US investigators believe the cognitive phenomenon of plan continuation bias led an Envoy Air Embraer 170 crew to maintain an approach to, and land on, the wrong runway at Chicago O’Hare.
Plan continuation bias is a tendency to stay with an original course of action despite evidence of changing circumstances.
The crew of the aircraft – arriving from Norfolk on 25 September 2024 – had planned for the ILS approach to runway 27R, before receiving information to expect runway 9L.
After being assigned the ESSPO5 arrival pattern, which was briefed and programmed into the flight-management computer, the crew expected runway 10R but were ultimately given runway 10C.
The captain, who was monitoring, planned a visual approach to 10C and programmed the ILS approach to 10C as a back-up.
But the National Transportation Safety Board states that the crew was “not receiving” the ILS identifier for 10C.
The captain reloaded the approach and tried manual tuning in an attempt to troubleshoot the reason for the absent localiser frequency.
“Unable to resolve the issue [the crew] elected to proceed visually,” says the inquiry.
Although the captain informed the O’Hare tower controller that the aircraft was on visual approach to 10C – with the tower then granting landing clearance – the jet was actually aligned with runway 10L, on which it touched down.
The cockpit-voice recorder was overwritten by subsequent flights.
Flight-data recorder information showed that, while flying a heading to intercept the ILS for 10C, the Nav 1 radio was correctly tuned – for about 4s – to the 10C localiser frequency of 108.95MHz.
During this 4s interval the localiser and glideslope displays indicated that the correct course was “to the right and above the aircraft”, says the inquiry.
The Nav 1 and Nav 2 radio frequencies were subsequently changed to 108.4MHz and 113MHz respectively for the remainder of the flight.
Investigators state that the pilots’ decision to continue the approach without the correct ILS frequency was “likely affected by their task saturation and planned continuation bias”.
This left the crew unable to “perceive and efficiently integrate” available information which might have revealed the runway-alignment error.
Plan continuation bias, the inquiry points out, is a phenomenon in which changing conditions or stimuli that necessitate a change of plan become harder to notice.
“As workload increases, conditions that may appear obvious to individuals external to the situation are difficult for people caught up in the plan to recognise,” it adds.
Runways 10C and 10L are closely-spaced parallels, separated by around 365m (1,200ft). The approach was conducted in daylight.
Although the tower controller saw the E170’s misalignment they co-ordinated with the controller for runway 10L to allow the landing because there were no traffic conflicts – but the aircraft’s crew was not notified of the error. None of the 68 occupants was injured.
