Charts, Dead Reckoning and Flight Planning
Projections
A Mercator chart is conformal, shows rhumb lines as straight lines and great circles as curves, and its scale increases away from the equator by secant latitude, so distances must be measured at the latitude in use. A Lambert conformal conic has straight lines that closely approximate great circles and true scale on its standard parallels. Polar stereographic suits high latitudes, while transverse and oblique Mercator are used for specific grids.
Chart reading
Scale is a representative fraction: 1:500,000 means 1 cm represents 5 km, and a small-scale chart covers a large area with less detail. Candidates must read contours, spot heights, maximum elevation figures, airspace and aerodrome data, and must be able to convert between map measurement and ground distance.
Dead reckoning
The triangle of velocities combines heading and TAS with the wind vector to give track and groundspeed. Drift is the angle between heading and track. Track error is the angular difference between the planned and actual track, measured at the fix, and closing angle is computed from the remaining distance to destination.
Flight planning
Fuel required = burn rate × time, plus taxi, contingency, alternate and final reserves. The plan must respect MTOW, MZFW, MLW and centre-of-gravity limits. Points of no return and equal-time points depend on wind and fuel, not on distance alone.
Rule of thumb: the 1-in-60 rule
An error of 1 nm in 60 nm subtends about 1°. Worked example: after 60 nm the aircraft is 6 nm off track, so track error is 6°. If 120 nm remain to destination, closing angle = 6 × 60/120 = 3°, so the heading change needed is 6° + 3° = 9°.
Traps: measuring distance off the Mercator scale, ignoring wind when converting heading to track, and using TAS in place of groundspeed for timing.