Narrative:

The event occurred during an arrival period at iad while simultaneous ILS approaches were being conducted to runway 01C and runway 01R. I was working iadfc (final center) operating as the 'high' side in the operation. I believe air carrier Y was straight in on 01R; cleared for the approach at 3;000 ft; when I turned air carrier X on a left base for 01C descending to 4;000 ft; just outside an intermediate approach fix with a crossing altitude of 3;900 ft. Air carrier X; on the downwind; was descending and indicating a ground speed of around 220-230 KTS; however when I turned air carrier X on a standard left base the aircraft increased ground speed to around 250 KTS indicated. Air carrier X was instructed to turn to a heading of 040 and intercept the 01C localizer. As I observed air carrier X in a turn which I found acceptable to join the final; I cleared air carrier X for the 01C ILS instructing the aircraft to maintain 4;000 ft until established on the localizer. As I believed the aircraft was joining the localizer I told the aircraft to maintain 170 KTS until the FAF. Right after this transmission; air carrier X flew through the 01C localizer beyond the intermediate fix and while correcting back to the localizer the aircraft began descending out of 4;000 ft. As the aircraft started its descent it did not maintain minimum vertical or lateral separation with the other aircraft straight in for 01R. The aircraft in question was turned on to the final at an altitude that maintained appropriate vertical separation with other potential traffic. The aircraft was then issued a clearance that ensured appropriate vertical separation until established on the approach. Was the aircraft fast on the base turn? Yes. Should I have controlled the situation better? Yes. However; there are procedures in place that were adhered to that should have prevented this incident. On initial check-in all pilots should have received the ATIS broadcast which stated that simultaneous ILS approaches were being conducted to 01C and 01R. This ATIS information should have alerted a pilot going to 01C that there could be traffic to the east on approach for 01R. Furthermore the phraseology 'until established' was used to ensure that vertical separation would be maintained until on the approach. I understand that the speed caused the aircraft to go through the localizer and that during the correction back the aircraft was put in a position most likely above the glide scope making an approach difficult. Be this as it may; being too high for the approach does not give an aircraft the right to disregard an ATC instruction. If by maintaining its assigned altitude the aircraft was put into a position that made it unable to comply with both the controller's instruction and the published approach then the pilot should have complied with the ATC control instruction and informed the controller that he would be unable to accept the approach. The aircraft could then have been re-sequenced and hopefully received a better turn on to final. I believe this incident illustrates discrepancies between controllers and pilots as to the true meaning of the phraseology: 'established on the localizer.' doing some research myself; it seems that there is a large split between both pilots and controllers as to the nature of this term with a healthy debate on ICAO; far; and company guidelines. To me; established means that you are stable and fixed on the navigation aide or route in question. However; with autopilots and various equipment aircraft could believe they are established even as they are flying through the course. Better guidance and collaboration from both users and decision makers would go a long way in preventing situations like this in the future.

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Original NASA ASRS Text

Title: PCT Controller experienced a loss of separation during Simultaneous Approach operations to Runways 01 as an aircraft flew through the final but started a descent reportedly due to the ambiguity of the term 'established on final.'

Narrative: The event occurred during an arrival period at IAD while simultaneous ILS approaches were being conducted to Runway 01C and Runway 01R. I was working IADFC (Final Center) operating as the 'high' side in the operation. I believe Air Carrier Y was straight in on 01R; cleared for the approach at 3;000 FT; when I turned Air Carrier X on a left base for 01C descending to 4;000 FT; just outside an intermediate approach fix with a crossing altitude of 3;900 FT. Air Carrier X; on the downwind; was descending and indicating a ground speed of around 220-230 KTS; however when I turned Air Carrier X on a standard left base the aircraft increased ground speed to around 250 KTS indicated. Air Carrier X was instructed to turn to a heading of 040 and intercept the 01C localizer. As I observed Air Carrier X in a turn which I found acceptable to join the final; I cleared Air Carrier X for the 01C ILS instructing the aircraft to maintain 4;000 FT until established on the localizer. As I believed the aircraft was joining the localizer I told the aircraft to maintain 170 KTS until the FAF. Right after this transmission; Air Carrier X flew through the 01C localizer beyond the intermediate fix and while correcting back to the localizer the aircraft began descending out of 4;000 FT. As the aircraft started its descent it did not maintain minimum vertical or lateral separation with the other aircraft straight in for 01R. The aircraft in question was turned on to the final at an altitude that maintained appropriate vertical separation with other potential traffic. The aircraft was then issued a clearance that ensured appropriate vertical separation until established on the approach. Was the aircraft fast on the base turn? Yes. Should I have controlled the situation better? Yes. However; there are procedures in place that were adhered to that should have prevented this incident. On initial check-in all pilots should have received the ATIS broadcast which stated that simultaneous ILS approaches were being conducted to 01C and 01R. This ATIS information should have alerted a pilot going to 01C that there could be traffic to the east on approach for 01R. Furthermore the phraseology 'until established' was used to ensure that vertical separation would be maintained until on the approach. I understand that the speed caused the aircraft to go through the localizer and that during the correction back the aircraft was put in a position most likely above the glide scope making an approach difficult. Be this as it may; being too high for the approach does not give an aircraft the right to disregard an ATC instruction. If by maintaining its assigned altitude the aircraft was put into a position that made it unable to comply with both the controller's instruction and the published approach then the pilot should have complied with the ATC control instruction and informed the controller that he would be unable to accept the approach. The aircraft could then have been re-sequenced and hopefully received a better turn on to final. I believe this incident illustrates discrepancies between controllers and pilots as to the true meaning of the phraseology: 'established on the localizer.' Doing some research myself; it seems that there is a large split between both pilots and controllers as to the nature of this term with a healthy debate on ICAO; FAR; and company guidelines. To me; established means that you are stable and fixed on the navigation aide or route in question. However; with autopilots and various equipment aircraft could believe they are established even as they are flying through the course. Better guidance and collaboration from both users and decision makers would go a long way in preventing situations like this in the future.

Data retrieved from NASA's ASRS site as of July 2013 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.