Narrative:

On approach to ont, we were vectored to and cleared for the NDB runway 26L approach. After passing the pettis NDB and prior to reaching the fonta marker, the FAF, we descended to approximately 500' below the minimum altitude for this segment. The approach controller asked our altitude, then advised us the minimum altitude at fonta was 3000', and he showed us to be 1 mi east of fonta at that time. I immediately arrested the descent and we continued the approach west/O further incident. Several factors contributed to the incident, but I believe the most important was my inadequate preparation for this approach. My copilot had obtained the information in a timely manner, but as it was VFR, I failed to note that the NDB approach was in use. As is normal at ont, we were held high during the initial vectoring, and it was the first vector that I realized that I had to set up for the NDB approach. Since this is a high traffic density area and conditions were VFR, I got behind the aircraft while trying to slow down, descend and prepare for the approach all at once. We were still at 8000' when turned inbound to the pettis NDB, whose crossing altitude is 4200'. I quickly called for more flaps, gear down, final checklist, and promptly overloaded the copilot, who was on his second line flight after completing training. I stayed busy tracking the NDB indicator and scanning for traffic, and asked the copilot to call out station passage. Moments before he did so, I heard the altitude alert sound, indicating we were at 5100'. At this point, I called for 2 things which were probably confusing to the copilot. I asked him to set the minimum altitude, meaning the one for the next segment, and then asked him to confirm the MDA. I believe this caused him to believe I wanted the MDA set in the altitude alert window, and that is what he did. As a result, there was no backup for that altitude. I continued to believe that our descent was just barely adequate to make the airport and it wasn't until ATC questioned our altitude that I realized we hadn't already passed the final fix. If eel that if we had properly prepared for and briefed this approach, none of this would have happened. Complacency in VFR WX is a useless excuse for careless operation.

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING IAP NDB APCH IN VMC WX.

Narrative: ON APCH TO ONT, WE WERE VECTORED TO AND CLRED FOR THE NDB RWY 26L APCH. AFTER PASSING THE PETTIS NDB AND PRIOR TO REACHING THE FONTA MARKER, THE FAF, WE DSNDED TO APPROX 500' BELOW THE MINIMUM ALT FOR THIS SEGMENT. THE APCH CTLR ASKED OUR ALT, THEN ADVISED US THE MINIMUM ALT AT FONTA WAS 3000', AND HE SHOWED US TO BE 1 MI E OF FONTA AT THAT TIME. I IMMEDIATELY ARRESTED THE DSNT AND WE CONTINUED THE APCH W/O FURTHER INCIDENT. SEVERAL FACTORS CONTRIBUTED TO THE INCIDENT, BUT I BELIEVE THE MOST IMPORTANT WAS MY INADEQUATE PREPARATION FOR THIS APCH. MY COPLT HAD OBTAINED THE INFORMATION IN A TIMELY MANNER, BUT AS IT WAS VFR, I FAILED TO NOTE THAT THE NDB APCH WAS IN USE. AS IS NORMAL AT ONT, WE WERE HELD HIGH DURING THE INITIAL VECTORING, AND IT WAS THE FIRST VECTOR THAT I REALIZED THAT I HAD TO SET UP FOR THE NDB APCH. SINCE THIS IS A HIGH TFC DENSITY AREA AND CONDITIONS WERE VFR, I GOT BEHIND THE ACFT WHILE TRYING TO SLOW DOWN, DSND AND PREPARE FOR THE APCH ALL AT ONCE. WE WERE STILL AT 8000' WHEN TURNED INBND TO THE PETTIS NDB, WHOSE XING ALT IS 4200'. I QUICKLY CALLED FOR MORE FLAPS, GEAR DOWN, FINAL CHKLIST, AND PROMPTLY OVERLOADED THE COPLT, WHO WAS ON HIS SECOND LINE FLT AFTER COMPLETING TRNING. I STAYED BUSY TRACKING THE NDB INDICATOR AND SCANNING FOR TFC, AND ASKED THE COPLT TO CALL OUT STATION PASSAGE. MOMENTS BEFORE HE DID SO, I HEARD THE ALT ALERT SOUND, INDICATING WE WERE AT 5100'. AT THIS POINT, I CALLED FOR 2 THINGS WHICH WERE PROBABLY CONFUSING TO THE COPLT. I ASKED HIM TO SET THE MINIMUM ALT, MEANING THE ONE FOR THE NEXT SEGMENT, AND THEN ASKED HIM TO CONFIRM THE MDA. I BELIEVE THIS CAUSED HIM TO BELIEVE I WANTED THE MDA SET IN THE ALT ALERT WINDOW, AND THAT IS WHAT HE DID. AS A RESULT, THERE WAS NO BACKUP FOR THAT ALT. I CONTINUED TO BELIEVE THAT OUR DSNT WAS JUST BARELY ADEQUATE TO MAKE THE ARPT AND IT WASN'T UNTIL ATC QUESTIONED OUR ALT THAT I REALIZED WE HADN'T ALREADY PASSED THE FINAL FIX. IF EEL THAT IF WE HAD PROPERLY PREPARED FOR AND BRIEFED THIS APCH, NONE OF THIS WOULD HAVE HAPPENED. COMPLACENCY IN VFR WX IS A USELESS EXCUSE FOR CARELESS OPERATION.

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.