Two-VOR Cross-Fix Simulator: Find Your Position
How can a pilot determine an aircraft's position using two VOR stations? This free interactive simulator demonstrates how to use two VOR radials to find an aircraft's position on a navigation chart. By plotting a radial from each station, you can locate the point where the two lines intersect.
Move the aircraft, adjust the OBS on each VOR indicator, and read the TO/FROM indications. Plot the two radials to determine the aircraft's estimated position. You can also experiment with different crossing angles to understand why some position fixes are more reliable than others.
Two-VOR Cross-Fix
Move the aircraft on the chart and read both VOR indicators. Plot one radial from each station to estimate the aircraft's position where the two lines cross.
How to use this simulator (read this first)
The idea
A VOR receiver does not tell you your exact position. It provides a line of position: the radial you are on, measured from the station. One VOR tells you that you are somewhere along one radial. With two VOR stations, you can plot two radials and estimate your position where they intersect. This is called a position fix.
Words you need
- Radial
- A magnetic bearing FROM a VOR station. For example, R-065 extends northeast from the station. It describes the aircraft's position, not its heading.
- OBS
- The Omni Bearing Selector is the control used to select a course on a VOR indicator.
- Centred needle
- The CDI needle is in the middle when the aircraft is on the selected course line. On a typical VOR indicator, each dot represents 2° and full-scale deflection is 10°.
- TO / FROM
- Indicates whether the selected course leads toward or away from the VOR station. It does not indicate which direction the aircraft is flying.
- Line of position
- A line on the chart along which the aircraft may be located.
- Crossing angle
- The smaller angle between the two plotted lines, measured from 0° to 90°. It influences the reliability of the fix.
Identify each VOR station using its Morse identifier or another valid identification method, and use readings taken at essentially the same aircraft position.
This simulator uses fictional stations, an illustrative 80 NM reception range and distances calculated from the chart rather than a DME.
What the crossing angle means
The two lines provide the clearest position fix when they cross close to 90°. For example, R-065 from SFA and R-335 from SFB intersect at 90°. R-077 and R-032 intersect at 45°.
Small bearing errors can move the calculated position. When the crossing angle becomes shallow, the uncertainty increases because the lines intersect at a less distinct point.
- 60°–90° · Excellent Nearly perpendicular lines give a well-defined fix.
- 30°–60° · Acceptable The uncertainty area becomes more elongated.
- 15°–30° · Poor Small radial errors may move the fix considerably.
- Below 15° · Very poor Do not rely on this geometry alone. At 0°, the lines do not provide a unique position.
These categories are illustrative teaching values, not operational accuracy limits. Use the simulator's 90°, 45° and 20° examples to see how the uncertainty area changes.
Instructions for each mode
1. Move the aircraft
- Move the aircraft: drag the airplane on the chart, click a location, or select it with Tab and use the arrow keys. Both VOR indicators update.
- Centre the CDI: change the OBS using its slider or the ±10° and ±1° buttons. Read the TO/FROM flag when the needle is centred.
- Plot each radial: press Plot radial for SFA, then repeat for SFB. Their intersection indicates the estimated aircraft position.
- Random, hidden aircraft: hide the airplane and use the two VOR indicators to locate it. Reveal the aircraft to compare your result.
- Assist: centre it: lets you check your OBS setting.
- If the TO/FROM window is blank, try another OBS setting. A NAV indication means the station is outside this model's reception range.
2. Free plotting
- Choose a radial from SFA by dragging its coloured arm on the compass rose, moving the slider, or entering a value.
- Choose a second radial from SFB and press Plot both radials.
- Read the estimated position and the distances from the two stations on the chart.
- Turn either radial by just 1° and observe how far the estimated position moves.
- Compare the Crossing 90°, 45°, 20° and Near the baseline examples.
3. Challenge
- The aircraft is hidden. The exercise card shows two VOR indicators with centred needles and TO/FROM indications.
- Convert each indication into a radial FROM its station. Remember: FROM = OBS; TO = OBS ± 180°.
- Set both radials on the chart, plot them and press Check my answer.
- Compare your fix with the actual position. Use Show me how to convert or Show solution if you need help.
- Press New exercise to try another position.
Drag the aircraft anywhere (or click a spot; arrow keys also work once it is selected). The two indicators on the right follow it. Centre a needle, press Plot radial, then do the same with the other VOR: the position is inscribed where the lines cross. Dashed arcs mark the illustrative 80 NM reception range.
