Narrative:

After initial vectors leaving crp and joining the assigned route; ATC gave us a shortcut and cleared us direct to the hammu intersection; then fly the HAMMU1 RNAV arrival. We were issued a crossing restriction to cross hammu at 12;000 ft. I started the descent to 12;000 ft and planned to level off several miles prior to the hammu intersection. Due to our MEL; we were restricted to a maximum speed of 250 KTS/0.65M. This started leading to a compression of traffic on the arrival route; as they were asking aircraft behind us to maintain 280 KTS. A few minutes later; as we were still descending; ATC issued us vectors off of the arrival to allow traffic behind us to pass; and then they would vector us to rejoin the arrival. ATC instructed us to fly a heading of 340 degrees. I twisted the heading select knob to 340 degrees; then selected heading mode on the fgcp. After a few minutes of flying that heading; and once we had leveled out at 12;000 ft ATC instructed us to turn right; proceed direct to the hammu intersection; and rejoin the HAMMU1 RNAV arrival. I looked down onto my mfd where I had the TCAS screen up and then I looked out the right window and didn't see any traffic on the screen or out the window. The autopilot was still engaged at the time; so I twisted the heading select knob to initiate the right turn; then reached down to the FMS and programmed it to fly direct to hammu. Once we verified it was in the FMS correctly; I selected navigation mode on the fgcp. Once established in the turn; we were given a TA from the TCAS. We heard the 'traffic; traffic' annunciation and looked down at the TCAS display. There was traffic at our 02:00 position approximately 1;000 ft below our altitude ad climbing. We both looked for the traffic; but were unable to see anything. While we were both looking outside; we were given an RA from the TCAS. We heard the 'descend; descend' annunciation and I looked back inside as I pressed the tcs button and pushed the nose over for a quick descent. I was looking inside and keeping the nose down while the captain was looking outside for the traffic. The TCAS then stated 'adjust vertical speed; adjust' and I was able to shallow out the descent rate. A short time later the TCAS announced 'clear of conflict.' we never saw the other aircraft. At this point we were wings level heading northeast and I stopped the descent. We were slightly above 11;000 ft when I leveled off. The captain called ATC and said '[we are] at 11;000 ft in response to a TCAS RA.' ATC responded with a simple; 'roger'; so the captain then asked; 'do you want [us] back at 12;000 ft or should we stay here at 11;000 ft?' there was a brief pause before ATC responded with; 'maintain 12;000 ft.' the captain read back the instruction; I re-engaged the proper modes on the fgcp and we climbed back up to 12;000 ft and proceeded direct to the hammu intersection. The remainder of the flight continued without incident. Having that MEL was a threat; because if it weren't for the speed restriction; we would have been able to maintain speed to stay in sequence and we wouldn't have been vectored off of the arrival route. Complacency may have been a threat; as I had never before received a TCAS RA since starting at [company]; except for in training scenarios. There was certainly an error with our communications. I have no way of knowing whether or not ATC knew about this traffic; but if they did know and didn't call it out to us; that put us at a disadvantage. I made the error of pushing the tcs button during my response to the TCAS RA; instead I should have pressed the ap quick disconnect button. I think the aircraft was only in an undesired aircraft state briefly as I quickly pushed the nose forward to descend and remain clear of the traffic conflict. The aircraft was never out of control; or in a state in which recovery was every questionable; but it was the abrupt maneuver in response to the TCAS RA is typically undesired on a normal line flight.our rate of descent did not exceed 2;000 FPM and bank angle did not exceed 25 degrees throughout the maneuvering.being more alert and more vigilant for traffic would be beneficial; although I believe the captain and I were fairly proactive about looking both inside and outside for traffic before I initiated a turn. Remembering to push the correct button on the yoke would be helpful too; and even though it did not directly affect the outcome of this event; it has the potential to make a big difference. I think it's important to expose our pilots to TCAS RA events in their recurrent training. It doesn't take very much time; and it's a scenario that we don't see often on the line; but it is an urgent and dramatic event that requires an immediate and correct response in order to safely avoid a collision.

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Original NASA ASRS Text

Title: EMB-145 First Officer reported an airborne conflict resulting in an RA and an altitude deviation.

