Investigation of the Emirates Boeing 777-300 go-around accident in Dubai is likely to draw further attention to the issue of pilots’ awareness and understanding of aircraft system design logic.
The crew attempted to abort the landing and activated the go-around switches, without realising that the aircraft had briefly touched down on the runway – a situation which inhibits the go-around switches and requires manual advancement of the thrust levers.
Boeing says this logic is designed to prevent pilots from inadvertently activating go-around mode after touchdown, which risks a runway excursion.
But the crew’s “reliance on automation” and lack of training in flying go-arounds from points close to the runway – with the switches inhibited – meant they did not recognise that the thrust remained at idle as the go-around was initiated, says the United Arab Emirates General Civil Aviation Authority. The pilots omitted a crucial check to verify engine thrust.
The inquiry says Emirates’ training programme for the 777 was based on Boeing’s and the US FAA’s approved training scheme which “did not include” the inhibition logic, says the inquiry.
It says the flight crew operating manual mentioned the inhibition as a “statement of information, without any associated procedure” while the flight crew training manual contained a note that an automatic go-around “cannot be initiated after touchdown” without a clarification for this statement.
While both the captain and first officer had attended initial computer-based training for the 777, this did not cover go-around switch inhibiting.
“Neither [pilot] had a complete understanding of the [go-around] switches and they were not made aware during their training that [these] switches become inhibited [close to touchdown],” the inquiry says.
After completing his 777 conversion course the captain conducted 127 monitored landings in the simulator and during line operations, and 54 go-around manoeuvres in the simulator. All normal missed approaches were carried out at heights above 50ft, and based on activating the go-around switches. During upgrade training for captaincy he practiced rejected landings from below 50ft but before touchdown.
While the Emirates training programme included a particular manual-handling session specific to go-arounds after touchdown, the inquiry says the scenarios differed from the circumstances of the accident because the training was performed with the autopilot, autothrottle and flight directors disengaged.
“[The captain] stated that he had never practised normal go-arounds after touchdown with the autothrottle armed and active,” it says.
This is crucial because Emirates’ policy, in line with Boeing’s recommendations, is for pilots to use autothrottle for all phases of flight including normal go-around. But the inhibit logic characteristics for the go-around switches, says the inquiry, were “not clearly demonstrated” to pilots when the autothrottle was engaged and controlling the thrust.
“Neither [Boeing] nor [Emirates] thoroughly addressed training and procedures dealing with times when the [go-around] switches become inhibited,” it states.
Emirates has modified its training since the August 2016 accident, the inquiry points out, to reinforce training for go-around after touchdown and include information relating to the switch-inhibit logic in various training modules.
The airline has also been liaising with Boeing to develop “engineered defences” to alert the crew when a go-around switch is pushed during an inhibited phase, it adds.
Investigators have recommended that the FAA carries out a safety study, in consultation with Boeing, to enhance the 777’s autothrottle system and go-around switch inhibit logic to “avoid pilot errors due to over-reliance on automation”. The inquiry also says flight crew manuals should have the significance of the inhibit logic “appropriately” highlighted.