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20 August 2009
20. August 2009 Commercial Aircraft

EASA certifies new "Autopilot/Flight Director" TCAS mode for A380


Enhancing flight safety during TCAS manoeuvres

Enhancing flight safety during TCAS manoeuvres

Following recent successful development testing, a new Auto-Pilot/Flight-Director (AP/FD) TCAS* mode for the Airbus A380 has been approved and certified by the European Aviation Safety Agency (EASA).

The main benefit of the system is that it could further enhance safety during a traffic avoidance situation because the pilot can now fly the aircraft without switching out of one mode and into another. Thus, by simplifying the actions required by the pilot during a TCAS manoeuvre, this enhanced TCAS mode minimises potential overreactions or inverse reactions while preserving his or her concentration at a critical time.

In addition to now being certified on the A380, the AP/FD TCAS mode will also become available for retrofit on other Airbus Fly-By-Wire aircraft in the coming years.

AP/FD TCAS operation overview
The new AP/FD TCAS mode essentially completes the existing TCAS functionality by implementing a TCAS vertical guidance feature into the Auto Flight computer. The result is that now the Auto Flight computer can control the vertical speed of the aircraft which is adapted to each resolution advisory acquired from TCAS.

Moreover, with this new AP/FD TCAS mode activated, when a TCAS "Resolution Advisory" (RA) is received, the pilot no longer needs to disengage the autopilot or Flight Director before conducting the TCAS manoeuvres. Rather, the autopilot can now automatically conduct the correct TCAS manoeuvre, to position the aircraft clear of any potential traffic conflict.

Furthermore, in the case of the pilot flying the aircraft manually (i.e. without autopilot engaged) when a RA is received, previously the Flight Director 'pitch bar guidance' - indicated on the Primary Flight Display - had to be switched off, but with the new mode, the Flight Director bars remain active and smoothly guide pilot to fly the TCAS manoeuvre. At any time, the crew still retains the ability to override the proposed manoeuvre, so as to respond manually to a TCAS RA by flying according to "conventional" TCAS procedures, i.e. manually controlling the vertical speed by referring to TCAS indications on the pilot's vertical speed scale.

* Background to TCAS - Editors' note:
The 'Traffic Alert and Collision Avoidance System' - known as 'TCAS' - is designed to scan for, detect, and interrogate the transponders of other aircraft in the nearby airspace vicinity. It then uses the received transponder signals to compute a distance, bearing and altitude relative to the nearby aircraft. The evaluated traffic information is displayed as symbols on the Navigation Display. As TCAS checks the other aircraft?s relative distance permanently in short-time intervals, it can, therefore, also calculate the other aircraft?s closure rate relative to its own aircraft position. When TCAS detects that an aircraft's distance or closure rate becomes critical, it generates aural and visual annunciations for the pilots. Mandated on aircraft carrying more than 30 passengers since 1993, TCAS is now compulsory on all aircraft types.

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