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What is the practical difference between a great-circle and a rhumb-line route? start learning
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A great circle is the shortest route between two points but normally requires changing track; a rhumb line maintains a constant track but is generally longer.
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How are true, magnetic and compass directions related? start learning
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True corrected for variation gives magnetic; magnetic corrected for deviation gives compass.
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What does wind change: aircraft heading, track, or both? start learning
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Wind changes the relationship between heading and track; the pilot/FMS changes heading to maintain the required track.
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What is PBN fundamentally based on? start learning
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Specified navigation performance requirements for an operation, rather than prescribing a particular navigation sensor.
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What is the key difference between RNAV and RNP specifications? start learning
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RNP includes on-board performance monitoring and alerting; RNAV does not require it.
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What does the number in RNAV 1 or RNP 1 mean? start learning
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Lateral total system error of ±1 NM is expected for at least 95% of flight time.
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How should RNAV 5, RNAV 1 and RNP 1 be thought of operationally? start learning
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RNAV 5 is mainly en-route; RNAV 1 and RNP 1 support more accurate terminal navigation, with RNP 1 additionally monitoring and alerting navigation performance.
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What is the operational relationship between ANP and RNP? start learning
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The estimated actual navigation performance should remain within the required RNP; ANP greater than RNP means the required performance cannot be assured.
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What are the four key navigation-performance concepts? start learning
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Accuracy, integrity, continuity and availability.
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Why is integrity different from accuracy? start learning
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Accuracy describes how close the estimated position is to truth; integrity concerns timely warning when the navigation solution should not be trusted.
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What navigation accuracy applies to the final segment of an RNP APCH to LNAV or LNAV/VNAV minima? start learning
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What navigation accuracy normally applies to the initial, intermediate and missed-approach segments of RNP APCH? start learning
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What is the practical difference between LNAV, LNAV/VNAV and LPV? start learning
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LNAV provides lateral guidance only; LNAV/VNAV adds approved vertical guidance, commonly Baro-VNAV; LPV uses SBAS to provide precise lateral and vertical guidance.
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Does LPV use an ILS localizer or glide-slope transmitter? start learning
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No. The guidance is GNSS/SBAS based.
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Why can LPV nevertheless feel similar to an ILS? start learning
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It provides highly precise lateral and vertical guidance with a decision altitude.
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Why are correct QNH and temperature particularly important for Baro-VNAV? start learning
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The computed vertical path depends on barometric altitude, and temperature affects the relationship between indicated altitude and true geometric height.
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start learning
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An Authorization Required RNP approach using tighter containment and additional aircraft, crew, procedure and operator requirements.
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How low can the navigation accuracy requirement become on an RNP AR APCH? start learning
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Depending on the segment and procedure, it may be as low as RNP 0.1.
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Why does RNP AR require specific operational approval? start learning
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Tighter containment may require specialised aircraft capability, training, procedures, data management and monitoring.
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What is an RF leg and why is it different from a normal turn? start learning
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A Radius-to-Fix leg is a precisely defined constant-radius curved path that the navigation system must follow.
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Why should a direct-to clearance to a fix immediately preceding an RF leg normally not be accepted? start learning
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It can destroy the geometry required for correct RF-leg path capture.
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What is the practical difference between fly-by and fly-over waypoints? start learning
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A fly-by waypoint allows turn anticipation before the fix; a fly-over waypoint must be crossed before the turn begins.
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Why are path terminators important in an FMS database? start learning
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They define exactly how each procedure leg is to be flown, not merely where the next waypoint is located.
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Why should a published procedure normally be loaded from the navigation database rather than manually constructed? start learning
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The validated database contains the designed waypoint coordinates and leg coding on which procedure containment and obstacle protection depend.
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Why must the loaded FMS procedure still be compared with the chart? start learning
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To detect wrong procedure selection, unexpected coding or database discrepancies.
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Why should crews avoid manually modifying waypoints in a coded PBN procedure? start learning
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The modification may alter the protected path or invalidate the assumptions of the procedure.
