Narrative:

While conducting a test flight to capture pressure altitude/vacuum pressure data to recertify my aircraft's standby vacuum system; I was involved in an near midair collision with a large high-wing aircraft. I departed ZZZ1 at XA00 am; jun/xa/08 with unrestr visibility. Departed ZZZ1 to the southeast; climbing up to 10000 ft; over-flying ZZZ2. I was in contact with ZZZ2 CTAF frequently making position calls. The flight test data I was capturing included RPM/mp settings for minimum vacuum hg for pressure altitudes at: 10000 ft; 8000 ft; 6000 ft; 4000 ft; and 2000 ft. I completed recording my first data point at 10000 ft; 12 NM south of ZZZ2 and 3 NM west of ZZZ; performed a wbound turn to the north and was on a heading of 330 degrees; when I started my gradual descent from 10000 ft down to 8000 ft to collect my next data point. Glancing out of the copilot side window; I saw a large high-wing aircraft in a high angle-of-attack; banking away from my aircraft. The aircraft passed out of my view within a blink of an eye. I was able to discern that the aircraft was a large high-wing passenger aircraft the size of either a cessna grand caravan or a dehavilland twin otter. The aircraft's color was red/orange on white. The aircraft climbed past my plane within 150 ft. ZZZ is designated as 'extremely heavy parachute jumping activity;' with jumping activity over the east of the airport. My guess; is that the aircraft which missed me by 150 ft; is/was engaged in skydiving activity at ZZZ. Due to the fact that my mooney is a low-wing aircraft; limits my ability to spot climbing aircraft from below. Due to the speeds at which the acfts passed; there was no reaction time on my part. In hindsight; I should have been in radio contact with center; for radar traffic services. The same holds true for the large high-wing aircraft.

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Original NASA ASRS Text

Title: M20 PLT ON A TEST FLT EXPERIENCES A NMAC WITH A HIGH WING ACFT.

Narrative: WHILE CONDUCTING A TEST FLT TO CAPTURE PRESSURE ALT/VACUUM PRESSURE DATA TO RECERTIFY MY ACFT'S STANDBY VACUUM SYS; I WAS INVOLVED IN AN NMAC WITH A LARGE HIGH-WING ACFT. I DEPARTED ZZZ1 AT XA00 AM; JUN/XA/08 WITH UNRESTR VISIBILITY. DEPARTED ZZZ1 TO THE SE; CLBING UP TO 10000 FT; OVER-FLYING ZZZ2. I WAS IN CONTACT WITH ZZZ2 CTAF FREQUENTLY MAKING POS CALLS. THE FLT TEST DATA I WAS CAPTURING INCLUDED RPM/MP SETTINGS FOR MINIMUM VACUUM HG FOR PRESSURE ALTS AT: 10000 FT; 8000 FT; 6000 FT; 4000 FT; AND 2000 FT. I COMPLETED RECORDING MY FIRST DATA POINT AT 10000 FT; 12 NM S OF ZZZ2 AND 3 NM W OF ZZZ; PERFORMED A WBOUND TURN TO THE N AND WAS ON A HDG OF 330 DEGS; WHEN I STARTED MY GRADUAL DSCNT FROM 10000 FT DOWN TO 8000 FT TO COLLECT MY NEXT DATA POINT. GLANCING OUT OF THE COPLT SIDE WINDOW; I SAW A LARGE HIGH-WING ACFT IN A HIGH ANGLE-OF-ATTACK; BANKING AWAY FROM MY ACFT. THE ACFT PASSED OUT OF MY VIEW WITHIN A BLINK OF AN EYE. I WAS ABLE TO DISCERN THAT THE ACFT WAS A LARGE HIGH-WING PAX ACFT THE SIZE OF EITHER A CESSNA GRAND CARAVAN OR A DEHAVILLAND TWIN OTTER. THE ACFT'S COLOR WAS RED/ORANGE ON WHITE. THE ACFT CLBED PAST MY PLANE WITHIN 150 FT. ZZZ IS DESIGNATED AS 'EXTREMELY HVY PARACHUTE JUMPING ACTIVITY;' WITH JUMPING ACTIVITY OVER THE E OF THE ARPT. MY GUESS; IS THAT THE ACFT WHICH MISSED ME BY 150 FT; IS/WAS ENGAGED IN SKYDIVING ACTIVITY AT ZZZ. DUE TO THE FACT THAT MY MOONEY IS A LOW-WING ACFT; LIMITS MY ABILITY TO SPOT CLBING ACFT FROM BELOW. DUE TO THE SPDS AT WHICH THE ACFTS PASSED; THERE WAS NO REACTION TIME ON MY PART. IN HINDSIGHT; I SHOULD HAVE BEEN IN RADIO CONTACT WITH CTR; FOR RADAR TFC SVCS. THE SAME HOLDS TRUE FOR THE LARGE HIGH-WING ACFT.

Data retrieved from NASA's ASRS site as of May 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.