Aircraft equipment certified for different operations is measured against a technical standard. These standards are developed by regulators across the globe including:
- US Federal Aviation Administration as a technical standard order (TSO)
- European Aviation Safety Agency as a European technical standard order (ETSO)
- CASA as an Australian technical standard order (ATSO).
Pilots can identify the TSO status of GPS equipment by referring to the compliance stamp on the receiver, or by referring to the operating handbook in the aircraft. Reference to a manufacturer’s model number is not a guarantee of TSO certification.
Non-TSO GPS receivers do not have to meet any regulatory standards for power supply, installation, lighting, database, integrity monitoring or performance. For example, many hand-held units not identified as suitable for aviation purposes are unable to operate when the aircraft groundspeed exceeds 99 knots.
Navigation information from non-TSO equipment should be treated with extra care until verified by another source.
CASA does not prescribe any required equipment standards and both panel-mount and hand-held equipment may be used for day VFR operations. Non-TSO equipment can be used to supplement visual navigation under VFR.
For night VFR operations you can also use a non-TSO receiver to supplement visual navigation, but such equipment cannot be used to meet alternate aerodrome, mandatory aircraft equipment, or flight crew qualification requirements.
A non-TSO receiver does not meet any of the requirements for IFR navigation.
Safety first with avionics
To ensure safety, pilots must use GNSS properly. Here are some safety tips:
|✓ Use appropriate standard avionics equipment||Hand-held and panel-mount VFR equipment does not ensure the integrity and reliability needed for IFR and some night VFR applications.|
|✓ Use a database valid for the operation||Many non-aviation databases lack accuracy, and currency is critical for operations relying on GNSS for navigation clear of terrain, obstacles and airspace boundaries.|
|✓ Check that all procedures that could be required are present in the database||Data storage limitations have resulted in some manufacturers omitting certain data, such as small aerodromes, from the receiver database.|
|✓ Always carry and use current VFR charts, as they are the primary reference for navigation||VFR receivers can be used to supplement map reading in visual conditions. Some VFR units show airspace boundaries and terrain, but there is no standard for this data and no guarantee that the depiction is correct.|
|✓ Portable receivers and related cables should be positioned carefully in the cockpit||Avoid the potential for electromagnetic interference (EMI), and to avoid interfering with aircraft controls.|
|✗ Don’t rest the GPS on the glareshield near the magnetic compass||This can create electromagnetic interference. Be aware also of the potential for EMI from mobile phones and other personal electronic devices.|
|✗ Do not be tempted to design your own approach||Approach designers receive special training and use specific tools. There are many levels of validation before an approach is commissioned.|
|✗ Never fly below published minimum altitudes while in instrument conditions||Accidents have resulted from pilots placing
too much reliance on the accuracy and integrity of GNSS.
|✗ Don’t rely on a backup battery to give a navigation solution following an electrical failure||The backup battery may also fail, so additional redundancies should be employed. Pilots should continue to use and practise navigation skills by running a basic plot at all times.|
|✗ Resist the urge to fly into marginal weather when navigating VFR||The risk of becoming lost is small when using GNSS, but the risk of controlled flight into terrain or obstacles increases in low visibility.|
Directions for GNSS use
There are various requirements for the use of GNSS in an aircraft. Details are in CAO 20.91 but in summary:
- If a GNSS database contains details of waypoints and navigation aids that are published in maps and charts required to be carried in the aircraft, those details must not be capable of modification by the aircraft operator or flight crew. This does not prevent the storage of ‘user-defined data’ within the equipment.
- The database must also be current and provided by an approved supplier.
- The manufacturer’s operating instructions for the GNSS receiver must be carried in the aircraft, in a place easily accessible to the pilot.
- If the aircraft is engaged in commercial operations, the operating instructions must be incorporated in the aircraft’s operations manual.
- GNSS equipment must be operated in accordance with its operating instructions.
- Additional requirements relating to the operation of GNSS equipment may be incorporated in an aircraft’s flight manual, if they are consistent with the operating instructions.
- Manually-entered data must be cross-checked by at least two flight crew members for accuracy.
- In the case of a single-pilot operation, manually entered data must be checked against other aeronautical information, such as current maps and charts.
A significant number of data errors in general applications occur as a result of human error during manual data entry. Whenever possible, navaid and waypoint positions should be derived from a commercially prepared aviation database which cannot be modified by the operator or crew.
In some situations, it may be necessary to create ‘user’ waypoints by manual entry. In this situation, pilots are responsible for the integrity of the data and must follow CASA’s directions for cross-checking. Manually entered data must not be used for navigation below the lowest safe altitude (LSALT) or minimum sector altitude (MSA), unless specifically authorised by CASA.
Stored user waypoints and stored flight plans are considered manually entered data and must be checked prior to use.