Pilots of an Air France Boeing 777-200 momentarily lost control of the aircraft's trajectory during a poorly-managed go-around in low visibility, French investigators have determined.
Although a go-around was called at an altitude of nearly 500ft, the crew allowed the twinjet to descend - over the course of the next 20s - to barely 60ft above ground before the aircraft climbed away.
The crew, reinforced by a third pilot in the cockpit, had been conducting a Category III approach to runway 08R at Paris Charles de Gaulle on 16 November 2011.
While the jet was established on the glideslope and localiser, with its autopilot engaged, a master caution alarm signalled a change in landing capability which raised the decision height from 20ft to 50ft.
The third pilot called the alarm and - as required by Air France's Category III procedures - the first officer, monitoring, declared a go-around.
Eight seconds passed, however, before the captain advanced the thrust levers. French investigation authority BEA suggests he might have had "difficulty in refocusing", and experienced a decision-making conflict, noting that he initially disengaged the autothrottle instead of engaging go-around thrust.
While the flight recorder registered movement of the captain's control yoke, it was not enough to disengage the autopilot. The horizontal stabiliser began to change position, in response to a nose-down command, and the third pilot called a pitch warning as the 777 dipped 2° nose-down.
Both the captain and the first officer "almost simultaneously" gave a pitch-up input, says the inquiry. It says the autopilot disengaged and the pilots then applied opposite inputs - the captain's nose-down effectively cancelling the first officer's nose-up - and the aircraft pitched rapidly to 7°, at 1.8g, then lowered to 4°. The BEA says this pitch was "insufficient" for a go-around.
The captain then relaxed his nose-down input and the aircraft pitched up again, at 1.7g, reaching 11° in 2s and 19° over the next 10s. BEA says the aircraft descended to a minimum of 63ft, and accelerated to 180kt, before the 777 climbed. It subsequently returned to land safely.
All three pilots were highly experienced - with a combined 15,000h on type - but the inquiry says the crew's monitoring of the flight parameters was "inadequate" and the pilots did not intervene to change the aircraft's trajectory. Air France subsequently issued safety information to 777 crews on handling missed approaches without engaging the go-around mode.