Narrative:

The flight was a requalification IOE for the first officer. The student was making normal progress with no indicated problems toward requaling. Our STAR was discontinued by approach control on initial contact; replaced by vectors for an ILS to [runway] 28R. Initial descent [was] to 6;000 MSL; then to 4;000 then 3;000. Aircraft was capturing 3;000 ft with alt*[capture] exactly at the same time the first officer selected land to arm the ILS as we were given an intercept at about a seven mile final. I noticed on the fcp and fmas that altitude hld and lvl chg began flashing back from one to the other at a rate of about twice a second for about ten seconds while the airplane leveled at 3;000 ft. I pointed this out to the first officer and confirmed fcp land mode was armed and fmas showed good for localizer and GS capture. Flashing fmas stopped at about localizer* [capture]. As we were cleared to land I had finished the landing check we were twice alerted by GPWS of an obstacle and the terrain display came up automatically on nd. I took control of the airplane and disconnected the autopilot and began a climb that leveled off at about 2;000 ft where I assessed the situation; got the airplane stable and waited for the glideslope to come down to center after which I continued the approach off the autopilot to an uneventful landing. Tower gave us an altitude alert call almost exactly at same time as GPWS obstacle alert. After the capture of 3;000 ft; I am not sure what mode the airplane went into vertically. I'm pretty sure however; it was flying pitch on speed at idle power and responded to the first officer setting approach speed on the fcp by descending quickly. I figure the airplane descended to about 2;000 ft in about 20 seconds. This put us about 800 ft above the ground at about a five mile final; well below glideslope. There must be a potential for the automation to get confused if land is armed exactly at the same time as altitude* [capture] happens. I was aware of abnormal fcp and FMA indications; but dismissed them when they went away. [I] got distracted for about 20 seconds checking in with tower and finishing the before landing checklist. [We might want to] make crews aware of FMA/fcp indications of an improper sequence of land mode arming in conjunction with altitude* [capture]. Make localizer* [capture] and GS*[capture] sterile environment events; not allowing radio communication or checklist activity until confirmed capture of both.

Google
 

Original NASA ASRS Text

Title: An A300 flight crew suffered a CFTT incident when the autoflight system malfunctioned and the aircraft failed to arrest its descent at 3;000 MSL as cleared prior to intercepting the ILS.

Narrative: The flight was a requalification IOE for the First Officer. The student was making normal progress with no indicated problems toward requaling. Our STAR was discontinued by Approach Control on initial contact; replaced by vectors for an ILS to [Runway] 28R. Initial descent [was] to 6;000 MSL; then to 4;000 then 3;000. Aircraft was capturing 3;000 FT with alt*[capture] exactly at the same time the First Officer selected land to arm the ILS as we were given an intercept at about a seven mile final. I noticed on the FCP and FMAs that ALT HLD and LVL CHG began flashing back from one to the other at a rate of about twice a second for about ten seconds while the airplane leveled at 3;000 FT. I pointed this out to the First Officer and confirmed FCP land mode was armed and FMAs showed good for LOC and GS capture. Flashing FMAs stopped at about LOC* [capture]. As we were cleared to land I had finished the landing check we were twice alerted by GPWS of an obstacle and the terrain display came up automatically on ND. I took control of the airplane and disconnected the autopilot and began a climb that leveled off at about 2;000 FT where I assessed the situation; got the airplane stable and waited for the glideslope to come down to center after which I continued the approach off the autopilot to an uneventful landing. Tower gave us an altitude alert call almost exactly at same time as GPWS obstacle alert. After the capture of 3;000 FT; I am not sure what mode the airplane went into vertically. I'm pretty sure however; it was flying pitch on speed at idle power and responded to the First Officer setting approach speed on the FCP by descending quickly. I figure the airplane descended to about 2;000 FT in about 20 seconds. This put us about 800 FT above the ground at about a five mile final; well below glideslope. There must be a potential for the automation to get confused if LAND is armed exactly at the same time as ALT* [capture] happens. I was aware of abnormal FCP and FMA indications; but dismissed them when they went away. [I] got distracted for about 20 seconds checking in with Tower and finishing the Before Landing Checklist. [We might want to] make crews aware of FMA/FCP indications of an improper sequence of LAND mode arming in conjunction with ALT* [capture]. Make LOC* [capture] and GS*[capture] sterile environment events; not allowing radio communication or checklist activity until confirmed capture of both.

Data retrieved from NASA's ASRS site as of July 2013 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.