Air carrier medium large transport altitude deviation excursion from clearance altitude.

Attributes
ACN	100376
Time
Date	198812
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ott
State Reference	MD
Altitude	msl bound lower : 31500 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : atp pilot : cfi
Experience	flight time last 90 days : 195 flight time total : 15500 flight time type : 2100
ASRS Report	100376
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 50 flight time total : 9500 flight time type : 3800
ASRS Report	100174
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Operational Deviation Pilot Deviation other

Narrative:

Controller gave our flight # and 'cross nottingham at FL240. Start descent now.' I read back the clearance verbatim, by the book, and the captain started descent. Passing FL317 the controller advised 'show you 1000' low.' I advised him that we had read back the above clearance and were complying. He responded, 'oh, my mistake. Maintain FL310.' in general controllers are very bad to key the microphone and immediately start talking--west/O allowing an instant for the transmitter to 'warm up'--cutting off the first word or so of the transmission. I don't recall this having been a problem in the above case, but it happens often. And the first of the transmission is--you guessed it!: the aircraft call sign. In addition, there was an air carrier Y flight on frequency with the same last 2 #'south as our flight #. Could this have contributed to the problem? I believe this was an incident where the heavy controller workload and large vol of communications contributed to a potentially unsafe condition. Supplemental information from acn 100174: he responded, 'my mistake, maintain 310.'

Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION EXCURSION FROM CLRNC ALT.

Narrative: CTLR GAVE OUR FLT # AND 'CROSS NOTTINGHAM AT FL240. START DSCNT NOW.' I READ BACK THE CLRNC VERBATIM, BY THE BOOK, AND THE CAPT STARTED DSCNT. PASSING FL317 THE CTLR ADVISED 'SHOW YOU 1000' LOW.' I ADVISED HIM THAT WE HAD READ BACK THE ABOVE CLRNC AND WERE COMPLYING. HE RESPONDED, 'OH, MY MISTAKE. MAINTAIN FL310.' IN GENERAL CTLRS ARE VERY BAD TO KEY THE MIC AND IMMEDIATELY START TALKING--W/O ALLOWING AN INSTANT FOR THE XMITTER TO 'WARM UP'--CUTTING OFF THE FIRST WORD OR SO OF THE XMISSION. I DON'T RECALL THIS HAVING BEEN A PROB IN THE ABOVE CASE, BUT IT HAPPENS OFTEN. AND THE FIRST OF THE XMISSION IS--YOU GUESSED IT!: THE ACFT CALL SIGN. IN ADDITION, THERE WAS AN ACR Y FLT ON FREQ WITH THE SAME LAST 2 #'S AS OUR FLT #. COULD THIS HAVE CONTRIBUTED TO THE PROB? I BELIEVE THIS WAS AN INCIDENT WHERE THE HEAVY CTLR WORKLOAD AND LARGE VOL OF COMS CONTRIBUTED TO A POTENTIALLY UNSAFE CONDITION. SUPPLEMENTAL INFO FROM ACN 100174: HE RESPONDED, 'MY MISTAKE, MAINTAIN 310.'

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.