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At cruise altitude; B-777 TCAS issued a RA and; as a result; the flight crew deviated from assigned altitude by 500 ft. TCAS issued a verbal 'clear of conflict' and the crew returned the aircraft to assigned altitude and notified center of the deviation. Neither ATC nor the crew observed traffic in the area. Review of the aircraft maintenance history revealed an earlier-reported false RA.
| Attributes | |
| ACN | 1258804 |
| Time | |
| Date | 201504 |
| Place | |
| Locale Reference | CZQX.ARTCC |
| State Reference | NF |
| Environment | |
| Flight Conditions | VMC |
| Aircraft 1 | |
| Make Model Name | B777 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Cruise |
| Route In Use | Oceanic |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Traffic Collision Avoidance System (TCAS) |
| Person 1 | |
| Function | Pilot Not Flying First Officer Relief Pilot |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 250 Flight Crew Total 17600 Flight Crew Type 14000 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude |
Narrative:
While in cruise with the autopilot and seatbelt on the TCAS initiated a RA indicating traffic. There was no TA preceding the event. I scanned the instruments and a target was displayed at our altitude in our immediate vicinity. I tried to acquire the target visually as well. The TCAS issued the aural warning 'descend! Descend!' and the pilot flying initiated a descent and turned the autopilot off. I initiated a radio call broadcasting our position and actions on frequency 123.45. The TCAS then issued an additional warning of 'increase descent! Increase descent!' and we descended approximately 500 feet below our assigned altitude at which time it indicated we were clear of the conflict. We returned to our assigned altitude and the pilot flying engaged the autopilot. We contacted gander center and explained our actions. They confirmed our altitude and that they showed no traffic in our vicinity at the time. We reviewed the maintenance history showing the TCAS had indicated false RA reports as early as the same day of our departure. I contacted dispatch and maintenance and wrote it up. I suggested we switch from the left transponder to the right and maintenance agreed. We fully briefed the captain and flying first officer when they returned from break. The flight was completed without further occurrence or incident.
Original NASA ASRS Text
Title: At cruise altitude; B-777 TCAS issued a RA and; as a result; the flight crew deviated from assigned altitude by 500 ft. TCAS issued a verbal 'Clear of conflict' and the crew returned the aircraft to assigned altitude and notified Center of the deviation. Neither ATC nor the crew observed traffic in the area. Review of the aircraft maintenance history revealed an earlier-reported false RA.
Narrative: While in cruise with the autopilot and seatbelt on the TCAS initiated a RA indicating traffic. There was no TA preceding the event. I scanned the instruments and a target was displayed at our altitude in our immediate vicinity. I tried to acquire the target visually as well. The TCAS issued the aural warning 'Descend! Descend!' and the pilot flying initiated a descent and turned the autopilot off. I initiated a radio call broadcasting our position and actions on frequency 123.45. The TCAS then issued an additional warning of 'Increase descent! Increase descent!' and we descended approximately 500 feet below our assigned altitude at which time it indicated we were clear of the conflict. We returned to our assigned altitude and the pilot flying engaged the autopilot. We contacted Gander Center and explained our actions. They confirmed our altitude and that they showed no traffic in our vicinity at the time. We reviewed the maintenance history showing the TCAS had indicated false RA reports as early as the same day of our departure. I contacted Dispatch and Maintenance and wrote it up. I suggested we switch from the left transponder to the right and Maintenance agreed. We fully briefed the Captain and flying First Officer when they returned from break. The flight was completed without further occurrence or incident.
Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.