Narrative:

We were cleared as filed to our destination with a clearance to fly the ARSNL4 departure out of khef and climb via the SID. The departure runway was 34R. The first fix on this route was shrli with a crossing altitude of 2000 ft MSL. Prior to departure; both crew members verified the flight management system (FMS) and flight director (FD) were programmed correctly to level the aircraft at 2000 prior to shrli and then to continue the climb to cross csn at 3000. The departure was briefed thoroughly prior to takeoff. After a normal takeoff; the crew selected the appropriate vertical and lateral modes on the FD to track towards shrli and level at 2000. Despite this; the FD did not command a level-off as intended at 2000. The error was caught by the crew but by the time action was taken; the aircraft had climbed to approximately 2300 MSL. The aircraft was hand-flown back down to 2000 ft expeditiously. About the same time; ATC noticed the altitude deviation and commanded a left turn to 230 degrees and a return to 2000 ft. As ATC was speaking; the crew received a TA warning for 2-3 seconds for an aircraft above at 3000 ft. This quickly went away and never escalated to an RA. ATC advised the crew of a possible pilot deviation and gave a number to call. The remainder of the flight was conducted without further incident. Analysis/mitigation strategies:the PF has over ten years and 4000 hours operating this aircraft's particular avionics system (collins pro line 21) - both as a pilot and instructor. There is little doubt to him that the FMS and FD were set up properly to fly the SID correctly. It is not understood at this point why the airplane did not level as it should have. All systems in the aircraft are in good working order with no previous anomalies noted. With 'climb via' sids; guidance from the manufacturer suggests setting the 'top altitude' in the altitude pre-select; arming VNAV and then allowing the FMS to set any intermediate level-off altitudes. In this particular case; 3000 ft was set with the altitude pre-select and 2000 ft was verified as the initial FMS-driven altitude.although it shouldn't be necessary; a possible mitigation strategy going forward would be to set the altitude pre-select to the first target altitude and then manage the subsequent altitude restrictions manually. The PF could have chosen a reduced initial climb rate which would have allowed for a more rapid correction to the correct altitude and earlier detection of the impending error. ATC could have queried the crew prior to 2000 ft to ensure level off at the correct altitude. The IFR clearance given to crews could be amended to simply maintain 2000 ft instead of 'climb via' the SID. Altitudes above 2000 ft could be issued by potomac departure once airborne.

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Original NASA ASRS Text

Title: A corporate flight crew properly programmed their Collins Pro Line 21 for the HEF ARSNL4 Departure with a 2;000 ft level off. LNAV and VNAV were engaged but the aircraft did not level at 2;000 ft. At 2;300 ft the crew descended just as the TCAS alerted a TA.

Narrative: We were cleared as filed to our destination with a clearance to fly the ARSNL4 departure out of KHEF and climb via the SID. The departure runway was 34R. The first fix on this route was SHRLI with a crossing altitude of 2000 ft MSL. Prior to departure; both crew members verified the Flight Management System (FMS) and Flight Director (FD) were programmed correctly to level the aircraft at 2000 prior to SHRLI and then to continue the climb to cross CSN at 3000. The departure was briefed thoroughly prior to takeoff. After a normal takeoff; the crew selected the appropriate vertical and lateral modes on the FD to track towards SHRLI and level at 2000. Despite this; the FD did not command a level-off as intended at 2000. The error was caught by the crew but by the time action was taken; the aircraft had climbed to approximately 2300 MSL. The aircraft was hand-flown back down to 2000 ft expeditiously. About the same time; ATC noticed the altitude deviation and commanded a left turn to 230 degrees and a return to 2000 ft. As ATC was speaking; the crew received a TA warning for 2-3 seconds for an aircraft above at 3000 ft. This quickly went away and never escalated to an RA. ATC advised the crew of a possible pilot deviation and gave a number to call. The remainder of the flight was conducted without further incident. ANALYSIS/MITIGATION STRATEGIES:The PF has over ten years and 4000 hours operating this aircraft's particular avionics system (Collins Pro Line 21) - both as a pilot and instructor. There is little doubt to him that the FMS and FD were set up properly to fly the SID correctly. It is not understood at this point why the airplane did not level as it should have. All systems in the aircraft are in good working order with no previous anomalies noted. With 'Climb Via' SIDS; guidance from the manufacturer suggests setting the 'Top Altitude' in the Altitude Pre-Select; arming VNAV and then allowing the FMS to set any intermediate level-off altitudes. In this particular case; 3000 ft was set with the altitude pre-select and 2000 ft was verified as the initial FMS-driven altitude.Although it shouldn't be necessary; a possible mitigation strategy going forward would be to set the altitude pre-select to the first target altitude and then manage the subsequent altitude restrictions manually. The PF could have chosen a reduced initial climb rate which would have allowed for a more rapid correction to the correct altitude and earlier detection of the impending error. ATC could have queried the crew prior to 2000 ft to ensure level off at the correct altitude. The IFR clearance given to crews could be amended to simply maintain 2000 ft instead of 'Climb Via' the SID. Altitudes above 2000 ft could be issued by Potomac departure once airborne.

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.