Cpr X descent through occupied altitude had less than standard separation from cpr Y.

Attributes
ACN	271668
Time
Date	199405
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : djb
State Reference	OH
Altitude	msl bound lower : 16000 msl bound upper : 17000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : corporate
Make Model Name	Learjet 23
Operating Under FAR Part	Part 91
Flight Phase	descent other
Route In Use	enroute : direct enroute airway : zob
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Dassault-Breguet Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	climbout : intermediate altitude
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 5
ASRS Report	271668
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 2350 flight time type : 70
ASRS Report	271982
Events
Anomaly	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 : reviewed incident with flight crew faa : investigated
Miss Distance	horizontal : 10800 vertical : 600
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Cpr Y DA05/right departed bkl en route to sfo via sky vwv fwa and was cleared to climb to FL160. Cpr X, a LR23/right, en route to yip via djb.junkr.JUNKR1 was cleared to descend to FL170. TA's were issued to both aircraft and X was told to expect lower when clear of Y, X reported having the falcon in sight. Shortly thereafter, X descended through his assigned altitude, causing the loss of separation with Y. Supplemental information from acn 271982: X cleared to continue our descent to 13000 ft on the altimeter setting of 30.13. I was the PF and the captain was the PNF. He acknowledged the descent to 13000 ft on the radio and set 13000 ft in the altitude alerter, which I confirmed. In the descent we were issued traffic at 3 O'clock, which we called in sight and leveled off at 13000 ft. It would seem that some confusion could have occurred between the altitude and altimeter setting. We both believed we were cleared to 13000 ft which could have been a transposition of the altimeter of 30.13.

Original NASA ASRS Text

Title: CPR X DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM CPR Y.

Narrative: CPR Y DA05/R DEPARTED BKL ENRTE TO SFO VIA SKY VWV FWA AND WAS CLRED TO CLB TO FL160. CPR X, A LR23/R, ENRTE TO YIP VIA DJB.JUNKR.JUNKR1 WAS CLRED TO DSND TO FL170. TA'S WERE ISSUED TO BOTH ACFT AND X WAS TOLD TO EXPECT LOWER WHEN CLR OF Y, X RPTED HAVING THE FALCON IN SIGHT. SHORTLY THEREAFTER, X DSNDED THROUGH HIS ASSIGNED ALT, CAUSING THE LOSS OF SEPARATION WITH Y. SUPPLEMENTAL INFO FROM ACN 271982: X CLRED TO CONTINUE OUR DSCNT TO 13000 FT ON THE ALTIMETER SETTING OF 30.13. I WAS THE PF AND THE CAPT WAS THE PNF. HE ACKNOWLEDGED THE DSCNT TO 13000 FT ON THE RADIO AND SET 13000 FT IN THE ALT ALERTER, WHICH I CONFIRMED. IN THE DSCNT WE WERE ISSUED TFC AT 3 O'CLOCK, WHICH WE CALLED IN SIGHT AND LEVELED OFF AT 13000 FT. IT WOULD SEEM THAT SOME CONFUSION COULD HAVE OCCURRED BTWN THE ALT AND ALTIMETER SETTING. WE BOTH BELIEVED WE WERE CLRED TO 13000 FT WHICH COULD HAVE BEEN A TRANSPOSITION OF THE ALTIMETER OF 30.13.

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.