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What makes the difference with VFR flight which uses visual means, IFR fligth or "on top" VFR ( overhead the cloud layer) uses instruments to fly from one airport to another like VOR, NDB, with or without DME or also GPS.

GPS navigation won't be teached here as the technique is so simple to master, that you only have to follow what is indicated.

But with the VOR or the NDB, different techniques have to be practiced to manage a complete flight.

Homing :

VOR or NDB is used to fly directly to a station using a QDM : this way you fly from one station to another to join your destination.
Careful, with the NDB, the indicator always locates the station.
With the VOR, you have to "tune" the indicator to get the "to" information in order to read a QDM, otherwise, with a "from" you will get a QDR ( a fly away radial). But with this way of tuning, other methods are becoming possible !

Distance measurements :

Choose a reference QDR or QDM which is different than the one we are using.

• In the direction we need.
• >10° from your present position if the station is a VOR.
• >20° from your position if the station is a NDB.

Fly at a magnetic heading 90° from the reference radial and calculate starting and ending QDMs or QDRs .

• 5° before and after reference QDM if you use a VOR.
• 10° before and after the refenrence QDM if you use an NDB.

Write the time passed while flying between these two radials ( in seconds).

You can calculate : T (mn) to join the station = T (sec) / ß
and ß = 10° for a VOR or 20 ° for a NDB.

Changing axis method :

enables to fly from your origin to the willing QDM.

•(180-A) / 2 method :
This method enables to change to any QDM while staying at the same distance from a station so as not to loose the estimated work. This method works for angles <120°.

• The diverting angle is (180-A)/2.
• The diverting heading is : originate QDM ± (180-A)/2
• We will proceed to a distance measurement to get T.
• Watch for the anticipation to the return curve to the arrival QDM which is ß (anticipative angle in degrees) = 30 / T where T is the calculated time.

• Semi-variation method :
When homing, on a QDM, you can join another axis while reaching 30 seconds before the station. This procedure will begin 3 minutes before the station.

• At 3 mn, the pilot turns by 30 ° towards the desired QDM.
• At every 30° change on the indicator, the pilot closes his turn by 10° until arriving 10° before the desired QDM.
• At this moment, he tursn directly with a continuous curve towards the desired QDM and will arrive automatically, 30 seconds before overhead.

Careful : this method works mainly with 90° variation maximum..

• Equal side triangle method :
If the angle between the departure and arrival QDM's is between 15 and 45°, turn at an A angle to the desired side and mark the time with a "top".
When reaching the arrival QDM, turn to the station.

•  Time elapsed until turning = Time left before overhead.

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