Aviation SMS #3

Understanding Human Factors

Human factors is an umbrella term for the study of people’s performance in their work and nonwork environments. The term human factors can mean many things to many people, and trying to understand all its implications can be daunting. Perhaps because the term is often used following human error of some type, it is easy to think of it negatively. However, human factors also includes all the positive aspects of human performance: the unique things human beings do well.

The primary focus of any human factors initiative is to improve safety and efficiency by reducing and managing human error made by individuals and organizations. Human factors is about understanding humans—our behaviour and performance. Then, from an operational perspective, we apply that human factors knowledge to optimise the fit between people and the systems in which they work, to improve safety and performance.

ICAO uses the SHEL model to represent the main components of human factors. SCHELL is an expanded version of this model. The SCHELL model gives an idea of the scope of human factors. SCHELL stands for:

? S = software: the procedures and other aspects of work design

? C = culture: the organisational and national cultures influencing interactions

? H = hardware: the equipment, tools and technology used in work

? E = environment: the environmental conditions in which work occurs

? L = liveware: the human aspects of the system of work

? L = liveware: the interrelationships between humans at work

The SCHELL model emphasises that the whole system shapes how individuals behave. Any breakdown or mismatch between two or more components can lead to human performance problems. For example, an accident where communication breaks down between pilots in the cockpit, or engineers at shift handover, would be characterised by the SCHELL model as a liveware-liveware problem. Situations where pilots or engineers disregarded a rule would be characterised as liveware-software.

Controlled Flight into Terrain | case study

On 7 May 2005, a Fairchild Aircraft Inc. SA227-DC Metro 23 aircraft, registered VHTFU, with two pilots and 13 passengers, was being operated by Transair on an IFR regular public transport service from Bamaga to Cairns, with an intermediate stop at Lockhart River, Queensland. At 11:43:39 Eastern Standard Time, the aircraft crashed in the Iron Range National Park on the north-western slope of South Pap, a heavily timbered ridge, approximately 11km north-west of the Lockhart River Aerodrome. At the time of the accident, the crew was conducting an area navigation global navigation satellite system (RNAV [GNSS]) non-precision approach to runway 12. The aircraft was destroyed by the impact forces and an intense, fuel-fed, post-impact fire. There were no survivors. According to the Australian Transport Safety Bureau (ATSB) investigation report, the accident was almost certainly the result of controlled flight into terrain; that is, an airworthy aircraft under the control of the flight crew was flown unintentionally into terrain, probably with the crew unaware how close the aircraft was to the ground. The investigation report identified a range of contributing and other human factors safety issues relating to the crew of the aircraft, including: ? The crew commenced the Lockhart River runway 12 approach, even though they were aware that the co-pilot did not have the appropriate endorsement and had limited experience of conducting this type of instrument approach. ? The descent speed, approach speed and rate of descent were greater than those specified for the aircraft in the Transair operations manual. ? During the approach, the aircraft descended below the segment minimum safe altitude for its position on the approach. ? The aircraft’s high rate of descent, and the descent below the segment minimum safe altitude, were not detected and/or corrected by the crew before the aircraft collided with terrain. ? The crew probably experienced a very high workload during the approach. ? The crew probably lost situational awareness of the aircraft’s position along the approach. ? The pilot in command PIC) had a previous history of conducting RNAV (GNSS) approaches with crew without appropriate endorsements, and operating the aircraft at speeds higher than those specified in the Transair operations manual. ? The co-pilot had no formal training and limited experience to act effectively as a crew member during the type of approach conducted into Lockhart River.

ATSB Transport Safety Investigation Report 2005 019.77: ‘Collision with terrain; 11km, Lockhart River Aerodrome’. left: VH-TFU at Bamaga Aerodrome on a previous flight.

If we apply the SCHELL model to the Lockhart River accident, we can quickly see that there is a poor fit between a number of the different components in the SCHELL model. What led to the accident goes far beyond the actions of the pilot in command alone:

? Software–liveware mismatch: there were contradictory and unclear procedures for conducting instrument approaches. The company operations manual did not provide clear guidance on approach speeds, or when to select aircraft configuration changes during an approach. It also had no clear criteria for a stabilised approach, nor standardised phraseology for crew members to challenge others’ safety-critical decisions. ? Culture–liveware mismatch: the operator’s flight crew training program had significant limitations, such as superficial or incomplete ground-based instruction, no formal training for new pilots in the operational use of GPS, no structured training on minimising the risk of controlled flight into terrain, and no structured training in crew resource management in a multi-crew environment. There was also a lack of independent evaluation of training and checking, and a culture suggesting disincentives and restricted opportunities to report safety concerns about management decisions. ? Hardware–liveware mismatch: the aircraft was not fitted with any terrain awareness and warning system, such as an enhanced ground proximity warning system. ? Environment–liveware: the crew experienced a very high workload during the approach. The lack of visibility and poor weather also contributed to their poor situational awareness. ? Liveware–liveware mismatch: the pilot in command did not detect and correct the aircraft’s high rate of descent, and the descent below the segment minimum safe altitude before the aircraft crashed. The co-pilot did not have the appropriate endorsement and had limited experience of this type of instrument approach. This example illustrates how important it is to understand the human contribution to an accident in context, rather than simply labelling what somebody did as ‘operator error’.

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