Altitude deviation resulting in a potential conflict with less than standard separation.

Attributes
ACN	159563
Time
Date	199010
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : prb
State Reference	CA
Altitude	msl bound lower : 23600 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : instrument pilot : commercial
Experience	flight time last 90 days : 98 flight time total : 5400 flight time type : 208
ASRS Report	159563
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : required legal separation non adherence : clearance
Independent Detector	other controllera
Resolutory Action	none taken : detected after the fact
Consequence	faa : investigated faa : reviewed incident with flight crew
Miss Distance	horizontal : 15000 vertical : 600
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was flying an small transport on an INS flight plan form sun, identification to sbp, proceeding direct to prb VOR at FL280 approximately. 50 NM northwest of sbp on an approximately heading of 225 degrees in radio contact with ZOA. ZOA cleared me to FL240 from FL280 and gave me an altimeter setting for prb (to the best of my recollection). I was flying with the autoplt engaged and used my altitude preselect to descend with the autoplt on to FL240. I started my descent immediately. I do not recollect if I put in the new altimeter setting, but to the best of my recollection I did not change my altimeter from 29.29. I also requested lower when able at this time. ZOA cleared me to turn right to a new heading of 250 degrees for descent to FL240. I complied and again requested lower. ZOA informed me of traffic, a civil jet at FL230 passing n-s. I immediately sighted the civil jet. It appeared to pass in front of my aircraft at approximately 1000' lower, at approximately 1.5-2 mi. I reported the civil jet in sight and for the third time requested lower. ZOA informed me that they needed a minimum of 5 mi sep in order to clear me for a lower altitude, and handed me off to ZOA on 128.7. I contacted ZOA on 128.7 and requested lower and on course to sbp. ZOA informed me they would have lower for mi in a moment. Approximately 1 min later ZOA cleared me direct to prb and to descend to 11000'. I complied and turned left direct to prb and started my descent from FL240 to 11000' using my autoplt. At approximately 14000' MSL ZOA requested my altitude. I informed them. Before handing me off to ZLA ZOA requested that I call the shift supervisor at 415/#. Approximately 12 mi north of sbp I contacted ZLA and cancelled my IFR and proceeded VFR to sbp and landed. After landing I called ZOA and talked to controller supervisor. He informed me that ZOA's radar tape had shown that I had descended approximately 400' below my assigned altitude of FL240 before I was cleared to do so, and also that my aircraft passed within 2.5 mi from a civil jet and requested that I tell him to the best of my recollection my actions during this time frame.

Original NASA ASRS Text

Title: ALT DEVIATION RESULTING IN A POTENTIAL CONFLICT WITH LESS THAN STANDARD SEPARATION.

Narrative: I WAS FLYING AN SMT ON AN INS FLT PLAN FORM SUN, ID TO SBP, PROCEEDING DIRECT TO PRB VOR AT FL280 APPROX. 50 NM NW OF SBP ON AN APPROX HDG OF 225 DEGS IN RADIO CONTACT WITH ZOA. ZOA CLRED ME TO FL240 FROM FL280 AND GAVE ME AN ALTIMETER SETTING FOR PRB (TO THE BEST OF MY RECOLLECTION). I WAS FLYING WITH THE AUTOPLT ENGAGED AND USED MY ALT PRESELECT TO DSND WITH THE AUTOPLT ON TO FL240. I STARTED MY DSNT IMMEDIATELY. I DO NOT RECOLLECT IF I PUT IN THE NEW ALTIMETER SETTING, BUT TO THE BEST OF MY RECOLLECTION I DID NOT CHANGE MY ALTIMETER FROM 29.29. I ALSO REQUESTED LOWER WHEN ABLE AT THIS TIME. ZOA CLRED ME TO TURN RIGHT TO A NEW HDG OF 250 DEGS FOR DSNT TO FL240. I COMPLIED AND AGAIN REQUESTED LOWER. ZOA INFORMED ME OF TFC, A CIVIL JET AT FL230 PASSING N-S. I IMMEDIATELY SIGHTED THE CIVIL JET. IT APPEARED TO PASS IN FRONT OF MY ACFT AT APPROX 1000' LOWER, AT APPROX 1.5-2 MI. I RPTED THE CIVIL JET IN SIGHT AND FOR THE THIRD TIME REQUESTED LOWER. ZOA INFORMED ME THAT THEY NEEDED A MINIMUM OF 5 MI SEP IN ORDER TO CLR ME FOR A LOWER ALT, AND HANDED ME OFF TO ZOA ON 128.7. I CONTACTED ZOA ON 128.7 AND REQUESTED LOWER AND ON COURSE TO SBP. ZOA INFORMED ME THEY WOULD HAVE LOWER FOR MI IN A MOMENT. APPROX 1 MIN LATER ZOA CLRED ME DIRECT TO PRB AND TO DSND TO 11000'. I COMPLIED AND TURNED LEFT DIRECT TO PRB AND STARTED MY DSNT FROM FL240 TO 11000' USING MY AUTOPLT. AT APPROX 14000' MSL ZOA REQUESTED MY ALT. I INFORMED THEM. BEFORE HANDING ME OFF TO ZLA ZOA REQUESTED THAT I CALL THE SHIFT SUPVR AT 415/#. APPROX 12 MI N OF SBP I CONTACTED ZLA AND CANCELLED MY IFR AND PROCEEDED VFR TO SBP AND LANDED. AFTER LNDG I CALLED ZOA AND TALKED TO CTLR SUPVR. HE INFORMED ME THAT ZOA'S RADAR TAPE HAD SHOWN THAT I HAD DSNDED APPROX 400' BELOW MY ASSIGNED ALT OF FL240 BEFORE I WAS CLRED TO DO SO, AND ALSO THAT MY ACFT PASSED WITHIN 2.5 MI FROM A CIVIL JET AND REQUESTED THAT I TELL HIM TO THE BEST OF MY RECOLLECTION MY ACTIONS DURING THIS TIME FRAME.

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.