Narrative:

During cruise at FL350 and slightly west of the route sby J209 orf J174 diw while being controled by washington center and deviating off airways for heavy thunderstorms, a cruise climb to FL370 was requested by my copilot to avoid WX. Per center, this request was denied due to traffic. My copilot and I discussed a climb to FL390 (in the cockpit) but dismissed it due to lack of aircraft performance. During this period the altitude hold mode of the flight director was engaged and coupled to the autoplt which was holding 35000 ft (FL350). However, my copilot selected 39000 ft on the altitude selector (asel) anticipating a climb from 35000 -- without my knowledge or discussion. This asel unit in this aircraft is located on the copilot's instrument panel above the attitude, out of the pilot's normal field of view. The asel selected altitude does not read out (not displayed) anywhere else in the cockpit. After this climb discussion with washington center and the aircraft was on autoplt holding FL350, I (the pilot) left the cockpit to assist a passenger for approximately 8 mins. Within a couple (2) of mins after returning to the cockpit, I noticed that the aircraft was climbing through approximately 36200 ft and is 'psa' (preselected altitude) mode. I (the pilot) rapidly descended the aircraft back to 35000 ft (FL350). During the descent the center also noticed that our altitude was incorrect since they asked what our altitude was. Since we were descending very rapidly, we replied that our altitude was 35200 ft and leveled off quickly at 35000 ft. We had no further discussion with center regarding this altitude excursion (deviation) but within approximately 3 to 5 mins, we did hear an aircraft check in on frequency at FL370 but never saw him (aircraft), even though we were VFR and steady FL350. During the remainder of the flight, we saw the asel malfunction at least twice but without altitude deviation since the asel was then always set at the assigned altitude. The asel controller was causing the flight directors to automatically trip from altitude hold mode into psa mode without pilot action, explaining why the aircraft had previously disengaged altitude at 35000 and had climbed to 36200 ft in psa mode aiming for the anticipated altitude of 39000 that the copilot had incorrectly set in the altitude selector. This was a copilot problem and an aircraft system problem combined. This occurrence will be prevented in the future by: 1) repair and analysis of the faulty asel controller. 2) disciplinary action for the copilot to leave asel selected to assigned altitude, not target on desired altitude and to improve cockpit awareness. 3) the copilot will announce altitude when changing asel altitude on this aircraft. 4) designing EFIS that display asel altitude on both pilot and copilot instruments.

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Original NASA ASRS Text

Title: ALT EXCURSION WHEN FO ANTICIPATED CLB TO HIGHER.

Narrative: DURING CRUISE AT FL350 AND SLIGHTLY W OF THE RTE SBY J209 ORF J174 DIW WHILE BEING CTLED BY WASHINGTON CENTER AND DEVIATING OFF AIRWAYS FOR HVY TSTMS, A CRUISE CLB TO FL370 WAS REQUESTED BY MY COPLT TO AVOID WX. PER CENTER, THIS REQUEST WAS DENIED DUE TO TFC. MY COPLT AND I DISCUSSED A CLB TO FL390 (IN THE COCKPIT) BUT DISMISSED IT DUE TO LACK OF ACFT PERFORMANCE. DURING THIS PERIOD THE ALT HOLD MODE OF THE FLT DIRECTOR WAS ENGAGED AND COUPLED TO THE AUTOPLT WHICH WAS HOLDING 35000 FT (FL350). HOWEVER, MY COPLT SELECTED 39000 FT ON THE ALT SELECTOR (ASEL) ANTICIPATING A CLB FROM 35000 -- WITHOUT MY KNOWLEDGE OR DISCUSSION. THIS ASEL UNIT IN THIS ACFT IS LOCATED ON THE COPLT'S INST PANEL ABOVE THE ATTITUDE, OUT OF THE PLT'S NORMAL FIELD OF VIEW. THE ASEL SELECTED ALT DOES NOT READ OUT (NOT DISPLAYED) ANYWHERE ELSE IN THE COCKPIT. AFTER THIS CLB DISCUSSION WITH WASHINGTON CENTER AND THE ACFT WAS ON AUTOPLT HOLDING FL350, I (THE PLT) LEFT THE COCKPIT TO ASSIST A PAX FOR APPROX 8 MINS. WITHIN A COUPLE (2) OF MINS AFTER RETURNING TO THE COCKPIT, I NOTICED THAT THE ACFT WAS CLBING THROUGH APPROX 36200 FT AND IS 'PSA' (PRESELECTED ALT) MODE. I (THE PLT) RAPIDLY DSNDED THE ACFT BACK TO 35000 FT (FL350). DURING THE DSCNT THE CENTER ALSO NOTICED THAT OUR ALT WAS INCORRECT SINCE THEY ASKED WHAT OUR ALT WAS. SINCE WE WERE DSNDING VERY RAPIDLY, WE REPLIED THAT OUR ALT WAS 35200 FT AND LEVELED OFF QUICKLY AT 35000 FT. WE HAD NO FURTHER DISCUSSION WITH CENTER REGARDING THIS ALT EXCURSION (DEV) BUT WITHIN APPROX 3 TO 5 MINS, WE DID HEAR AN ACFT CHK IN ON FREQ AT FL370 BUT NEVER SAW HIM (ACFT), EVEN THOUGH WE WERE VFR AND STEADY FL350. DURING THE REMAINDER OF THE FLT, WE SAW THE ASEL MALFUNCTION AT LEAST TWICE BUT WITHOUT ALT DEV SINCE THE ASEL WAS THEN ALWAYS SET AT THE ASSIGNED ALT. THE ASEL CTLR WAS CAUSING THE FLT DIRECTORS TO AUTOMATICALLY TRIP FROM ALT HOLD MODE INTO PSA MODE WITHOUT PLT ACTION, EXPLAINING WHY THE ACFT HAD PREVIOUSLY DISENGAGED ALT AT 35000 AND HAD CLBED TO 36200 FT IN PSA MODE AIMING FOR THE ANTICIPATED ALT OF 39000 THAT THE COPLT HAD INCORRECTLY SET IN THE ALT SELECTOR. THIS WAS A COPLT PROBLEM AND AN ACFT SYS PROBLEM COMBINED. THIS OCCURRENCE WILL BE PREVENTED IN THE FUTURE BY: 1) REPAIR AND ANALYSIS OF THE FAULTY ASEL CTLR. 2) DISCIPLINARY ACTION FOR THE COPLT TO LEAVE ASEL SELECTED TO ASSIGNED ALT, NOT TARGET ON DESIRED ALT AND TO IMPROVE COCKPIT AWARENESS. 3) THE COPLT WILL ANNOUNCE ALT WHEN CHANGING ASEL ALT ON THIS ACFT. 4) DESIGNING EFIS THAT DISPLAY ASEL ALT ON BOTH PLT AND COPLT INSTS.

Data retrieved from NASA's ASRS site as of July 2007 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.