Dead reckoning and the navigation computer
Navigation · Chapter 6 · DGCA CPL and ATPL
Why wind moves the aircraft, and how to answer every wind, runway, TAS and Mach question on the CX-3, the computer the DGCA exam uses.
Remember
- The aircraft flies inside a moving block of air: heading is where the nose points, track is where you go; the angle is drift.
- Wind Correction: type the four lines you know (all true); the CX-3 fills in the rest. WCA minus = nose left.
- Wind Component: WSpd, WDir, Runway number. X Wnd plus = from the right; H Wnd minus = tailwind. Runways are magnetic.
- Airspeed: OAT, CAS, PAlt → TAS and Mach. OAT and MACH 1 → the speed of sound. Below zero: number, then ±.
- Compass Heading: CHdg = THdg + Var + Dev, with west as plus and east as minus.
Why does the aircraft not go where its nose points?
What wind does
- Still water • A boat at A points straight across and goes 10 kt through the water • No current: after an hour it is at B, straight opposite
- Now the river flows • Same boat, same heading: the nose still points at B (gold) • The current carries the water, and the boat in it, 5 NM downstream • It lands at C (pink)
- The air is a river too • An aircraft flies inside a huge body of moving air, an air mass • The whole block of air moves over the ground: that movement is the wind • It carries the aircraft with it, wherever the nose points
- Heading, track, drift • heading: where the nose points (gold) • track: where you really go over the ground (pink) • drift: the angle between them
How does one CX-3 screen answer every wind question?
The Wind Correction screen
- No drawing in the exam • In the DGCA exam you do not draw a wind triangle • You type the numbers into the CX-3 and read the answer • One screen, Wind Correction, answers the heading, the track and the wind questions
- Seven lines • GS ground speed · TAS true airspeed • TCrs the track (true course) · THdg the true heading • WSpd, WDir the wind (direction it blows from) • WCA wind correction angle: the CX-3 always works it out
- Type four, read the rest • Type the four lines you know: the CX-3 fills in the others • Lines you do not type: leave them empty (press C on any old number)
- Reading WCA • WCA = heading − track • Minus: the nose points left of the track (wind from the left) • Plus: the nose points right (wind from the right) • drift is the same size, the other way: WCA −9 → drift 9° right (starboard, S)
Which heading flies the track you want, and how fast over the ground?
Heading and GS from track
This lesson is part of the Navigation plan. See plans
Where will you go if you hold a heading?
Track and GS from heading
This lesson is part of the Navigation plan. See plans
How do you work out the wind from what you fly?
Finding the wind
This lesson is part of the Navigation plan. See plans
How fast must you fly to arrive on time?
The TAS you need
This lesson is part of the Navigation plan. See plans
How much of the wind is along the runway, and how much across?
Head and cross components
This lesson is part of the Navigation plan. See plans
How do you get the head and cross parts on the CX-3?
Runway winds on the CX-3
This lesson is part of the Navigation plan. See plans
Solve it: wind sums on the CX-3
Solve it: wind on the CX-3
This lesson is part of the Navigation plan. See plans
What is the average wind between two levels?
The mean of two winds
This lesson is part of the Navigation plan. See plans
Why is the true airspeed higher than the indicated one?
TAS from CAS
This lesson is part of the Navigation plan. See plans
How do you turn a Mach number into a speed, and back?
Speed of sound and Mach
This lesson is part of the Navigation plan. See plans
How long does a whole flight take, with the wind?
Climb, cruise and descent
This lesson is part of the Navigation plan. See plans
How do you fill a whole line of the navigation log on the CX-3?
A whole nav-log line
This lesson is part of the Navigation plan. See plans
Test yourself on chapter 6
Test yourself
This lesson is part of the Navigation plan. See plans