Dead reckoning and in-flight navigation
Dead reckoning and in-flight navigation
This domain tests the wind triangle, the 1-in-60 rule, and conversions between true, magnetic and compass directions. The exam wants a heading you can fly and a track you can prove.
Wind triangle. Heading and TAS combined with the wind vector give track and groundspeed. Drift = track made good minus heading (right positive). Track error = desired track minus track made good.
1-in-60. Off-track distance ≈ (track error in degrees × distance flown) / 60. To regain track, heading change = track error + closing angle, where closing angle = (off-track distance × 60) / distance to go.
True to compass. Going true to magnetic, subtract easterly variation or add westerly; then going magnetic to compass, subtract easterly deviation or add westerly.
Worked example. Planned track 090°T, variation 20°E, deviation 3°W, forecast drift 6° right. Magnetic track = 090 − 20 = 070°M. Heading to hold track = 070 − 6 = 064°M. Compass heading = 064 + 3 = 067°C. If after 30 NM you are 3 NM left of track, track error = (3 × 60)/30 = 6°; closing angle to a point 30 NM ahead = 6°; turn right 12°.
NZ specifics. Isogonals run roughly 18°E in Northland to 25°E in Southland and change by minutes of arc per year; use the chart value and annual change, not a remembered number. Grid lines on NZ VNCs are true, so variation must be applied before comparing with a magnetic compass.
Traps. Adding easterly variation instead of subtracting; using groundspeed to compute drift; forgetting that wind velocity is "from"; and reporting a magnetic bearing when the question asked for true.