Medium large transport flight crew continues approach when RVR decreases below minimums.

Attributes
ACN	236342
Time
Date	199303
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 5000 msl bound upper : 5000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent : approach landing other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 78 flight time total : 3838 flight time type : 1471
ASRS Report	236342
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	inflight encounter : weather non adherence : far other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : detected after the fact
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were preparing for the ILS runway 32L at ord. The approach controller announced that he intended to start putting aircraft on the ILS and let us determine for ourselves whether or not we could complete the approach. The minimum RVR authority/authorized for the approach was 1800 ft, and the current RVR was 1800 ft. We began the ILS approach, and while on the GS at about 5000 ft, the RVR decreased to 1600 ft. At about 4000 ft on the GS the RVR decreased further to 1400 ft. We mistakenly believed that if the RVR had been at least at the required minimums of 1800 ft when we intercepted the GS, that it could decrease to below the minimums and we could continue the approach to decision ht. This is what we did, and completed the approach and landing. In fact, we were required to discontinue the approach any time that the RVR decreased below 1800 ft and we were still above 2500 ft on the GS. Since we did not discontinue the approach, we executed an unauthorized approach. We should have referenced our company flight manual to determine whether or not we were authority/authorized to fly the approach, instead of trusting our memory. We were simply unprepared for how quickly the WX deteriorated at ord. We had checked the WX before leaving, and it appeared fine. We also became rushed to be sequenced onto the approach, and made a decision based on what we thought we remembered from our flight manual.

Original NASA ASRS Text

Title: MLG FLC CONTINUES APCH WHEN RVR DECREASES BELOW MINIMUMS.

Narrative: WE WERE PREPARING FOR THE ILS RWY 32L AT ORD. THE APCH CTLR ANNOUNCED THAT HE INTENDED TO START PUTTING ACFT ON THE ILS AND LET US DETERMINE FOR OURSELVES WHETHER OR NOT WE COULD COMPLETE THE APCH. THE MINIMUM RVR AUTH FOR THE APCH WAS 1800 FT, AND THE CURRENT RVR WAS 1800 FT. WE BEGAN THE ILS APCH, AND WHILE ON THE GS AT ABOUT 5000 FT, THE RVR DECREASED TO 1600 FT. AT ABOUT 4000 FT ON THE GS THE RVR DECREASED FURTHER TO 1400 FT. WE MISTAKENLY BELIEVED THAT IF THE RVR HAD BEEN AT LEAST AT THE REQUIRED MINIMUMS OF 1800 FT WHEN WE INTERCEPTED THE GS, THAT IT COULD DECREASE TO BELOW THE MINIMUMS AND WE COULD CONTINUE THE APCH TO DECISION HT. THIS IS WHAT WE DID, AND COMPLETED THE APCH AND LNDG. IN FACT, WE WERE REQUIRED TO DISCONTINUE THE APCH ANY TIME THAT THE RVR DECREASED BELOW 1800 FT AND WE WERE STILL ABOVE 2500 FT ON THE GS. SINCE WE DID NOT DISCONTINUE THE APCH, WE EXECUTED AN UNAUTH APCH. WE SHOULD HAVE REFED OUR COMPANY FLT MANUAL TO DETERMINE WHETHER OR NOT WE WERE AUTH TO FLY THE APCH, INSTEAD OF TRUSTING OUR MEMORY. WE WERE SIMPLY UNPREPARED FOR HOW QUICKLY THE WX DETERIORATED AT ORD. WE HAD CHKED THE WX BEFORE LEAVING, AND IT APPEARED FINE. WE ALSO BECAME RUSHED TO BE SEQUENCED ONTO THE APCH, AND MADE A DECISION BASED ON WHAT WE THOUGHT WE REMEMBERED FROM OUR FLT MANUAL.

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.