C172 pilot and a cessna had an near midair collision in hef class D, and dc ADIZ.

Attributes
ACN	589573
Time
Date	200307
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : hef.airport
State Reference	VA
Altitude	msl single value : 2000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : pct.tracon tower : hef.tower
Operator	general aviation : personal
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : pct.tracon tower : hef.tower
Make Model Name	Cessna Aircraft Undifferentiated or Other Model
Flight Phase	climbout : takeoff climbout : initial
Route In Use	departure sid : arsenal 1
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 70 flight time total : 1005 flight time type : 70
ASRS Report	589573
Events
Anomaly	conflict : nmac non adherence : far non adherence : published procedure non adherence : required legal separation other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 25 vertical : 25
Supplementary
Problem Areas	Flight Crew Human Performance Airspace Structure ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

I was on right base on a visual approach to runway 16R at manassas (hef) I was squawking a discrete code in dc ADIZ on an IFR flight plan talking to hef tower. Other cessna was climbing to my 2 O'clock position and I descended fast avoiding a collision. I figure the other plane had just departed runway 16R and was talking to potomac departure. All planes leaving hef now have to use the arsenal 1 departure so I couldn't imagine how the plane was where I was. I called tower and said 'I just missed that plane by 25 ft!' and the controller said 'I have no idea who that was.' after I landed I called tower again and asked incredulously, 'you didn't know who that other plane was, that there was another plane there?' and the controller replied 'nope. But I'm sorry that happened to you.' what I wonder is how, with all this security and all these layers of control and all of us in radar contact squawking discrete transponder codes in the dc ADIZ, 2 planes could come close to colliding and one of them was not even noticed by the tower, and a long way away from arsenal 1 and departure control was not keeping us apart.

Original NASA ASRS Text

Title: C172 PLT AND A CESSNA HAD AN NMAC IN HEF CLASS D, AND DC ADIZ.

Narrative: I WAS ON R BASE ON A VISUAL APCH TO RWY 16R AT MANASSAS (HEF) I WAS SQUAWKING A DISCRETE CODE IN DC ADIZ ON AN IFR FLT PLAN TALKING TO HEF TWR. OTHER CESSNA WAS CLBING TO MY 2 O'CLOCK POS AND I DSNDED FAST AVOIDING A COLLISION. I FIGURE THE OTHER PLANE HAD JUST DEPARTED RWY 16R AND WAS TALKING TO POTOMAC DEP. ALL PLANES LEAVING HEF NOW HAVE TO USE THE ARSENAL 1 DEP SO I COULDN'T IMAGINE HOW THE PLANE WAS WHERE I WAS. I CALLED TWR AND SAID 'I JUST MISSED THAT PLANE BY 25 FT!' AND THE CTLR SAID 'I HAVE NO IDEA WHO THAT WAS.' AFTER I LANDED I CALLED TWR AGAIN AND ASKED INCREDULOUSLY, 'YOU DIDN'T KNOW WHO THAT OTHER PLANE WAS, THAT THERE WAS ANOTHER PLANE THERE?' AND THE CTLR REPLIED 'NOPE. BUT I'M SORRY THAT HAPPENED TO YOU.' WHAT I WONDER IS HOW, WITH ALL THIS SECURITY AND ALL THESE LAYERS OF CTL AND ALL OF US IN RADAR CONTACT SQUAWKING DISCRETE XPONDER CODES IN THE DC ADIZ, 2 PLANES COULD COME CLOSE TO COLLIDING AND ONE OF THEM WAS NOT EVEN NOTICED BY THE TWR, AND A LONG WAY AWAY FROM ARSENAL 1 AND DEP CTL WAS NOT KEEPING US APART.

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.