An HS125 first officer reported an near midair collision with a twin cessna in the pattern at dts.

Attributes
ACN	588306
Time
Date	200307
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dts.airport
State Reference	FL
Altitude	agl bound lower : 1500 agl single value : 36
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : corporate
Make Model Name	Harrier
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 2 Eng, Retractable Gear
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Person 1
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : cfi pilot : commercial pilot : atp
Experience	flight time last 90 days : 150 flight time total : 3400 flight time type : 850
ASRS Report	588306
Person 2
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : nmac non adherence : far non adherence : published procedure
Independent Detector	other flight crewa
Resolutory Action	flight crew : took precautionary avoidance action
Miss Distance	horizontal : 75 vertical : 0
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

As we were established on left downwind for runway 14, a twin cessna approached us from our 12:30 O'clock position, at our altitude. I grabbed the aircraft from the captain and rolled the aircraft right to evasively avoid a collision. The twin cessna rolled right as well and narrowly missed us. My company does not equipment all its aircraft with TCASII. Our aircraft did not have TCASII, otherwise this near miss could have been prevented.

Original NASA ASRS Text

Title: AN HS125 FO RPTED AN NMAC WITH A TWIN CESSNA IN THE PATTERN AT DTS.

Narrative: AS WE WERE ESTABLISHED ON L DOWNWIND FOR RWY 14, A TWIN CESSNA APCHED US FROM OUR 12:30 O'CLOCK POS, AT OUR ALT. I GRABBED THE ACFT FROM THE CAPT AND ROLLED THE ACFT R TO EVASIVELY AVOID A COLLISION. THE TWIN CESSNA ROLLED R AS WELL AND NARROWLY MISSED US. MY COMPANY DOES NOT EQUIP ALL ITS ACFT WITH TCASII. OUR ACFT DID NOT HAVE TCASII, OTHERWISE THIS NEAR MISS COULD HAVE BEEN PREVENTED.

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.