CALCULATING IN-FLIGHT
WINDS
SITUATION:
• The TH of your aircraft is 350 with the TAS
of 150 kts. GS has been determined to be
160 kts, and the Track is 355. What is the
wind?
• ESTIMATE! First compare TAS to GS to determine
HW/TW component: GS<TAS =HW.
•
Now, compare TH to TK: TH<TK means a Right
Drift which is caused by a Left Crosswind.
• We know that we are experiencing a Left Tailwind.
The 10% Rule states that at a TAS of 150 kts, 15 kts
of crosswind will give us about 6º of drift. A drift angle
of 5º would only require about 13 knots of crosswind.
The in-flight wind would be closer to the wing line at
about 225º/18 knots
Heading
• The word heading refers to the direction in which
an aircraft is pointing. Heading may be
measured from true north, magnetic north, or
compass north, and is always expressed in
degrees as a three figure notation.
• Thus, an aircraft heading true west is said to be
heading 270(T). This could be 265(M) or 262(C),
depending upon the amount of variation at the
aircraft's position and deviation concerned.
Similarly, an aircraft heading in a true direction
of north east is said to be heading 045(T).
Track
• The track of an aircraft is the general term used to
indicate the path followed by the aircraft over the
ground. It will usually differ from the heading due to the
wind velocity. If the aircraft is flying in conditions of zero
wind then the track and the heading will be the same.
Also, if the aircraft is heading directly into wind, or flying
directly downwind, the track and the heading will be the
same.
• In all other cases there will be an angular difference
between track and heading, called 'drift', which is
governed by the wind velocity. The angular difference
occurs because the aircraft now has two forces acting on
it simultaneously, and will therefore move in the resultant
direction
• Direction of the route between two wishes places is
called the required track or course.
• The path which the aircraft subsequently follows is called
the actual track and if the calculations made by the
pilot are accurate, and the forecast wind velocities are
correct, then the required track and the track made
good will be the same. In these circumstances the
aircraft should remain on track. However, if the actual
track made good is not the same as the required track
the aircraft is said to be off track and the angular
difference which then exists between the actual track
and the required track is called the track error.
• Track error is expressed in degrees port (P) or starboard
(S) of the required track.
Velocity
• A velocity comprises two elements, a
direction and a speed. In navigation the
direction is measured clockwise from a
given datum which is usually true north.
Speed is the rate of movement per unit of
time. The speeds used in navigation are
nautical miles per hour which are named
knots or abbreviated kt.
True Airspeed (TAS) and
Groundspeed (GS)
• The speed of movement of an aeroplane
relative to the undisturbed air is referred to
as the true airspeed. If the speed is
measured relative to the path over the
surface of the Earth, it is referred as the
groundspeed of the aircraft (G/S).
Heading.
Wind Velocity.
• A heading of an aircraft is the direction in
which the nose is pointing.
•
Wind velocity is the direction from
which the wind is blowing and its speed of
movement over the Earth.
EXAMPLE
• An aircraft has a TAS of 300 kt and
heading 290°(T). The drift is 17° port and
the groundspeed as 345 kt.
• Determine by vector construction the wind
velocity affecting the aircraft at this time.
SOLUTION
• Remember that drift is the angle between the aircraft's heading and
track measured left or right (port or starboard) of the heading.
• Construct true north datum.
• Select a suitable scale ic. 1cm - 25nm
• Plot the true heading 290(T). Mark with one arrow.
• Measure the distance to scale for 1 hour at TAS (300nm = 12cm).
This point is the air position.
5. Calculate the true track (290-17) = 273°(T)
• Plot the track 273(T). Mark with two arrows.
• Along the track to the same scale, measure I hour at groundspeed
(345nm = 13.8cm). This point is the ground position.
• Join the ends of the two vectors.
• Remember that wind blows from air position to ground position.
Mark with three arrows.
• Measure the length of the wind vector (approx. 4.2cm).
Solution
TN
Scale 1cm : 25kt
TAS 300kt
WS/WD
105kt/2100
Hdg 2900 (T)
Drift 170 Port
Ground speed 345kt;
Track 273 0 (T)
EXAMPLES
• An aircraft heading 070°(T) at TAS 250 kts is making actual
track of 090°(T) at a ground speed of 270 kts. Find the wind
velocity
• An aircraft is heading 270 (T) at TAS 240 kts when the
Wind Velocity is 200/60. Find the track and ground speed
• An aircraft is required to fly between two positions such that
the required track between them is 045(T). The forecast
W/V is 090/70. The aircraft's TAS is 260 kts. Find the
heading to steer and expected ground speed for the flight
• Aircraft Hdg 090(T), TAS 450kts, W/V 025/50. What are TA
and GS