PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Flight Crew Commercial; Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Flight Crew Last 90 Days 34; Flight Crew Total 5440; Flight Crew Type 2845
Conflict NMAC
General None Reported / Taken
Aircraft; Human Factors
We were cruising at 2;500 FT enroute to N57.  Our position was in Class E airspace; below and just east of the edge of the Washington DC Class B airspace and about 8-9 miles west of the ESN airport.  We had just descended from 3;500 FT to 2;500 FT after crossing the bay.  Weather conditions were CAVU.  Even though we were continually scanning for other aircraft and monitoring the ESN Tower frequency we did not notice the other aircraft; a Cessna 172 (possibly a 182) until it passed directly under us in a slight climbing left turn.  Evasive action on our part was after the fact.  I would like to believe the other pilot saw us in time to take evasive action; but I think he probably also failed to see us in time to maneuver.  We were both very lucky.My analysis of what happened is as follows:  Both aircraft were operating in class E airspace in VFR conditions.  We were cruising in level flight.  The other aircraft was probably either climbing or doing training maneuvers.  This was a typical case of low wing - high wing conflict.  He approached me from my blind spot; below and behind my wing; whereas I was probably in his blind spot above and behind his wing.  A contributing factor is that the very clear air and non-relative motion would have made it very difficult for me to distinguish the lower Cessna against the background.  I think a discussion of this event is a good training lesson for any pilot.
PA28 pilot reports a NMAC at 2;500 feet 8 NM west of ESN with a C172. Neither pilot saw the other until it was too late to take any action.