to reinforce this association. This card, located beneath the lubber line, indicates the aircraft's current heading.
As the aircraft's heading changes, the bug rotates with the compass card, thu s alerting the pilot to the difference between the selected heading (located under the bug) and the actual aircraft heading. The heading bug may also be coupled to an autopilot or flight director system.
WHAT'S AN HSI? An HSI, or Horizontal Situation Indicator, is a combination of two familiar cockpit instruments: the directional gyro with a heading bug and a VOR/ILS indicator.
The horizontal situation indicator (HSI) is a key instrument in IFR flight. It combines the functions of a heading indicator and navigational indicator into a single instrument. For HSI questions, first determine the aircraft heading shown at the top of the indicator. This may allow you to rule out some answers.
In cases where an ILS is installed, a back course may be available in conjunction with the localizer. Like the localizer, the back course does not offer a glideslope, but the back course CAN project a false glideslope signal and the glideslope should be ignored.
The HSI is a combination of two instruments: the heading indicator and the VOR. By bringing these two instruments together you are able to get a much clearer picture in a quicker amount of time. This instrument is particularly handy when flying on instruments or under an IFR flight plan. For me it just makes the job of flying much easier, but you first need to completely understand how to read and gather information from the HSI.
The TO/FROM indicator is a triangular-shaped pointer. When this indicator points to the head of the course arrow, it indicates that the course selected, if properly intercepted and flown, will take the aircraft TO the selected facility, and vice versa.
The glide slope deviation pointer indicates the relationship of the aircraft to the glide slope. When the pointer is below the center position, the aircraft is above the glide slope, and an increased rate of descent is required.
To orient where the aircraft is in relation to the facility, first determine which radial is selected (look at the arrowhead). Next, determine whether the aircraft is flying to or away from the station (look at the TO/FROM indicator) to find which hemisphere the aircraft is in. Next, determine how far from the selected course the aircraft is (look at the deviation bar) to find which quadrant the aircraft is in. Finally, consider the aircraft heading (under the lubber line) to determine the aircraft’s position within the quadrant.
The CDI acts somewhat like a course line, showing the pilot the relationship of the airplane to the selected course. If you’re flying westbound, for example, and the OBS is properly tuned and the CDI is to the left (or south), you know the airplane is north of the desired course.
To show a course line the navigation radio receives two signals from the VOR station, one fixed and one variable. The fixed signal is the same regardless of the radial selected, while each radial produces a slightly different variable signal.
There’s a reason VORs are going out of vogue. They are challenging to use, not as accurate as more modern methods of navigation, and the ground stations are expensive to maintain.
But not every VOR is oriented to magnetic north. In northern Canada where compasses aren’t reliable, VORs are oriented to true north, or the geographic north pole. Curiously, some VORs in the continental United States are also oriented to true north, most notably a few in central Florida.
To-From Indicator: This indicator is a white triangle and appears underneath the VOR/ILS deviation indicator. It shows whether the selected course will take the aircraft either to or from the VOR station.
Combining the directional gyro and the NAV indicator into one instrument reduces pilot workload by providing heading, course reference, course deviation, and glideslope information all in one visual aid. In addition, an HSI:
Glideslope Mask: This mask will cover the glide slope deviation indicator in the absence of a usable signal or when a VOR frequency is selected.
Glideslope Deviation Indicator: This yellow wedge relates the vertical glide path centerline to the aircraft's position. The aircraft is "on glide slope" when the wedge covers the horizontal index. Each dot on this vertical scale represents approximately 0.4 degrees vertical deviation from the centerline. An up deviation is a fly up command while a down deviation means to fly down in order to place the aircraft "on glide slope."
Heading Flag: This red warning flag indicates loss of vacuum and/or electrical power to the gyro. Heading information is then unusable, but all course information (comparable to a standard VOR/ILS) remains valid.
Slaving Meter: A slaving meter is located in the upper right-hand corner of the instrument face on slaved models. If equipped with a slaving feature, an HSI will automatically update its compass card with a magnetic sensor to correct for precession. In flight, the meter needle will oscillate slowly when the compass card is properly aligned with the magnetic compass.
Reference Aircraft: Representing the actual aircraft, this symbol is fixed and is located in line with the lubber line. Lubber Line: This orange line, located at the top of the display, indicates the aircraft's magnetic heading on the compass card. The lubber line is in line with the reference symbol to reinforce this association.