CASA 32/97 Determination under paragraph 178(1)(b) of the Civil Aviation Regulations (Cth)

INSTRUMENT NUMBER:  CASA   32/97

CIVIL AVIATION ACT 1988

CIVIL AVIATION REGULATIONS

DETERMINATION

UNDER PARAGRAPH 178 (1) (b) OF THE

CIVIL AVIATION REGULATIONS

I, TERRY CHARLES ARTHUR WILSON, General Manager Flying Operations Branch, a delegate of the Civil Aviation Safety Authority, under paragraph 178 (1) (b) of the Civil Aviation Regulations:

(a)  revoke instrument number SRS 2/1992; and

(b)  determine that the method of calculating the lowest safe altitude for a route segment for which a lowest safe altitude has not been determined is the method set out in the Schedule.

[Signed T. Wilson]

Terry Wilson

General Manager

Flying Operations Branch

12 February 1997

__________________

SCHEDULE

Interpretation

1.         In this Determination, unless the contrary intention appears:

“corrected highest terrain”, in relation to the effective area of a route segment, has the meaning given in section 4;

“effective area”, in relation to a route segment, has the meaning given in section 3;

“Grid LSALT” means the LSALT shown for a grid square on an En Route Chart (ERC) or Terminal Area Chart (TAC);

“LSALT” means lowest safe altitude;

“navigation tolerance area”, in relation to a route segment, is the area calculated in accordance with section 5.

Lowest safe altitudes

2.1       Subject to paragraph 2.2, if the LSALT for a route segment has not been determined under paragraph 178 (1) (a) of the Civil Aviation Regulations, the LSALT for the route segment is the highest of the following altitudes, rounded up (if necessary) to the next 100 feet:

(a)  1,000 feet above the top of the highest reported obstacle in the effective area;

(b)  if an aeronautical topographical chart is used to calculate the lowest safe altitude—1,000 feet above the height of the corrected highest terrain in the effective area;

(c)  1,500 feet above mean sea level.

2.2       If the LSALT for a route segment has not been determined under paragraph 178(1)(a) of the Civil Aviation Regulations and is to be determined by reference to Grid LSALTs, the LSALT for the route segment is the highest grid LSALT shown for the effective area.

Effective area—meaning

3.1       If the LSALT for a route segment is determined by reference to the Grid LSALTs shown on an ERC or TAC, the effective area of the route segment is the area of the earth’s surface represented by all the grid squares over which the navigation tolerance area determined in accordance with paragraph 5.1 is shown to extend wholly or in part.

3.2       If the LSALT for a route segment is determined by any other means, the effective area of the route segment is the area that comprises:

(a)  the navigation tolerance area of the route segment, determined in accordance with paragraph 5.2; and

(b)  a 5-mile wide area surrounding the navigation tolerance area.

Calculating the height of the corrected highest terrain

4.1       The height of the corrected highest terrain in the effective area of a route segment is the higher of the following:

(a)  the highest spot height in the effective area plus 360 feet;

(b)  the height of the highest contour in the effective area as shown on an aeronautical topographical chart  plus the height equal to the height between 2 successive contours as shown on the chart plus 360 feet.

Calculating the navigation tolerance area:

5.1       If the LSALT for a route segment is determined by reference to Grid LSALTs, the navigation tolerance area of the route segment is the area of the earth’s surface ascertained by applying on either side of the planned track the navigation error allowance appropriate to the navigation aids, system or method used for the navigation of the aircraft.

5.2       If paragraph 5.1 does not apply, the navigation tolerance area of a route segment is the area of the earth’s surface bounded by 2 imaginary lines that:

(a)  start at the beginning of the route segment and diverge, one on each side, from the planned track:

(i)  if a navigation aid is used at the beginning of the route segment—at an angle of 10.3°; and

(ii)  if a navigation aid is not used at the beginning of the route segment—at an angle of 15°; and

(b)  if an area navigation system is being used—continue until:

(i)  each line reaches a point abeam the end of the route segment; or

(ii)  each line reaches a point 30 miles abeam the planned track; or

(iii)  each line reaches a point in the rated coverage area of the navigation aid at the end of the route segment from which a straight line drawn to the end of the route segment would converge with the planned track at an angle of not less than 10.3°;

whichever happens first; and

(c)  if an area navigation system is not being used—continue until:

(i)  each line reaches a point abeam the end of the route segment; or

(ii)  each line reaches a point 50 miles abeam the planned track; or

(iii)  each line reaches a point in the rated coverage area of the navigation aid at the end of the route segment from which a straight line drawn to the end of the route segment would converge with the planned track at an angle of not less than 10.3°;

whichever happens first; and

(d)  if the lines first reach the points abeam the planned track and a navigation aid is used at the end of the route segment—continue parallel to the planned track until each line reaches a point in the rated coverage area of the navigation aid at the end of the route segment from which a straight line drawn to the end of the route segment would converge with the planned track at an angle of not less than 10.3°, and then go straight to the end of the route segment; and

(e)  if the lines first reach the points abeam the planned track and a navigation aid is not used at the end of the route segment—continue parallel to the planned track until each line reaches a point abeam the end of the route segment, and then converge to form a semicircle, centred on the end of the route segment, with a radius of 30 miles or 50 miles, as the case requires; and

(f)  if the lines first reach the points abeam the end of the route segment—converge from those points to form a semicircle, centred on the end of the route segment, with a radius equal to the distance between those points and the end of the route segment.

5.3       If the route segment is served by a VOR, the rated coverage of the VOR, for the purposes of subparagraphs 5.2(b), (c) and (d) is taken to be 60 miles, or the coverage published in ERSA for the route segment, whichever is less.