Narrative: After initial vectors leaving CRP and joining the assigned route; ATC gave us a shortcut and cleared us direct to the HAMMU intersection; then fly the HAMMU1 RNAV Arrival. We were issued a crossing restriction to cross HAMMU at 12;000 FT. I started the descent to 12;000 FT and planned to level off several miles prior to the HAMMU intersection. Due to our MEL; we were restricted to a maximum speed of 250 KTS/0.65M. This started leading to a compression of traffic on the arrival route; as they were asking aircraft behind us to maintain 280 KTS. A few minutes later; as we were still descending; ATC issued us vectors off of the arrival to allow traffic behind us to pass; and then they would vector us to rejoin the arrival. ATC instructed us to fly a heading of 340 degrees. I twisted the heading select knob to 340 degrees; then selected HDG mode on the FGCP. After a few minutes of flying that heading; and once we had leveled out at 12;000 FT ATC instructed us to turn right; proceed direct to the HAMMU intersection; and rejoin the HAMMU1 RNAV arrival. I looked down onto my MFD where I had the TCAS screen up and then I looked out the right window and didn't see any traffic on the screen or out the window. The autopilot was still engaged at the time; so I twisted the Heading Select knob to initiate the right turn; then reached down to the FMS and programmed it to fly direct to HAMMU. Once we verified it was in the FMS correctly; I selected NAV mode on the FGCP. Once established in the turn; we were given a TA from the TCAS. We heard the 'Traffic; Traffic' annunciation and looked down at the TCAS display. There was traffic at our 02:00 position approximately 1;000 FT below our altitude ad climbing. We both looked for the traffic; but were unable to see anything. While we were both looking outside; we were given an RA from the TCAS. We heard the 'Descend; Descend' annunciation and I looked back inside as I pressed the TCS button and pushed the nose over for a quick descent. I was looking inside and keeping the nose down while the Captain was looking outside for the traffic. The TCAS then stated 'Adjust Vertical Speed; Adjust' and I was able to shallow out the descent rate. A short time later the TCAS announced 'Clear of Conflict.' We never saw the other aircraft. At this point we were wings level heading northeast and I stopped the descent. We were slightly above 11;000 FT when I leveled off. The Captain called ATC and said '[We are] at 11;000 FT in response to a TCAS RA.' ATC responded with a simple; 'Roger'; so the Captain then asked; 'Do you want [us] back at 12;000 FT or should we stay here at 11;000 FT?' There was a brief pause before ATC responded with; 'maintain 12;000 FT.' The Captain read back the instruction; I re-engaged the proper modes on the FGCP and we climbed back up to 12;000 FT and proceeded direct to the HAMMU intersection. The remainder of the flight continued without incident. Having that MEL was a threat; because if it weren't for the speed restriction; we would have been able to maintain speed to stay in sequence and we wouldn't have been vectored off of the arrival route. Complacency may have been a threat; as I had never before received a TCAS RA since starting at [Company]; except for in training scenarios. There was certainly an error with our communications. I have no way of knowing whether or not ATC knew about this traffic; but if they did know and didn't call it out to us; that put us at a disadvantage. I made the error of pushing the TCS button during my response to the TCAS RA; instead I should have pressed the AP Quick Disconnect button. I think the aircraft was only in an undesired aircraft state briefly as I quickly pushed the nose forward to descend and remain clear of the traffic conflict. The aircraft was never out of control; or in a state in which recovery was every questionable; but it was the abrupt maneuver in response to the TCAS RA is typically undesired on a normal line flight.Our rate of descent did not exceed 2;000 FPM and bank angle did not exceed 25 degrees throughout the maneuvering.Being more alert and more vigilant for traffic would be beneficial; although I believe the Captain and I were fairly proactive about looking both inside and outside for traffic before I initiated a turn. Remembering to push the correct button on the yoke would be helpful too; and even though it did not directly affect the outcome of this event; it has the potential to make a big difference. I think it's important to expose our pilots to TCAS RA events in their recurrent training. It doesn't take very much time; and it's a scenario that we don't see often on the line; but it is an urgent and dramatic event that requires an immediate and correct response in order to safely avoid a collision.

Data retrieved from NASA's ASRS site as of July 2013 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.