ILS & DME systems
The student should gain an understanding of DME operation and the instrument landing system, and be able to apply that knowledge to flight scenarios.
Elements
- Radio theory review
- CDI display review
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ILS
- Localizer
- Glideslope
- Marker beacons
- Runway markings
- Approach lighting
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DME
- General usage
- Arcing
Resources
- pen and paper
- Instrument Flying Handbook and The Pilot's Manual: Instrument Flying
- instrument procedure charts
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laptop with flight simulator and internet access
- Tim's Navigation Simulator works with multiple technologies
- Selkirk IFR trainers
- AIM Chapter 1: Air Navigation
Instructor actions
- Introduce and motivate with the question of how we gauge distance and arrive at the airport without visual references
- Describe new navigation systems and their operation in a predominantly lecture format
- Illustrate techniques using Tim's simulator
- Review each system before moving on to the next
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Evaluate student knowledge with questions emphasizing understanding rather than rote
- Have the student solve multiple scenarios
- Conclude with an oral quiz, identifying and correcting errors
Student actions
- Arrive with completed homework assignment
- Maintain active involvement by responding to questions and taking notes
- Guide the instructor through the intercepting and tracking of several simulator scenarios
- Complete an oral quiz and demonstration of the concepts
Completion Standards
The lesson will be complete when the student can describe DME and ILS equipment - and demonstrate an understanding of the techniques required to smoothly and accurately intercept and track a localizer and glideslope - with minimal instructor guidance.
Teaching outline
Review radio principles
- What are the three types of waves?
- Which kind of frequency does the ILS use? How about DME?
CDI with localizer and glideslope
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Not all CDIs can be used with an ILS, but all should work with a localizer
- when flying a localizer, it is four times as sensitive - every dot is .5° rather than 2°
- the glideslope needle will be flown just like a normal lateral course - the center is the airplane
- performance instrument, used as a reference to adjust control inputs
Instrument Landing System, IF 309 & IFH 7-27
The ILS is a precision approach, providing both lateral and vertical guidance down a predetermined flight path.
- As a precision approach, it is designed to transition from instrument to visual flight
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Uses a system of 'lobes'; overlapping points define the approach
- VHF band
- operates between 108.10 and 111.9 MHz
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Five parts make up the ILS in actual use:
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localizer provides lateral (directional) guidance
- broadcast from the non-arrival end of the runway (illustration from IFH 7-28)
- 40 channels, on odd tenths between 108.10 and 111.95
- the 'full scale' of 5° will extend to 700 ft wide at the threshold, varying the localizer width
- service volume reaches 18 nm, between 1000 agl and 4500 above the antenna
- lateral area is ±10° to 18nm, ±35° to 10 nm, providing proper off-course indications within the volume
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glideslope provides vertical guidance with a UHF signal
- broadcast from antennas located approximately 1,000 ft from the approach end
- 40 channels, paired with the localizer
- full deflection occurs .7° high or low; useful width is 1.4°
- average angle of 3°, but may be as low as 2.5° or as high as 4°
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calibrated out to 10 nm from threshold, but reception is common further false glideslope forms at approximately 12° above the horizontal
- this is the danger of intercepting from above
- reverse sensing makes it somewhat apparent
- intercepts marker beacons at 1400 feet HAT (OM) and 200 feet (MM)
- crosses the threshold at approximately 50 feet
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marker beacons, IF 324
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essentially an extremely low power ADF; designed to create an elliptical 'fan' (alternate name: fan marker) that is 2400 feet wide and 4200 feet long at 1000 feet above the antenna
- use 'low' setting if available to detect marker beacons
- outer marker (OM, ––, blue) is 4 to 7 nm from the threshold, and roughly 1400 feet HAT
- middle marker (MM, –·–·–·, amber) is .6 nm from the threshold, 200 feet HAT, and indicates the DH and/or missed approach point
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inner marker (IM, ······, white) is used on higher-precision (Cat II or greater) approaches and is between the MM and threshold, usually indicating an altitude of 100 feet or less
- designates a specific decision height for that approach
- backcourse marker (BC, ·· ··) is used to indicate a backcourse localizer FAF, where the descent is to be commenced
- some marker beacon sites are colocated with compass locators, which are much higher powered and are terminal area NDBs
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- approach lighting systems, IF 326
- runway markings
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- DME, radar, and LOM beacons can also be included in or required for ILS approaches
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Variations on the localizer exist - IF 339-340
- SDF - simplified directional facility; 6° or 12° wide
- LDA - localizer directional aid; not aligned with the runway
Distance Measuring Equipment, IF 207 & IFH 7-13
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Determines the slant range to the DME station
- hypotenuse of the aircraft's actual distance and altitude
- errors show up when extremely close
- accurate as long as we are 1 nm away for every 1,000 ft of altitude above the station
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Display unit shows distance in nm; our units also show ground speed and eta
- inside of 200 nm, with an accuracy of less than 1/2 nm or 3% of the distance
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Airborne transmitter (interrogator) broadcasts a signal
- this is picked up by ground stations (transponder)
- ground station replies to the aircraft
- The DME hardware measures the time lapse
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Ground stations are limited to approximately 100 aircraft at a time
- UHF equipment, generally colocated with a VOR as a VOR/DME
DME Arcs - IF 553
- "Arc northwest" - what does the phraseology mean?
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Used as a transition to a VOR or ILS approach
- essentially, we're drawing a constant-radius circumference
- flown as a series of short, straight segments with heading changes
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Prior to entry, tune and identify
- set up the OBS to read TO the station (with two, set the second to the final approach course) - make sure we're not using the GPS
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1/2 to 1 nm from the arc, turn in the arc direction - generally 90° from the intercept heading
- GS/200 gives the radius of a standard rate turn; 100 knots is .5 nm, 200 is 1 nm
- twist the OBS 10° ahead - we want to cross the next radial
- as the CDI centers, turn 10° in the direction of the arc
- twist the OBS another 10° ahead and repeat
- when two dots from centering on the approach course, or when crossing the lead-in radial (on some approaches), start a standard rate turn to intercept
- Illustrate with Tim's simulator, using approach terminology