Navigation
This domain tests dead reckoning, magnetism, the triangle of velocities, radio navigation and chart work.
Magnetism
- Variation is the angle between true and magnetic north at a place; deviation is the error within the aircraft caused by its own magnetic fields.
- Variation east, magnetic least: heading magnetic = heading true minus easterly variation. Deviation east, magnetic least as well.
- Deviation is read from the compass swing card; it changes with heading and with electrical load.
- The direct-reading compass has turning and acceleration errors: it under-reads in a turn through northerly headings and over-reads through southerly. During acceleration it under-reads on easterly or westerly headings (ANDS: accelerate north, decelerate south).
Triangle of velocities
- Track and groundspeed come from the true heading and true airspeed combined with wind velocity.
- Drift is the angle between heading and track; correct into wind.
1-in-60 rule
- A 1 degree error over 60 nm puts you 1 nm off track. A 60 nm leg flown with 5 nm of closing error needs a 5 degree heading change to regain the track and 10 degrees to converge.
Radio navigation
- VOR gives a radial from the station - magnetic, referenced to the station. To fly inbound on the 270 radial, the aircraft track is 270 degrees magnetic and the OBS is set to 270 with a TO indication.
- NDB and ADF give relative bearing; track equals heading plus relative bearing with no wind.
- GNSS with RAIM is increasingly the primary means; check notams for jamming and receiver autonomy before desert operations.
Worked example
After 40 nm on a 090 degree track you are 4 nm left of track. Closing angle = (4/40) x 60 = 6 degrees. To parallel the track, turn right 6 degrees; to regain the waypoint at the planned distance, turn right about 12 degrees.
Traps
Applying deviation to the chart instead of variation; forgetting that VOR radials are magnetic; using groundspeed for a time calculation done on TAS.