Date: 201308
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Piper Single Undifferentiated or Other Model
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Initial Approach
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument
Human factors: Communication Breakdown; Confusion; Situational Awareness
Anomaly: Conflict NMAC; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I was approaching [the airport] from the northwest. My plane; a PA-15 only cruises at 80 KTS and has no electrical system. Communication is with a handheld radio with external antenna. ATIS reported Runways XX Left and Right were in use. I called Tower at 10 miles out and was told to expect [Runway] XX and call back again 3 miles out. Another plane called Tower; reporting his position. I missed where he was and called Tower to confirm the other plane's position. He reported his position in my area. I reported again at 3 miles out; setting up for a left downwind for XX Left. Tower requested position of both planes. I reported where I was and at an altitude of 1;200 FT. The other plane reported a similar position at 1;500 FT. When I learned to fly at [this airport] many years ago; pattern altitude was 1;200 FT. I have since learned it is now 1;500 FT. When I was entering left downwind; the other plane also reported downwind. Right after that; the other plane flew right over the top of my plane at a wingspan or less to the right. It's hard to judge actual number of feet but the altitude difference was very little. There was some confusion on the part of the other plane which runway he was supposed to use; but finally understood to take XX Right. I was cleared for XX Left. After landing I turned right; off XX Left on to taxiway Bravo which parallels Runway YY. The other plane turned left off XX Right on to taxiway Bravo. I was told to taxi along Bravo to FBO ramp. The other plane was told to turn right on another taxiway then left on to runway YY and taxi along runway YY until he passed me; then left to his parking. The other plane did not initially respond to; nor comply with his taxi instructions; so Tower again advised him to turn right and taxi out to Runway YY then left on YY and taxi on that runway. The other plane did as instructed; but did not read back taxi instructions before entering runway YY. Tower did not request plane to read back his taxi instructions. I taxied to ramp; refueled; then called for departure. Before I took runway XX Right for departure I asked Tower if he thought the other plane would have flown so close to me on downwind if he had seen me. Controller said he thought the other plane never saw me. In hindsight; I now know I was at the wrong pattern altitude for [this airport]. I also know that since my plane is so slow; and always in danger of getting run over from behind; I should have gotten a better idea where the other plane was as soon as he reported his position in my area.




Synopsis: Two General Aviation pilots operating in the pattern of a Tower controlled airport experienced a Near Mid Air Collision when they could not make visual contact. One pilot mistook the pattern altitude and the other misunderstood the runway instructions.