Air carrier medium large transport altitude deviation overshot during climb when PF deactivated alti...

Attributes
ACN	84975
Time
Date	198803
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : dfw
State Reference	TX
Altitude	msl bound lower : 29000 msl bound upper : 29600
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 63 flight time total : 10524
ASRS Report	84975
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 160 flight time total : 6233
ASRS Report	84883
Events
Anomaly	altitude deviation : overshoot
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
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:

We were climbing as cleared by ATC from 23000' to FL290 with the autoplt engaged. The first officer called, 'out of 28 for 29,' as we were passing through 28000', I noticed I had not pushed the IAS-mach button to change from IAS hold to mach hold, so I selected mach hold at this time. When I did this I did not notice that altitude capture turned off. Due to the change from IAS to mach speed, the vertical climb speed increased. The aircraft was passing through approximately 29200' before I realized what had happened. The aircraft reached approximately 29600' before I could start descending back to 29000'. The ATC controller requested our altitude about this time. I'm not sure of the reply we gave since we were concerned with getting back down to 29000', but it was something like 'descending to 29000'' or 'leveling at 29000'.' he then informed us our traffic was opp direction, 20 NM ahead. At this point the flight returned to normal. While recognizing the fact as captain I am to control the aircraft at all times, I do feel there is a design problem with the flight guidance control panel (fgcp) of the medium large transport X. Having flown the medium large transport Y for over 3 yrs, I know that with the proper altitude set on the fgcp the aircraft will capture and hold the selected altitude regardless of what other modes or speed changes are selected. This type of software design is much better than the present design of the medium large transport X fgcp.

Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING CLIMB WHEN PF DEACTIVATED ALT CAPTURE BY CHANGING FGCP FROM IAS TO MACH MODE.

Narrative: WE WERE CLBING AS CLRED BY ATC FROM 23000' TO FL290 WITH THE AUTOPLT ENGAGED. THE F/O CALLED, 'OUT OF 28 FOR 29,' AS WE WERE PASSING THROUGH 28000', I NOTICED I HAD NOT PUSHED THE IAS-MACH BUTTON TO CHANGE FROM IAS HOLD TO MACH HOLD, SO I SELECTED MACH HOLD AT THIS TIME. WHEN I DID THIS I DID NOT NOTICE THAT ALT CAPTURE TURNED OFF. DUE TO THE CHANGE FROM IAS TO MACH SPD, THE VERT CLB SPD INCREASED. THE ACFT WAS PASSING THROUGH APPROX 29200' BEFORE I REALIZED WHAT HAD HAPPENED. THE ACFT REACHED APPROX 29600' BEFORE I COULD START DSNDING BACK TO 29000'. THE ATC CTLR REQUESTED OUR ALT ABOUT THIS TIME. I'M NOT SURE OF THE REPLY WE GAVE SINCE WE WERE CONCERNED WITH GETTING BACK DOWN TO 29000', BUT IT WAS SOMETHING LIKE 'DSNDING TO 29000'' OR 'LEVELING AT 29000'.' HE THEN INFORMED US OUR TFC WAS OPP DIRECTION, 20 NM AHEAD. AT THIS POINT THE FLT RETURNED TO NORMAL. WHILE RECOGNIZING THE FACT AS CAPT I AM TO CTL THE ACFT AT ALL TIMES, I DO FEEL THERE IS A DESIGN PROB WITH THE FLT GUIDANCE CTL PANEL (FGCP) OF THE MLG X. HAVING FLOWN THE MLG Y FOR OVER 3 YRS, I KNOW THAT WITH THE PROPER ALT SET ON THE FGCP THE ACFT WILL CAPTURE AND HOLD THE SELECTED ALT REGARDLESS OF WHAT OTHER MODES OR SPD CHANGES ARE SELECTED. THIS TYPE OF SOFTWARE DESIGN IS MUCH BETTER THAN THE PRESENT DESIGN OF THE MLG X FGCP.

Data retrieved from NASA's ASRS site as of August 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.

Air carrier medium large transport altitude deviation overshot during climb when PF deactivated altitude capture by changing fgcp from IAS to mach mode.