Air carrier X descent below assigned altitude. Pilot deviation. TCASII. GPWS.

Attributes
ACN	178092
Time
Date	199105
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : bld
State Reference	NV
Altitude	msl bound lower : 6500 msl bound upper : 6500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : las
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other
Route In Use	arrival star : star
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	descent other
Route In Use	approach : visual
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 10000 flight time type : 3000
ASRS Report	178092
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : clearance other spatial deviation
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 3000 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Air carrier X was cleared for a creso 1 arrival to las. After crossing whigg intersection at 10000', 250 KIAS, we were cleared to 9000'. At about 15 mi from bld, we were cleared to 8000', heading 015 degrees. Las approach advised us of traffic at 1-2 O'clock--small aircraft Y, who had us in sight. We looked, but did not see the traffic. The first officer advised las approach that we did not see the traffic, but we were looking. We were then cleared to 6100'. As we passed about 6500' at 240 KIAS with speed brakes extended we received a TCAS TA, 'traffic, traffic!' almost immediately we received a TCAS alert, 'descend, crossing descend,' followed by a 'monitor vertical speed' alert. The TA/vsi showed a green arc at about 2000 FPM descent, traffic at about 1/2 mi, 400' above us, descending. At about that time we received the first TCAS alert the second officer spotted the whitish, low wing, single engine aircraft at our 2 O'clock. The aircraft appeared to me to be very slightly above our altitude. I followed the TCAS RA through our assigned altitude of 6100' to about 5800'. We then heard the TCAS 'clear of conflict' alert, and then the ground proximity warning, 'terrain, pull up!' I initiated a climb back to 6100'. The first officer advised las approach control of the traffic, and that we had descended 300' below our assigned altitude due to the TCAS RA. The controller replied grumpily that he had advised us of that traffic that the other aircraft had us in sight (I feel compelled to mention the obvious: we had no way of knowing specifically which aircraft caused our alert). We were then cleared for a visibility approach to runway 25R in las, which we flew to a normal landing. I feel that the other aircraft, if he indeed had us in sight (he was looking into the sun)--maneuvered his aircraft too close to us. I question the wisdom of permitting a light aircraft to maintain visibility sep on an air carrier aircraft--given the range of experience of those pilots.

Original NASA ASRS Text

Title: ACR X DESCENT BELOW ASSIGNED ALT. PLT DEVIATION. TCASII. GPWS.

Narrative: ACR X WAS CLRED FOR A CRESO 1 ARR TO LAS. AFTER XING WHIGG INTXN AT 10000', 250 KIAS, WE WERE CLRED TO 9000'. AT ABOUT 15 MI FROM BLD, WE WERE CLRED TO 8000', HDG 015 DEGS. LAS APCH ADVISED US OF TFC AT 1-2 O'CLOCK--SMA Y, WHO HAD US IN SIGHT. WE LOOKED, BUT DID NOT SEE THE TFC. THE F/O ADVISED LAS APCH THAT WE DID NOT SEE THE TFC, BUT WE WERE LOOKING. WE WERE THEN CLRED TO 6100'. AS WE PASSED ABOUT 6500' AT 240 KIAS WITH SPD BRAKES EXTENDED WE RECEIVED A TCAS TA, 'TFC, TFC!' ALMOST IMMEDIATELY WE RECEIVED A TCAS ALERT, 'DSND, XING DSND,' FOLLOWED BY A 'MONITOR VERT SPD' ALERT. THE TA/VSI SHOWED A GREEN ARC AT ABOUT 2000 FPM DSNT, TFC AT ABOUT 1/2 MI, 400' ABOVE US, DSNDING. AT ABOUT THAT TIME WE RECEIVED THE FIRST TCAS ALERT THE S/O SPOTTED THE WHITISH, LOW WING, SINGLE ENG ACFT AT OUR 2 O'CLOCK. THE ACFT APPEARED TO ME TO BE VERY SLIGHTLY ABOVE OUR ALT. I FOLLOWED THE TCAS RA THROUGH OUR ASSIGNED ALT OF 6100' TO ABOUT 5800'. WE THEN HEARD THE TCAS 'CLR OF CONFLICT' ALERT, AND THEN THE GND PROX WARNING, 'TERRAIN, PULL UP!' I INITIATED A CLB BACK TO 6100'. THE F/O ADVISED LAS APCH CTL OF THE TFC, AND THAT WE HAD DSNDED 300' BELOW OUR ASSIGNED ALT DUE TO THE TCAS RA. THE CTLR REPLIED GRUMPILY THAT HE HAD ADVISED US OF THAT TFC THAT THE OTHER ACFT HAD US IN SIGHT (I FEEL COMPELLED TO MENTION THE OBVIOUS: WE HAD NO WAY OF KNOWING SPECIFICALLY WHICH ACFT CAUSED OUR ALERT). WE WERE THEN CLRED FOR A VIS APCH TO RWY 25R IN LAS, WHICH WE FLEW TO A NORMAL LNDG. I FEEL THAT THE OTHER ACFT, IF HE INDEED HAD US IN SIGHT (HE WAS LOOKING INTO THE SUN)--MANEUVERED HIS ACFT TOO CLOSE TO US. I QUESTION THE WISDOM OF PERMITTING A LIGHT ACFT TO MAINTAIN VIS SEP ON AN ACR ACFT--GIVEN THE RANGE OF EXPERIENCE OF THOSE PLTS.

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.