Aircraft Systems Topic 22.
B767 EHSI - Full VOR mode
|This mode provides the same
360 degree compass rose presentation as does a conventional HSI. The FULL
VOR and FULL ILS are sometimes referred to as “ROSE MODE”.
Like the EXPANDED VOR it is oriented magnetic HEADING UP. Weather radar returns CANNOT be displayed in FULL VOR mode, but can be in “Expanded VOR” mode.
Like the conventional VOR, the aircraft symbol is shown in the centre of the compass rose.
It is displayed in white.
The VOR receiver that is feeding tracking information to the screen is displayed in green at the bottom left-hand corner of the screen, whilst the distance to that station is in the upper left corner. In this case the left VOR navigation radio is providing info to this display screen.
CDI bar/aircraft orientation
If the CDI bar is to the left of the aircraft, the desired track is to the left, and vice versa. Turn toward the needle to intercept track.
This is displayed at the 005M compass rose position.
Drift angle pointer
When related to the current heading, this shows the degrees of drift occurring. In this case eight degrees left drift. Track made good (TMG) is 030M/heading 038M. This is logical as the wind arrow shows a wind from the right, being about 070M at 20 knots.
Course selector arrow
The present VOR course selection is 050M, and the aircraft is slightly right of that course but closing on it, as witnessed by the “drift angle pointer” showing TMG of 030M. The calibration of the instrument in VOR mode is 2 degrees per dot. This calibration is automatically loaded when a VOR frequency is tuned. If an ILS frequency was tuned, the calibration would be automatically set at half a degree per dot. With this combination of wind from the right, aircraft close to the station, and an effective cut angle of 20 degrees, the aircraft would soon need to be turning right so as not to pass through the selected course.
Just ahead of the aircraft’s right wing, the TO flag is showing. The aircraft is flying TOward the VOR station. On capturing the VOR course of 050M, the aircraft would be tracking inbound on the 230 radial (ie: 050 + 180). The TO/FROM flag is NOT shown when an ILS is tuned. When the aircraft passes overhead the VOR station, the TO flag will change to FROM. The aircraft would then be tracking away FROM the station on the 050 radial.
This appears at 90 degrees to the course selector arrow on a HSI, not horizontally as is the case in the basic VOR instrument.
This mini-editorial is an abbreviated sample from the book “Flying Glass”, and from the soon to be released online ATPL “Aerodynamics and Aircraft Systems” course. Knowledge of EHSI modes form part of the Australian Civil Aviation Safety Authority (CASA) ICAO ATPL syllabus.
For more information go to http://www.aviationshop.com.au/avfacts/Study_texts.htm
This is one of a series on the B767 EFIS displays - check the editorial index for the others.
An interesting website within Boeing is that related to the quarterly AERO e-magazine.
One particular article to complement what you have read here can be found at:
This e-magazine number 9 includes details of the new B767-400 flight deck.