AMC1 ACNS.E.TAWS.060 Positioning information

ED Decision 2013/031/R

(a)     The TAWS positioning information can be generated internally to the TAWS (e.g. GPS receiver) or acquired by interfacing to other installed avionics on the aeroplane (e.g. FMS).

(1)     For Class A TAWS an RNAV system may be used as an aeroplane horizontal position sensor provided that:

—         it has been approved for navigation in accordance with ETSO-C115() or ETSO-C129a  or ETSO-C145() or ETSO-C146() or ETSO-C196a; or

—         it satisfies FAA AC 20-138 or FAA AC 20-130A.

(2)     For Class A and B TAWS a GNSS sensor may be used as an aeroplane horizontal position sensor provided that it is compliant with ETSO-C196 or ETSO-C145.

Note: For TAWS relying on GNSS sensor, the TAWS design should consider the use of other horizontal position sensors to ensure TAWS availability in case of GNSS failures

(3)     Equipment that uses a GNSS internal to the TAWS for horizontal position information, and that are capable of detecting a positional error that exceeds the appropriate alarm limit for the particular phase of flight in accordance with ED-72A is considered acceptable.

(4)     Vertical position for TAWS may come from a barometric source such as an altimeter or an air data computer, or from a geometric source, such as GNSS provided that:

—         the barometric altitude equipment is approved in accordance with ETSO-C106 Air data computer or ETSO-C10b Altimeter, Pressure Actuated, Sensitive Type;

—         the radio altimeter equipment is approved in accordance with ETSO-2C87 Low-Range Radio Altimeter; 

—         the vertical velocity equipment is compliant with ETSO-C8 Vertical Velocity Instruments or ETSO-C105 Air Data Computer;

—         the GNSS equipment is approved in accordance with:

—         ETSO-C129a, Airborne Supplemental Navigation Equipment Using Global Positioning System (GPS); or

—         ETSO‑C145, Airborne Navigation Sensors Using the Global Positioning System Augmented by the Satellite Based Augmentation System; or

—         ETSO‑C146, Stand-Alone Airborne Navigation Equipment Using the Global Positioning System Augmented by the Satellite Based Augmentation System.

Note: TAWS should mitigate potential vertical positioning source inaccuracies by appropriate blending of available vertical position information.

(b)     When the GPS alert limit is activated, the GPS computed position is considered unsuitable for TAWS, and a TAWS unsuitability indication should be given.

(c)      Geometric altitude should be enabled if the system has the facility.