AIR TAXI HAS RWY CHANGE CLOSE IN MISREADS APCH PLATE; DSNDS BELOW MDA.

Narrative

WE WERE APCHING PONTIAC; MI; FROM THE W; WITH INTENTIONS OF LNDG AT PONTIAC-OAKLAND ARPT. THE ATIS WAS ADVERTISING THAT THE LOC BACK COURSE 27L WAS THE APCH IN USE. THE CAPT STARTED TO BRIEF BOTH OF US ON THE APCH AS PER COMPANY POLICY. WE WERE BEING RADAR VECTORED BY DETROIT APCH CTL. WE WERE ON A HDG OF 120 DEGS AND ABOUT 15 MI OUT FROM THE ARPT WHEN THE DETROIT APCH CTLR CAME OVER THE RADIO AND ADVISED US THAT PONTIAC HAD JUST SWITCHED APCHS FROM THE LOC BACK COURSE 27L TO THE ILS 9R FRONT COURSE. THIS MEANT THAT WE HAD MUCH LESS TIME TO RESET UP FOR THE APCH; DUE TO OUR POS IN RELATION TO THE ARPT. AT OUR PRESENT SPD; WE WERE NOW ABOUT 2 MINS FROM THE FINAL APCH FIX INSTEAD OF ABOUT THE 10 MINS OUT FROM THE BACK COURSE FINAL APCH FIX THAT WE WERE PLANNING. HE FURTHER WENT ON TO TELL US THAT THE GS SIGNAL WAS UNUSABLE AND WE WERE TO DISREGARD ANY GS INDICATIONS. THAT MEANT THAT THIS PRECISION APCH HAD JUST TURNED INTO A NON PRECISION APCH. THE CAPT QUICKLY TUNED IN THE LOC FREQ AND IDENTED IT. AS THE INDICATION CAME UP ON MY HSI; I REALIZED THAT WE WERE FULL SCALE TO THE R OF COURSE; I BEGAN TO CORRECT WITH A TURN TO A HDG OF 060 DEGS. AT ABOUT THAT TIME; THE CTLR CAME ON AND TOLD US THAT WE WERE CLR FOR THE ILS 9R APCH INTO PONTIAC. THINGS WERE REALLY HAPPENING QUICKLY IN THE COCKPIT AT ABOUT THIS TIME. WE WERE ENCOUNTERING LIGHT TURB. THE COCKPIT WAS DARK SO AS TO HELP US MAINTAIN OUR NIGHT VISION. THE CAPT WAS ATTEMPTING TO RUN THE 'BEFORE LNDG CHKLIST.' WE WERE JUST GIVEN A NEW APCH AND ALT THAT WE WERE NOT EXPECTING. I WAS ATTEMPTING TO SLOW THE ACFT TO APCH SPDS AND DSND OUT OF 9000 FT TO THE NEWLY ASSIGNED 3000 FT PROC TURN ALT. DUE TO OUR PROX AND THE TURB; A RAPID DSCNT WAS A TAXING MANEUVER. WE NEEDED A QUICK LOSS OF ALT BUT WE HAD TO STAY BELOW THE ACFT'S TURBULENT AIR PENETRATION SPD. ATC'S SWITCHING OF THE APCHS THAT CLOSE TO THE ARPT HAD THROWN OUR NORMAL PATTERNS AND RHYTHMS OFF; AND WE HAD TO QUICKEN OUR NORMAL PACE IN ORDER TO MAKE THE APCH. WE MAY HAVE FELT A LITTLE PRESSURED TO MAKE THIS APCH BECAUSE WE ONLY HAD .3 LEFT ON THE HOBBS BEFORE WE WENT OVER AN INSPECTION TIME LIMIT. IF WE HAD TO BE REVECTORED FOR THE NEW APCH; WE MAY NOT HAVE MADE OUR HOBBS TIME LIMIT. WE HAD TO MAKE A 60 DEG HDG CHANGE ON THE LOC. WE HAD TO BRIEF FOR A NEW APCH. WE HAD TO QUICKLY ASCERTAIN OUR POS AND ASSESS THE SIGNIFICANCE OF IT; BUT MOST IMPORTANTLY; WE HAD TO DETERMINE OUR MIN DSCNT ALT AND STAY ABOVE IT. THE CAPT HAD BRIEFED ME AS TO THE MDA; OF WHAT HE MISTOOK TO BE AND I ACCEPTED; OF 1230 MSL. AS WE CROSSED OVER THE OM ON THE APCH I ASKED THE CAPT TO START THE TIMER I BEGAN THE DSCNT DOWN TO 1230 MSL; THE ALT WE HAD AGREED WOULD BE OUR MDA ON THAT APCH. USING OUR IFR APPROVED LORAN; THE CAPT WAS READING OFF DISTANCE TO THE ARPT AS WELL AS OUR ELAPSED TIME. I WAS USING THE DISTANCE INFO ONLY AS A SECONDARY SOURCE OF INFO AND AS A BACKUP TO CONFIRM THE TIME REMAINING ON THE APCH. I REACHED THE MDA WE HAD AGREED UPON ABOUT 1 MI FROM THE APCH END OF THE ARPT. IN THE LEVEL OFF; I CLBED ABOUT 50 FT. AS THE MISSED APCH TIME WAS APCHING; THE CAPT TURNED OFF THE LNDG LIGHTS IN THE HOPES OF BETTER BEING ABLE TO IDENT THE RWY LIGHTS. JUST AS OUR LNDG LIGHTS CAME OFF; HE CAUGHT SIGHT OF THE RWY LIGHTS. AT THAT POINT; HE ASKED FOR THE CTLS AND PROCEEDED TO MAKE THE LNDG. LATER; AFTER THE LNDG; HE TOLD ME THAT HE HAD TAKEN THE CTLS FROM ME BECAUSE AFTER BREAKOUT; HE (AND I) OBSERVED LOWER THAN RPTED RVR VALUES. ON THE LNDG ROLLOUT; I OBSERVED THE RVR AS BEING NO BETTER THAN 2400 FT; LESS THAN HALF THE 6000 RVR THE ATIS WAS ADVERTISING. THE CAPT KNEW THAT I HAD NOT LANDED THIS ACFT AT NIGHT AND UNDER REDUCED VISIBILITY CONDITIONS; SO HE DECIDED TO TAKE THE LNDG. AFTER TURNING OFF THE RWY; I ASKED HIM IF EVERYTHING SEEMED NORMAL ON THE APCH; TO WHICH HE ANSWERED IN THE AFFIRMATIVE. I THOUGHT THAT WE HAD BROKEN OUT QUITE LOW; BUT AFTER DISCUSSING IT WITH THE CAPT; I SIMPLY DISMISSED IT AS AN OPTICAL ILLUSION DUE TO THE PREVAILING WX AND LIGHTING CONDITIONS AS WELL AS HAVING RELATIVELY LOW TIME IN THIS TYPE OF ACFT. AFTER THE SHUTDOWN; I WENT TO ASK AGAIN ABOUT THE APCH. BY THIS TIME HE HAD FIGURED OUT THAT WE HAD DSNDED TOO LOW ON THE APCH. THE MDA SHOULD HAVE BEEN 1520 MSL. WHAT THE CAPT HAD READ WAS THE DECISION HEIGHT WITH AN INOP MIDDLE MARKER; AND NOT THE LOC ONLY MDA.