LR45 pilot with local controller experienced TCAS RA with unrpted traffic while on ILS to stp.

Attributes
ACN	697693
Time
Date	200605
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : stp.airport
State Reference	MN
Environment
Flight Conditions	VMC
Aircraft 1
Controlling Facilities	tower : stp.tower
Operator	general aviation : corporate
Make Model Name	Learjet 45
Operating Under FAR Part	Part 91
Navigation In Use	ils localizer & glide slope : 32
Flight Phase	descent : approach
Aircraft 2
Controlling Facilities	tower : stp.tower
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
ASRS Report	697693
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	conflict : airborne critical
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Miss Distance	horizontal : 1000 vertical : 200
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Ambiguous

Narrative:

I was pilot of an LR45 landing at stp runway 32 ILS in VMC conditions. About 1/2 way down the GS we noticed a seaplane paralleling our course. Suddenly he turned 90 degrees towards us and crossed the final approach course approximately 1000 ft horizontally and 200-300 ft under us. We experienced an RA advising check descent. We leveled off momentarily and avoided him. Tower at stp says they were not talking to him; but would try to see if approach control could track him. If there are issues with seaplanes on the river; someone should fix the problem.

Original NASA ASRS Text

Title: LR45 PLT WITH LCL CTLR EXPERIENCED TCAS RA WITH UNRPTED TFC WHILE ON ILS TO STP.

Narrative: I WAS PLT OF AN LR45 LNDG AT STP RWY 32 ILS IN VMC CONDITIONS. ABOUT 1/2 WAY DOWN THE GS WE NOTICED A SEAPLANE PARALLELING OUR COURSE. SUDDENLY HE TURNED 90 DEGS TOWARDS US AND CROSSED THE FINAL APCH COURSE APPROX 1000 FT HORIZLY AND 200-300 FT UNDER US. WE EXPERIENCED AN RA ADVISING CHK DSCNT. WE LEVELED OFF MOMENTARILY AND AVOIDED HIM. TWR AT STP SAYS THEY WERE NOT TALKING TO HIM; BUT WOULD TRY TO SEE IF APCH CTL COULD TRACK HIM. IF THERE ARE ISSUES WITH SEAPLANES ON THE RIVER; SOMEONE SHOULD FIX THE PROB.

Data retrieved from NASA's ASRS site as of January 2009 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.