{"id":"F2005B01529","name":"CASA 32/97 - Determination under paragraph 178(1)(b) of the Civil Aviation Regulations","slug":"casa-32-97-determination-under-paragraph-178-1-b-of-the-civil-aviation-regulations","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":32610,"registerId":"commonwealth-F2005B01529-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"CASA 32/97 - Determination under paragraph 178(1)(b) of the Civil Aviation Regulations","content":"INSTRUMENT NUMBER: CASA 32/97\n\nCIVIL AVIATION ACT 1988\n\nCIVIL AVIATION REGULATIONS\n\nDETERMINATION\n\nUNDER PARAGRAPH 178 (1) (b) OF THE\n\nCIVIL AVIATION REGULATIONS\n\nI, 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:\n\n(a) revoke instrument number SRS 2/1992; and\n\n(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.\n\n\\[Signed T. Wilson\\]\n\nTerry Wilson\n\nGeneral Manager\n\nFlying Operations Branch\n\n12 February 1997\n\n\\_\\_\\_\\_\\_\\_\\_\\_\\_\\_\\_\\_\\_\\_\\_\\_\\_\\_\n\nSCHEDULE\n\nInterpretation\n\n1. In this Determination, unless the contrary intention appears:\n\n“corrected highest terrain”, in relation to the effective area of a route segment, has the meaning given in section 4;\n\n“effective area”, in relation to a route segment, has the meaning given in section 3;\n\n“Grid LSALT” means the LSALT shown for a grid square on an En Route Chart (ERC) or Terminal Area Chart (TAC);\n\n“LSALT” means lowest safe altitude;\n\n“navigation tolerance area”, in relation to a route segment, is the area calculated in accordance with section 5.\n\n  \nLowest safe altitudes\n\n2.1 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:\n\n(a) 1,000 feet above the top of the highest reported obstacle in the effective area;\n\n(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;\n\n(c) 1,500 feet above mean sea level.\n\n2.2 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.\n\nEffective area—meaning\n\n3.1 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.\n\n3.2 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:\n\n(a) the navigation tolerance area of the route segment, determined in accordance with paragraph 5.2; and\n\n(b) a 5-mile wide area surrounding the navigation tolerance area.\n\n![](image.001.png)\n\n![](image.002.png)Calculating the height of the corrected highest terrain\n\n4.1 The height of the corrected highest terrain in the effective area of a route segment is the higher of the following:\n\n(a) the highest spot height in the effective area plus 360 feet;\n\n(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.\n\nCalculating the navigation tolerance area:\n\n5.1 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.\n\n  \n5.2 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:\n\n(a) start at the beginning of the route segment and diverge, one on each side, from the planned track:\n\n(i) if a navigation aid is used at the beginning of the route segment—at an angle of 10.3; and\n\n(ii) if a navigation aid is not used at the beginning of the route segment—at an angle of 15; and\n\n(b) if an area navigation system is being used—continue until:\n\n(i) each line reaches a point abeam the end of the route segment; or\n\n(ii) each line reaches a point 30 miles abeam the planned track; or\n\n(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;\n\nwhichever happens first; and\n\n(c) if an area navigation system is not being used—continue until:\n\n(i) each line reaches a point abeam the end of the route segment; or\n\n(ii) each line reaches a point 50 miles abeam the planned track; or\n\n(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;\n\nwhichever happens first; and\n\n(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\n\n(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\n\n(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.\n\n5.3 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.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":7,"scope_assessment":{"changed":false,"description":"The instrument revokes SRS 2/1992 and sets a specific method for calculating LSALT (preamble; s.2–5). The text of the revoked instrument (SRS 2/1992) is not included here, so whether the substantive scope differs from that earlier instrument cannot be determined from this document alone."},"complexity_factors":["Multiple conditional branches for choosing the governing altitude (s.2.1–2.2)","Dependence on external chart products (ERC/TAC) and Grid LSALTs (s.1, s.3)","Geometric construction of navigation tolerance areas with angle and distance rules (s.5.1–5.2)","Calculation of 'corrected highest terrain' using spot heights and contour intervals (s.4.1)","Numeric rounding rule to next 100 ft and fixed safety margins (s.2.1)","Interaction with radio navigation coverage (VOR rated coverage limits) and published ERSA data (s.5.3)"],"plain_english_summary":"This Determination revokes SRS 2/1992 and prescribes how to calculate the lowest safe altitude (LSALT) for route segments lacking a set LSALT (preamble; s.2): the highest of 1,000 ft above the highest obstacle, 1,000 ft above corrected highest terrain (from charts), or 1,500 ft MSL, or the grid LSALT where used (s.2.1–2.2).