Imprecise clearance phraseology and the failure to confirm understanding of the clearance resulted i...

Narrative:

Level cruise at FL390; eastbound on J42; east of bkw. Washington center issued the following clearance to us. 'Descend now to FL350; maintain a descent rate of 1500 FPM or greater and then cross denny at FL330.' we read back the clearance exactly as it was issued; ('descend now to FL350 at 1500 FPM or greater and cross denny at FL330'); and immediately began our descent at 1500 FPM. The controller did not reply and proceeded to communicate with other aircraft on the frequency; as expected. While in the descent; we calculated that a 1500 FPM descent would allow us to level at denny exactly at FL330 and planned to maintain that descent rate all the way down to FL330. After approximately 60-90 seconds; while descending through approximately FL370 the controller said to us; 'descend to FL350 and maintain a descent rate of 1500 FPM or greater.' we immediately read back 'we are descending to FL350 with a descent rate of 1500 FPM and will cross denny at FL330.' the controller again did not reply and went on to communicate with other aircraft. We figured she issued the clearance again because either 1) she did not copy our original read back or 2) she was verifying our descent rate was at least 1500 FPM. While leveling at FL330 just west of denny; the controller came on and told us we were only cleared to FL350. We replied that we were cleared to descend to FL350 immediately; at 1500 FPM or greater; and cross denny at FL330 and that we read that back twice. We then confirmed that we were level at FL330 and asked her what she wanted us to do now. She instructed us to maintain FL330 and said there was a misunderstanding. We maintained FL330 and continued the flight without incident.in my opinion; the second clearance was not clear. It never occurred to us that she was attempting to get us to level at FL350. (It appears to be much clearer when only our transmissions are highlighted; as in this report. However; in real time on a busy frequency; we did not comprehend the controllers' intentions) I feel the clearance would have been easily understood if the controller added only a few extra words; such as 1) 'descend to FL350 only' 2) 'descend to FL350 and delete the crossing restriction at denny' or another variation of this.

Original NASA ASRS Text

Title: Imprecise clearance phraseology and the failure to confirm understanding of the clearance resulted in the flight crew of a DA-90 descending to an altitude not intended by the Controller.

Narrative: Level cruise at FL390; eastbound on J42; east of BKW. Washington Center issued the following clearance to us. 'Descend now to FL350; maintain a descent rate of 1500 FPM or greater and then cross DENNY at FL330.' We read back the clearance exactly as it was issued; ('descend now to FL350 at 1500 FPM or greater and cross DENNY at FL330'); and immediately began our descent at 1500 FPM. The Controller did not reply and proceeded to communicate with other aircraft on the frequency; as expected. While in the descent; we calculated that a 1500 FPM descent would allow us to level at DENNY exactly at FL330 and planned to maintain that descent rate all the way down to FL330. After approximately 60-90 seconds; while descending through approximately FL370 the Controller said to us; 'Descend to FL350 and maintain a descent rate of 1500 FPM or greater.' We immediately read back 'we are descending to FL350 with a descent rate of 1500 FPM and will cross DENNY at FL330.' The Controller again did not reply and went on to communicate with other aircraft. We figured she issued the clearance again because either 1) she did not copy our original read back or 2) she was verifying our descent rate was at least 1500 FPM. While leveling at FL330 just west of DENNY; the Controller came on and told us we were only cleared to FL350. We replied that we were cleared to descend to FL350 immediately; at 1500 FPM or greater; and cross DENNY at FL330 and that we read that back twice. We then confirmed that we were level at FL330 and asked her what she wanted us to do now. She instructed us to maintain FL330 and said there was a misunderstanding. We maintained FL330 and continued the flight without incident.In my opinion; the second clearance was not clear. It never occurred to us that she was attempting to get us to level at FL350. (It appears to be much clearer when only our transmissions are highlighted; as in this report. However; in real time on a busy frequency; we did not comprehend the Controllers' intentions) I feel the clearance would have been easily understood if the Controller added only a few extra words; such as 1) 'descend to FL350 ONLY' 2) 'descend to FL350 and delete the crossing restriction at DENNY' or another variation of this.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1094269
Time
Date	201306
Local Time Of Day	1201-1800
Place
Locale Reference	ZDC.ARTCC
State Reference	VA
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Make Model Name	Falcon 900
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Airway J42
Flight Plan	IFR
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 70 Flight Crew Total 10200 Flight Crew Type 600
Person 2
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 40 Flight Crew Total 16000 Flight Crew Type 2500
Events
Anomaly	ATC Issue All Types Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

Imprecise clearance phraseology and the failure to confirm understanding of the clearance resulted in the flight crew of a da-90 descending to an altitude not intended by the controller.