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TheLSALT specified for a route segment is that for IFRprocedures.Where
anNDB or VORmark the segment, the tolerances applicable to theNDB are
used. Unreported obstacles up to 360 ftmay exist in navigation tolerance
areas. Therefore, LSALT is calculated by adding:
• 1000 ft to the highest obstacle, where the highest obstacle ismore
than 360 ft above the height determined for terrain, or
• 1360 ft to the height determined for terrainwhere thehighest charted
obstacle is less than 360 ft above the height determined for terrain.
Theminimum LSALT published is 1500 ft due to lack of data concerning
terrain near sea level.
LSALT details for RNAV routes are shown ineach grid square formedby the
parallels andmeridians. On theERCs-H, thegrid is at 4° intervals, and at 1°
intervals on theERC-L and TACs (See alsoAIPGEN 3.3para 4.2).
Lowest safe altitudes for IFRflights are published inMAP, NOTAM or AIP
Supplement.
GridLSALTs have been determined for ERC andTAC. On eachERC-H thegrid
for each LSALT is a squarewith the dimensions of four degrees of latitude
by four degrees of longitude. OnERC-L and TAC, the grid squares comprise
onedegree of latitude by one degree of longitude. TheGridLSALT is normally
displayed in the centre of the grid square.
A pilot usingGrid LSALT for obstacle clearance is responsible for determining
the allowance for navigation error that shouldbe applied, considering the
limitations of thenavigation aids ormethod of navigation being used for
position fixing. This navigation error allowancemust be applied to the
proposed track. The highest Grid LSALT fallingwithin the area covered by the
determined navigation errormust beused.
If the navigation of the aircraft is inaccurate, or the aircraft is deliberately
flown off track, orwhenever there is failure of any radionavigation aid
normally available, the pilot in commandmust ensure that the aircraft is flown
not lower than 1000 ft above thehighest terrain or obstaclewithin a circle,
centred on theDR position, with a radius of 5 nmplus 20%of the air distance
flown from the last positivefix.
lowest safe altitude
3 – n i ght v fr