Operational error less than standard separation when an air carrier E120 conflicts with a company E1...

Attributes
ACN	383037
Time
Date	199710
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : sfo
State Reference	CA
Altitude	msl bound lower : 6000 msl bound upper : 7000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : oak
Operator	common carrier : air carrier
Make Model Name	Brasilia EMB-120 All Series
Operating Under FAR Part	Part 135
Navigation In Use	Other
Flight Phase	descent other
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Brasilia EMB-120 All Series
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time total : 12000 flight time type : 8000
ASRS Report	383037
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 9000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

We were approaching sfo from the southeast. As per normal practice we had been descended to 8000 ft prior to entering bay's airspace. Bay approach then, again as per normal practice, cleared us to descend and maintain 6000 ft. My first officer read back the 6000 ft clearance and I acknowledged it by setting 6000 ft in the altitude alerter and holding my finger there until he acknowledged me. Descending through 7000 ft I noticed a target on our tcasi (bfg TCAS-91). I selected the closest range (5 NM) to better visualize the target. The target (aircraft B) was at our 10-11 O'clock position, 1-2 mi, and 1000 ft below us, and we appeared to be slowly overtaking them. In other words they were where we were supposed to go. I quickly acquired the target visually (they were popping in and out of the cloud tops). Since this aircraft appeared to be at 6000 ft and we were cleared to 6000 ft, which both my first officer and I reconfirmed with each other and with the altitude alerter, I slowed my descent and we asked ATC if they had any traffic there. The controller responded casually that he did, it was a company EMB120 at 6000 ft going in the same direction. His demeanor implied, why are you asking?, he is no factor. At this time we were descending through 6700-6600 ft. I responded that we had the aircraft (aircraft B) in sight, we had been cleared to 6000 ft, did they want us to go back up to 7000 ft? Bay approach did want us to climb back to 7000 ft, and we stopped our descent by 6500 ft.

Original NASA ASRS Text

Title: OPERROR LTSS WHEN AN ACR E120 CONFLICTS WITH A COMPANY E120 AT 6000 FT AFTER RECEIVING, READING BACK AND BEGINNING A DSCNT TO 6000 FT.

Narrative: WE WERE APCHING SFO FROM THE SE. AS PER NORMAL PRACTICE WE HAD BEEN DSNDED TO 8000 FT PRIOR TO ENTERING BAY'S AIRSPACE. BAY APCH THEN, AGAIN AS PER NORMAL PRACTICE, CLRED US TO DSND AND MAINTAIN 6000 FT. MY FO READ BACK THE 6000 FT CLRNC AND I ACKNOWLEDGED IT BY SETTING 6000 FT IN THE ALT ALERTER AND HOLDING MY FINGER THERE UNTIL HE ACKNOWLEDGED ME. DSNDING THROUGH 7000 FT I NOTICED A TARGET ON OUR TCASI (BFG TCAS-91). I SELECTED THE CLOSEST RANGE (5 NM) TO BETTER VISUALIZE THE TARGET. THE TARGET (ACFT B) WAS AT OUR 10-11 O'CLOCK POS, 1-2 MI, AND 1000 FT BELOW US, AND WE APPEARED TO BE SLOWLY OVERTAKING THEM. IN OTHER WORDS THEY WERE WHERE WE WERE SUPPOSED TO GO. I QUICKLY ACQUIRED THE TARGET VISUALLY (THEY WERE POPPING IN AND OUT OF THE CLOUD TOPS). SINCE THIS ACFT APPEARED TO BE AT 6000 FT AND WE WERE CLRED TO 6000 FT, WHICH BOTH MY FO AND I RECONFIRMED WITH EACH OTHER AND WITH THE ALT ALERTER, I SLOWED MY DSCNT AND WE ASKED ATC IF THEY HAD ANY TFC THERE. THE CTLR RESPONDED CASUALLY THAT HE DID, IT WAS A COMPANY EMB120 AT 6000 FT GOING IN THE SAME DIRECTION. HIS DEMEANOR IMPLIED, WHY ARE YOU ASKING?, HE IS NO FACTOR. AT THIS TIME WE WERE DSNDING THROUGH 6700-6600 FT. I RESPONDED THAT WE HAD THE ACFT (ACFT B) IN SIGHT, WE HAD BEEN CLRED TO 6000 FT, DID THEY WANT US TO GO BACK UP TO 7000 FT? BAY APCH DID WANT US TO CLB BACK TO 7000 FT, AND WE STOPPED OUR DSCNT BY 6500 FT.

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.

Operational error less than standard separation when an air carrier E120 conflicts with a company E120 at 6000 ft after receiving, reading back and beginning a descent to 6000 ft.