Air carrier climbed above assigned altitude and conflicted with another air carrier.

Attributes
ACN	122906
Time
Date	198909
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : orf
State Reference	VA
Altitude	msl bound lower : 31000 msl bound upper : 32200
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	122906
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 140 flight time total : 8000 flight time type : 1000
ASRS Report	121353
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : required legal separation non adherence : clearance other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 18000 vertical : 800
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I cleared air carrier X from FL280 to FL310, his final requested altitude. After accepting a handoff on northbound traffic at FL290 I restr air carrier X to climb to reach FL310 within 1 minute to insure separation. Shortly thereafter, while on a handoff line, I noticed air carrier X's mode C reporting level at FL310 and heard air carrier X call (over the loudspeaker), and at the time I believed he reported level at FL310. I responded, 'air carrier X thank you'. Approximately 30 seconds later I observed air carrier X's mode C displaying FL314 and asked him to verify that he was indeed level at FL310. Air carrier X then stated he was climbing to FL330. Air carrier X was then quickly cleared to FL310 and a traffic call was issued. Air carrier X called the traffic in sight. At XA14Z air carrier X returned to my frequency, of his own volition, to explain the reason for what he called the 'altitude deviation'. The captain of air carrier X stated that he heard and understood his clearance was to reach FL310 within 1 minute. However, the copilot differed and was instructed to verify assigned altitude with center. The response he said they received was 'thank you'. Air carrier X said they then 'assumed' they were cleared to FL330. I feel that there was obviously some confusion in the cockpit as to what their assigned altitude was and they should have pursued the matter further. Supplemental information from acn 121353: as we approached FL310 ZDC called us and asked us to be level at FL310 in 1 min. I interpreted the transmission that we were to be level at FL330 in 1 min and read back climb to FL330 in 1 min. I received no verification or response from the controller. The captain questioned the altitude passing FL310. I again questioned the controller that we were cleared to FL330. The controller's response was 'thank you'. This didn't make sense, then the controller immediately asked our altitude and called out traffic at 12 O'clock and FL330. There was a misinterp on what I heard and what the controller stated. It was not caught on the readback. The captain and second officer heard different clrncs also. Neither the crew nor the controller caught the communications problem which caused the altitude deviation.

Original NASA ASRS Text

Title: ACR CLIMBED ABOVE ASSIGNED ALT AND CONFLICTED WITH ANOTHER ACR.

Narrative: I CLRED ACR X FROM FL280 TO FL310, HIS FINAL REQUESTED ALT. AFTER ACCEPTING A HANDOFF ON NBOUND TFC AT FL290 I RESTR ACR X TO CLIMB TO REACH FL310 WITHIN 1 MINUTE TO INSURE SEPARATION. SHORTLY THEREAFTER, WHILE ON A HANDOFF LINE, I NOTICED ACR X'S MODE C REPORTING LEVEL AT FL310 AND HEARD ACR X CALL (OVER THE LOUDSPEAKER), AND AT THE TIME I BELIEVED HE REPORTED LEVEL AT FL310. I RESPONDED, 'ACR X THANK YOU'. APPROX 30 SECONDS LATER I OBSERVED ACR X'S MODE C DISPLAYING FL314 AND ASKED HIM TO VERIFY THAT HE WAS INDEED LEVEL AT FL310. ACR X THEN STATED HE WAS CLIMBING TO FL330. ACR X WAS THEN QUICKLY CLRED TO FL310 AND A TFC CALL WAS ISSUED. ACR X CALLED THE TFC IN SIGHT. AT XA14Z ACR X RETURNED TO MY FREQ, OF HIS OWN VOLITION, TO EXPLAIN THE REASON FOR WHAT HE CALLED THE 'ALT DEVIATION'. THE CAPT OF ACR X STATED THAT HE HEARD AND UNDERSTOOD HIS CLRNC WAS TO REACH FL310 WITHIN 1 MINUTE. HOWEVER, THE COPLT DIFFERED AND WAS INSTRUCTED TO VERIFY ASSIGNED ALT WITH CENTER. THE RESPONSE HE SAID THEY RECEIVED WAS 'THANK YOU'. ACR X SAID THEY THEN 'ASSUMED' THEY WERE CLRED TO FL330. I FEEL THAT THERE WAS OBVIOUSLY SOME CONFUSION IN THE COCKPIT AS TO WHAT THEIR ASSIGNED ALT WAS AND THEY SHOULD HAVE PURSUED THE MATTER FURTHER. SUPPLEMENTAL INFORMATION FROM ACN 121353: AS WE APCHED FL310 ZDC CALLED US AND ASKED US TO BE LEVEL AT FL310 IN 1 MIN. I INTERPRETED THE XMISSION THAT WE WERE TO BE LEVEL AT FL330 IN 1 MIN AND READ BACK CLIMB TO FL330 IN 1 MIN. I RECEIVED NO VERIFICATION OR RESPONSE FROM THE CTLR. THE CAPT QUESTIONED THE ALT PASSING FL310. I AGAIN QUESTIONED THE CTLR THAT WE WERE CLRED TO FL330. THE CTLR'S RESPONSE WAS 'THANK YOU'. THIS DIDN'T MAKE SENSE, THEN THE CTLR IMMEDIATELY ASKED OUR ALT AND CALLED OUT TFC AT 12 O'CLOCK AND FL330. THERE WAS A MISINTERP ON WHAT I HEARD AND WHAT THE CTLR STATED. IT WAS NOT CAUGHT ON THE READBACK. THE CAPT AND S/O HEARD DIFFERENT CLRNCS ALSO. NEITHER THE CREW NOR THE CTLR CAUGHT THE COMS PROBLEM WHICH CAUSED THE ALT DEVIATION.

Data retrieved from NASA's ASRS site as of August 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.