Airbus A340 approach error leads to high-pitch excursion at Paris CDG

Casualties unknown • FR

An Air France Airbus A340 experienced a sudden pitch increase to 26 degrees during a precision approach at Paris Charles de Gaulle after the autopilot captured a secondary ILS signal lobe.

What happened

On March 13, 2012, an Air France Airbus A340-300, registration F-GLZU, was performing a precision CAT III approach to runway 08R at Paris Charles de Gaulle. During the descent, the aircraft was flying significantly above the established glide path. The approach controller, managing heavy traffic, had previously instructed the crew to maintain a high speed and had inadvertently failed to authorize a descent at the appropriate time.

As the aircraft attempted to intercept the ILS signal, it entered a secondary lobe of the ILS signal, which was centered at approximately 10 degrees. When the crew engaged the glide slope capture mode, the autopilot interpreted the signal as being below the path and commanded a significant pitch increase. Within 12 seconds, the aircraft's pitch rose from 1° to 26°, causing the vertical speed to swing from -1,600 ft/min to +3,300 ft/min. The crew responded by disconnecting the autopilots and manually pitching the nose down to stabilize the aircraft. After a second approach, the aircraft landed safely.

The investigation

The investigation focused on why the aircraft was allowed to remain above the glide path and why the autopilot response was so extreme. Investigators examined radar data, flight data, and crew testimonies. The investigation looked into the controller's instructions, the crew's monitoring of the flight path, and the technical behavior of the ILS signal lobes. The inquiry also considered the impact of fatigue on both the flight crew and the air traffic controllers, as the event occurred in the early morning hours.

Findings

  • The primary cause was insufficient monitoring of the aircraft's trajectory by both the controller and the flight crew.
  • The crew decided to continue the approach after passing the final approach fix (FAF) despite being above the glide path.
  • The crew used an inappropriate method (vertical descent mode OP DES) to intercept the glide path from above, rather than using vertical speed mode.
  • The aircraft's autopilot captured a secondary ILS signal lobe, which led to the excessive pitch excursion.
  • The controller's radar screen lacked visual markers for intercepts below 5,000 ft, making it difficult to verify the aircraft's vertical position.
  • Fatigue among the crew and controllers likely contributed to errors in coordination and decision-making.

Probable cause

The incident was caused by a lack of adequate trajectory monitoring by both the crew and air traffic control, compounded by the crew's decision to continue an approach while above the glide path using an unsuitable automated descent mode. This led to the autopilot capturing a secondary ILS signal lobe, triggering a dangerous pitch excursion.

Frequently asked questions

What happened in the 2012-03-13 INCIDENT GRAVE www.bea.aero Approche au-dessus du plan de descente, interception d’un signal ILS secondaire, augmentation de l’assiette commandée par le pilote automatique Sauf précision contraire, les heures figurant dans ce rapport sont exprimées en temps universel coordonné (UTC). accident near FR?

An Air France Airbus A340 experienced a sudden pitch increase to 26 degrees during a precision approach at Paris Charles de Gaulle after the autopilot captured a secondary ILS signal lobe.

What aircraft was involved and where did it happen?

The accident on 2012-03-13 involved a INCIDENT GRAVE www.bea.aero Approche au-dessus du plan de descente, interception d’un signal ILS secondaire, augmentation de l’assiette commandée par le pilote automatique Sauf précision contraire, les heures figurant dans ce rapport sont exprimées en temps universel coordonné (UTC)., registration F-GLZU, at FR.

What was the probable cause of the accident?

The incident was caused by a lack of adequate trajectory monitoring by both the crew and air traffic control, compounded by the crew's decision to continue an approach while above the glide path using an unsuitable automated descent mode. This led to the autopilot capturing a secondary ILS signal lobe, triggering a…

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