BRAA Calls: Bearing and Relative Bearing

The TID is capable of displaying the Bearing to a hooked contact. This reading is, however, not the common bearing used, for instance, in a BRAA call. This value is relative to the aircraft (from now on, I called it RBRG for Relative BRG) and “locked” to the orientation of the F-14: this means that RBRG 0 will always be straight ahead, RBRG 180 to 6 o’clock, RBRG 010 will be 10° to the right of the nose, and so on.
The Relative Bearing is useful to perform minor adjustments and give indications to the pilot because it gives the direction (0<RBRG<180 = turn right; 180<RBRG<360 = turn left) and the angle, but it is not a useful number to share with a controller or other flights.

There are a number of way to approximate or calculate the Bearing. The crew can eyeball it from the Electronic Countermeasures Display (ECMD), the Bearing Distance Heading Indicator (BDHI) or calculate it by means of the readings provided by the TID, by combining the values of HDG and RBRG.

The following images show how to simply calculate the Bearing.
In primis, obtain the Magnetic Heading (HDG) from the TID (CAP: OWN AC, CLEAR, 8):

rio-BRAA-bearing-MHDG — F-14: Magnetic Heading reading from the TID

Then the Relative Bearing (RBRG) to the Hooked target (CAP: CLEAR, 0):

rio-BRAA-bearing-BRG — F-14: Relative Bearing reading from the TID

The Magnetic Heading is highlighted with a red line, the Relative Bearing with a blue one.

The Bearing values is equal to, if TGT_RBRG between 0° and 180°:

Bearing = F-14_MHDG + TGT_RBRG

Otherwise:

Bearing = F-14_MHDG + TGT_RBRG – 360

In this case, the result is 82°.
The following is the same situation displayed by the F-10 map:

rio-BRAA-bearing-F10-map — Bearing displayed by the F10 map.

The BRG value here displayed differs from the result we calculated because the F10 maps displays True Heading, whereas the F-14 uses Magnetic. The Tunb Kochak airport has MagVar of 1.9°; by adding it to our Magnetic Bearing, the True Bearing now resulting is 84° (approximated because the TID doesn’t use decimals).

Other examples:

Black arrow: 0° Relative BRG;
Red arrow: Magnetic Heading reading;
Blue arrow: Relative Bearing reading;
Green arrow: Bearing to Target.

MHDG=069°; RBRG 13° BRG= 069 + 13 = 082°
MHDG=090°; RBRG 350° BRG= 090 + 350 – 360 = 080°
MHDG=270°; RBRG 45° BRG= 270 + 45 = 315°
MHDG=270°; RBRG 270° BRG= 270 + 270 – 360 = 180°
MHDG=135°; RBRG 180° BRG= 135 + 180 = 315°
MHDG=285°; RBRG 105° BRG= 285 + 105 = 390° → 30°