Narrative:

During established cruise flight; mach .75; FL390; I exited the cockpit to use the lavatory. After approximately 2-4 mins; I returned to the cockpit and while in the process of closing and securing the cockpit door; the autoplt disconnected and the aircraft entered a slight roll (approximately 5-10 degrees maximum). My initial thought was that the first officer disconnected the autoplt; yet I immediately turned to him and a pfd (the first officer had canceled the autoplt disconnect audible warning). He looked bewildered and the pfd indicated the low speed and an indicated airspeed approximately 5 KTS above stall. I immediately set maximum thrust and simultaneously instructed the first officer to push the nose over. Still standing; my observance was the pitch attitude reduction. Indicated airspeed increase and rate of descent were not progressing as I desired and I issued several additional instructions to push the nose down and then knelt on my seat and pushed nose down on my yoke; telling the first officer I was assisting the recovery procedure. I declared an emergency descent with ATC to FL290 when conditions permitted. During the recovery process; the first officer indicated he was having difficulty with the aircraft trim and we received a 'trim in motion' aural. I instructed him to stop trimming to ascertain if the issue was automation or manual by the first officer. The pitch trim indicator was showing some erratic movement; ie; +4 units down to +1 units quickly. I flew the aircraft to ascertain its control ability (approximately FL350) and it appeared to handle well; yet my perception at the time was it was 'sluggish' in pitch. The first officer told me that he had no idea as to the cause of the low speed condition; that he hadn't touched the thrust or intentionally slowed the aircraft. Based upon these factors; my initial impression was some type of pitch anomaly; and I elected to divert to ZZZ (nearest suitable). Callback conversation with reporter revealed the following information: at the time the reporter left the cockpit; a cabin attendant was in the cockpit per company security SOP. The flight attendant should have been seated and strapped in per SOP but was not. In addition; the first officer had not donned his oxygen mask as required by the FARS although the reporter felt he was in the process of doing so when he left the cockpit. The reporter believes the first officer had reduced the thrust slightly; and apparently had not monitored the effects of the thrust reduction. The first officer intended to reduce airspeed slightly to the cruise mach of .75. Indicated airspeed at that time was approximately 227 KIAS. When the captain returned; the first officer was turned physically away from the instrument panel and engaged in conversation with the flight attendant. The airspeed had dropped off to just under 180 KIAS. In quick succession; the autoplt disconnected and simultaneously the stick shaker and autoplt warnings sounded. The recovery events detailed in the original narrative then occurred. Reporter noted that this air carrier's carj's are equipped with both laterally and vertically compliant fmcs system but that autothrottles are not part of their installation. He felt that autothrottles would have prevented the incident; notwithstanding the first officer's unprofessional lack of attention to the aircraft. He emphasized that no loss of separation occurred notwithstanding their descent through at least 4 potentially occupied rvsm altitudes. Also; that he transmitted the emergency descent and was cleared through FL290 if necessary by ZZZ. Callback conversation with reporter acn 651597 revealed the following information: reporter stated maintenance checked the aircraft and replaced the stabilizer control unit.

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Original NASA ASRS Text

Title: CAPT OF CARJ RETURNS FROM PHYSIOLOGICAL BREAK TO DISCOVER INCIPIENT STALL DUE TO UNMONITORED AIRSPD FOLLOWING MINOR THRUST REDUCTION BY FO. AUTOPLT DISCONNECTED AND RECOVERY OF AIRSPD AND ACFT CTL RESULTS IN LOSS OF 4000 FT FROM ASSIGNED ALT OF FL390.

