Nav aids Flashcards
What’s an NDB’s use?
Show the direction of the NDB in the cockpit on the ADF needle.
What are the 5 classes of VDF and their accuracy?
- Class A +/- 2 degrees
- Class B +/- 5 degrees
- Class C +/- 10 degrees
- Class D > 10 degrees
- Digital resolution direction finding (DRDF) +/- 1 degree
What is GPS?
Global positioning system is a precision 3D area navigation aid. It obtains multiple fixes from orbiting satellites. Its accuracy is 100m for civil and 1-3m for military and is range is global. If GPS satellites are u/s NOTAMS are issued.
What are the 3 limitations of VOR?
- Provides no distance info
- Large site required
- Expensive to build and maintain
What does DME stand for?
Distance measuring equipment
What are the 7 limitations of NDBs?
- Static effect
- Night effect
- Station interference
- Coastal refraction
- Mountain effect
- Quadrantal error
- Absence of failure warning
What does VOR stand for?
VHF omni-directional range
What des NDB stand for?
Non-directional beacon
What does ILS stand for?
Instrument landing system
How does and NDB work?
A radio transmits in all directs and can be picked up by the a/c and shown by the ADF needle. Runs on MF and has a max range of 50nm in the UK (more power = more range).
What does a DME do?
Provides an accurate measure of distance from the a/c to the beacon by interrogating the transponder. Not usually stand alone often added to VORs, ILS or NDBs. They’re a secondary radar system as they can differentiate a/c.
What is a limitation of DME?
Inaccuracy caused by slant range.
What is the arrival segment of an instrument approach?
The a/c routes from the en-route phase to an initial approach fix.
What does a VOR do?
Shows the direction to or from the VOR.
What are the 5 ILS categories, their RVR and decision heights?
- CAT I 550m 200ft
- CAT II 250m 100ft
- CAT III a 200m Nil
- CAT III b 50m Nil
- CAT III c 0m Nil
What does VDF stand for?
VHF direction finding
What is height in reference to?
The height above a fixed point on land e.g. the runway.
What is altitude in reference to?
The altitude above mean sea level (MSL)
What are the 5 segments of an instrument approach?
- Arrival
- Initial
- Intermediate
- Final approach
- Missed approach
What is an FMS?
A fight management system takes information from nav aids, GPS, INS, engine data and route information to formulate routing and control autopilot. They vary is complexity from controlling heading to full autopilot.
What is an INS?
The Inertial navigation system provides self contained van abilities. It must have pre-programmed, accurate location data. The IRS can update itself using other Nav aids to increase accuracy. The accuracy decays by 0.6nm/hr. (GIGO)
What are the instrument approach fixes?
- Initial approach fix (IAF)
- Intermediate approach fix (IF)
- Final approach fix (FAF)
- Final approach point (FAP)
- Missed approach point (MAP)
How does VDF work?
Uses a ground based array of receiving aerials to measure the phase difference between radio signals received by the outer circular and single central aerials. Displays unit in the tower. Civil uses VHF, military uses UHF.
How does a VOR work?
VOR gorund station sends out an omni-directional master signal then sends out a highly directional second signal and measures the phase difference. They rotate clockwise 30 times per second and have accuracy of +/- 1 degree. Range is line of sight.
What is decision height / altitude?
The point along the glide path at which if a visual reference height has not been established a missed approach is initiated.
What is the beam pattern of the localiser?
Uses two overlapping beans (90&50Hz) to centre the a/c on the runway. Has a range of 25nm and accuracy of 0.5 degrees. Freq 108.1-111.95MHz.
Whats the beam patter of the glide path?
Uses two overlapping beans (90&50Hz) to make sure the a/c approaches on the correct path of descent. Bounces signals off of the ground. Has a range of 10nm and accuracy of 0.14 degrees. Freq 328.6-335.4MHz (UHF).
What are 5 limitations of the ILS?
- The beam must be protected
- They’re expensive
- False ILS can be encountered outside DOC
- Mirrored glide path if the approach is too high
Glide path affected by weather disruptions on the ground
How does a DME work?
The interrogator onboard the a/c sends a signal to the DME ground station, it then times how long the response take and calculates the distance. Has an accuracy of +/-0.2nm, its range is line of sight and uses VHF.
What does VDF do?
Provides ATC with a bearing of the a/c from the VDF aerial and the track that the a/c should fly to the VDF.
What are 3 VDF limitations?
- Line of sight
- Reflection
- Range of 200nm
Name 3 instrument approach aids
- VOR (non-precision)
- NDB (non-precision)
- ILS (precision)
What is minimum descent height/altitude?
The lowest level at which a plane can fly until it sees a visual reference or has to go around.
What is a step down fix?
A step down fix allows a plane to fly down to its MDH/A and take terrain clearance into account.
What is obstacle clearance altitude / height?
The lowest height / altitude above the elevation of the relevant runway threshold to maintain obstacle clearance.
What is the missed approach point?
The point in an instrument approach procedure at/before which the missed approach procedure must be initiated in order to ensure that the minimum obstacle clearance is not infringed. This may be: the point of intersection on the glidepath, a navigation facility, a fix or a specified distance from the FAF.
What are 3 limitations of GPS.
- The number of satellites visible
- It’s military controlled
- Signal due to the atmosphere or jamming
What are reporting points?
They are beacons used as referance points. Most have Lat and Long listed so they can be used when beacons are u/s. They can now be put in places without beacons e.g. over seas if a/c has RNAV.
What is the initial segment of an instrument approach?
Marks the beginning of the intermediate segment.
What is the intermediate segment of an instrument approach?
The point between the IF and the FAF/FAP.
What is the final approach segment of an instrument approach?
Starting at the FAF to when the a/c has landed, can visually manoeuvre or initiates missed approach. This segments is where alignment and decent for landing are accomplished.
How can you identify an NDB?
NDBs will have a 2/3 letter identification
How can you identify a VOR?
VORs have 3 letter identifications that tie closely to its geographical location.
What are waypoints?
Reporting point not located overhead beacons but defined by other means such as distance/bearing from a Nav aid. Given a 5 letter designator that should be pronounceable.
What 3 components make up the INS?
- Gyroscope
- Accelerometer
- Navigational computer
