Corp aircraft descends below assigned altitude.

Attributes
ACN	313100
Time
Date	199508
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : vxv
State Reference	TN
Altitude	msl bound lower : 20000 msl bound upper : 22000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	general aviation : corporate
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 91
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 130 flight time total : 5500 flight time type : 1400
ASRS Report	313100
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation

Narrative:

In a king air 300, we were cleared from FL290 to FL240, and later handed off to low center control. Upon calling ZTL at FL240 the controller asked if we could be at FL220 in a 'min and a half.' we said yes and both myself and my copilot, who was working the radios, understood the controller to say 'descend to FL200 and down to FL220 within a minute and a half.' copilot read that back very clearly and we started down. Passing about FL228 the controller asked altitude. We reported and added that we would 'be through FL220 in 30 seconds.' (well within the min and a half). The controller seemed interested in the progress of our descent, so I told the copilot, 'when we pass FL220 tell him,' as I know that during a rapid descent radar returns lag. However, when we passed FL220 others were talking on the frequency and by the time the copilot had a chance to talk again the controller had time to see for himself on the radar that we were safely out of FL220. Presently we moderated our descent and continued at a more normal rate. A moment later the controller asked our altitude. We reported 'passing FL202 to FL200.' he then said 'well, you were supposed to stop at FL220, but that's all right. Just stay at FL200.' uh-oh. I've never filed one of these reports before, and I am surprised at how long this narrative became for such a brief incident. Sorry about that, but if controllers would listen to readbacks a little better, maybe I wouldn't have written it.

Original NASA ASRS Text

Title: CORP ACFT DSNDS BELOW ASSIGNED ALT.

Narrative: IN A KING AIR 300, WE WERE CLRED FROM FL290 TO FL240, AND LATER HANDED OFF TO LOW CTR CTL. UPON CALLING ZTL AT FL240 THE CTLR ASKED IF WE COULD BE AT FL220 IN A 'MIN AND A HALF.' WE SAID YES AND BOTH MYSELF AND MY COPLT, WHO WAS WORKING THE RADIOS, UNDERSTOOD THE CTLR TO SAY 'DSND TO FL200 AND DOWN TO FL220 WITHIN A MINUTE AND A HALF.' COPLT READ THAT BACK VERY CLRLY AND WE STARTED DOWN. PASSING ABOUT FL228 THE CTLR ASKED ALT. WE RPTED AND ADDED THAT WE WOULD 'BE THROUGH FL220 IN 30 SECONDS.' (WELL WITHIN THE MIN AND A HALF). THE CTLR SEEMED INTERESTED IN THE PROGRESS OF OUR DSCNT, SO I TOLD THE COPLT, 'WHEN WE PASS FL220 TELL HIM,' AS I KNOW THAT DURING A RAPID DSCNT RADAR RETURNS LAG. HOWEVER, WHEN WE PASSED FL220 OTHERS WERE TALKING ON THE FREQ AND BY THE TIME THE COPLT HAD A CHANCE TO TALK AGAIN THE CTLR HAD TIME TO SEE FOR HIMSELF ON THE RADAR THAT WE WERE SAFELY OUT OF FL220. PRESENTLY WE MODERATED OUR DSCNT AND CONTINUED AT A MORE NORMAL RATE. A MOMENT LATER THE CTLR ASKED OUR ALT. WE RPTED 'PASSING FL202 TO FL200.' HE THEN SAID 'WELL, YOU WERE SUPPOSED TO STOP AT FL220, BUT THAT'S ALL RIGHT. JUST STAY AT FL200.' UH-OH. I'VE NEVER FILED ONE OF THESE RPTS BEFORE, AND I AM SURPRISED AT HOW LONG THIS NARRATIVE BECAME FOR SUCH A BRIEF INCIDENT. SORRY ABOUT THAT, BUT IF CTLRS WOULD LISTEN TO READBACKS A LITTLE BETTER, MAYBE I WOULDN'T HAVE WRITTEN IT.

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.