Less than standard separation in TCA, small aircraft descended without clearance.

Attributes
ACN	156050
Time
Date	199009
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pye airport : sfo
State Reference	CA
Altitude	msl bound lower : 4000 msl bound upper : 4000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : oak tower : ogd
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : intermediate altitude cruise other
Route In Use	departure other enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft
Flight Phase	descent other
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 150 flight time total : 21000 flight time type : 500
ASRS Report	156050
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 6000 vertical : 200
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Shortly after liftoff departure control instructed us to level at 4000' for traffic. We acknowledged and reset the altitude. Shortly after this we received and acknowledged clearance to turn to heading of 180 degrees. During the turn and while leveling off at 4000' I noticed a red, single engine jet trainer at our altitude headed southwest on an intercept heading. I called the traffic in sight and climbed to evade. The other captain with me reported the traffic to bay departure and informed the controller of our evasive action. The controller asked the other aircraft operator his altitude. That pilot reported that he was descending to 3500'. Apparently the small aircraft Y transponder either did not have altitude reporting or it was inoperative. This aircraft continued to vny west/O an operating mode C. We continued to lax as scheduled.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION IN TCA, SMA DESCENDED WITHOUT CLRNC.

Narrative: SHORTLY AFTER LIFTOFF DEP CTL INSTRUCTED US TO LEVEL AT 4000' FOR TFC. WE ACKNOWLEDGED AND RESET THE ALT. SHORTLY AFTER THIS WE RECEIVED AND ACKNOWLEDGED CLRNC TO TURN TO HDG OF 180 DEGS. DURING THE TURN AND WHILE LEVELING OFF AT 4000' I NOTICED A RED, SINGLE ENG JET TRAINER AT OUR ALT HEADED SW ON AN INTERCEPT HDG. I CALLED THE TFC IN SIGHT AND CLBED TO EVADE. THE OTHER CAPT WITH ME RPTED THE TFC TO BAY DEP AND INFORMED THE CTLR OF OUR EVASIVE ACTION. THE CTLR ASKED THE OTHER ACFT OPERATOR HIS ALT. THAT PLT RPTED THAT HE WAS DSNDING TO 3500'. APPARENTLY THE SMA Y XPONDER EITHER DID NOT HAVE ALT RPTING OR IT WAS INOP. THIS ACFT CONTINUED TO VNY W/O AN OPERATING MODE C. WE CONTINUED TO LAX AS SCHEDULED.

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.