Narrative:

Our flight departed dca. After contacting departure control (dulles departure), we were given a series of heading, airspeed, and altitude changes. Other aircraft which departed dca were also subject to this maneuvering. It was apparent that departure control was dealing with a large number of aircraft. Departing aircraft were apparently being vectored in-trail through a series of climbing right hand turns to facilitate airways sequencing. At the time of the incident, our aircraft was in IMC heading 300 degrees at 13000 ft. Both the copilot and I saw an amber target at the 3 O'clock position of our TCASII indicators. Almost immediately, we heard the aural warning 'descend now!' the TCASII target was at our altitude and approaching our position! The copilot, who had been flying on the autoplt, disconnected the autoplt, smoothly lowered the nose of the aircraft and began an immediate descent. I called dulles departure and told them we were leaving our assigned altitude in response to an actual RA on TCASII. We were given an immediate clearance to 12000 ft. While descending through about 12500 ft in broken clouds, we caught a glimpse of what appeared to be a B-727 crossing above us. It could not be determined if the aircraft was climbing. The entire event consumed no more than 15 or 20 seconds. It appears the problem arose due to a saturation of the airspace and controling capability of the ATC agency. Contributing factors must be the large numbers of aircraft transiting this airspace. The problem was discovered utilizing the on-board TCASII. Corrective actions were merely those prescribed by the traffic RA mode of TCASII. I am of the opinion that the copilot's actions of immediately disconnecting the autoplt and positively changing altitude resulted in the adequate amount of altitude separation which we achieved. The visual sighting of the target aircraft certainly gave position reinforcement of the efficiency of our on-board TCASII system. Unfortunately, the incident also highlights the deficiencies and inadequacies inherent in the ATC radar environment under the pressures of high traffic volume and controller workload.

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Original NASA ASRS Text

Title: SYS ERROR SUGGESTED IN THIS NMAC RPT.

Narrative: OUR FLT DEPARTED DCA. AFTER CONTACTING DEP CTL (DULLES DEP), WE WERE GIVEN A SERIES OF HDG, AIRSPD, AND ALT CHANGES. OTHER ACFT WHICH DEPARTED DCA WERE ALSO SUBJECT TO THIS MANEUVERING. IT WAS APPARENT THAT DEP CTL WAS DEALING WITH A LARGE NUMBER OF ACFT. DEPARTING ACFT WERE APPARENTLY BEING VECTORED IN-TRAIL THROUGH A SERIES OF CLBING RIGHT HAND TURNS TO FACILITATE AIRWAYS SEQUENCING. AT THE TIME OF THE INCIDENT, OUR ACFT WAS IN IMC HDG 300 DEGS AT 13000 FT. BOTH THE COPLT AND I SAW AN AMBER TARGET AT THE 3 O'CLOCK POS OF OUR TCASII INDICATORS. ALMOST IMMEDIATELY, WE HEARD THE AURAL WARNING 'DSND NOW!' THE TCASII TARGET WAS AT OUR ALT AND APCHING OUR POS! THE COPLT, WHO HAD BEEN FLYING ON THE AUTOPLT, DISCONNECTED THE AUTOPLT, SMOOTHLY LOWERED THE NOSE OF THE ACFT AND BEGAN AN IMMEDIATE DSCNT. I CALLED DULLES DEP AND TOLD THEM WE WERE LEAVING OUR ASSIGNED ALT IN RESPONSE TO AN ACTUAL RA ON TCASII. WE WERE GIVEN AN IMMEDIATE CLRNC TO 12000 FT. WHILE DSNDING THROUGH ABOUT 12500 FT IN BROKEN CLOUDS, WE CAUGHT A GLIMPSE OF WHAT APPEARED TO BE A B-727 XING ABOVE US. IT COULD NOT BE DETERMINED IF THE ACFT WAS CLBING. THE ENTIRE EVENT CONSUMED NO MORE THAN 15 OR 20 SECONDS. IT APPEARS THE PROB AROSE DUE TO A SATURATION OF THE AIRSPACE AND CTLING CAPABILITY OF THE ATC AGENCY. CONTRIBUTING FACTORS MUST BE THE LARGE NUMBERS OF ACFT TRANSITING THIS AIRSPACE. THE PROB WAS DISCOVERED UTILIZING THE ON-BOARD TCASII. CORRECTIVE ACTIONS WERE MERELY THOSE PRESCRIBED BY THE TFC RA MODE OF TCASII. I AM OF THE OPINION THAT THE COPLT'S ACTIONS OF IMMEDIATELY DISCONNECTING THE AUTOPLT AND POSITIVELY CHANGING ALT RESULTED IN THE ADEQUATE AMOUNT OF ALT SEPARATION WHICH WE ACHIEVED. THE VISUAL SIGHTING OF THE TARGET ACFT CERTAINLY GAVE POS REINFORCEMENT OF THE EFFICIENCY OF OUR ON-BOARD TCASII SYS. UNFORTUNATELY, THE INCIDENT ALSO HIGHLIGHTS THE DEFICIENCIES AND INADEQUACIES INHERENT IN THE ATC RADAR ENVIRONMENT UNDER THE PRESSURES OF HIGH TFC VOLUME AND CTLR WORKLOAD.

Data retrieved from NASA's ASRS site as of July 2007 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.