Transcript Slide 1

VFR Navigation
The Standard Closing
Angle Technique
Richard Champion
The Standard Closing Angle Technique
• Aim
– To learn how to get back on to your planned course
during a cross country flight.
• Objective
– By the end of this briefing, you should be able to use the
Standard Closing Angle technique to return to your
planned course when your map reading indicates you
have deviated.
• Airmanship
– Good navigation, avoiding airspace busts
• Agenda
–
–
–
–
–
Background
Advantages/Disadvantages
How to use it
Examples
Summary
Background
• The Standard Closing Angle is a heading change that will bring
you back onto your planned course in the same number of
minutes as you are miles off course.
• Mathematically, it is calculated by dividing 60 by the aircraft’s
True Air Speed (TAS) expressed in nautical miles per minute. A
table can be prepared:TAS
60
70
80
90
100
110
120
Miles / Minute
1.0
1.2
1.3
1.5
1.7
1.8
2.0
Basic SCA
60
51
45
40
36
33
30
Modified SCA
30
26
23
20
18
16
15
• Angles of more than 30° are undesirable, so for speeds of less
than 120 kts, the Modified SCA is used and the new heading is
flown for twice the time – i.e. 2 x the number of miles off track
Advantages/Disadvantages
Advantages
• Simple
– all you need to remember is the
modified SCA for your normal
cruise TAS
• Quick
– Gets you back onto your
planned track as soon as
possible
• No mental maths required
– Leaves you free to fly the
aircraft
• It Works!
– It is a proven technique,
approved by examiners.
Disadvantages
• Not perfect
– The calculations are not 100%
correct (because based on
TAS, not groundspeed), so
some purists object.
– Does not work for very large
drift errors.
How do you use it
1. Mark your actual position on your chart.
2. Estimate or measure the number of miles off course.
3. Add or subtract the modified SCA to your heading:
–
–
Add if you are turning right to regain course
Subtract if turning left
4. Turn onto heading and note time (or start watch).
5. Fly for 2 minutes for every mile off course.
6. During this time, analyse the reasons for being off course:
–
–
–
–
Forecast wind incorrect?
Bad flying?
Misaligned DI?
Lucky horseshoe left next to compass?
7. When the time is up, turn back onto original heading, adjusted if
necessary to take into account the reason for the original deviation.
8. If you are too close to your next turning point to allow 2 minutes per
mile, double the angle and halve the time.
Example 1
• TAS 90 Kts = SCA 20°, Heading 051°, Time for leg 32mins
• After 8 minutes:– Actual Position Lewis, 2Nm off track
• Turn on to new heading = 031° (=051° – 20°)
• Time on new heading – 4 mins (ie 2Nm x 2)
350/20
• Actual position- Uckfield, back on track
• Consider reason for being off track
– (DI misaligned with compass by 15°)
• Realign DI, Turn back to 051°
• Continue Flight
Example 2
• TAS 90 Kts = SCA 20°, Heading 051°, Time for leg 32mins
• After 16 minutes:– Actual Position Crowborough, 3 Nm off track
• Turn on to new heading = 071° (=051° + 20°)
• Time on new heading – 6 mins (i.e. 3 Nm x 2)
• Actual position- Bewl, back on track
• Consider reason for being off track
– (Wind not as forecast, less drift than expected)
•
•
•
•
Turn back to 051°.
Adjust for lower drift (+5°)
New heading 056°
Continue Flight
350/20
Example 3
• TAS 90 Kts = SCA 20°, Heading 051°, Time for leg 32mins
• After 24 minutes:– Actual Position 6 Nm off track
• Consider turn to 031° (=051°- 20°)
– But, time required on new heading – 12 mins (i.e. 6 Nm x 2)
– Too close! Only 8 minutes left to run.
• Double the angle, halve the time.
• Turn on to 011° (=051° - 40°)
• Fly for 6 minutes (ie 6nm x 1 min per mile)
• Actual position– 2mins from Headcorn.
350/20
Summary
• We have learned about:– What the Standard Closing Angle is
– How it is calculated.
– The advantages and disadvantages to the SCA
technique.
– Using the modified SCA for TAS less than 120kts.
– How the SCA is used in flight to regain planned track.
• Now memorise the (modified) SCA for the normal
cruise TAS for your aeroplane. It is all you need
to know in order to fly an accurate cross country.
• Do your FREDA checks !