II. BIRDSTRIKE

The Lessons Emergency

CREW

ACAS / TCAS

The ACAS II equipment, known as TCAS II, provides an independent airborne last resort safety net designed to prevent collisions between aircraft.

ECAC common policy for ACAS II requires that:

· From January 2000 all civil fixed wing aircraft exceeding 15,000Kg, or with a passenger seating configuration of more than 30 must have ACAS II

· From January 2005 all civil fixed wing aircraft exceeding 7,500 Kg, or with a passenger seating configuration of more than 19 must have ACAS II

When a risk of collision is detected, TCAS II calculates the necessary manoeuvre and communicates the solution directly to the flight crew.

ACAS II can issue two types of advisory

· Traffic Advisory (TA), warns the flight crew to be ready for a potential Resolution Advisory and helps the crew in the visual search for the intruder aircraft. The TA is triggered between 20 and 48 seconds before the Closest Point of Approach (CPA)

· Resolution Advisory (RA), an advisory to the flight crew to execute avoidance manoeuvres in the vertical plane. The RA is activated between 15 and 35 seconds before the CPA

Airborne Collision Avoidance System Traffic Alert and Collision Avoidance System

Communication of TA or RA

The TA or RA is communicated to the flight crew by means of both a visual display and an aural alert message.

The following can be expected:

· Climb or descent without prior warning

· No emergency squawk

· Two aircraft or more involved

· Notification from pilot of “TCAS climb” or “TCAS descent”

Effects of turbulence

If an aircraft experiences severe turbulence that makes it deviate very suddenly towards another aircraft, the altitude varies with an important acceleration.

TCAS II computes a high vertical speed and an advisory may be triggered.

Even though these are rare events, TAs or RAs may be triggered between aircraft on adjacent flight levels because of turbulence.

ATC

In the event of a pilot reporting a manoeuvre induced by an RA, Remember:

· The controller shall not attempt to modify the aircraft flight path

· The controller shall provide traffic information as appropriate

· Pilots very busy

· TCAS II altitude data is more accurate than radar data

NB: Once an aircraft departs from its clearance in compliance with an RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft affected as a direct consequence of the manoeuvre induced by the RA

1. The controller acknowledges a report from the flight crew that the aircraft has resumed the current clearance

2. The controller acknowledges a report from the flight crew that the aircraft is resuming the current clearance and issues an alternative clearance which is acknowledged by the flight crew

Following an RA event, or other significant ACAS event, pilots and controllers should complete an air traffic incident report.

CREW

II. BIRDSTRIKE