Lesson 26 - Navigation

This was another series of lessons I had been looking forward to. I enjoy ground based navigation, love maps, etc and so was looking forward to translating this to the air.

We had quite a lengthy pre-flight briefing, as there was a lot to cover. Out with the maps and the plotters and the Flight Computer (or "whizzy-wheel"). First off was to draw the route on the map: we were going to Hanningfield Reservoir, then heading off to Tonbridge Wells, then to Sheerness and then back over the Thames to Southend.

To track the route I was introduced to a flight plan. The order of calculation is as follows:
- from the routes on the map work out the safety altitude and - considering any restricted airspace, safety altitudes, etc, work out the altitude for each leg.
- Using the square protractor meassure the required track.
- Note the wind direction and velocity for each leg (for this exercise, we assumed they were all the same 110/15)
- Note the airspeed of the aircraft for each leg.
- Using the "whizzy-wheel" calculate the drift due to the wind for each leg and thus calculate the true heading.
- Read the magnetic variance off the map and recalculate the heading to give the magnetic heading. This will be the reading I would follow on the direction indicator for each leg.
- Using the "whizzy-wheel" again work out, given the effect of the wind, what the groundspeed would be.
- Measure the distance between the waypoints
- Calculate the time between the waypoints given the groundspeed and the distance.
- Repeat the above for each leg!!

So far, so good. Now we had the route planned out, Tim went through the brief on what we would be doing in the air.

At each waypoint, I would follow a set process: TURN - TIME - TALK
TURN = Turn onto the next heading
TIME = Reset the time or calculate the ETA at the next waypoint (or mid-point for longer legs)
TALK = Do I need to report to whichever Air Traffic Information Service I happen to be talking to?

Following this, once I had settled into the next leg, it is good practice to carry out a cruise check - also known as a FREDA check:
F = Fuel (is it on, do I have sufficient?)
R = Radio (am I tuned to the correct frequency, when do I need to change and have I dialed in the next frequency?)
E = Engine (temperature & pressure, carb heat, sucking, charging)
D = Direction (are the Direction Indicator and Compass in alignment, am I headed in the right direction?)
A = Altimeter (is the Altimeter set to the correct pressure setting? Am I flying at the correct altitude?)

Tim's other main tip for navigation is "Map Away - Fly the Heading". Given that all the calculations are correct, then it is better to fly the heading in a straight line for the required amount of minutes and you will reach your destination. If you try to follow the map all the time, you won't fly in a straight line and you are more likely to get lost or get distracted with the map rather than in flying the plane.

Keeping an eye on the time, however, 2 minutes before you reach either the mid-point or the waypoint, out with the map again. Look at the map and identify what you expect to see, then look to see what you actually see. You should identify your position using three factors, one of which can be the time, e.g. I expect to be here at this time (1) and I expect to see a small town (2) nestling in a bend in the river (3).

If you are doing this at the waypoint, then you may need to correct your heading/time calculation. For heading, you use the 1 in 60 rule: After 60 miles, if you are 1 mile either side of your intended destination, then you are 1 degree out. This can be extrapolated back, for example if you are a mile out after 15 miles, then your track error is 4 degrees. To get back to your intended destination, you would need to correct by double the track error - for example if I am 1 mile to the right of the halfwaypoint after 15 miles of flying at 180 degrees, I have a track error of 4 degrees, which means I need to fly 4 x 2 = 8 degrees to the left to get back to my intended direction: i.e. 172 degrees.

Confused yet??

Anyway, the flying went pretty well. Tim was quite happy that I had decided on the route of keeping the navigation simple and so had flown fairly accurately to each waypoint. I needed to get into the habit of TURN-TIME-TALK at each waypoint, but my height keeping was OK and I worked out my drift error at the half way point between Hanningfield and Tonbridge Wells.

I just had a bit of a hiccup on the radio communications with Southend Tower when I was rejoining. But otherwise an excellent and fun lesson.