Narrative:

During an ILS approach to boeing field, a light single engine aircraft was spotted and evasive action taken to avoid collision. I was PIC and was manually flying at the time. The approach was in excellent visual flight conditions and I was flying ILS raw data for reference, but primarily using visual cues to fly the approach. The final portion of the approach is over a heavily industrialized area. The copilot called traffic dead ahead. Although I had just looked straight ahead, I had not seen the aircraft. I looked again and was then able to see him against the multiple patterned background. The coloring of his aircraft did not contrast with the ground and since we were on an overtaking collision course (he was also on the ILS localizer), there was little relative motion. We leveled off and turned right to avoid collision. After evasion, we re-established on the ILS and completed the approach. After the incident, we spoke with the tower personnel. They stated that the small aircraft was in radio contact with tower at the time of the incident. He had no transponder and tower was trying to judge relative distances between us visually with the aid of binoculars. The tower controller did not perceive a potential conflict since he saw the small aircraft as being behind us. Neither the tower nor the pilot of the small aircraft was aware of a problem until we took evasive action. At that time, I estimate that there was approximately 20 seconds until impact. Although both myself and my copilot were scanning outside, only he saw the aircraft in time to prevent the development of an extremely dangerous situation. Perhaps non IFR aircraft should use the standard visual entries to the field and not the instrument approach.

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Original NASA ASRS Text

Title: CLOSE PROX MLG GA-SMA ON APCH TO BFL.

Narrative: DURING AN ILS APCH TO BOEING FIELD, A LIGHT SINGLE ENG ACFT WAS SPOTTED AND EVASIVE ACTION TAKEN TO AVOID COLLISION. I WAS PIC AND WAS MANUALLY FLYING AT THE TIME. THE APCH WAS IN EXCELLENT VISUAL FLT CONDITIONS AND I WAS FLYING ILS RAW DATA FOR REF, BUT PRIMARILY USING VISUAL CUES TO FLY THE APCH. THE FINAL PORTION OF THE APCH IS OVER A HEAVILY INDUSTRIALIZED AREA. THE COPLT CALLED TFC DEAD AHEAD. ALTHOUGH I HAD JUST LOOKED STRAIGHT AHEAD, I HAD NOT SEEN THE ACFT. I LOOKED AGAIN AND WAS THEN ABLE TO SEE HIM AGAINST THE MULTIPLE PATTERNED BACKGROUND. THE COLORING OF HIS ACFT DID NOT CONTRAST WITH THE GND AND SINCE WE WERE ON AN OVERTAKING COLLISION COURSE (HE WAS ALSO ON THE ILS LOC), THERE WAS LITTLE RELATIVE MOTION. WE LEVELED OFF AND TURNED RIGHT TO AVOID COLLISION. AFTER EVASION, WE RE-ESTABLISHED ON THE ILS AND COMPLETED THE APCH. AFTER THE INCIDENT, WE SPOKE WITH THE TWR PERSONNEL. THEY STATED THAT THE SMA WAS IN RADIO CONTACT WITH TWR AT THE TIME OF THE INCIDENT. HE HAD NO TRANSPONDER AND TWR WAS TRYING TO JUDGE RELATIVE DISTANCES BTWN US VISUALLY WITH THE AID OF BINOCULARS. THE TWR CTLR DID NOT PERCEIVE A POTENTIAL CONFLICT SINCE HE SAW THE SMA AS BEING BEHIND US. NEITHER THE TWR NOR THE PLT OF THE SMA WAS AWARE OF A PROB UNTIL WE TOOK EVASIVE ACTION. AT THAT TIME, I ESTIMATE THAT THERE WAS APPROX 20 SECS UNTIL IMPACT. ALTHOUGH BOTH MYSELF AND MY COPLT WERE SCANNING OUTSIDE, ONLY HE SAW THE ACFT IN TIME TO PREVENT THE DEVELOPMENT OF AN EXTREMELY DANGEROUS SITUATION. PERHAPS NON IFR ACFT SHOULD USE THE STANDARD VISUAL ENTRIES TO THE FIELD AND NOT THE INSTRUMENT APCH.

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.