A C550 on an ILS approach at 2500 ft executed an avoidance maneuver following a TCAS alert.

Attributes
ACN	632495
Time
Date	200410
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : gmu.airport
State Reference	SC
Altitude	msl single value : 2500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : gsp.tracon
Operator	general aviation : corporate
Make Model Name	Citation II S2/Bravo
Operating Under FAR Part	Part 91
Navigation In Use	ils localizer & glide slope : 1
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent : approach
Route In Use	approach : traffic pattern
Person 1
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 90 flight time total : 2800 flight time type : 1100
ASRS Report	632495
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : nmac
Independent Detector	aircraft equipment : tcas other flight crewa
Resolutory Action	flight crew : took evasive action
Miss Distance	vertical : 700
Supplementary
Problem Areas	Airspace Structure Flight Crew Human Performance Airport
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Established at 2500 ft MSL and cleared for the ILS runway 1 at gmu, we received a traffic alert that showed traffic at -100 ft. I immediately initiated a climb away from the traffic. We climbed a maximum of 200-300 ft above assigned altitude. Once cleared of traffic, I descended on the GS and landed uneventfully. In my opinion, the conflicting traffic was in the pattern at a nearby airfield and was 300 ft above the traffic pattern altitude.

Original NASA ASRS Text

Title: A C550 ON AN ILS APCH AT 2500 FT EXECUTED AN AVOIDANCE MANEUVER FOLLOWING A TCAS ALERT.

Narrative: ESTABLISHED AT 2500 FT MSL AND CLRED FOR THE ILS RWY 1 AT GMU, WE RECEIVED A TFC ALERT THAT SHOWED TFC AT -100 FT. I IMMEDIATELY INITIATED A CLB AWAY FROM THE TFC. WE CLBED A MAX OF 200-300 FT ABOVE ASSIGNED ALT. ONCE CLRED OF TFC, I DSNDED ON THE GS AND LANDED UNEVENTFULLY. IN MY OPINION, THE CONFLICTING TFC WAS IN THE PATTERN AT A NEARBY AIRFIELD AND WAS 300 FT ABOVE THE TFC PATTERN ALT.

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.