Date: 201309
Local time of day: 0601-1200
Location: FWA.TRACON, IN
Flight conditions: VMC
Weather elements / visibility: 15
Light: Daylight
Aircraft: PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Cruise
Airspace: Class E FWA
ATC / advisory: TRACON FWA
Aircraft component: Transponder
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Instrument
Human factors: Other / Unknown
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Aircraft; Environment - Non Weather Related; Human Factors
Primary problem: Ambiguous

Narrative: This was a daytime VFR flight. The route was JOT-V8-CGT-V422-BOONE-V422-OXI-V340-FWA-V144-. Over JOT at 3;500 MSL we requested flight following with Chicago Approach and were assigned a discrete squawk. At CGT we requested 5;500 MSL and were approved. We were then worked progressively by Chicago Center; South Bend Approach; and Fort Wayne Approach. We reported level at 5;500 on each check in; with no discrepancies between our indicated altitude (altimeter) and Mode C altitude squawk to ATC. Changes to the altimeter settings received from ATC while enroute were small and we were careful to enter each new setting upon receipt. After each change; both the new setting and our altitude were confirmed by my co-pilot/passenger; a rated and current Private Pilot. We fly together often and try to work as a team exercising good CRM. After being handed off to Fort Wayne Approach; but prior to reaching FWA VOR; we requested and were granted a descent to 3;500 MSL. This was to maintain VFR and stay clear of a scattered to broken cloud layer that was building ahead of us at about 4;000-5;000 MSL. After descending to 3;500 MSL we continued on course and crossed over FWA and the on-field FWA VOR with no issues. This is where the story gets interesting. We were about 15 minutes past FWA on V144 at 3;500. I was momentarily heads-down checking weather; while my co-pilot minded the flight controls and watched for traffic. Suddenly he blurted; 'Did you see that?!' I looked up; said; 'No' and asked him what he saw. He replied that he had just seen what looked like a 'flat black bar' flying head-on toward the airplane; which then quickly maneuvered and passed under the aircraft. I suggested that it was probably a bird; but my copilot was firm that it did not look like one. (He later noted; 'The object looked like a flat black bar with squared off edges and was extremely long and rigid. No bending of any kind as it dove under us. I've seen birds dive under the plane before and this did not seem the same. The profile never changed.') Since there had been no actual strike and things seemed otherwise normal; we dismissed the matter and continued our flight. But a short time later something peculiar began to happen. The fluid compass suddenly started to dip violently in quasi-rhythmic pulses. The card was being yanked downward in a pulsing fashion; all the way to its limits; while the azimuth oscillated 20 degrees left and right of course. The airplane itself was not bouncing around and the gyroscopic heading indicator was stable.  Only the wet compass seemed to be affected. In level flight and fully under control; we remained on course at 3;500 MSL. The panel mounted KLN-90B GPS and a centered needle on the VOR agreed as we tracked our outbound course on V144 from FWA. Several backup devices; including a Garmin portable aviation GPS and an iPad running ForeFlight; verified the panel equipment indications.  But the compass anomaly continued. We tried shutting down all on-board electronics including the portable devices but it had no effect. Nor did turning off lights; strobes; etc. We also tried Left and Right magnetos separately but it did not help. One thing we did not try but possibly should have done was to momentarily cut the alternator field and run solely on battery power. We were basically trying to think of anything that might create a magnetic field but we were running out of ideas. But with everything else operating normally; it seemed possible that the 6-month old compass might have simply just failed.Then another strange thing happened. Fort Wayne Approach called and asked us to confirm our altitude. We checked and confirmed 3;500 MSL. Approach then said they were showing us at 2;400 and asked us to check our altimeter setting. My co-pilot and I then individually cross-checked both our indicated altitude and the altimeter setting in order to be certain we hadn't misread anything. We agreed that we were definitely at 3;500 MSL and weconfirmed this back to Approach. (Our GPS altitude display also helped us confirm 3;500. And yes; we do understand the difference between GPS and barometric altitude). We then 'recycled' the transponder and verified our squawk code to be certain Approach was looking at the correct target. It had no effect. Approach reported that they were still seeing us at 2;400 MSL. We continued to fly for a few minutes but the ambiguities were beginning to stack up. My co-pilot and I were busy discussing options for terminating the flight when Approach called again to say they were showing us back at 3;500 FT. The thing is; we had never changed our altitude in the first place! Then - as if things weren't already weird enough - the compass then began to settle down. After few minutes was pretty much back to normal. In the end we elected to continue on to our destination. Along the way we received additional flight following from Columbus Approach and Indianapolis Center with no issues. The balance of our trip was uneventful; as was the return flight later on that day. At the time of this writing the aircraft is being checked out by an FAA Approved maintenance shop. The normal 24-month IFR checks were current for this flight (last completed in the spring of 2013) but everything including the compass is being evaluated. If there are any equipment problems we'll find and fix them. We don't know and will probably never know what my co-pilot saw or whether it had anything to do with the anomalies we experienced. We've speculated that it might have been a UAV (Indiana is currently vying to become a test ground for them); perhaps even some military contractor horsing around. Or maybe it was all just a creepy coincidence. It is almost Halloween.




Synopsis: PA28 pilot with pilot passenger report a UFO at 3;500 FT 30 NM east of FWA that may have affected the wet compass and the Mode C read out to ATC.