\n\nPilots, operators and chart providers must use the specified chart data and navigation‑tolerance geometry when planning routes; operators bear any extra cost from higher or altered routings, and CASA (the delegate) prescribes the method (s.1–5)."},"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":6,"scope_assessment":{"changed":false,"description":"This instrument appears to perform its intended function within the scope of paragraph 178(1)(b) of the Civil Aviation Regulations. It provides a specific methodological determination for calculating lowest safe altitudes, which is precisely what the enabling provision authorises. There is no evidence of scope creep beyond the original regulatory purpose."},"complexity_factors":["Multiple calculation methods (standard vs grid-based) with different triggering conditions in sections 2.1 and 2.2","Nested conditional logic in section 5.2 with five sub-paragraphs (a)-(f) containing multiple 'whichever happens first' clauses and angle/distance specifications","Cross-references between defined terms and substantive provisions (e.g., 'effective area' defined in section 3 but used throughout)","Technical aviation terminology requiring domain knowledge (VOR, ERC, TAC, ERSA, area navigation systems, rated coverage areas)","Geometric calculations involving angles (10.3°, 15°), distances (30 miles, 50 miles, 5 miles), and conditional boundary determinations","5 defined terms in the interpretation section, but several are self-referential or depend on other defined sections","Exception structure: paragraph 2.2 operates as an exception to 2.1; section 5.1 and 5.2 are mutually exclusive alternatives"],"plain_english_summary":"This is a technical aviation safety rule made by the Civil Aviation Safety Authority (CASA) in 1997. It tells pilots and airlines how to calculate the **lowest safe altitude** (LSALT) for flying a particular route when that altitude hasn't already been officially set.\n\n**Why this matters:** Flying too low is dangerous. Pilots need to stay well above mountains, towers, and other obstacles. This rule sets the maths for working out that safe height.\n\n**Who it affects:** Commercial pilots, flight planners, and airlines operating in Australian airspace.\n\n**What it does:**\n\n* **Revokes an old rule** (SRS 2/1992) and replaces it with this new method.\n* **Sets two main ways to calculate LSALT:**\n  1. **The standard method:** Take the highest obstacle or terrain in the \"effective area\" (a buffer zone around the flight path), add 1,000 feet, or use 1,500 feet above sea level — whichever is highest. Round up to the nearest 100 feet.\n  2. **The grid method:** If using special charts with pre-calculated grid squares, just take the highest grid value shown for your area.\n* **Defines \"effective area\":** This is essentially a safety buffer around the planned flight path that accounts for navigation errors — how far off course a plane might drift depending on what navigation equipment it's using (GPS, radio beacons, etc.). The width varies: 10.3 degrees divergence if using navigation aids, 15 degrees if not, with different rules for how far out the buffer extends (30 or 50 miles depending on equipment).\n* **Terrain calculations:** When using topographical charts, pilots must add 360 feet to the highest spot height or contour line to account for vegetation and unmapped obstacles.\n\nIn short, this is a mathematical safety standard that ensures planes fly high enough to clear all obstacles even if their navigation drifts off course."}},"importantCases":[],"_links":{"self":"/api/acts/casa-32-97-determination-under-paragraph-178-1-b-of-the-civil-aviation-regulations","history":"/api/acts/casa-32-97-determination-under-paragraph-178-1-b-of-the-civil-aviation-regulations/history","analysis":"/api/acts/casa-32-97-determination-under-paragraph-178-1-b-of-the-civil-aviation-regulations/analysis","conflicts":"/api/acts/casa-32-97-determination-under-paragraph-178-1-b-of-the-civil-aviation-regulations/conflicts","importantCases":"/api/acts/casa-32-97-determination-under-paragraph-178-1-b-of-the-civil-aviation-regulations/important-cases","documents":"/api/acts/casa-32-97-determination-under-paragraph-178-1-b-of-the-civil-aviation-regulations/documents"}}