Narrative:

I experienced a partial power loss during an IFR training flight with a student with whom I was giving instrument instruction. We were on an IFR flight plan at 6;000 ft in cruise. We changed the fuel selector valve from the both position to the right tank position. This was done so as to correct the fuel imbalance. We had taken on full fuel and were an hour into the flight (after completing a practice approach) when we switched tanks in cruise. I estimate that within 5 minutes of switching tanks; we experienced a power loss of roughly 500 RPM's. The engine was also running extremely rough and responded even worse with throttle changes. We ran through the emergency power loss in flight checklist; but this did not solve the problem. Next; I alerted ATC to our problem and coordinated a diversion to the nearest airport. I did not use standard phraseology in communicating the extent of the emergency; however; the controller was fully aware of the situation and approved the diversion. We landed; under power; and without incident. Despite the fact that there was no incident with air traffic; the situation got me thinking about all the 'what if's'. What if I had been in IMC in a more congested area? What if the radio frequency was full of chatter? What if the controller hadn't fully realized the nature of my situation? A definitive; 'mayday; mayday; mayday' or 'declaring an emergency' could have prevented any potential miscommunication and/or traffic issues. In retrospect; I would have made a different decision and would have declared the emergency over the radio with standard ICAO phraseology.

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Original NASA ASRS Text

Title: Flight Instructor and student on IFR cross country at 6;000 FT experience a power loss and divert to the nearest suitable airport. The reporter believes that he conveyed the urgency of the situation to the Controller but did not actually declare an emergency; which he regrets.

Narrative: I experienced a partial power loss during an IFR training flight with a student with whom I was giving instrument instruction. We were on an IFR flight plan at 6;000 FT in cruise. We changed the fuel selector valve from the both position to the right tank position. This was done so as to correct the fuel imbalance. We had taken on full fuel and were an hour into the flight (after completing a practice approach) when we switched tanks in cruise. I estimate that within 5 minutes of switching tanks; we experienced a power loss of roughly 500 RPM's. The engine was also running extremely rough and responded even worse with throttle changes. We ran through the emergency power loss in flight checklist; but this did not solve the problem. Next; I alerted ATC to our problem and coordinated a diversion to the nearest airport. I did not use standard phraseology in communicating the extent of the emergency; however; the Controller was fully aware of the situation and approved the diversion. We landed; under power; and without incident. Despite the fact that there was no incident with air traffic; the situation got me thinking about all the 'what if's'. What if I had been in IMC in a more congested area? What if the radio frequency was full of chatter? What if the Controller hadn't fully realized the nature of my situation? A definitive; 'Mayday; Mayday; Mayday' or 'Declaring an Emergency' could have prevented any potential miscommunication and/or traffic issues. In retrospect; I would have made a different decision and would have declared the emergency over the radio with standard ICAO phraseology.

Data retrieved from NASA's ASRS site as of April 2012 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.