FMS mode confusion. Incorrect programming.

Attributes
ACN	317930
Time
Date	199510
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : cip
State Reference	PA
Altitude	msl bound lower : 22000 msl bound upper : 24500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob tower : hgr
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
ASRS Report	317930
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Captain flying, autoplt on, autothrottles on, digital flight guidance system #1 used for vertical and lateral navigation, speed 310 KTS at FL240 power management system programmed but not engaged. ATC gave descent clearance to FL220. Captain selected 'perf' on the digital flight guidance system to engage the power management system. On the descent page of the power management system he selected vertical speed. To start 1000 FPM descent the power management system recalculated the optimum speed to be 320 KTS. As the throttles began to advance he turned them off to prevent the speed increase. He then tried to change the speed in the power management system to 310 KTS, but it would not accept it. During this time either the captain selected or autoplt automatically reverted to IAS. I saw on the FMA we were in IAS and because the autothrottles were off but had been advanced when power management system was selected, we were in a climb of approximately 1000 FPM and at approximately 24500 ft. I called out altitude and captain initiated descent. Contributing factors: normal cruise speed 320 KTS/.76 mach captain used 310 KTS. Power management system should have been programmed with desired speeds to prevent use of optimum speeds. Power management system should have been selected while in cruise or after descent started not in the middle of a 'mode' change. Autothrottles turned off. Altitude alerter armed for FL220.

Original NASA ASRS Text

Title: FMS MODE CONFUSION. INCORRECT PROGRAMMING.

Narrative: CAPT FLYING, AUTOPLT ON, AUTOTHROTTLES ON, DIGITAL FLT GUIDANCE SYS #1 USED FOR VERT AND LATERAL NAV, SPD 310 KTS AT FL240 PWR MGMNT SYS PROGRAMMED BUT NOT ENGAGED. ATC GAVE DSCNT CLRNC TO FL220. CAPT SELECTED 'PERF' ON THE DIGITAL FLT GUIDANCE SYS TO ENGAGE THE PWR MGMNT SYS. ON THE DSCNT PAGE OF THE PWR MGMNT SYS HE SELECTED VERT SPD. TO START 1000 FPM DSCNT THE PWR MGMNT SYS RECALCULATED THE OPTIMUM SPD TO BE 320 KTS. AS THE THROTTLES BEGAN TO ADVANCE HE TURNED THEM OFF TO PREVENT THE SPD INCREASE. HE THEN TRIED TO CHANGE THE SPD IN THE PWR MGMNT SYS TO 310 KTS, BUT IT WOULD NOT ACCEPT IT. DURING THIS TIME EITHER THE CAPT SELECTED OR AUTOPLT AUTOMATICALLY REVERTED TO IAS. I SAW ON THE FMA WE WERE IN IAS AND BECAUSE THE AUTOTHROTTLES WERE OFF BUT HAD BEEN ADVANCED WHEN PWR MGMNT SYS WAS SELECTED, WE WERE IN A CLB OF APPROX 1000 FPM AND AT APPROX 24500 FT. I CALLED OUT ALT AND CAPT INITIATED DSCNT. CONTRIBUTING FACTORS: NORMAL CRUISE SPD 320 KTS/.76 MACH CAPT USED 310 KTS. PWR MGMNT SYS SHOULD HAVE BEEN PROGRAMMED WITH DESIRED SPDS TO PREVENT USE OF OPTIMUM SPDS. PWR MGMNT SYS SHOULD HAVE BEEN SELECTED WHILE IN CRUISE OR AFTER DSCNT STARTED NOT IN THE MIDDLE OF A 'MODE' CHANGE. AUTOTHROTTLES TURNED OFF. ALT ALERTER ARMED FOR FL220.

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.