An air carrier MD80 crew overshot its assigned altitude when they changed the mach number just as the autoplt was leveling off. Altitude deviation.

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Attributes
ACN	341150
Time
Date	199607
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : roc
State Reference	NY
Altitude	msl bound lower : 28000 msl bound upper : 28400
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
ASRS Report	341150
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	341149
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : became reoriented flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Just prior to leveloff at FL280, we were told to increase speed from mach .74 to mach .78 or better. Apparently FMA had gone to altitude capture, but the vertical speed window had not changed from the mach speed to a vertical speed for leveloff. I used the speed wheel to increase the speed selected from mach .74 to mach .78. After a second or 2, the pitch window on the FGS went from .78, displayed to +3100 ft. Altitude capture was lost and, after recognition of the situation, autoplt was disengaged at approximately FL282 for a leveloff at FL280. Maximum deviation of 400 ft (FL284) occurred. Better awareness on my part of the current FMA mode would have prevented this. I should have waited until leveloff and used the speed select knob instead of the IAS function for the speed increase. Supplemental information from acn 341149: altitude capture was inadvertently disarmed. This could have been prevented by waiting until altitude capture was completed before adjusting speed. Perf mode inoperative. First officer at the controls who has been on this aircraft only a short time.

Original NASA ASRS Text

Title: AN ACR MD80 CREW OVERSHOT ITS ASSIGNED ALT WHEN THEY CHANGED THE MACH NUMBER JUST AS THE AUTOPLT WAS LEVELING OFF. ALTDEV.

Narrative: JUST PRIOR TO LEVELOFF AT FL280, WE WERE TOLD TO INCREASE SPD FROM MACH .74 TO MACH .78 OR BETTER. APPARENTLY FMA HAD GONE TO ALT CAPTURE, BUT THE VERT SPD WINDOW HAD NOT CHANGED FROM THE MACH SPD TO A VERT SPD FOR LEVELOFF. I USED THE SPD WHEEL TO INCREASE THE SPD SELECTED FROM MACH .74 TO MACH .78. AFTER A SECOND OR 2, THE PITCH WINDOW ON THE FGS WENT FROM .78, DISPLAYED TO +3100 FT. ALT CAPTURE WAS LOST AND, AFTER RECOGNITION OF THE SIT, AUTOPLT WAS DISENGAGED AT APPROX FL282 FOR A LEVELOFF AT FL280. MAX DEV OF 400 FT (FL284) OCCURRED. BETTER AWARENESS ON MY PART OF THE CURRENT FMA MODE WOULD HAVE PREVENTED THIS. I SHOULD HAVE WAITED UNTIL LEVELOFF AND USED THE SPD SELECT KNOB INSTEAD OF THE IAS FUNCTION FOR THE SPD INCREASE. SUPPLEMENTAL INFO FROM ACN 341149: ALT CAPTURE WAS INADVERTENTLY DISARMED. THIS COULD HAVE BEEN PREVENTED BY WAITING UNTIL ALT CAPTURE WAS COMPLETED BEFORE ADJUSTING SPD. PERF MODE INOP. FO AT THE CTLS WHO HAS BEEN ON THIS ACFT ONLY A SHORT TIME.

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.