A320
Distraction; Confusion; Communication Breakdown; Time Pressure
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Airspace Structure; Procedure; Human Factors; Chart Or Publication
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.
Reporter advised that; being based on the East Coast; this had been his first departure from IAH utilizing the newly formatted SIDs and that he wasn't; at the time; completely conversant with the specific implications of the 'climb via' phraseology. His Captain on the flight had only recently returned from flying primarily international operations and was in a similar situation; thus the delay in proper programming of the climb via clearance.He responded affirmatively to the analyst's question as to the presence of the phrase '...top altitude 4;000...' in the PDC. In response to a follow up question he stated that the phrase 'climb via (the assigned SID)' was also included although he couldn't remember the exact sequence or how the two restrictive phrases had been juxtaposed when transmitted. Reporter followed up these responses by addressing his displeasure for the lack of a common format for PDC clearances and the fact that they often included information not germane to their actual cleared route. He also commented that their intent is often difficult to derive due to 'coding' and/or the inclusion of filed routes that are eclipsed by actual cleared routes given in a separate section of the clearance.
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.