10-Mile Nav Technique?

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Member for

24 years 2 months

Posts: 2,606

Does anyone use a 10-mile nav technique? (as professed by Irv Lee). I have CPL nav coming so am considering using it as an overlay to the traditional method - would this be permissible?

The conventional method has you work out track, TAS, wind, drift etc etc from the chart+214. Now fly the heading, fly the time... That's the theory. However that 214 is an unreliable data source sometimes. How then would you go about correcting any deviation without being accused of "feature-crawling" (a no-no for CPL)?

The 10-mile method breaks the leg up into 10 mile segments back from the first waypoint. Therefore the inital segment is a non-standard length, but the segments thereafter are all 10nm and so times can be determined. So if you're lucky enough to be doing 120kts, i.e. 2 miles per minute, each 10nm leg is 5 minutes. At each segment point (usually spotted by proximity to a ground feature) you can assess your deviation off-track, then your ETA versus the ATA. So if the segment took 6 minutes, you can then apply revised 6min timing to the next segment and so on. Thing is I can't quite remember how to adjust for drift :o Max drift calc?

Anyway my theory is that the 10-mile method can be used airborne to validate the conventional method. My worry is that on a bad day it may look like you could be also throwing the conventional plan into the bin!

Original post

Member for

20 years 7 months

Posts: 2,623

BR I think the important thing is not to over complicate it, what you may find is that if you start adopting this technique your instructor "may" say "naa don't do it like that, do it like this".
I guess the bottom line is, use what works for you, if your nav technique works now that you have learnt from PPL/Hr building then don't change it.
In answer to your original question I haven't heard of, or used that technique before

Member for

24 years 2 months

Posts: 2,606

My "hour-building" has taken 5 years ;) But I went out and did what Rufus, Moggy etc suggested.

Bad habits set in following the PPL. I would say many pilots don't even go so far as drawing a line on their chart. Some are embarrassingly too reliant on GPS even on short, easy trips. With this mindset, no wonder the NOTAMs don't get checked...

Tried the 10nm thing again on FS last night using my PPL NFT route (Wellesbourne, Hay-on-Wye, Montford Bridge) works rather well. I'll try it again for divert today, iirc I did Hay-Montford diverting part way to Tewkesbury with its distinctive river system. (yes EGBJ is also a big giveaway!)

Member for

24 years 2 months

Posts: 2,606

Well I diverted about 15nm into my Hay-on-Wye to Montford Bridge track. Eyeballed about 120 deg to Tewkesbury and ran on 6 minutes for each segment. This pretty much gave me the ETA there but further segments got it to within 30 seconds. Besides external features, I used VOR crosscuts from BCN/SWB/HON to confirm segments. With some bumpy weather (yesterdays download), not knowing the accurate wind and poor track keeping, I ended up 3nm north of track over Malvern town. But for a 40nm-odd divert I suppose that's not too bad.

Remind me, is the 1:60 rule

Track Error = (Distance Offtrack / Distance Gone) * 60
Closing Angle = (Distance Offtrack/ Distance Remainin) * 60

?

Member for

20 years 6 months

Posts: 199

Wow. It sounds like you really like to complicate matters.

Here's what I do - it's very similar but a bit more friendly.

Look alongside your map track for good identifiable features, which are approximately 5 minutes apart. It's better to find great features which are not common, and that stand out, and head for/past them, rather than find yet another bridge along a river... Then figure the ETA for these features. Write that time on the track.

Your closing angle calculation depends on whether you wish to get on track early (best advised most of the time) or whether you simply want to overfly your next turnpoint (from a different track). Also remember to add/subtract your original heading error that got you off course in the first place....

Member for

24 years 2 months

Posts: 2,606

I have since....

- learnt to keep my head out of the cockpit and look where I'm going at the risk of going outside altitude/heading tolerances. Also helps with the lookout
- remembered (just) that I can calc times using the whizz wheel on my watch bevel :rolleyes:
- I have a 4 minute thumb, at 120knots on a half mil, the most accurate method yet for a diversion
- bent my half mil every which way so have sliced it down just to an extended training area. Stick interferes with amount of lap space available (oh for a yoke). Cut down chart easily folds and fits on my A5 kneeboard (its AFE and grey if Moggy is interested ;) )
- learnt to keep updating positions with times on the chart with soluble ohp pen
- found that a square protractor on your position can be helpful for course corrections
- have a quarter mil on standby

With the first £2.5k down, we start on the Twin Star next week.