Narrative:

Approaching phl for approach, ATIS WX (200 ft and 3/4 mi visibility). Cleared for approach approximately 10 NM from OM at 3000 ft MSL. Intercepted localizer and then GS approximately 6-7 NM from OM. Commenced descent on GS. Approaching OM (approximately 1-2 NM out) tower reported RVR touchdown zone 3500 ft then 800 ft and tower visibility 3/4 mi. Captain and I assumed, for CAT I approach, tower visibility of 3/4 mi prevailed and we were on final approach. Shortly after passing OM on GS, tower reported RVR of 3500 ft and we continued approach. Runway sighted at approximately 3/4 mi before decision ht. Uneventful landing followed. After questioning our decision if RVR or visibility prevails on CAT I approach, I looked up in our operations specifications and found that RVR prevails over visibility and we should have executed a missed approach just before OM when RVR dropped to 800 ft even though it was reported 3500 ft just after passing OM. Since both captain and I made a wrong assumption, we both need to review our operations specifications. I don't blame tower or ATIS, but they could help. Tower contributed by making several rapid calls and changes to RVR. ATIS could have been updated with variable RVR reports especially with reports that RVR was at times going below minimums so that we had more time to evaluate (or look up to be sure) instead of having to make decision approaching the OM. Callback conversation with reporter revealed the following information: the first officer flies the F-28 for a major united states air carrier. He had never flown with his captain before this incident. He was near the bottom of reserve in february. 'Lack of knowledge on both parts' was the cause of this incident. The captain acknowledged that the first officer was right when shown the 'book' on the ground. The tower was not unhappy and the reporter has not heard from the FAA. The reporter has filed an anonymous report with his air carrier and expects that this will be a topic of further discussion at recurrent training.

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Original NASA ASRS Text

Title: BELOW MINIMUMS APCH.

Narrative: APCHING PHL FOR APCH, ATIS WX (200 FT AND 3/4 MI VISIBILITY). CLRED FOR APCH APPROX 10 NM FROM OM AT 3000 FT MSL. INTERCEPTED LOC AND THEN GS APPROX 6-7 NM FROM OM. COMMENCED DSCNT ON GS. APCHING OM (APPROX 1-2 NM OUT) TWR RPTED RVR TOUCHDOWN ZONE 3500 FT THEN 800 FT AND TWR VISIBILITY 3/4 MI. CAPT AND I ASSUMED, FOR CAT I APCH, TWR VISIBILITY OF 3/4 MI PREVAILED AND WE WERE ON FINAL APCH. SHORTLY AFTER PASSING OM ON GS, TWR RPTED RVR OF 3500 FT AND WE CONTINUED APCH. RWY SIGHTED AT APPROX 3/4 MI BEFORE DECISION HT. UNEVENTFUL LNDG FOLLOWED. AFTER QUESTIONING OUR DECISION IF RVR OR VISIBILITY PREVAILS ON CAT I APCH, I LOOKED UP IN OUR OPS SPECS AND FOUND THAT RVR PREVAILS OVER VISIBILITY AND WE SHOULD HAVE EXECUTED A MISSED APCH JUST BEFORE OM WHEN RVR DROPPED TO 800 FT EVEN THOUGH IT WAS RPTED 3500 FT JUST AFTER PASSING OM. SINCE BOTH CAPT AND I MADE A WRONG ASSUMPTION, WE BOTH NEED TO REVIEW OUR OPS SPECS. I DON'T BLAME TWR OR ATIS, BUT THEY COULD HELP. TWR CONTRIBUTED BY MAKING SEVERAL RAPID CALLS AND CHANGES TO RVR. ATIS COULD HAVE BEEN UPDATED WITH VARIABLE RVR RPTS ESPECIALLY WITH RPTS THAT RVR WAS AT TIMES GOING BELOW MINIMUMS SO THAT WE HAD MORE TIME TO EVALUATE (OR LOOK UP TO BE SURE) INSTEAD OF HAVING TO MAKE DECISION APCHING THE OM. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FO FLIES THE F-28 FOR A MAJOR UNITED STATES ACR. HE HAD NEVER FLOWN WITH HIS CAPT BEFORE THIS INCIDENT. HE WAS NEAR THE BOTTOM OF RESERVE IN FEBRUARY. 'LACK OF KNOWLEDGE ON BOTH PARTS' WAS THE CAUSE OF THIS INCIDENT. THE CAPT ACKNOWLEDGED THAT THE FO WAS RIGHT WHEN SHOWN THE 'BOOK' ON THE GND. THE TWR WAS NOT UNHAPPY AND THE RPTR HAS NOT HEARD FROM THE FAA. THE RPTR HAS FILED AN ANONYMOUS RPT WITH HIS ACR AND EXPECTS THAT THIS WILL BE A TOPIC OF FURTHER DISCUSSION AT RECURRENT TRAINING.

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.