AN ACR GOT A TERRAIN WARNING ON A NIGHT INST APCH.

Narrative

THE BACK COURSE ILS 22 APCH REQUIRES 1 PLT TO BE ON YQX UNTIL THE MISSED APCH POINT. THEREFORE THERE IS NO BACKUP TO THE PF. WHEN THE LOC WAS TUNED; A DME MILEAGE APPEARED THAT APPEARED TO BE AN ILS DME -- IS THERE ONE? WE THINK THE COPLT STARTED DOWN ON HIS DME (PF) AND THIS WAS NOT CAUGHT DUE TO WORKLOAD; I.E.; LNDG CHK; LNDG CLRNC WITH FREQ CHANGE; SPD BUG AND FLAP CHANGE. THE RESULT WAS EARLY DSCNT TO MINIMUMS OVER DARK; UNLIT TERRAIN RESULTING IN A 'PULL UP' WHICH PROBABLY SAVED SERIOUS PROBS. CLB WAS INITIATED TO APPROX VISUAL GS AND LNDG MADE IN NORMAL MANNER. CREW FATIGUE AND 'BACK OF THE CLOCK' WERE CONTRIBUTORS. ILS DME? UNRPTED WAS A MAJOR CONTRIBUTOR. LACK OF SPATIAL AND ALT AWARENESS WAS; ULTIMATELY; THE CARDINAL SIN. IT IS POSSIBLE; BUT UNLIKELY; THAT THE APCH WAS FLOWN LEGALLY BUT DSCNT WAS STARTED TOO RAPIDLY TO INSURE 'COMFORTABLE' TERRAIN CLRNC. MISSED CALLOUTS BY CAPT AT SHEA WERE PROBABLY A BIG REASON THINGS WENT SO POORLY. SUPPLEMENTAL INFORMATION FROM ACN 254823: ALL CREW MEMBERS WERE CONFUSED ON WHAT HAD HAPPENED AND AFTER LENGTHY DISCUSSION AND INVESTIGATION THE FOLLOWING WAS DISCOVERED. LOC BACK COURSE RWY 22 APCH (EFFECTIVE SEP/XX/93) FREQ 109.5 HAS A CO-LOCATED DME THAT IS NOT NOTED ON THE APCH PLATE. FO LOOKED QUICKLY AT THE DME AND SAW 7.9 MI BUT IT WAS ON THE LOC NOT OFF OF YQX AS REQUIRED BY THE APCH. RESULT WAS DSCNT TO MDA 3 MI EARLY! A CRITICAL ERROR WAS MADE BUT WAS INITIATED BY A DME NO ONE WAS PREPARED FOR. THIS IS A POTENTIALLY DANGEROUS APCH THAT CAUGHT US.