instrument-training

Instrument Flying: Day 4, Instrument Navigation

Now we’re getting into the fun stuff-how to navigate with our heads in the clouds. I have to say that having a map display is worth its message in gold for improved situational awareness.

Before we progress to some of the challenges in this lesson, you must remember one formula.

MH+RB = MB
Magnetic Heading + Relative Bearing = Magnetic Bearing.
Or, as my instructor says:
More Hobbs + Real Beer + More Beer.

One thing you’ll learn about flying, when there are a lot of facts to remember, we make anything up to help job the memory. The point being, when you go in to take your test, make sure you write this formula down and use it. Don’t get too confused. You’re just solving for the missing piece.

If we’re flying on a Magnetic Heading of 270 and the question is, what is our Relative Bearing to the station if we’re on a 120-degree radial?

Note: Radials are always out of a station, whereas bearings are always to the station. Therefore, if we are on the 120 radial the Magnetic Bearing to the station would be the reciprocal of the radial (300).

RB= MB-MH

We subtracted the RB from both sides, keeping the equation equal, and now we have to solve for RB.

MB= 120+ 180 (reciprocal) = 300 MH
MH= 270

RB = 300-270 = 30 degrees. Relative bearing to the station is 30 degrees. What does this mean? It means that the station is 30 degrees off the nose of the station.

Don’t be lulled into complacency. They will ask you what the bearing “from’ the station is. You’ll need to figure the reciprocal.

VOR Navigation. One of the greatest navigation inventions was the HSI-Horizontal Situation Indicator-an instrument that overlays the VOR information over the rotating compass card. You always know where you’re going and in relationship to the VOR.

If class there was a bit of confusion about where am I? I’m going to give you the basic “how to’ know gouge.

The Course set knob (with the yellow arrow) can be rotated to any course to or from. If you want to know where you are, turn it until that center needle, depicted off to the right, moves inline with the head and tail of the arrow. Now, you are on a course to or from the station. But which course and where are you?

It doesn’t matter which direction you point the head of the needle, as long as you realize that the white triangle is going to be pointing to the station. If that’s the case, the number that is on the same side as the white “to’ triangle, is the heading “to’ the station. Whatever the other end of the needle is pointing to, opposite side of the to arrow, that is the radial you’re on.

Also, the little hashed white marks across the center of the middle of the indicator… those are 2 degree marks. So, in this instrument above, the needle is 6 degrees to the right. If you rotated that course knob to the right to 086, the needle would center.

In this case, the head of the course needle is pointing the same direction as the to the station, white triangle. The radial we are on is the reciprocal of 086. Add 180 degrees to 086 and we’re on the-266 degree radial.

What if you spun that course selector all the way around to 266? Would anything change? No. The needle would still be centered. The white triangle would still be pointing to the station. You can still know where you are despite the where you set the course.

Now, a VOR indicator is an entirely different animal, and can get confusing. You have to move the heading to match up with your heading. And it really helps to visualize which direction your plane is flying, and then note if the needle is to the left or right of your course.

Test question time:

VOR station passage is the first positive, complete reversal of the TO/FROM indicator.

Almost forgot about the RMI: The tail of the needle set to a VOR station indicates the radial you are on FROM the station. The head of a RMI needle set to an ADF shows the bearing TO the station and the tail of the needle indicates the bearing FROM the station.

Time and Distance:

Did you know – if you hold a constant heading, the time to the station is equal to the time it takes for the relative bearing to double?

Equipment check: Within the previous 30 days.

  • To make a VOR receiver check on the ground, set the OBS on the desired radial, and the CDI must center within plus or minus 4 degrees of that radial with a “FROM’ indication.
  • Allowable error when using an airborne checkpoint is plus or minus 6 degrees.
  • Allowable error on the ground or in the sky when comparing two VORs against each other is plus or minus four degrees.

More to come with Day 5: The Flight Enviornment

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