Narrative:

I was given a vector to 180 degrees from the airway course of 139 degrees for traffic conflict avoidance. Shortly after receiving and changing to the vector of 180 degrees; the controller told me to do the following: 1) descend to 8000 ft; 2) proceed direct to darts intersection and; 3) contact another controller. My aircraft is equipped with a GNS480 and an MX20 mfd. The simultaneous items to accomplish and comply with the controller's commands are as follows: 1) reduce power by manually adjusting the two waste gate positions of the turbo chargers via vernier controls (one of which failed; disabling the vernier feature). 2) changing the GNS480 display from map mode to flight plan mode (3 button pushes). 3) highlighting the darts intersection (1 button push to expand the flight plan details; rotating a knob to highlight the darts intersection; and then performing 3 button pushes to go direct to the darts intersection. 4) select the new frequency by pressing 1 button to activate the frequency change capability; rotating 2 knobs to select the new frequency and then pressing 1 button to activate the new frequency. While accomplishing all the foregoing activity and occasionally looking at the instruments and also changing the CDI to the new heading to go to darts; I descended to 7500 ft; thereby descending below my assigned altitude inadvertently. Comments: the workload in the technically advanced aircraft in the foregoing environment is very high compared to the environment prior to GPS. Prior to GPS; the controller would have provided a vector to go direct to darts intersection and the frequency change would have been accomplished with 2 knob rotations and the CDI would have been left on the V459 course line. In the future; I will slow down my response to accomplish simultaneous commands and scan the instruments more.

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Original NASA ASRS Text

Title: AN ADVANCED NAV PA30 PLT OVERSHOT HIS DSNT CLRNC ALT WHEN GIVEN FREQ; HDG; AND ALT CHANGES ALL AT ONCE.

Narrative: I WAS GIVEN A VECTOR TO 180 DEGS FROM THE AIRWAY COURSE OF 139 DEGS FOR TFC CONFLICT AVOIDANCE. SHORTLY AFTER RECEIVING AND CHANGING TO THE VECTOR OF 180 DEGS; THE CTLR TOLD ME TO DO THE FOLLOWING: 1) DSND TO 8000 FT; 2) PROCEED DIRECT TO DARTS INTXN AND; 3) CONTACT ANOTHER CTLR. MY ACFT IS EQUIPPED WITH A GNS480 AND AN MX20 MFD. THE SIMULTANEOUS ITEMS TO ACCOMPLISH AND COMPLY WITH THE CTLR'S COMMANDS ARE AS FOLLOWS: 1) REDUCE POWER BY MANUALLY ADJUSTING THE TWO WASTE GATE POSITIONS OF THE TURBO CHARGERS VIA VERNIER CTLS (ONE OF WHICH FAILED; DISABLING THE VERNIER FEATURE). 2) CHANGING THE GNS480 DISPLAY FROM MAP MODE TO FLT PLAN MODE (3 BUTTON PUSHES). 3) HIGHLIGHTING THE DARTS INTXN (1 BUTTON PUSH TO EXPAND THE FLT PLAN DETAILS; ROTATING A KNOB TO HIGHLIGHT THE DARTS INTXN; AND THEN PERFORMING 3 BUTTON PUSHES TO GO DIRECT TO THE DARTS INTXN. 4) SELECT THE NEW FREQ BY PRESSING 1 BUTTON TO ACTIVATE THE FREQ CHANGE CAPABILITY; ROTATING 2 KNOBS TO SELECT THE NEW FREQ AND THEN PRESSING 1 BUTTON TO ACTIVATE THE NEW FREQ. WHILE ACCOMPLISHING ALL THE FOREGOING ACTIVITY AND OCCASIONALLY LOOKING AT THE INSTRUMENTS AND ALSO CHANGING THE CDI TO THE NEW HDG TO GO TO DARTS; I DSNDED TO 7500 FT; THEREBY DSNDING BELOW MY ASSIGNED ALT INADVERTENTLY. COMMENTS: THE WORKLOAD IN THE TECHNICALLY ADVANCED ACFT IN THE FOREGOING ENVIRONMENT IS VERY HIGH COMPARED TO THE ENVIRONMENT PRIOR TO GPS. PRIOR TO GPS; THE CTLR WOULD HAVE PROVIDED A VECTOR TO GO DIRECT TO DARTS INTXN AND THE FREQ CHANGE WOULD HAVE BEEN ACCOMPLISHED WITH 2 KNOB ROTATIONS AND THE CDI WOULD HAVE BEEN LEFT ON THE V459 COURSE LINE. IN THE FUTURE; I WILL SLOW DOWN MY RESPONSE TO ACCOMPLISH SIMULTANEOUS COMMANDS AND SCAN THE INSTRUMENTS MORE.

Data retrieved from NASA's ASRS site as of January 2009 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.