Narrative:

We were flying a night approach to oakland international airport, communicating with approach control and given instructions 'cleared for the visual approach runway 29 maintain 2000 ft until 6 DME and 180 KTS as long as practical, contact tower at the marker.' the first officer was flying the approach using the ILS for GS information since runway 29 has no visual GS indicator. As we approached 2000 ft, I switched my HSI display to VOR mode and noted that we were outside the 6 DME arc. I told the first officer that we had not yet reached the 6 DME and that he needed to maintain 2000 ft. Since he was established on a published GS, and the runway was clearly visible and getting very close, he hesitated slightly since it seemed quite unreasonable to abandon an otherwise stable approach so close to the runway. By the time we reached the 6 DME we were 250-300 ft below our 2000 ft crossing restr. This event occurred during a period of high radio traffic while multiple cockpit duties were being performed. No conflicting traffic was observed either visually or on the TCASII. We had briefed the approach noting the proximity of a small airport near the localizer course to runway 29. However, neither of us was aware that an altitude restr would require us to abandon the ILS GS, and then reacquire it from above at such a low altitude. This led to some ambiguity as to what was the proper procedure for this approach. I cannot recall any other such situation which exists anywhere at the low altitudes involved. The perspective of the very long runway 29 with very few surrounding lights also gives the illusion of being even closer than you are.

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Original NASA ASRS Text

Title: ACR CREW DSNDED BELOW THE 6 DME AT 2000 FT RESTR WHILE ON APCH TO RWY 29 AT OAK.

Narrative: WE WERE FLYING A NIGHT APCH TO OAKLAND INTL ARPT, COMMUNICATING WITH APCH CTL AND GIVEN INSTRUCTIONS 'CLRED FOR THE VISUAL APCH RWY 29 MAINTAIN 2000 FT UNTIL 6 DME AND 180 KTS AS LONG AS PRACTICAL, CONTACT TWR AT THE MARKER.' THE FO WAS FLYING THE APCH USING THE ILS FOR GS INFO SINCE RWY 29 HAS NO VISUAL GS INDICATOR. AS WE APCHED 2000 FT, I SWITCHED MY HSI DISPLAY TO VOR MODE AND NOTED THAT WE WERE OUTSIDE THE 6 DME ARC. I TOLD THE FO THAT WE HAD NOT YET REACHED THE 6 DME AND THAT HE NEEDED TO MAINTAIN 2000 FT. SINCE HE WAS ESTABLISHED ON A PUBLISHED GS, AND THE RWY WAS CLRLY VISIBLE AND GETTING VERY CLOSE, HE HESITATED SLIGHTLY SINCE IT SEEMED QUITE UNREASONABLE TO ABANDON AN OTHERWISE STABLE APCH SO CLOSE TO THE RWY. BY THE TIME WE REACHED THE 6 DME WE WERE 250-300 FT BELOW OUR 2000 FT XING RESTR. THIS EVENT OCCURRED DURING A PERIOD OF HIGH RADIO TFC WHILE MULTIPLE COCKPIT DUTIES WERE BEING PERFORMED. NO CONFLICTING TFC WAS OBSERVED EITHER VISUALLY OR ON THE TCASII. WE HAD BRIEFED THE APCH NOTING THE PROX OF A SMALL ARPT NEAR THE LOC COURSE TO RWY 29. HOWEVER, NEITHER OF US WAS AWARE THAT AN ALT RESTR WOULD REQUIRE US TO ABANDON THE ILS GS, AND THEN REACQUIRE IT FROM ABOVE AT SUCH A LOW ALT. THIS LED TO SOME AMBIGUITY AS TO WHAT WAS THE PROPER PROC FOR THIS APCH. I CANNOT RECALL ANY OTHER SUCH SIT WHICH EXISTS ANYWHERE AT THE LOW ALTS INVOLVED. THE PERSPECTIVE OF THE VERY LONG RWY 29 WITH VERY FEW SURROUNDING LIGHTS ALSO GIVES THE ILLUSION OF BEING EVEN CLOSER THAN YOU ARE.

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.