The term Base Effect refers to the gradual erosion of safety margins in daily flight operations at an aerodrome. Most aerodromes host locally-based aircraft, pilots, and often air traffic controllers. Over time, these individuals become very familiar with their environment, including traffic flows and air traffic management (ATM) procedures. This familiarity can lead to complacency, resulting in the acceptance of deviations from standard procedures. Such normalization of deviance stems from a heightened sense of trust among local operators and air traffic control.
While these adjusted local procedures may function adequately day-to-day, they can fall short when transient aircraft arrive, during mixed Visual Flight Rules (VFR) and Instrument Flight Rules (IFR) traffic, or in emergencies. Numerous examples illustrate these localized deviations, which vary by location. They include, but are not limited to, ignoring published arrival or departure procedures, flying at incorrect airspeeds, neglecting standard circuit joining methods, using non-standard patterns, omitting position reports, and flying at improper altitudes. Over time, these non-standard practices can become the norm for local operations, potentially leading to confusion, increased workload for controllers, diminished situational awareness, and a higher risk of loss of separation when unexpected situations arise.
Preventing the Base Effect relies on good airmanship and discipline. Key principles include: refusing to bend rules to complete a task, understanding that Standard Operating Procedures (SOPs) apply to all levels of experience, rejecting shortcuts that compromise safety, and preparing for potential problems in advance. A disciplined pilot adheres to the proper rules and procedures, whether at their home aerodrome or elsewhere, unless an emergency demands deviation. Likewise, a disciplined air traffic controller follows established protocols and ensures compliance among operators in their jurisdiction.
Eliminating or reducing the Base Effect can significantly enhance flight safety. For example, on June 27, 2016, an Airbus A319 nearly collided with an AS532 Cougar helicopter near Marseille, France. The helicopter’s transponder had failed, and both aircraft were cleared to land while positioning visually. The investigation revealed that neither crew detected the other due to a temporary radar loss and non-compliance with altitude regulations by the helicopter crew, highlighting the critical nature of adhering to established procedures.