Drag the arm around a compass rose (or type the radial), then plot. A radial is the magnetic bearing from the station. Once the aircraft is inscribed, keep turning an arm: the position follows, and you can see how a 1° error moves it.
The pilot has centred the needle on each VOR. Here is what the two indicators show. 1) Work out the radial from each station. 2) Set those radials on the chart (drag the arms or type them) and plot them. 3) The aircraft is where the lines cross.
Goal: bring the needle to the centre (use ±10° first, then ±1°), read the flag, then plot.
Radial = bearing from the station to the aircraft. You can also drag the coloured arm on the chart.
Goal: bring the needle to the centre (use ±10° first, then ±1°), read the flag, then plot.
Radial = bearing from the station to the aircraft. You can also drag the coloured arm on the chart.
* Worst-case error: the largest distance between the position and the corners of the uncertainty area, if each radial is off by the chosen tolerance. Distances come from the plotted lines (a VOR gives bearings, not distance). Idealised chart: magnetic bearings only, fictional stations and landmarks, no terrain or reception effects. The 80 NM reception range is illustrative: in reality it depends on altitude, terrain and the station’s coverage. The tolerance and the quality thresholds are teaching values, not equipment tolerances. In real navigation, identify each station by its Morse ident before using it, and make sure both readings are taken at the same moment, i.e. at the same aircraft position. The distances shown are measured on the chart from the plotted lines; they do not come from a DME. For ground study only — not for navigation.
Understanding Your Two-VOR Position Fix
After plotting both radials, the simulator displays the estimated aircraft position and several navigation values. Understanding these results is just as important as finding the intersection on the chart.
Radials and Distances
The position readouts show the radial and chart distance from each VOR station. Both describe the same intersection point from different locations. Remember that these distances are measured on the simulated chart. A VOR receiver alone does not provide distance information.
Crossing Angle
The crossing angle describes how the two position lines meet. An intersection close to 90° provides clearer geometry. When the lines meet at a shallow angle, small bearing errors can produce a much larger change in the estimated position.
Worst-Case Error
The shaded area illustrates how the position could vary if each radial contained the angular error selected with the uncertainty control. The displayed worst-case value is calculated from this simplified model. It is not a prediction of actual VOR navigation accuracy.
A Practical Example: Two Radials Crossing at 90°
Select Crossing 90° in the simulator. The example uses radial 065° from SFA and radial 335° from SFB.
These two radials meet at a right angle. Once both lines have been plotted, the simulator marks their intersection as the estimated aircraft position.
Now switch to Crossing 20°. Notice how the intersection becomes more sensitive to small changes in either radial. Try adjusting one radial by 1° and compare the resulting position.
Two-VOR Cross-Fix: Frequently Asked Questions
Why can a centered VOR needle give the wrong radial?
A centered CDI indicates that the aircraft is aligned with the selected course, but it does not necessarily mean that the selected OBS value is the radial you should plot.
Always check the TO/FROM indication. With a centered needle and a FROM indication, the radial equals the OBS setting. With a centered needle and a TO indication, the radial is the reciprocal of the OBS setting.
For example, OBS 245° with TO corresponds to radial 065°. Plotting 245° as the radial would place the aircraft on the wrong side of the station.
What if the two plotted radials do not produce a position fix?
Check both OBS settings and TO/FROM indications. A reciprocal radial plotted in the wrong direction is a common source of error.
Also consider the crossing angle. When two lines are nearly parallel, their intersection becomes highly sensitive to small bearing errors. If the lines coincide, they cannot establish a unique position.
In the simulator, try the 90°, 45° and 20° crossing examples to compare how the geometry affects the resulting fix.
Do I need DME to determine a position using two VOR stations?
No. Two VOR radials provide two lines of position. Their intersection establishes a position fix without requiring distance information from DME.
DME can provide an additional distance measurement when suitable equipment and a compatible station are available, but it is not required for a two-radial cross-fix.
The distances displayed by this simulator are measured on its chart. They are not readings from a DME receiver.
Why does the calculated fix sometimes differ from the aircraft position?
A position fix is based on measured bearings, which may contain small errors. Even when both radials are close to their correct values, their intersection can differ from the aircraft's actual position.
The crossing angle determines how strongly those errors affect the result. Near-perpendicular radials generally produce a better-defined fix, while radials that cross at a narrow angle can create a much larger position uncertainty.
Adjust the simulator's uncertainty setting and compare the example crossing angles. The shaded area illustrates how the possible position error changes with the geometry.
