What happened
On 12 February 2019, two commercial passenger flights experienced a loss of separation at London Stansted Airport. The first aircraft, an Airbus A320 with registration OE-IHD, was arriving at the airport. Due to ATC-imposed speed restrictions and a descent profile that placed the aircraft in a state of excess energy, the crew found themselves unable to maintain a stable approach. After an inadvertent climb mode was triggered by the co-pilot, the commander ordered a go-around.
During the go-around, the crew faced significantly increased workload. Confusion regarding flap and thrust settings led the commander to take manual control of the aircraft. While the crew was focused on managing the aircraft's configuration and responding to ATC instructions to change headings, they experienced a delayed response to a specific ATC command.
Simultaneously, a Saab-Scania SS340B, registration G-LGNK, was departing Stansted. The aircraft had been cleared for takeoff and was climbing through 1,000 ft when ATC notified the crew of an aircraft on approach performing a go-around. As G-LGNK climbed, the TCAS system issued a Traffic Advisory (TA) and subsequently a Resolution Advisory (RA) 'level off' instruction to the crew.
Radar analysis confirmed that the two aircraft passed with a lateral separation of 87 m and a vertical separation of 600 ft.
The investigation
The AAIB examined radar and ATC transponder data, which provided a 3D reconstruction of the encounter. The investigation also reviewed the flight crew's actions and the human factors involved during the high-workload period of the OE-IHD go-around. The investigation established that the crew of OE-IHD was managing a complex situation involving a change of pilot flying, manual flight, and conflicting flight director commands.
Findings
- The Airbus A320 was operating in a state of excess energy during its arrival due to ATC speed reductions.
- A sudden increase in crew workload was triggered by the autopilot capturing a 2,000 ft altitude, which disrupted the descent profile.
- The delayed response to ATC instructions by the A320 crew was caused by high workload and a breakdown in situational awareness during the go-around.
- The crew's focus was directed internally toward stabilizing the aircraft, leading to a temporary loss of separation with the departing Saab-Scania SS340B.