Narrative: DURING ESTABLISHED CRUISE FLT; MACH .75; FL390; I EXITED THE COCKPIT TO USE THE LAVATORY. AFTER APPROX 2-4 MINS; I RETURNED TO THE COCKPIT AND WHILE IN THE PROCESS OF CLOSING AND SECURING THE COCKPIT DOOR; THE AUTOPLT DISCONNECTED AND THE ACFT ENTERED A SLIGHT ROLL (APPROX 5-10 DEGS MAX). MY INITIAL THOUGHT WAS THAT THE FO DISCONNECTED THE AUTOPLT; YET I IMMEDIATELY TURNED TO HIM AND A PFD (THE FO HAD CANCELED THE AUTOPLT DISCONNECT AUDIBLE WARNING). HE LOOKED BEWILDERED AND THE PFD INDICATED THE LOW SPD AND AN INDICATED AIRSPD APPROX 5 KTS ABOVE STALL. I IMMEDIATELY SET MAX THRUST AND SIMULTANEOUSLY INSTRUCTED THE FO TO PUSH THE NOSE OVER. STILL STANDING; MY OBSERVANCE WAS THE PITCH ATTITUDE REDUCTION. INDICATED AIRSPD INCREASE AND RATE OF DSCNT WERE NOT PROGRESSING AS I DESIRED AND I ISSUED SEVERAL ADDITIONAL INSTRUCTIONS TO PUSH THE NOSE DOWN AND THEN KNELT ON MY SEAT AND PUSHED NOSE DOWN ON MY YOKE; TELLING THE FO I WAS ASSISTING THE RECOVERY PROC. I DECLARED AN EMER DSCNT WITH ATC TO FL290 WHEN CONDITIONS PERMITTED. DURING THE RECOVERY PROCESS; THE FO INDICATED HE WAS HAVING DIFFICULTY WITH THE ACFT TRIM AND WE RECEIVED A 'TRIM IN MOTION' AURAL. I INSTRUCTED HIM TO STOP TRIMMING TO ASCERTAIN IF THE ISSUE WAS AUTOMATION OR MANUAL BY THE FO. THE PITCH TRIM INDICATOR WAS SHOWING SOME ERRATIC MOVEMENT; IE; +4 UNITS DOWN TO +1 UNITS QUICKLY. I FLEW THE ACFT TO ASCERTAIN ITS CTL ABILITY (APPROX FL350) AND IT APPEARED TO HANDLE WELL; YET MY PERCEPTION AT THE TIME WAS IT WAS 'SLUGGISH' IN PITCH. THE FO TOLD ME THAT HE HAD NO IDEA AS TO THE CAUSE OF THE LOW SPD CONDITION; THAT HE HADN'T TOUCHED THE THRUST OR INTENTIONALLY SLOWED THE ACFT. BASED UPON THESE FACTORS; MY INITIAL IMPRESSION WAS SOME TYPE OF PITCH ANOMALY; AND I ELECTED TO DIVERT TO ZZZ (NEAREST SUITABLE). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: AT THE TIME THE RPTR LEFT THE COCKPIT; A CABIN ATTENDANT WAS IN THE COCKPIT PER COMPANY SECURITY SOP. THE FLT ATTENDANT SHOULD HAVE BEEN SEATED AND STRAPPED IN PER SOP BUT WAS NOT. IN ADDITION; THE FO HAD NOT DONNED HIS OXYGEN MASK AS REQUIRED BY THE FARS ALTHOUGH THE RPTR FELT HE WAS IN THE PROCESS OF DOING SO WHEN HE LEFT THE COCKPIT. THE RPTR BELIEVES THE FO HAD REDUCED THE THRUST SLIGHTLY; AND APPARENTLY HAD NOT MONITORED THE EFFECTS OF THE THRUST REDUCTION. THE FO INTENDED TO REDUCE AIRSPD SLIGHTLY TO THE CRUISE MACH OF .75. INDICATED AIRSPD AT THAT TIME WAS APPROX 227 KIAS. WHEN THE CAPT RETURNED; THE FO WAS TURNED PHYSICALLY AWAY FROM THE INST PANEL AND ENGAGED IN CONVERSATION WITH THE FLT ATTENDANT. THE AIRSPD HAD DROPPED OFF TO JUST UNDER 180 KIAS. IN QUICK SUCCESSION; THE AUTOPLT DISCONNECTED AND SIMULTANEOUSLY THE STICK SHAKER AND AUTOPLT WARNINGS SOUNDED. THE RECOVERY EVENTS DETAILED IN THE ORIGINAL NARRATIVE THEN OCCURRED. RPTR NOTED THAT THIS ACR'S CARJ'S ARE EQUIPPED WITH BOTH LATERALLY AND VERTICALLY COMPLIANT FMCS SYS BUT THAT AUTOTHROTTLES ARE NOT PART OF THEIR INSTALLATION. HE FELT THAT AUTOTHROTTLES WOULD HAVE PREVENTED THE INCIDENT; NOTWITHSTANDING THE FO'S UNPROFESSIONAL LACK OF ATTN TO THE ACFT. HE EMPHASIZED THAT NO LOSS OF SEPARATION OCCURRED NOTWITHSTANDING THEIR DSCNT THROUGH AT LEAST 4 POTENTIALLY OCCUPIED RVSM ALTS. ALSO; THAT HE XMITTED THE EMER DSCNT AND WAS CLRED THROUGH FL290 IF NECESSARY BY ZZZ. CALLBACK CONVERSATION WITH RPTR ACN 651597 REVEALED THE FOLLOWING INFO: RPTR STATED MAINT CHECKED THE ACFT AND REPLACED THE STABILIZER CTL UNIT.

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.