Plan Continuation Bias & IIMC in Kenyan Police AW119 Accident (NPSAW 5Y-NPW, Meru, Kenya)
On 13 June 2020 Leonardo AW119 Mk II Koala 5Y-NPW of the Kenyan National Police Service Air Wing (NPSAW) was destroyed when it collided with trees in fog while attempting a precautionary landing at Cyompiou, Meru. Two of the occupants were seriously injured, and 4 suffered minor injuries.
The Kenyan Aircraft Accident Investigation Department (AAID) explain in their safety investigation report, issued creditably promptly in March 2021, that the AW119 and an AW139 were tasked with supporting an operation in Badan Arero, Marsabit. The aim was to “reconcile two communities that were embroiled in cattle rustling in the region”.
NPSAW operated 13 civil registered aircraft including the AW119, four MI-17s, two AW139s, four Agusta Bell 206Bs and two Cessna 208Bs at the time. NPSAW are considered to operate State aircraft and in Kenya they needed no approval and are not subject to Kenyan CAA oversight of their operations.
The aircraft commander (33) had 987 hours of flight experience, 764 on type. The co-pilot (29) had 623 hours, 352 on type. Both where police inspectors and holders of a CPL(H) but neither were instrument rated. Their last proficiency checks were in late 2016 according to the AAID. The aircraft commander undertook factory training on the AW119 in Philadelphia in 2017.
The weather forecast for 13 June 2020, valid from 1700 (2100) for 24 hours and issued on 12 June 2020 for Meru and other areas; “Showers are expected over a few places tonight. Cloudy morning with light rains breaking to sunny intervals expected tomorrow. Showers expected over a few places in the afternoon.”
The helicopter made a first precautionary landing four miles west of the Ndula marker due to bad weather, however it took off again after conditions improved. It reached Embu after a low level transit and three more passengers boarded. The helicopter then took off for Isiolo rather than Wajir, to refuel before the final sector to Badan Arero. While en route from Embu to Isiolo…
At around Meru area, the weather conditions deteriorated prompting the crew to contemplate landing at an identified field within the vicinity, but opted to continue flying hoping that they will be able to break through the clouds for better visibility. Within a short time, they were engulfed in clouds and decided to approach and make a landing in another location identified suitable for landing, with better but deteriorating visibility.
As they approached the landing area [which was c 4700 ft AMSL], in poor visibility, the pilot flying stated that he noticed overhead electric power line ahead of the flight path at approximately 100 ft above ground level, banked to the left to avoid the same. He elected to land on the second identified landing area to the right.
He further stated that the aircraft rate of descent was high, he therefore flared to reduce the ROD. He additionally indicated that though he avoided the cables, the main rotors of the helicopter contacted the trees that led to severe vibrations in the cabin. The helicopter collided with two other trees before it impacted the ground and came to rest on its starboard with the main rotor blades impacting the terrain while still rotating.
The PF shut off the fuel valve and switched off the battery. The cockpit crew exited the helicopter from the left side. All the passengers were evacuated from the helicopter from the left emergency window.
The cabin of the helicopter was generally intact after the accident. All occupant seats were neither damaged nor distorted. The cockpit doors and cabin doors were intact without deformation and their function was normal.
AAID Safety Investigation and Analysis
The investigators note that:
The weather conditions kept deteriorating below VFR minima, compelling the flight crew to initiate a precautionary landing at an area they had sited. As the helicopter initiated descent to land at the landing spot identified; the aircraft was engulfed in fog. The rate of descend increased considerably prompting the copilot to advise the pilot flying [the aircraft commander] to reduce the rate of descend. The…approach…was performed at short notice in fog without adequate visual reference to the ground. In addition, the flight crew did not conduct the required briefings. As a result, neither crew member had developed a correct or complete understanding of the characteristics and challenges of the landing site.
Given the lack of an instrument rating and the transition from visual meteorological conditions to instrument meteorological conditions, it`s highly likely that when the VFR pilot entered the clouds; in the absence of the horizon, with changes in flight attitude, and manoeuvres that may have resulted in g forces, while trying to reduce the ROD, the pilot`s sense of balance was affected that resulted to spatial illusions and disorientation (somatogravic and somatogyral illusion) that may have caused spatial disorientation.
The investigators comment that:
NPSAW Standard Operating Procedure Manual discusses the VFR weather minimums and states that, for passenger day flight operations, a cloud base of 500 ft above the highest ground or obstacle with 5nm of track or a horizontal visibility of ½ nm or 900 m. A review of NPSAW documentation found no operational procedures or guidance specified in standard operating procedures (SOPs) or operations manual for flight crew to deal with deteriorating VFR weather conditions (such as reduced visibility and ceilings), inadvertent instrument meteorological conditions (IIMC) avoidance procedures, or IIMC recovery procedures. The investigation further established that the SOPs provided little guidance in a number of areas, which contributed to poor decision-making and coordination by the crew.
NPSAW had not established an effective safety management system (SMS) that would have assisted the organization identify and mitigate the risks associated with its operations.
There are numerous classic behavioral traps that can ensnare the unwary pilot. Pilots, particularly those with considerable experience, try to complete a flight as planned, please passengers, and meet schedules. This basic drive to achieve can have an adverse effect on safety and can impose an unrealistic assessment of piloting skills under stressful conditions. These tendencies ultimately may bring about practices that are dangerous and sometimes illegal and may lead to a mishap. Pilots develop awareness and learn to avoid many of these operational pitfalls through effective single pilot management training.
AAID postulate that the crew “may have suffered from “get-home-itis”, or “plan continuation bias”, i.e. following the plan even when evolving circumstances justify adaptation”. They elaborate that:
The tendency to want to continue, despite the situation having changed, seems to have more compelling and stronger as the end of a task approaches. It is especially flying under VFR conditions that increase the risk of accidents, where in order to arrive, and one fly into such poor visibility conditions that visual references are lost. In such circumstances, the danger of losing control of the aircraft increases dramatically.
This may explain that they continued the flight even though the visibility and weather conditions appeared to deteriorate below defined VFR weather minima. It may be that a combination of “plan continuation bias” and lack of instrument ratings for the pilots could be factors that have contributed to the accident.
Probable Cause: The crew’s lack of situational awareness and the decision to continue the flight into deteriorating weather conditions that occasioned spatial disorientation, and subsequent loss of helicopter control.
The major contributing factors were:
- Internal (personal-self-induced) and external (social), real or perceived pressure may have influenced the pilots‟ decisions to continue the flight even when objective assessment of the situation suggested they should do otherwise;
- The crew’s decision to operate into an area surrounded by rising terrain in fog;
- Failure to conduct risk assessment before flight;
- Lack of an effective SMS.
AAID Safety Recommendations
Three safety recommendations were raised:
Safety Recommendation 01/01/02/2021: NPSAW to implement training programs that needs to embrace:
- Plan an appropriate CRM training to facilitate implementation of NPSAW missions.
- Enhance the training of the flight crew in threat management, situation awareness, and decision-making.
- Safety Management System
Safety Recommendation 02/01/02/2021: NPSAW to review and approve at an appropriate level the Standard Operating procedure and Maintenance manuals.
Safety Recommendation 01/01/02/2021 [sic]: NPSAW to develop and implement an effective Safety Management System with emphasis on adequate risk assessment programs
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