Is a CDI and Heading Indicator packed into one unit. it provides both left right deviation along with glide slope information as well as heading indication in turns. Many HSI's are coupled to auto pilots and may allow course selection via a heading knob if they are connected to do so.
Full Answer
The HSI is an improvement on the standalone CDI instrument in that it takes into consideration your actual heading. The old CDI would just have a radial set in the OBS and show your deviation (which could have reverse sensing depending on which radial you tuned) in relation to that radial.
But if the CDI shows a “TO” indication, you have reverse sensing (meaning that if the needle is deflected to the right, you are actually right of course and must correct to the left). It isn’t a malfunction of the instrument, just something you have to be keenly aware of particularly when flying IFR.
The CDI will react as shown in the figure below in function of the TO/FROM zone. As you can see in the CDI, if the aircraft follows the desired radial heading, the radial direction is represented by the location of the course deviation bar on the instrument.
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.
A standalone CDI (Course Deviation Indicator) is an instrument that shows your deviation from a VOR radial that is selected using the OBS (Omnibearing Selector) knob located on the instrument itself. An HSI (Horizontal Situation Indicator) is an entirely separate instrument that combines a CDI and a heading 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. If the location of the aircraft is to the left of this course, the needle deflects to the right, and vice versa.
What can be said about the course information displayed by the standard VOR indicator with respect to the aircraft heading? The information displayed is independent of aircraft heading.
OBS vs CDI The OBS (Omni-Bearing Selector) is the knob that the pilot adjusts. On the other hand, the CDI (Course Deviation Indicator) is the needle in the window that shows your desired course. So the pilot turns and sets the OBS but sees their course by looking at the CDI needle.
horizontal situation indicatorThe 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.
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.
CardsTerm (Refer to figure 30) Which restriction to the use of the OED VORTAC would be applicable to the (GNATS1.MOURN) departure?Definition R-333 beyond 30 NM below 6,500 feetTerm What angular deviation from a VOR course centerline is represented by a full-scale deflection of the CDI?Definition 10 degrees223 more rows•Jul 11, 2013
Horizontal Situation Indicator (HSI) 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).
The OBS reading is the magnetic course from the VOR station to the aircraft.
Area navigationJune 2021) Area navigation (RNAV, usually pronounced as /ˈɑːrnæv/ "ar-nav") is a method of instrument flight rules (IFR) navigation that allows an aircraft to choose any course within a network of navigation beacons, rather than navigate directly to and from the beacons.
The OBS (Omni Bearing Selector) knob is on the CDI, it is not its own instrument. The knob allows the selection (via the outer ring) of the radial (course) you wish to track from a VOR ground station.
2.5°ILS/VOR CDI Deviation RNAV In ILS mode, full scale deflection in the localiser is 2.5°. Remember you can only get to half full scale deflection before you must initiate a go around. In ILS mode, full scale deflection in the glidepath is 0.7°.
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. If the location of the aircraft is to the left of this course, ...
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.
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.
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 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.
CDI display is independent from the aircraft heading. Note that in the CDI instrument, the display is independent from the aircraft heading. This can be strange for novice pilots to instrument navigation. The instrument displays the information in the perspective of an aircraft with course equals heading.
In the CDI instrument, the radial indicator is a needle which is clearly visible on the top of the instrument. If the location of the aircraft is to the left off course, the needle deflects to the right. If the location of the aircraft is to the right off course, the needle deflects to the left. If the location of the aircraft is on ...
If the course selector is rotated until the deviation needle is centred, the radial (magnetic course “FROM” the station) or its reciprocal (magnetic course “TO” the station) can be determined. The course deviation needle also moves to the right or left if the aircraft is flown or drifting away from the radial which is set in the course selector.
The white triangle is pointing to the bottom of the instrument. The yellow triangle represents the selected radial . Do not mix up the selected RADIAL on the compass card with aircraft HEADING. The two regions are dependent from the radial selected in the aircraft.