<< >> NASA ASRS Report 401549, May 1998

BE9L aircraft, with DC9 in sight was cleared to descend through the other aircraft's altitude while maintaining visual separation. Reporter pilot misjudged the separation distance resulting in both aircraft receiving TCASII RA's and near midair collision.

Attributes
ACN	401549
Time
Date	199805
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : bae
State Reference	WI
Altitude	msl bound lower : 9500 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau
Operator	general aviation : corporate
Make Model Name	King Air C90 E90
Operating Under FAR Part	Part 91
Flight Phase	descent other
Route In Use	enroute airway : zau
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument pilot : cfi pilot : atp
Experience	flight time last 90 days : 100 flight time total : 4000 flight time type : 160
ASRS Report	401549
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : nmac other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 500 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance

Narrative:

My aircraft was level 11000 ft nebound. ATC reported traffic 2 O'clock 10 mi. DC9 at 10000 ft nwbound. Traffic reported in sight. Approximately 30 seconds later I was cleared to maintain visual separation, pilot discretion descend and maintain 8000 ft. After checking TCASII and observing no traffic, I reported vacating 11000 ft for 8000 ft. As my aircraft descended through approximately 10600 ft traffic was observed on TCASII at 3 O'clock position and level 10000 ft (600 ft below me) and range of 6 mi. I increased rate of descent in an attempt to get below the DC9. As the DC9 approached within 2 NM and less than 1000 ft of vertical separation TCASII issued an RA. I increased my rate of descent, and the DC9 passed approximately 500 ft above my aircraft. The DC9 reported to ATC that he had also received a TCASII RA and had initiated a climb. In reference to regulation far 91.111, the distance between aircraft should have been greater.

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Original NASA ASRS Text

Title: BE9L ACFT, WITH DC9 IN SIGHT WAS CLRED TO DSND THROUGH THE OTHER ACFT'S ALT WHILE MAINTAINING VISUAL SEPARATION. RPTR PLT MISJUDGED THE SEPARATION DISTANCE RESULTING IN BOTH ACFT RECEIVING TCASII RA'S AND NMAC.

Narrative: MY ACFT WAS LEVEL 11000 FT NEBOUND. ATC RPTED TFC 2 O'CLOCK 10 MI. DC9 AT 10000 FT NWBOUND. TFC RPTED IN SIGHT. APPROX 30 SECONDS LATER I WAS CLRED TO MAINTAIN VISUAL SEPARATION, PLT DISCRETION DSND AND MAINTAIN 8000 FT. AFTER CHKING TCASII AND OBSERVING NO TFC, I RPTED VACATING 11000 FT FOR 8000 FT. AS MY ACFT DSNDED THROUGH APPROX 10600 FT TFC WAS OBSERVED ON TCASII AT 3 O'CLOCK POS AND LEVEL 10000 FT (600 FT BELOW ME) AND RANGE OF 6 MI. I INCREASED RATE OF DSCNT IN AN ATTEMPT TO GET BELOW THE DC9. AS THE DC9 APCHED WITHIN 2 NM AND LESS THAN 1000 FT OF VERT SEPARATION TCASII ISSUED AN RA. I INCREASED MY RATE OF DSCNT, AND THE DC9 PASSED APPROX 500 FT ABOVE MY ACFT. THE DC9 RPTED TO ATC THAT HE HAD ALSO RECEIVED A TCASII RA AND HAD INITIATED A CLB. IN REF TO REG FAR 91.111, THE DISTANCE BTWN ACFT SHOULD HAVE BEEN GREATER.

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.