thomas.ljung

The VBI provides 3 fields: FPA (Flight Plan Angle) is the vertical path in degrees that the aircraft is currently flying. V/B (Vertical Bearing) is the vertical path in degrees that the aircraft SHOULD be flying to reach the keyed waypoint. V/S (Vertical Speed) is the vertical bearing (V/B) converted into vertical speed for easy input into the MCP. FPA is the actual flight path angle of the aircraft. It is typically 3 to 4 degrees in a descent. V/B is the required vertical bearing to reach the WPT/ALT. This would be an altitude restriction in the LEGS page that you could enter (or delete) manually or with the ALT INTV button on the MCP. V/S is the required vertical speed to make good the V/B. As you approach your ToD the FPA will remain at zero (because the aircraft is in level flight), but the V/B and V/S will both increase until the V/B is at about 3 to 4 degrees, or whatever the FMC has calculated is the optimum value. If VNAV is engaged the aircraft will descend with a FPA equal to the V/B. The actual V/S will however be slightly different to the computed V/S because V/S changes during the descent. Read more about the FMC: http://www.b737.org.uk/fmc.htm This is also informative: http://www.flaps2approach.com/journal/2012/7/23/vertical-bearing-indicator-vbi-how-to-calculate-a-controlled.html