When the flight crew of an A320 misinterpreted ATC's 'climb via except maintain 16;000 ft' clearance...

Attributes
ACN	1204865
Time
Date	201409
Local Time Of Day	1801-2400
Place
Locale Reference	IAH.Airport
State Reference	TX
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Climb
Route In Use	SID GUMBY1
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	First Officer Pilot Not Flying
Events
Anomaly	ATC Issue All Types Deviation - Altitude Crossing Restriction Not Met Deviation - Procedural Clearance

Narrative:

On the GUMBY1 RNAV SID from iah; runway 15L; we were assigned a top altitude of 4;000 ft on the pre departure clearance. When we contacted departure they [cleared us to] climb via the SID except maintain 16;000 ft. I read back climb to 16;000 ft and continue via the SID. Departure stated again to climb via the SID except maintain 16;000 ft. By the time we correctly interpreted the clearance we had already removed the restriction to cross dwsun intersection at or below 5;000 ft from the FMS. Subsequently; we crossed dwsun above the charted altitude. Departure handed us off to the center and the flight continued uneventfully. During high task loading and during a RNAV departure we should have queried ATC about any doubt or confusion of a clearance before entering a change into the FMS or selecting a new altitude.

Original NASA ASRS Text

Title: When the flight crew of an A320 misinterpreted ATC's 'climb via except maintain 16;000 FT' clearance they had already exceeded 5;000 FT prior to passing DWSUN which must be crossed at or below 5;000 FT.

Narrative: On the GUMBY1 RNAV SID from IAH; Runway 15L; we were assigned a top altitude of 4;000 FT on the PDC. When we contacted Departure they [cleared us to] climb via the SID except maintain 16;000 FT. I read back climb to 16;000 FT and continue via the SID. Departure stated again to climb via the SID except maintain 16;000 FT. By the time we correctly interpreted the clearance we had already removed the restriction to cross DWSUN Intersection at or below 5;000 FT from the FMS. Subsequently; we crossed DWSUN above the charted altitude. Departure handed us off to the center and the flight continued uneventfully. During high task loading and during a RNAV departure we should have queried ATC about any doubt or confusion of a clearance before entering a change into the FMS or selecting a new altitude.

Data retrieved from NASA's ASRS site 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.

When the flight crew of an A320 misinterpreted ATC's 'climb via except maintain 16;000 ft' clearance they had already exceeded 5;000 ft prior to passing dwsun which must be crossed at or below 5;000 ft.