Ops below LSALT/MSA Flashcards
When can you fly below your LSALT?
An aircraft must not be flown under the IFR, lower than the published lowest safe altitude, MSA, or calculated lowest safe altitude unless:
1. The aircraft is being flown in VMC by day;
2. The aircraft is taking off or landing;
3. The aircraft is being flown in accordance with:
a. Requirements relating to visual approach or departure procedures published in the authorised aeronautical information for the flight; or
b. An authorised instrument departure procedure or an authorised instrument approach procedure; or
c. An air traffic control clearance and RADAR ID.
REF: AIP GEN 3.3, 4.4 – Calculation of Lowest Safe Altitude & CASR Part 91.305 – Minimum Heights – IFR Flights
How do you work out what your LSALT is at any given time?
LSALT are published for IFR flights on specified routes on IFR charts, NOTAMs or AIP supplements. The LSALT specified for a route segment (ERC – Low) is only valid for RNP 2 operations. For operations other than RNP 2 operations, operators and pilots must use a pilot calculated LSALT or grid LSALT.
Grid LSALTs have been determined for all ERC and TAC and for all low charts these grids are 60nm by 60nm squares.
Where a pilot uses grid LSALT (when not on an IFR published route), for obstacle clearance, they are responsible for determining the allowance for navigation error that should be applied, when considering the navaids available and the method of navigation used for obtaining position fixes.
This navigation error must be applied to the proposed track and the highest grid LSALT falling within the area covered by the determined navigation error must be used.
REF: AIP GEN 3.3, 4.1, 4.2, 4.3 – Calculation of Lowest Safe Altitude & Aeronautical Chart User Guide 6.4.2 – LSALT.
LSALT area under RNP2?
RNP2 operations require 5nm surrounding and including the departure point and destination each side of the normal track to be considered.
REF: AIP GEN 3.3, 4.7 – Calculation of Lowest Safe Altitude
How do you calculate the tolerance area, for routes not shown on IFR charts, when using ground-based navaids?
The area to be considered must be within an area of 5nm surrounding and including an area defined by lines drawn from the departure point or en route navaid, 10.3°each side of nominal track (where guidance is via navaid only) to a limit of 50nm each side of track.
Where the lines thus drawn come at any time within the coverage of an en route navaid (able to be used), they will converge by straight lines to that aid. The minimum angle of convergence which must be used in this case is 10.3°.
On shorter routes where the lines are displaced by less than 50nm abeam the destination, they shall converge by a radius based on the lesser distance.
REF: AIP GEN 3.3, 4.6 – Calculation of Lowest Safe Altitude
How do you calculate the tolerance area, for routes not shown on IFR charts, when destination has no navaids (DR)?
Q: How do you calculate the tolerance area, for routes not shown on IFR charts, when destination has no navaids (DR)?
The area to be considered must be within an area of 5nm surrounding and including an area defined by lines drawn from the departure point or en route navaid, 10.3°each side of nominal track (where guidance is via navaid only) to a limit of 50nm each side of track, then paralleling track to abeam the destination and converging by a semicircle of 50nm radius centred on the destination.
REF: AIP GEN 3.3, 4.6 – Calculation of Lowest Safe Altitude
How do you calculate the tolerance area, for routes not shown on IFR charts, when departure aerodrome has no navaids (DR)?
Q: How do you calculate the tolerance area, for routes not shown on IFR charts, when departure aerodrome has no navaids (DR)?
The area to be considered must be within an area of 5nm surrounding and including an area defined by lines drawn from the departure point 15°each side of nominal track to a limit of 50nm each side of track, then paralleling track till where the lines thus drawn come at any time within the coverage of an en route navaid (able to be used), they will converge by straight lines to that aid.
The minimum angle of convergence which must be used in this case is 10.3°.
REF: AIP GEN 3.3, 4.6 – Calculation of Lowest Safe Altitude
How do you calculate the LSALT altitude within an LSALT area?
- Where the highest obstacle is more than 360ft above the height determined for terrain, the LSALT must be 1000ft above the highest obstacle; or
- Where the highest obstacle is less than 360ft above terrain or there are no chartered obstacles, the LSALT must be 1360ft above the elevation determined for terrain.
BUT where the elevation of the highest terrain or obstacle in the tolerance area is not above 500ft, the LSALT must not be less than 1500ft.
REF: AIP GEN 3.3 4.3 – Calculation of Lowest Safe Altitude
How do you calculate the tolerance, area for routes not shown on IFR charts, navigating with RNAV-GNSS?
The area to be considered must be within an area of 5nm surrounding and including an area defined by lines drawn from the departure point not less than 15.0°each side of nominal track to a maximum of 7nm. Thence paralleling track to abeam the destination and converging by a semicircle of the same radius centred on the destination.
Note: Area Navigation – Non GNSS; See AIP GEN 3.3, 4.8.c RNAV-GNSS:
REF: AIP GEN 3.3, 4.8 – Calculation of Lowest Safe Altitude
When can a helicopter be flown below LSALT when NVFR?
A helicopter may not be flown under NVFR lower than the published LSALT, MSA, or the pilot calculated LSALT unless:
1. The aircraft is taking off or landing; or
2 .The aircraft is within 3nm of the aerodrome from which the aircraft has taken off, or at which the aircraft will land; or
3. The aircraft is being flown in accordance with an air traffic control clearance.
REF: CASR Part 91.277 – Minimum Heights – VFR Flights at Night
How do you calculate the tolerance area for routes not shown on IFR charts when NVFR?
Q: How do you calculate the tolerance area for routes not shown on IFR charts when NVFR?
The area to be considered must be the same as that specified depending on whether using radio navaids, DR, or RNAV-GNSS; or 1000ft above the highest obstacle on the ground or water within a radius of 10nm from any point along the aircrafts nominal track.
However, the pilot of an aircraft who has positively determined by visual fix that a critical obstruction has been passed may nevertheless descend immediately to a lower altitude, provided that the required obstacle clearance above significant obstructions ahead of the aircraft is maintained.
REF: AIP GEN 3.3, 4.9 – VFR Flights at Night & CASR Part 91.277 – Minimum Heights – VFR Flights at Night
