Air carrier mdt started final approach segment and landed after WX reported below minimums.

Attributes
ACN	102062
Time
Date	198901
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : mcn
State Reference	GA
Altitude	agl bound lower : 0 agl bound upper : 1600
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : mcn
Operator	common carrier : air carrier
Make Model Name	Medium Transport, High Wing, 2 Turboprop Eng
Flight Phase	descent : approach landing other
Route In Use	approach : straight in
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 8000 flight time type : 3500
ASRS Report	102062
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	non adherence : far other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	Pilot Deviation

Narrative:

On starting the ILS into mcn with WX at 2400' RVR which is the min RVR to shoot the approach, the WX dropped to an RVR of 2200'. We continued the approach and landed. We later realized that we should not have landed if the RVR was below 2400'. I believe that this was a misunderstanding of a somewhat confusing far. Get the FARS rewritten into english. Callback conversation with reporter revealed the following: determined the flight was not established on the final approach segment per the definition of final approach segment in the far so the approach was in fact illegal. Explained to the reporter how the final approach segment on an ILS approach is defined and where it was located in the far.

Original NASA ASRS Text

Title: ACR MDT STARTED FINAL APCH SEGMENT AND LANDED AFTER WX REPORTED BELOW MINIMUMS.

Narrative: ON STARTING THE ILS INTO MCN WITH WX AT 2400' RVR WHICH IS THE MIN RVR TO SHOOT THE APCH, THE WX DROPPED TO AN RVR OF 2200'. WE CONTINUED THE APCH AND LANDED. WE LATER REALIZED THAT WE SHOULD NOT HAVE LANDED IF THE RVR WAS BELOW 2400'. I BELIEVE THAT THIS WAS A MISUNDERSTANDING OF A SOMEWHAT CONFUSING FAR. GET THE FARS REWRITTEN INTO ENGLISH. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: DETERMINED THE FLT WAS NOT ESTABLISHED ON THE FINAL APCH SEGMENT PER THE DEFINITION OF FINAL APCH SEGMENT IN THE FAR SO THE APCH WAS IN FACT ILLEGAL. EXPLAINED TO THE REPORTER HOW THE FINAL APCH SEGMENT ON AN ILS APCH IS DEFINED AND WHERE IT WAS LOCATED IN THE FAR.

Data retrieved from NASA's ASRS site as of August 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.