<< >> NASA ASRS Report 266931, March 1994

TCASII RA forces flight crew and ATC to amend the clearance altitude as flight was descending through to occupied altitude.

Attributes
ACN	266931
Time
Date	199403
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dca
State Reference	DC
Altitude	msl bound lower : 4700 msl bound upper : 5000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dca
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 180 flight time total : 10100 flight time type : 1400
ASRS Report	266931
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation non adherence : far other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 15000 vertical : 700
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Flight inbound to dca from cmh. On descent between aml and dca, about ready for turn downwind for ILS runway 37 at dca. Descending through 5000 ft for clearance altitude of 2500 ft got TA on TCASII for target at 11 O'clock less than 1000 ft below and believe less than 3 mi. (Estimate at about 2 1/2 mi.) then got RA to 'stop descent.' took manual control and leveled off at about 4700 ft. First officer notified approach control who told us to maintain 5000 ft. Ascended to 5000 ft, leveled off and reengaged autoplt. We were overtaking target and were at a speed of about 240 KTS. TCASII probably saved a very close call. Dca approach should have been able to see potential conflict. Conditions were hard IMC in light rain.

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Original NASA ASRS Text

Title: TCASII RA FORCES FLC AND ATC TO AMEND THE CLRNC ALT AS FLT WAS DSNDING THROUGH TO OCCUPIED ALT.

Narrative: FLT INBOUND TO DCA FROM CMH. ON DSCNT BTWN AML AND DCA, ABOUT READY FOR TURN DOWNWIND FOR ILS RWY 37 AT DCA. DSNDING THROUGH 5000 FT FOR CLRNC ALT OF 2500 FT GOT TA ON TCASII FOR TARGET AT 11 O'CLOCK LESS THAN 1000 FT BELOW AND BELIEVE LESS THAN 3 MI. (ESTIMATE AT ABOUT 2 1/2 MI.) THEN GOT RA TO 'STOP DSCNT.' TOOK MANUAL CTL AND LEVELED OFF AT ABOUT 4700 FT. FO NOTIFIED APCH CTL WHO TOLD US TO MAINTAIN 5000 FT. ASCENDED TO 5000 FT, LEVELED OFF AND REENGAGED AUTOPLT. WE WERE OVERTAKING TARGET AND WERE AT A SPD OF ABOUT 240 KTS. TCASII PROBABLY SAVED A VERY CLOSE CALL. DCA APCH SHOULD HAVE BEEN ABLE TO SEE POTENTIAL CONFLICT. CONDITIONS WERE HARD IMC IN LIGHT RAIN.

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.