What happened
During the flight, the crew received a traffic advisory (TA) from the Traffic Alert and Collision Avoidance System (TCAS), which was followed by an aural resolution advisory (RA) instructing the crew to "CLIMB, CLIMB." In response, the first officer disconnected the autopilot and began a climb at 1,500 feet per minute. The captain then took control of the aircraft and increased the pitch angle. During this ascent, a flight attendant fell to the floor, resulting in one injury (a broken ankle).
After the TCAS announced "clear of conflict," the captain leveled the aircraft at 30,000 feet before returning controls to the first officer and descending the aircraft back to its assigned altitude of FL 290.
The investigation
An analysis of radar data and air traffic control information showed that the aircraft was climbing at 2,500 feet per minute with an airspeed of 483 knots. The other aircraft involved in the traffic alert, an MD-80, was climbing at 2,000 feet per minute with an airspeed of 433 knots. The minimum separation between the two aircraft was 1,54 nautical miles and 1,500 feet.
A review of the radar data indicated that the maneuver performed by the crew consisted of a 1,000-foot climb followed immediately by a descent back to the assigned altitude. This sequence involved an initial 1.15 G pull-up, a 0.05 G push-over to arrest the climb, and a 1.4 G pull-up to level off. The time between the push-over and the final level-off was approximately 5 seconds.
Findings
According to the operator's Flight Standards Manual, the proper response to a corrective RA is to fly from the red zone into the green zone, a maneuver that should be executed within 5 seconds using approximately a 0.25g maneuver.