VFR C172 at 4500 ft with I90 experienced traffic conflict with unrpted twin otter.

Attributes
ACN	664039
Time
Date	200507
Place
Locale Reference	airport : sgr.airport
State Reference	TX
Altitude	msl single value : 4500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : i90.tracon tower : oak.tower
Operator	general aviation : personal
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	None
Aircraft 2
Controlling Facilities	tracon : i90.tracon
Make Model Name	Twin Otter DHC-6
Flight Phase	cruise : level
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument
Experience	flight time last 90 days : 15 flight time total : 520 flight time type : 520
ASRS Report	664039
Person 2
Function	oversight : pic
Events
Anomaly	conflict : airborne less severe other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Miss Distance	horizontal : 0 vertical : 750
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance

Narrative:

En route from sugarland airport; tx; to college station airport; tx; cruising at 4500 ft MSL and receiving flight following from houston TRACON. WX was VMC. At approximately XA00 I observed a twin otter at same altitude at approximately 2 O'clock position. That aircraft was headed southwest. Evasive action was required. I initiated a rapid descent and the other plane flew directly overhead. I received no advisory from houston departure. I contacted the controller who then advised me to squawk 1200 and terminated radar services. The controller did not acknowledge the aircraft.

Original NASA ASRS Text

Title: VFR C172 AT 4500 FT WITH I90 EXPERIENCED TFC CONFLICT WITH UNRPTED TWIN OTTER.

Narrative: ENRTE FROM SUGARLAND ARPT; TX; TO COLLEGE STATION ARPT; TX; CRUISING AT 4500 FT MSL AND RECEIVING FLT FOLLOWING FROM HOUSTON TRACON. WX WAS VMC. AT APPROX XA00 I OBSERVED A TWIN OTTER AT SAME ALT AT APPROX 2 O'CLOCK POS. THAT ACFT WAS HEADED SW. EVASIVE ACTION WAS REQUIRED. I INITIATED A RAPID DSCNT AND THE OTHER PLANE FLEW DIRECTLY OVERHEAD. I RECEIVED NO ADVISORY FROM HOUSTON DEP. I CONTACTED THE CTLR WHO THEN ADVISED ME TO SQUAWK 1200 AND TERMINATED RADAR SVCS. THE CTLR DID NOT ACKNOWLEDGE THE ACFT.

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.