DA42 Twin Star
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 100; Flight Crew Total 825; Flight Crew Type 10
Training / Qualification; Workload; Communication Breakdown; Situational Awareness
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Air Traffic Control Provided Assistance; Aircraft Aircraft Damaged; Flight Crew Took Evasive Action; Flight Crew Diverted; General Flight Cancelled / Delayed; General Maintenance Action
Procedure; Company Policy; Aircraft; Staffing
The aircraft is a twin DIESEL engine Diamond DA42 which does NOT have the special adapter to indicate that it requires Jet A although it is placarded. Company had a disgruntled employee who despite the instructional aircraft being hangered at Company; placed AV Gas into the tanks. The school didn't have checks and balances on fueling and no new employee orientation. The tanks were 50/50 Jet A/Av Gas and we had burned approximately 1/2-2/3 of the Jet A when Company CSA noticed the 'wrong truck' number on the ticket; confirmed the lineman did indeed put the wrong fuel in and contacted Tower who told us we needed 'to return'. We were well outside Bravo and no communication reason was provided; nor that an [issue] existed. It was only by mistake that we had communication with anyone since we were well outside the Tower's airspace and the school has no flight following policy. Had ZZZ Tower communicated the [event]; we would have landed at ZZZ1 which was very close.  While enroute back; the Instructor used her cell phone to find out that AVGAS had been used to refuel the diesel engine tanks. Planning was then instituted for dual engine failure and potential off airport landing. At that point; ZZZ1 was the closest airport and the flight terminated without incident.  Diamond AC manufactures both diesel and AVgas singles and diesel twins with no gas intake modifications like turbines have to restrict or indicate type of fueling. This WILL happen again or the reverse with dire consequences eventually. Checks and balances on refueling on both the school and the FBO as well as US standards of fuel tank nozzles could also have prevented this. Sumping did nothing as AVGAS is lighter than diesel.
DA42 flight crew reported aircraft was deliberately serviced with the incorrect fuel; causing an immediate diversion.