Air carrier X clearance to wrong altitude descent through occupied altitude had TCASII RA climb had ...

Attributes
ACN	211778
Time
Date	199206
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : swl
State Reference	MD
Altitude	msl bound lower : 35000 msl bound upper : 35400
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 22
ASRS Report	211778
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 6000 flight time type : 150
ASRS Report	211850
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	faa : investigated
Miss Distance	horizontal : 24000 vertical : 400
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X at FL410 40 south swl. I had to have air carrier X at FL370 per 'manops' by 30 south sie. I had 2 pieces of traffic at FL390 15 north sby and another 30 north swl. I gave air carrier X a clearance to FL370 and after several updates, the aircraft had not left FL410. I told air carrier X to begin descent at 2000 FPM, which the pilot said would be no problem. After observing air carrier X leave FL373, I knew he was no longer a factor for my FL390 traffic. I began a recorded position relief briefing at this time and my attention was diverted from air carrier X. When I next noticed air carrier X was out of FL358 descending head-on to air carrier Y at FL350. After listening to the tapes, I found that instead of issuing clearance to FL370, I said FL270. Much to my dismay, I also did not catch the pilots readback. Supplemental information from acn 211850: air carrier X descent was initiated using VNAV and the autoplt. Even before the autoplt had attained its normal 1500 FPM descent rate to a new cruise level, ZDC called and told us to increase our rate of descent to over 2000 FPM. The captain switched the autoplt to vertical speed mode and dialed in 2500 FPM. At approximately FL360, the TCASII gave us a RA requiring over 1700 FPM climb. The captain disengaged the autoplt and manually flew the aircraft to the appropriate vertical climb indicated by the TCASII to avoid traffic. In the transition from 2500 FPM descent to a 1700 FPM climb, the aircraft probably descended to FL355. Even before I could call center to ask about the traffic, they called us and said we were only cleared to FL370 and to make an immediate descent to FL330. I advised them that we had the TCASII generated RA and were already in a climb to avoid traffic. I also advised them that I had read back clearance to FL270 and that we would continue our climb to FL370 since we were already above FL360 and still climbing. Just as I completed my transmission, I saw traffic pass directly below us at what the TCASII indicated as FL350.

Original NASA ASRS Text

Title: ACR X CLRNC TO WRONG ALT DSCNT THROUGH OCCUPIED ALT HAD TCASII RA CLB HAD LTSS FROM ACR Y. SYS ERROR. EVASIVE ACTION TAKEN.

Narrative: ACR X AT FL410 40 S SWL. I HAD TO HAVE ACR X AT FL370 PER 'MANOPS' BY 30 S SIE. I HAD 2 PIECES OF TFC AT FL390 15 N SBY AND ANOTHER 30 N SWL. I GAVE ACR X A CLRNC TO FL370 AND AFTER SEVERAL UPDATES, THE ACFT HAD NOT LEFT FL410. I TOLD ACR X TO BEGIN DSCNT AT 2000 FPM, WHICH THE PLT SAID WOULD BE NO PROBLEM. AFTER OBSERVING ACR X LEAVE FL373, I KNEW HE WAS NO LONGER A FACTOR FOR MY FL390 TFC. I BEGAN A RECORDED POS RELIEF BRIEFING AT THIS TIME AND MY ATTN WAS DIVERTED FROM ACR X. WHEN I NEXT NOTICED ACR X WAS OUT OF FL358 DSNDING HEAD-ON TO ACR Y AT FL350. AFTER LISTENING TO THE TAPES, I FOUND THAT INSTEAD OF ISSUING CLRNC TO FL370, I SAID FL270. MUCH TO MY DISMAY, I ALSO DID NOT CATCH THE PLTS READBACK. SUPPLEMENTAL INFO FROM ACN 211850: ACR X DSCNT WAS INITIATED USING VNAV AND THE AUTOPLT. EVEN BEFORE THE AUTOPLT HAD ATTAINED ITS NORMAL 1500 FPM DSCNT RATE TO A NEW CRUISE LEVEL, ZDC CALLED AND TOLD US TO INCREASE OUR RATE OF DSCNT TO OVER 2000 FPM. THE CAPT SWITCHED THE AUTOPLT TO VERT SPD MODE AND DIALED IN 2500 FPM. AT APPROX FL360, THE TCASII GAVE US A RA REQUIRING OVER 1700 FPM CLB. THE CAPT DISENGAGED THE AUTOPLT AND MANUALLY FLEW THE ACFT TO THE APPROPRIATE VERT CLB INDICATED BY THE TCASII TO AVOID TFC. IN THE TRANSITION FROM 2500 FPM DSCNT TO A 1700 FPM CLB, THE ACFT PROBABLY DSNDED TO FL355. EVEN BEFORE I COULD CALL CTR TO ASK ABOUT THE TFC, THEY CALLED US AND SAID WE WERE ONLY CLRED TO FL370 AND TO MAKE AN IMMEDIATE DSCNT TO FL330. I ADVISED THEM THAT WE HAD THE TCASII GENERATED RA AND WERE ALREADY IN A CLB TO AVOID TFC. I ALSO ADVISED THEM THAT I HAD READ BACK CLRNC TO FL270 AND THAT WE WOULD CONTINUE OUR CLB TO FL370 SINCE WE WERE ALREADY ABOVE FL360 AND STILL CLBING. JUST AS I COMPLETED MY XMISSION, I SAW TFC PASS DIRECTLY BELOW US AT WHAT THE TCASII INDICATED AS FL350.

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.

Air carrier X clearance to wrong altitude descent through occupied altitude had TCASII RA climb had less than standard separation from air carrier Y. System error. Evasive action taken.