A question on VOR approach . . .

[cookmg]

Hello,

The OCN Vor-A approach in San Diego starts with a hold on the 270 degree radial. You fly inbound to the Vor bearing 090 and upon crossing the vor you track outbound on the 096 degree radial. This is the final approach course. My question is, if after station passage you do you 5Ts and twist the obs to 096, if you show a full scale deflection is it a missed? Or, can you attempt to correct heading and track the 096? When must the full scale deflection be considered a missed?

Thanks.

Mike

 

[Andy Neill]

Let me take a stab at this.

First, recognize that even if the final approach course continued on a course of 090 and you were dead center at station passage, you would wind up with a MOMENTARY excursion of greater than 10 degrees as you passed over the station.

Now consider the same scenario (continuing on a 090 course) and what your track would be relative to a 096 course. Once you passed OCN, you would see the needle stabilize 6 degrees off to the right when you turned the OBS to 096. Still not full scale deflection.

If I were doing the approach, I would lead the course change a LITTLE (only 6 degrees remember) and, as I changed the OBS and started the time at the station, I would expect to see the needle centering up from a half-scale left of course deflection. In a perfect world, as I rolled out of the turn, I would look down to see the course needle centered and would then make my final descent and wait for the 3.4 miles to drift by while looking for the field.

 

[GeorgeTG]

Agree

Another Thought:
Not all approaches are going to have "just a 6 degree" heading change. Based on the equipment in your aircraft you can select 2 methods for performing the intercept:

With Distance information (GPS RNAV DME):
Lead the turn as Andy mentioned. Your purpose is to quicly intercept the final approach course.
If your aircraft is flying between 120-140 you can use a rough guess of .9-1NM turn radius; this includes roll in time to establish the turn. You can further "guesstimate" your lead by using 10% of the angle to turn as your lead DME (90 deg .9NM, 30 deg .3NM)
The purpose of leading a turn is to begin the turn at a point that will allow you to roll out on the next course with the needle centered.
If you have an HSI you can line up the tip of the D-bar with the bottom end of the lubber line to smoothly roll out on course.


Without Distance Information:
Fly over the station, when you see a complete flip of the to from indicator start the time, turn the OBS to the next course and select a meaningful intercept heading to quickly get established on the final approach course.
Base your intercept angle on winds and turn angle. If this is the final approach course your goal is to get a "live" needle as quicly as possible. Only with positive course guidance can you begin even thinking about a descent...

Cheers
George