Reverse Sensing

In last months IFR Clinic we discussed how VORs work. Boring and repetitive as that is, we needed to start there to get the basis for understanding a localizer and a localizer back course using a conventional dedicated navigation indicator (VOR/LOC) and the need to sometimes chase the CDI to correct, and sometimes to pull it. Theres too much material for a proper review, so lets just skip right to the good stuff.

Frank Bowlin

Wednesday, June 08, 2016 at 12:00 AM ET

Verified

Key Takeaways:

Traditional VOR/LOC indicators require complex rules for localizer approaches (e.g., knowing when to "chase" or "pull" the needle) because the Omni-Bearing Selector (OBS) is ignored by the electronics.
The Horizontal Situation Indicator (HSI) simplifies localizer navigation by combining a gyro heading indicator with the VOR/LOC display, rotating the course indicator with the aircraft's heading.
By consistently setting the localizer's inbound front course on the HSI's OBS, pilots can always correct their course by "chasing the needle," eliminating the need for complex mental calculations regardless of front or back course.

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In last month’s IFR Clinic we discussed how VORs work. Boring and repetitive as that is, we needed to start there to get the basis for understanding a localizer and a localizer back course using a conventional dedicated navigation indicator (VOR/LOC) and the need to sometimes chase the CDI to correct, and sometimes to pull it. There’s too much material for a proper review, so let’s just skip right to the good stuff.

The Rules

Rule #1

Always (always!) put the localizer inbound front course under the omni-bearing selector (OBS). The OBS setting doesn’t matter to the electronics on a localizer, but this is a good rule as we’ll see a bit further down.