Altitude overshoot as the result of misunderstanding of clearance and readback correction.

Attributes
ACN	483490
Time
Date	200008
Day	Sat
Local Time Of Day	0601 To 1200
Place
State Reference	TX
Altitude	msl bound lower : 23000 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zhu.artcc
Operator	common carrier : air carrier
Make Model Name	DC-9 40
Operating Under FAR Part	Part 121
Route In Use	enroute : on vectors
Flight Plan	IFR
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 : 18600 flight time type : 6000
ASRS Report	483490
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 94 flight time total : 4200 flight time type : 1800
ASRS Report	483496
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllerb
Resolutory Action	controller : issued advisory controller : issued new clearance
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

After descent from FL330 to FL240, the controller issued a clearance for the arrival. I read back, 'descend to 150 and intercept the 300 degree radial to cwk' and asked him to repeat the intercept heading. He said that was heading 150 degrees (in hindsight he was correcting my interpretation of the '150'). I thought the heading was in conjunction with flight level 15000 ft. We turned to heading 150 degrees and left FL240 for 15000 ft. Out of approximately FL230 the controller asked 'what altitude are you descending to?' I said '15000 ft.' he replied 'that was heading 150 degrees' and that we had clarified that in the readback. He then issued a descent clearance to continue the descent to flight level 13000 ft. No further discussion. The problem was in communication and the readbacks. We had been flying all night also, and this was the end of our trip. So fatigue was also a factor on our part. Supplemental information from acn 483496: at this time, I was listening to the new ATIS, as it had just changed and the field had gone IMC. The captain (PNF) switched to ZHU and we were directed to a 150 degree heading and, we believed, a further descent clearance to 15000 ft. The captain read back the heading and altitude clearance and we proceeded as directed.

Original NASA ASRS Text

Title: ALT OVERSHOOT AS THE RESULT OF MISUNDERSTANDING OF CLRNC AND READBACK CORRECTION.

Narrative: AFTER DSCNT FROM FL330 TO FL240, THE CTLR ISSUED A CLRNC FOR THE ARR. I READ BACK, 'DSND TO 150 AND INTERCEPT THE 300 DEG RADIAL TO CWK' AND ASKED HIM TO REPEAT THE INTERCEPT HDG. HE SAID THAT WAS HDG 150 DEGS (IN HINDSIGHT HE WAS CORRECTING MY INTERP OF THE '150'). I THOUGHT THE HDG WAS IN CONJUNCTION WITH FLT LEVEL 15000 FT. WE TURNED TO HDG 150 DEGS AND LEFT FL240 FOR 15000 FT. OUT OF APPROX FL230 THE CTLR ASKED 'WHAT ALT ARE YOU DSNDING TO?' I SAID '15000 FT.' HE REPLIED 'THAT WAS HDG 150 DEGS' AND THAT WE HAD CLARIFIED THAT IN THE READBACK. HE THEN ISSUED A DSCNT CLRNC TO CONTINUE THE DSCNT TO FLT LEVEL 13000 FT. NO FURTHER DISCUSSION. THE PROB WAS IN COM AND THE READBACKS. WE HAD BEEN FLYING ALL NIGHT ALSO, AND THIS WAS THE END OF OUR TRIP. SO FATIGUE WAS ALSO A FACTOR ON OUR PART. SUPPLEMENTAL INFO FROM ACN 483496: AT THIS TIME, I WAS LISTENING TO THE NEW ATIS, AS IT HAD JUST CHANGED AND THE FIELD HAD GONE IMC. THE CAPT (PNF) SWITCHED TO ZHU AND WE WERE DIRECTED TO A 150 DEG HDG AND, WE BELIEVED, A FURTHER DSCNT CLRNC TO 15000 FT. THE CAPT READ BACK THE HDG AND ALT CLRNC AND WE PROCEEDED AS DIRECTED.

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.