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What is AIRAC and why does it matter to navigation databases? start learning
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Aeronautical information changes follow a standard 28-day cycle; an outdated database may contain obsolete procedures or coordinates.
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Why is WGS-84 important in modern navigation? start learning
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It provides a common geodetic reference so procedure coordinates and aircraft-computed position use the same Earth model.
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How does GNSS determine aircraft position? start learning
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By measuring pseudoranges to multiple satellites and solving for three-dimensional position plus receiver clock error.
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Why are at least four GNSS satellites normally required for a full 3-D solution? start learning
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The receiver must solve latitude, longitude, altitude and its clock error.
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What is RAIM and what does it provide? start learning
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Receiver Autonomous Integrity Monitoring uses redundant GNSS measurements to detect an unreliable navigation solution.
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What is the relationship between RAIM and ABAS? start learning
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RAIM is a form of Aircraft-Based Augmentation System functionality.
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What is the practical difference between SBAS and GBAS? start learning
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SBAS provides wide-area satellite-broadcast corrections and integrity; GBAS provides local ground-based augmentation around an aerodrome.
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What is the European SBAS called? start learning
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What is the difference between GNSS jamming and spoofing? start learning
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Jamming prevents or degrades reception; spoofing creates false GNSS-like information that may produce a misleading position or time solution.
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Why can spoofing be more insidious than jamming? start learning
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The navigation solution may continue to look plausible instead of simply becoming unavailable.
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What is the basic crew strategy when GNSS interference is suspected? start learning
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Cross-check independent navigation sources, identify unreliable information and follow aircraft/operator and ATC contingency procedures.
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Why are inertial systems valuable during GNSS interference? start learning
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After alignment they are self-contained and do not depend on external radio signals.
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What is the main limitation of pure inertial navigation? start learning
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Small sensor errors accumulate, so position error gradually increases with time.
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What is sensor blending in a modern navigation system? start learning
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Combining GNSS, inertial and radio-navigation information to produce the best available position estimate.
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Why is sensor independence important? start learning
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Independent sources allow erroneous or degraded navigation information to be detected rather than blindly accepted.
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What is the key limitation of DME distance close to and above a station? start learning
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DME measures slant range, so vertical distance becomes a significant part of the indication.
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Why does DME/DME navigation depend strongly on station geometry? start learning
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Poor intersection geometry magnifies range-measurement errors into larger position errors.
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What does a VOR radial describe? start learning
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The magnetic bearing FROM the VOR station, independent of aircraft heading.
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What is the purpose of raw-data cross-checking on a modern FMS aircraft? start learning
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To provide an independent reasonableness check of the computed navigation solution when suitable ground-based aids are available.
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How closely should an aircraft normally track the centreline during RNAV/RNP operations? start learning
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Normal cross-track deviation should generally remain within about half the applicable RNAV/RNP value.
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Why is a direct-to the FAF normally inappropriate on an RNP APCH? start learning
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The aircraft should be correctly established on the final approach track before the FAF; current EASA guidance does not accept direct-to the FAF.
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When may a direct-to the IF be acceptable on an RNP APCH? start learning
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When the aircraft can be established on the final approach track at least 2 NM before the FAF.
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When should an RNP APCH normally be discontinued because of navigation performance? start learning
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On navigation-system failure, excessive lateral/vertical deviation, or loss of required onboard monitoring and alerting unless an approved alternative capability or sufficient visual reference permits continuation.
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Does loss of GNSS always mean immediate loss of all PBN capability? start learning
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No. A suitably approved multi-sensor system may retain the required RNP capability using other sensors.
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What is the difference between loss of GNSS reception and loss of GNSS integrity? start learning
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Reception loss means the signal is unavailable; integrity loss means the system can no longer assure that the navigation solution is trustworthy.
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Why must crews understand navigation-system reversion modes? start learning
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After sensor degradation the FMS may continue operating but at a lower navigation capability that may no longer support the planned procedure.
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