TCAS Resolution Advisory error leads to near-collision between Embraer and Boeing aircraft

Casualties unknown • FR

A pilot's misinterpretation of TCAS display symbology on an Embraer ERJ 190 led to an unintended descent, resulting in a loss of separation with a Boeing B767.

What happened

On July 24, 2007, an Embraer ERJ 190-200 LR, operated by Flybe with registration G-FBEC, was descending from FL 380 to FL 350 near Cherbourg, France. During the descent, the flight crew increased the descent rate to -2.8°. At 11:04 UTC, the aircraft's Traffic Alert and Collision Avoidance System (TCAS) issued a Traffic Advisory (TA) due to a conflicting Boeing B76LE-300 (registration N362AA) flying on a perpendicular path at FL 340.

Shortly after, the ERJ 190's TCAS issued a Resolution Advisory (RA) instructing the crew to "ADJUST VERTICAL SPEED". In response to this RA, the pilot flying disconnected the autopilot and applied nose-down elevator input. This action caused the aircraft to descend at a rate of up to 3,300 ft/min, reaching a minimum altitude of 34,600 ft. This maneuver resulted in a significant loss of separation, with the minimum vertical distance between the two aircraft dropping to approximately 600 ft and the horizontal distance to 1.5 NM.

The investigation

The investigation focused on the flight crew's response to the TCAS RA and the technical presentation of the aircraft's flight instruments. Investigators examined the ERJ 190's flight data recorder, TCAS logs, and radar data to reconstruct the flight paths. The inquiry also reviewed the crew's training and their familiarity with the aircraft's "glass cockpit" interface, noting that both pilots had relatively limited experience (approximately 150 hours) on this specific aircraft type.

Findings

  • The primary cause of the incident was the pilot's misinterpretation of the TCAS RA symbology on the Primary Flight Display (PFD). The pilot initially failed to identify the green "fly-to" zone and incorrectly believed they needed to position the aircraft symbol below the red avoidance trapezoid.
  • The high rate of descent as the aircraft approached the target altitude (FL 350) contributed to the triggering of the TCAS alarm.
  • The pilot's difficulty in interpreting the digital display was exacerbated by their recent transition from traditional analog instruments to a modern glass cockpit.
  • The flight crew's ability to monitor the situation was limited by the rapid speed of the event.

Probable cause

The incident was caused by the pilot's incorrect interpretation of the TCAS Resolution Advisory display, leading to an unintended descent, compounded by a high vertical speed during altitude capture that triggered the alert.

Frequently asked questions

What happened in the 2007-07-24 aircraft accident near FR?

A pilot's misinterpretation of TCAS display symbology on an Embraer ERJ 190 led to an unintended descent, resulting in a loss of separation with a Boeing B767.

What aircraft was involved and where did it happen?

The accident on 2007-07-24 involved a aircraft, at FR.

What was the probable cause of the accident?

The incident was caused by the pilot's incorrect interpretation of the TCAS Resolution Advisory display, leading to an unintended descent, compounded by a high vertical speed during altitude capture that triggered the alert.

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