Events on January 20 in history

Air Inter Flight 148, an Airbus A320-111, crashes into a mountain near Strasbourg, France killing 87 of the 96 people on board.

On 20 January 1992, Air Inter Flight 148, a routine scheduled passenger service operated by the French domestic carrier Air Inter, tragically crashed during its approach to Strasbourg Airport (SXB). The flight originated from Lyon–Saint-Exupéry Airport (LYS), a major international gateway in France. The aircraft involved was an Airbus A320-111, one of the pioneering models of the revolutionary A320 family, which had only entered service a few years prior in 1988. The disaster occurred in the challenging terrain of the Vosges Mountains in eastern France, specifically near Mont Sainte-Odile, while the crew was preparing to land at Strasbourg. Out of the 96 individuals on board, including passengers and crew, 87 perished in the accident, making it one of the deadliest aviation incidents involving the Airbus A320 at the time. The remaining nine occupants, though survivors, sustained various injuries.

The Ill-Fated Flight and Its Advanced Aircraft

Air Inter, a prominent French airline before its integration into Air France, specialized in connecting major French cities. Flight 148 was a standard domestic route, carrying passengers from Lyon to Strasbourg. The Airbus A320-111, registration F-GGED, was equipped with state-of-the-art fly-by-wire technology, a significant departure from traditional mechanical flight control systems. This innovative system replaced manual controls with electronic interfaces, designed to enhance safety and efficiency by providing flight envelope protection and automating certain pilot inputs. However, this advanced automation would later become a critical point of focus in the accident investigation.

Circumstances of the Crash: Mont Sainte-Odile and a Steep Descent

The A320 was performing a non-precision approach to Strasbourg Airport's Runway 05 in low visibility conditions. During the final phase of the approach, the aircraft initiated an extremely rapid descent. Instead of maintaining a standard glide path, the aircraft descended at a rate of approximately 3,300 feet per minute (fpm), which is vastly steeper than a normal landing approach of around 700-800 fpm. This excessive descent rate, coupled with the mountainous terrain of the Vosges and poor visibility, led to the aircraft impacting trees and then the ground at a high speed. The crash site was specifically located on the slopes of the Bloss mountain, near the historical pilgrimage site of Mont Sainte-Odile, a location that quickly became synonymous with the tragedy.

Investigation and Contributing Factors

The subsequent investigation, led by France's Bureau d'Enquêtes et d'Analyses pour la sécurité de l'aviation civile (BEA), meticulously examined the chain of events that led to the crash. The findings highlighted several critical contributing factors:

• Misinterpretation of Flight Management System (FMS) Display: A primary cause identified was the flight crew's misinterpretation of the aircraft's FMS vertical mode. The crew inadvertently selected a vertical speed (VS) mode of 3,300 feet per minute (fpm) instead of a flight path angle (FPA) of 3.3 degrees, a common setting for a stable approach. The FMS display, showing "33" for both settings, lacked clear differentiation between these two distinct modes, leading to the crew's critical error.
• Lack of Adequate Ground Proximity Warning System (GPWS): The aircraft was equipped with an older generation GPWS that provided insufficient warnings for the specific type of terrain and descent profile. Modern Enhanced GPWS (EGPWS) systems, which became standard later, are designed to provide more timely and effective warnings against controlled flight into terrain (CFIT).
• Crew Workload and Environmental Factors: Poor weather conditions, including low cloud ceiling and snow, contributed to a high workload in the cockpit and eliminated visual cues that might have otherwise alerted the crew to their dangerously low altitude.
• Human-Machine Interface Issues: The accident underscored the importance of clear and unambiguous cockpit displays, especially in highly automated aircraft where pilots interact extensively with complex systems. The design of the A320's FMS display was found to be potentially confusing.

Legacy and Safety Enhancements

The Air Inter Flight 148 disaster served as a critical catalyst for significant enhancements in aviation safety, particularly concerning cockpit automation and pilot training. The key outcomes include:

• Revised Pilot Training: Emphasizing a deeper understanding of automated systems, FMS programming, and the importance of monitoring aircraft parameters and raw data, even when automation is engaged.
• Cockpit Display Improvements: Airbus and other manufacturers implemented clearer and more distinct visual cues on FMS displays to prevent confusion between vertical speed and flight path angle settings.
• Enhanced Ground Proximity Warning Systems (EGPWS): The accident reinforced the need for more sophisticated GPWS technology, leading to the widespread adoption of EGPWS, which provides proactive terrain warnings based on a worldwide terrain database.
• Crew Resource Management (CRM): Renewed focus on effective communication and teamwork within the cockpit to identify and correct errors.

Frequently Asked Questions About Air Inter Flight 148

What was the primary cause of the Air Inter Flight 148 crash?

The primary cause was the flight crew's misinterpretation of the Airbus A320's Flight Management System (FMS) display, leading them to inadvertently select an extremely high vertical descent rate (3,300 feet per minute) instead of a standard flight path angle (3.3 degrees) for their approach to Strasbourg Airport.

What is fly-by-wire technology, and how did it relate to the accident?

Fly-by-wire technology replaces traditional mechanical flight controls with electronic interfaces. While designed for safety and efficiency, in the case of Flight 148, the advanced automation and the design of the FMS display contributed to pilot confusion, as the system allowed for an inadvertently programmed steep descent.

Where exactly did Air Inter Flight 148 crash?

The aircraft crashed in the Vosges Mountains in eastern France, specifically on the slopes of the Bloss mountain, near the prominent landmark of Mont Sainte-Odile, while attempting to land at Strasbourg Airport.

What were the major safety changes implemented after the crash?

Following the accident, significant safety changes included improvements in Airbus A320 cockpit displays to clarify FMS readings, enhanced pilot training on automation, and the widespread adoption of more advanced Ground Proximity Warning Systems (EGPWS) to prevent controlled flight into terrain (CFIT).