Navigation Position Fix Challenge
Fixes from radials, DME and other navaids: mark your position on the map and get accuracy feedback.
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One line of position tells you only which line you are on; two that cross tell you where you are. Pick the kind of fix — two VOR radials, a radial and a DME, two DMEs, or an ADF bearing and a VOR radial — read the instruments, and mark your position on the map by tapping, dragging, or typing a bearing and distance from station A. Check draws the construction lines and shows where you really were.
Reading the instruments: with the needle centred and FROM, the OBS shows the radial you are on; with TO it shows the course to the station — your radial is the reciprocal. Off-centre (Hard), each dot is 2°: turn the OBS until the needle centres, or interpolate. DME is slant range: at altitude the horizontal distance is a little shorter. The ADF points at the NDB relative to the nose, so the magnetic bearing TO the NDB is heading + relative bearing, and you are on the reciprocal line FROM it.
Two DME circles cross twice: both points fit both readings, and the page shows the other one. A third line of position — a radial, or a third DME — removes the ambiguity. The same seed always gives the same challenge; share it with the link shown under the controls.
Assumption: fictional training stations on a flat map, one magnetic heading frame, an ideal VOR receiver on the IFR Trainer scale (2° per dot, 10° full scale), exact DME slant range and an ADF without errors; the aircraft is level at the stated altitude above the stations. The 1.5 NM pass mark is the IFR Trainer’s “Where am I?” fix tolerance and the score is a platform convention, not an FAA standard.
Readings come from the IFR Trainer’s receivers, unchanged: the VOR (radial, TO/FROM flag, needle in degrees, slant DME) and the ADF (relative bearing for the heading). The expert solution uses only the readings, as the IFR Trainer’s “Where am I?” does: radial = OBS − needle (FROM) or OBS + 180 + needle (TO); horizontal DME = √(slant² − height²); bearing to the NDB = heading + relative bearing; then the crossing of the two lines of position. On the IFR Trainer’s “Where am I?” scenarios (radial + DME and VOR + NDB) this tool's solution and grading equal the trainer's; this challenge extends them with two-radial and two-DME fixes, stations anywhere, seeds, levels and a tally.
Grading: the distance from your mark to the true position; with two DMEs a mark on the other crossing is measured to that crossing and flagged, because it fits both readings. Pass within 1.5 NM; score = 100 × (1 − error ÷ 3 NM), not below zero. Scenarios are generated from the seed (the IFR Trainer’s random generator) and retried until the geometry is fair: crossing angle of at least 50° / 40° / 30° (Easy / Medium / Hard), stations 8 NM or more apart, needles on scale, two clearly separate DME crossings.
Sources: AIM 1-1-3 (VOR), 1-1-7 b (DME is slant range), 1-1-2 (NDB, ADF); IFH FAA-H-8083-15B ch. 9 (radials, TO/FROM, the CDI, DME, “a DME/DME fix … provides a more accurate aircraft location than using a VOR and a DME fix”, ADF relative and magnetic bearing); PHAK FAA-H-8083-25C ch. 16 (“A VOR radial alone merely gives line of position information. With DME, a pilot may precisely locate the aircraft on a given line”).
- FAA Aeronautical Information Manual, para. 1-1-2 NDB (ADF bearings), 1-1-3 VOR, 1-1-7 b DME (slant range, not horizontal) (faa.gov HTML, read 2026-10-14)
- FAA Instrument Flying Handbook, FAA-H-8083-15B (2012), ch. 9 Navigation Systems: VOR radials and the TO/FROM indicator, CDI, ADF relative bearing (magnetic bearing = magnetic heading + relative bearing), DME and DME Errors (a DME/DME fix is more accurate than a VOR and a DME fix)
- FAA Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25C (2023), ch. 16 Navigation: a VOR radial alone gives a line of position; with DME the aircraft is located on the radial
- Cross-tool: the receivers and the “Where am I?” solution and grading of the IFR Trainer’s HSI module, extended here (two radials, two DMEs, stations anywhere, seeds, levels, tally)
- Garmin G1000 Pilot’s Guide for Cessna Nav III, 190-00498-08 Rev. A (system software 0563.30 or later), pp. 56-68 — the glass HSI option (Indicator: HSI (glass)): heading-up compass card, course pointer with a two-dot deviation scale (full scale as on a mechanical CDI for VOR and LOC), green for VOR / LOC and magenta for GPS, flight-phase and OBS / SUSP annunciations, glideslope / glidepath indicator; an equipment example, not a statement about every glass display