How can a combination of surprise event, visual illusion and cognitive lockup lead to a heavy landing? Human factor analysis by mindFly
Synopsis
The Spicejet Q400 was approaching to land at Delhi airport on a foggy night of Nov 2018. During approach for landing at around 500 feet AGL, the crew sighted the runway and continued the approach. At around 411 feet AGL, the Captain disengaged the autopilot and simultaneously inadvertently
pressed the go-around (GA) button. As the GA button was pressed, the flight director bars which were synchronised with the instrument landing system,
moved to 10° pitch up on Flight Director for go-around mode. The Captain disregarded the bar on Flight Director and continued approach visually.
As the FD bars were showing GA pitch, the PIC had no reference other than approach lights & PAPI.
During landing, there was a high Rate of Descent and in order to reduce the decent, PIC increased power to maintain glide slope. During approach while over the threshold of runway 27 the aircraft was above the glideslope and in order to correct the same, PIC reduced power. While reducing the power, the Captain lifted the lock of power lever and the power was reduced below flight idle. There was a momentary warning sound in the cockpit for the same. This reduction in power further increased the rate of descent.
Due to low visibility prevailing at that time, the Captain had depth perception and initiated flare very close to the runway by increasing the pitch attitude to 6.3°. This increase in pitch very close to the ground with a high rate of descent resulted in hard landing with a vertical acceleration of 3.77G and subsequent tail strike.
Final investigation DGCA report
Visual illusion
Visual illusions take place when conditions modify the pilot’s perception of the environment relative to his / her expectations. They may result in landing short of the runway, hard landing or runway overrun, but may also cause spatial disorientation and loss of control.
30 % of approach-and-landing accidents occur during the conduct of visual approaches or during the visual segment of an instrument approach.
Visual approaches at night present a greater exposure because of reduced visual cues, increased likelihood of visual illusions and risk of spatial disorientation.
Low visibility and/or precipitations are a circumstantial factor in more than 70 % of approach-and-landing accidents, including those involving CFIT.
How do Visual Illusions Affect the Pilot’s Perception?
Illusions result from the absence of or the alteration of visual references that modifies the pilot perception of his / her position relative to the runway threshold. They affect the perception of heights, distances and/or intercept angles.
Visual illusions are most critical when transitioning from IMC and instrument references to VMC and visual references.
Illusions (such as the black-hole effect) affect the flight crew vertical and horizontal situational awareness, particularly during the base leg and when turning final (as applicable) and during the final approach.
Visual illusions usually induce crew inputs (corrections) that cause the aircraft to deviate from the original and intended vertical or lateral flight path.
Illusion in fog
Flying in light rain, fog, haze, mist, smoke, dust, glare or darkness usually
create the illusion of being too high.
Shallow fog (i.e., fog layer not exceeding 300 ft in thickness) results in a low
obscuration but also in low horizontal visibility. When on top of a shallow fog layer, the ground (or airport and runway, if flying overhead) can be seen, but when entering the fog layer the forward and slant visibility usually are lost.
Entering a fog layer also creates the perception of a pitch up, thus inducing a tendency to push over and place the aircraft below the desired glide path
and in a steeper-than-desired attitude.
mindFly human factor analysis
The crew were on their last leg of the duty. The approach was stable till the pilot inadvertently pressed the go around switches which on gave the pitch command that would be required for a go around.
From the safety point of view this resulted in tight coupling of events. The visual transition from instruments, surprise event, optical illusion into fog and cognitive lockup.
A go-around could have prevented the incident for sure but the pilot decided to recover the situation and continue visually taking cues from his senses. Had the same event taken place at a 1000ft, the pilot would have in all probability carried out a safe landing. Due to the tight coupling of events, the physical reactions were excessive. This led to abrupt inputs on the thrust lever and the control column leading to an excessive rate of descent and the heavy landing. An event like the inadvertent pressing of the go-around switches can cause a surprise event. This can lead to distraction and /or disorientation. Cognitive lockup prevents a task switch over from approach to go-around since the pilots objective is for task completion and over 90% task is complete. Therefore there is a psychological lockup which insists that the pilot continues and land the aircraft.
Training is the only preventive strategy. Read my paper on Cognitive lockup to better understand the concept. The role of the pilot monitoring has been undermined in the prevailing training setup in India. The BEA study on the role of PM globally has highlighted the fact that in most of the events the PM does not know where to look!
