Narrative:

Flight XXX was amended to fly the Delta2 arrival into slc prior to the mlf VOR to facilitate 'landing south.' we were cleared to cross jammn at 17000 ft and 280 KTS. Both the new arrival and the altitude/speed at jammn clearances were put into the FMS at 10 miles from top of descent. The speeds and altitudes for the STAR were verified by both crew members. The des now prompt did not display prior to TOD and even though 17000 ft was placed in the altitude alert window; the aircraft did not descend at the TOD point. Level change was selected and the aircraft descended and crossed jammn at 17000 ft and 280 KTS. Back on profile; VNAV was re-engaged and the crew was issued the clearance to 'descend via the Delta2 arrival and comply with restrictions.' the captain put 11000 ft into the altitude alert window and the first officer pointed and confirmed the altitude. The crew was then told to maintain 280 KTS. Speed intv was utilized to comply. At drapr the crew anticipated a geometric path descent from 14000 to 13000 ft. However; the aircraft began pitch over to maintain 280 KTS. The first officer selected vertical speed since the aircraft was only descending 1000 ft in 11 nm and the descent rate was excessive. The aircraft descent rate was shallowed from 1800 ft per minute to 1000 ft per minute. The crew accomplished the approach checklist. The first officer then observed that the aircraft did not level at 13000 ft. The first officer annunciated 'the aircraft is descending through the step-down altitude.' the first officer immediately disengaged the autopilot and leveled off smoothly. The aircraft leveled off at 12700 ft. The captain selected 13000 ft in the altitude alert window and the crew began a vertical speed climb back to 13000 ft. Air traffic control then transmitted to 'flight XXX; maintain 13000 ft.' the captain stated; 'flight XXX is climbing back to 13000 ft.' the aircraft leveled off at 13000 ft. ATC issued a phone number to call and stated that there had been 'a possible deviation.' the aircraft resumed the arrival and approach without further incident. VNAV was not used for the remainder of the arrival. Once on the ground; the captain contacted the approach controller and the controller stated that 'he had a couple of hits at 12600 ft.' we were also told were not below the minimum vectoring altitude and that the aircraft was never in conflict with any traffic and the crew contacted the chief pilot and completed a report. This was done in a rushed manner as the ground time was only 1 hour. We were ready to go at our departure time; but received word that we would be pulled off the trip. The fundamental preventive measure was that the crew did not update the altitude window when the mode was changed from VNAV to vertical speed. The aircraft descended below the step-down altitude momentarily while the crew corrected. I believe that the aircraft could have been leveled at 12900 ft but my concern for passenger comfort caused me to level off less aggressively. The aircraft was in intermittent moderate turbulence. The crew had realized the problem and was correcting prior to any ATC transmission.callback conversation with reporter revealed the following information: reporter states that his aircraft type was a B737-800.

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Original NASA ASRS Text

Title: B737 First Officer reports altitude deviation during the DELTA2 RNAV arrival to SLC.

Narrative: Flight XXX was amended to fly the Delta2 arrival into SLC prior to the MLF VOR to facilitate 'landing south.' We were cleared to cross JAMMN at 17000 FT and 280 KTS. Both the new arrival and the altitude/speed at JAMMN clearances were put into the FMS at 10 miles from Top of Descent. The speeds and altitudes for the STAR were verified by both crew members. The DES NOW prompt did not display prior to TOD and even though 17000 FT was placed in the altitude alert window; the aircraft did not descend at the TOD point. Level Change was selected and the aircraft descended and crossed JAMMN at 17000 FT and 280 KTS. Back on profile; VNAV was re-engaged and the crew was issued the clearance to 'descend via the Delta2 arrival and comply with restrictions.' The Captain put 11000 FT into the altitude alert window and the First Officer pointed and confirmed the altitude. The crew was then told to maintain 280 KTS. Speed INTV was utilized to comply. At DRAPR the crew anticipated a geometric path descent from 14000 to 13000 FT. However; the aircraft began pitch over to maintain 280 KTS. The First Officer selected vertical speed since the aircraft was only descending 1000 FT in 11 nm and the descent rate was excessive. The aircraft descent rate was shallowed from 1800 FT per minute to 1000 FT per minute. The crew accomplished the Approach Checklist. The First Officer then observed that the aircraft did not level at 13000 FT. The First Officer annunciated 'the aircraft is descending through the step-down altitude.' The First Officer immediately disengaged the autopilot and leveled off smoothly. The aircraft leveled off at 12700 FT. The Captain selected 13000 FT in the altitude alert window and the crew began a vertical speed climb back to 13000 FT. Air Traffic Control then transmitted to 'Flight XXX; maintain 13000 FT.' The Captain stated; 'Flight XXX is climbing back to 13000 FT.' The aircraft leveled off at 13000 FT. ATC issued a phone number to call and stated that there had been 'a possible deviation.' The aircraft resumed the arrival and approach without further incident. VNAV was not used for the remainder of the arrival. Once on the ground; the Captain contacted the Approach Controller and the Controller stated that 'he had a couple of hits at 12600 FT.' We were also told were not below the minimum vectoring altitude and that the aircraft was never in conflict with any traffic and the crew contacted the Chief Pilot and completed a report. This was done in a rushed manner as the ground time was only 1 hour. We were ready to go at our departure time; but received word that we would be pulled off the trip. The fundamental preventive measure was that the crew did not update the altitude window when the mode was changed from VNAV to vertical speed. The aircraft descended below the step-down altitude momentarily while the crew corrected. I believe that the aircraft could have been leveled at 12900 FT but my concern for passenger comfort caused me to level off less aggressively. The aircraft was in intermittent moderate turbulence. The crew had realized the problem and was correcting prior to any ATC transmission.Callback conversation with reporter revealed the following information: Reporter states that his aircraft type was a B737-800.

Data retrieved from NASA's ASRS site as of April 2012 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.