Hi flightsimmers - This is a question about tracking a VOR radial. in fs9 i have noticed that the red tracer line of the airplane's route on the world map is not always exactly straight to the VOR, sometimes it appears that the airplane seems to be weaving slightly to the left and right of track, even at a distance of over 100 miles out. so i really just wanted to know if this is because of a simulator deficiency or in the real world does this happen as well? i'm sure sometimes that i can get a dead straight line to a VOR but it depends on the airplane in use.

The accurancy of maintaining a track on a specific radial goes down the further away you are from a VOR. It has to with beam dispurtion over distance.The weaving can be due to hunting back and forth around the beam due to the lower resolution of the indicator. Autopilots functioning on NAV also can weave just a bit as they leave the peak and head back toward it, go past a bit, and return. This is not like GPS navigation which is more accurate if the number of acquired satellites is maintained because there is more than one source to target.When you get really close to a VOR the beam is so tight that chasing the needle will get you all over the place by you overcorrecting. This is called PIO or "Pilot Induced Oscillation".The are very nice nav tutorials here:www.stoenworks.comwith practical hints from a retired corporate pilot.

Thanks for the helpful info everyone. Ron, just a heads-up: what you describe is not pilot induced oscillation.Pilot induced oscillation occurs in aircraft with neutral or negative static or dynamic longitudinal stability. It happens when the aircraft is pitched out of level flight, and the pilot tries to dampen the resulting pitch oscillations by moving the yoke back and forth. If the pilot is unsuccessful in dampening the pitch movement, then the oscillations can become exaggerated to the point of uncontrollability. Fortunately most aircraft are designed with positive static and dynamic stability which means that when the airplane is displaced from level flight there is a very strong tendency to return back to level flight and stay there. In this case there is no pilot-induced oscillation.What you do describe, when the pilot chases a CDI instead of bracketing and maintaing a course, there is no technical term to describe that other than just plain poor piloting technique.

Thanks for the correction. I thought it applied in both horizontal and vertical control.

My pleasure and thank you, Ron. Have a great holiday, best regards

Pilot induced oscillation was the reason why a prototype Raptor crashed back in 1992 and a Swedish, also prototype, J-39 Gripen crashed in the middle of Stockholm. Obviously there was a fault in the design of the flight control system and if the plane you are flying is naturally unstable, you really really want to be able to rely on the computer!

Thanks ronzie for your link to the nav tutorials, my airplane - the BAC 1-11 was on autopilot and tracking the radial on NAV. i'll do another flight later today.