German investigators have detailed a serious low-level airprox incident at Stuttgart during which a Germanwings Airbus A319's collision-avoidance system ordered the crew to descend while just 1,200ft above ground.

The aircraft had been conducting its initial climb after taking off from runway 07 when it encountered an ultralight which had been approaching from the south and had been instructed to cross behind the A319.

But radar data released by German investigation authority BFU indicates that the ultralight initially turned east before turning north and conflicting with the jet.

The A319 crew received a collision-avoidance warning, ordering the aircraft to descend, at a height of about 1,200ft above terrain.

BFU says the first officer initiated a descent rate of 1,600ft/min and, shortly afterwards, the enhanced ground-proximity warning system issued a "don’t sink" alert.

The captain decided that the collision-avoidance system should take priority if the aircraft was at least 400ft above ground.

There was too much radio traffic on the Stuttgart tower frequency and the captain was unable to transmit an advisory that the aircraft was executing an evasive manoeuvre. The "don't sink" warning could be heard over the radio.

The A319 lost around 300ft in height during the encounter before resuming its climb.

BFU did not have access to cockpit-voice or flight-data recordings from the 26 June incident, but calculated that the A319 had been 0.213nm (1,295ft) horizontally and 600ft vertically from the ultralight at closest approach.

Source: Cirium Dashboard