Date: 201304
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 60
Light: Daylight
Aircraft: Sail Plane
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Cruise
Airspace: Class E ZZZ
Aircraft component: Communication Systems
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Confusion; Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe; Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
Result: Flight Crew Returned To Departure Airport; General Declared Emergency
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: I and the pilot of the second glider briefed our cross country flight with the understanding that we would maintain 100 meter separation with each other ideally off to one side to double our chances of finding optimal thermals.   I received the communication 'I am following you' as we began our northeast leg at about 13;500 MSL.  Reliable communication between gliders was apparent on glider air-to-air frequency during this leg of about 80 KM.  After I announced 'now we are heading west' after our turn point from the 050 heading; I heard no further communication from the other glider; nor acknowledgement of my broadcast.  About seven minutes later; I scanned to my right; commenced a thermalling turn to the right and found myself in hazardous proximity to the second glider.  I immediately flew back to our departure airport; concerned that my fellow glider pilot had a physical or aircraft problem that precluded his answering my several subsequent radio calls.  Soon after the hazardous proximity event; I noted his aircraft straight and level; but then lost visual contact with his glider for the remainder of my flight.  As he did not respond to my calls; and I had no further visual contact with that aircraft; I broadcast on 121.5 a mayday concerning the lost or somehow disable aircraft.  I received no response on 121.5.  I landed routinely 20 minutes later; and the other glider only a minute later.  After examining my glider on the ground; it was learned that the speaker connection had failed sometime before the northwest turn point; so I could hear no transmissions.  I was unaware that the other glider had broadcasted that it was flying at various times at my 3:00; 6:00; and 9:00 positions to accomplish photos of my glider.   His broadcasts; I later learned on the ground; had requested that I maintain straight and level flight while he flew nearby; but these broadcasts were neither heard nor acknowledged.  For me the lessons have been:1. any transmission not acknowledged has not been heard.2. team flying should be conducted as per ground briefing agreements which should include contingency plans for lost radio communication.3. formation flying of any type should never be undertaken without reliable communication between aircraft.  4. see and avoid remains paramount in VMC flight; and team flying or contest flying gliders should be equipped with a rear view mirror within the canopy to allow sighting of aircraft directly behind and overhead.5. any aerial photography should not be done by pilot flying.6. equipment such as radios or speakers or microphone may fail in-flight despite proper operation before launch and during a portion of the flight.




Synopsis: Glider pilot reports lost communication with his wingman during a cross country formation flight.  Unable to communicate or see his wingman; a turn is initiated resulting in a NMAC.