Narrative:

Flying with pilot not rated in aircraft, but current in beechjet and typed in beechjet and hawker. Previous flts had gone fine with copilot using autoplt correctly. Copilot was descending from altitude and I noticed as aircraft was approaching FL250 that aircraft had not begun leveloff. Sitting in right seat as PNF, I called out that the aircraft had not begun leveloff, quickly looked and noticed altitude intercept mode was not engaged. Copilot began (or so I thought) to manually level aircraft, but as I came to realize too late, only had hands on control column and was not making an input forceful enough to stop descent before dropping 400 ft below assigned altitude (FL246). Copilot quickly adjusted to FL250, but controller questioned altitude. Copilot noted that in aircraft he normally flies that aircraft will automatically level at altitude dialed in without manually selecting altitude intercept mode. My error was not taking control of aircraft immediately, but had copilot made correction when placing hands on wheel little or no altitude loss would have occurred.

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Original NASA ASRS Text

Title: GLF-3 CREW HAD AN ALTDEV IN ZDC CLASS A AIRSPACE.

Narrative: FLYING WITH PLT NOT RATED IN ACFT, BUT CURRENT IN BEECHJET AND TYPED IN BEECHJET AND HAWKER. PREVIOUS FLTS HAD GONE FINE WITH COPLT USING AUTOPLT CORRECTLY. COPLT WAS DSNDING FROM ALT AND I NOTICED AS ACFT WAS APCHING FL250 THAT ACFT HAD NOT BEGUN LEVELOFF. SITTING IN R SEAT AS PNF, I CALLED OUT THAT THE ACFT HAD NOT BEGUN LEVELOFF, QUICKLY LOOKED AND NOTICED ALT INTERCEPT MODE WAS NOT ENGAGED. COPLT BEGAN (OR SO I THOUGHT) TO MANUALLY LEVEL ACFT, BUT AS I CAME TO REALIZE TOO LATE, ONLY HAD HANDS ON CTL COLUMN AND WAS NOT MAKING AN INPUT FORCEFUL ENOUGH TO STOP DSCNT BEFORE DROPPING 400 FT BELOW ASSIGNED ALT (FL246). COPLT QUICKLY ADJUSTED TO FL250, BUT CTLR QUESTIONED ALT. COPLT NOTED THAT IN ACFT HE NORMALLY FLIES THAT ACFT WILL AUTOMATICALLY LEVEL AT ALT DIALED IN WITHOUT MANUALLY SELECTING ALT INTERCEPT MODE. MY ERROR WAS NOT TAKING CTL OF ACFT IMMEDIATELY, BUT HAD COPLT MADE CORRECTION WHEN PLACING HANDS ON WHEEL LITTLE OR NO ALT LOSS WOULD HAVE OCCURRED.

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.