AN ON-BOARD safety system to keep aircraft from colliding in midair has been triggered three times over Irish airspace this year, according to the Irish Aviation Authority (IAA).
The closest calls this year were east of Shannon airport and south of Dublin airport, with both incidents involving medium-sized commercial passenger aircraft.
The aviation authority would not disclose the airlines involved, but the commercial aircraft involved are those used on medium-haul flights such as between Ireland and Europe.
In the case of the Shannon and Dublin incidents, air traffic control separations were implemented and automatic emergency instructions, which are issued directly by the on-board systems, were not given to the pilots. The other incident over Irish airspace occurred close to Cork airport and involved a single-engine Cessna and an executive jet.
A possible collision was prevented by air traffic controllers, who issued both pilots with separation instructions.
An authority spokesman described the incidents as “invalid” because air traffic controllers had already issued the pilots with “separation orders” which were not recognised by the on-board avoidance system.
The air accident investigation unit of the IAA did not undertake any further investigation into the incidents because there was no effect on safety, said the spokesman.
On-board safety systems were also triggered three times over Irish airspace in 2009, and these again involved commercial passenger aircraft. One of the incidents happened close to Dublin airport because an aircraft exceeded its instructed altitude.
The safety system is known as the traffic alert and collision avoidance system. It is pilot-interpreted and operates independently of air traffic control.
The system alerts the pilot to the presence of other aircraft in its vicinity and is also triggered if aircraft flight paths are conflicting. It orders both pilots to take evasive action when their sensors indicate a potential collision.
If the system is activated, a pilot must notify air traffic control, which then monitors the situation – but it cannot issue instructions to the aircraft until the pilot has responded to instructions from the traffic alert and collision avoidance system.