PA-38 Tomahawk
Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 177; Flight Crew Total 445; Flight Crew Type 75
Time Pressure; Troubleshooting
Aircraft Equipment Problem Critical; Deviation - Speed All Types; Ground Event / Encounter Loss Of Aircraft Control
Flight Crew Landed in Emergency Condition; General Maintenance Action
Aircraft
Upon completing a simulated soft-field landing with the student at ZZZ; I instructed that we will immediately add power and perform a takeoff; as we were working on precision takeoff and landings and flying in the traffic pattern the entire time. After lifting off the runway the airplane entered ground effect and I instructed the student to continue flying in ground effect until we gained sufficient airspeed to continue climbing from the runway environment. Once in ground effect I noticed an engine performance problem; and we were no longer gaining airspeed. After hearing and seeing anxious reactions from the student I ordered; 'My controls;' and I took control of the airplane. At that point I confirmed full throttle; checked outside visually to see the end of the runway approaching; and tried maneuvering the airplane to gain minimal amounts of airspeed. When I let the nose down to gain airspeed the airplane did not respond in the manner it should have; and we began to sink. I accepted that the airplane was not responsive to the amount of power applied; and made the decision to continue with the sink toward the ground. At this point the airplane was past the end of the runway and I saw grass ahead that was towering over my line of sight; meaning that we were about to impact the ground very soon. The touchdown in the grass was very smooth; as I teach all students and myself that soft-field landings must be treated with the utmost amount of precision. After touching down in the grass past the runway; the airplane struck an embankment/ditch though I was still able to have full directional control. The airplane came to a stop in tall grass and I repeated many times to the student; 'leave everything and exit to the rear of the airplane.' I made a call saying; 'ZZZ traffic; Aircraft X down;' secured the airplane; and exited immediately.
Instructor stated the aircraft is still sitting and no action has been taken or determined as to the cause of reduced engine power.
PA-38 instructor pilot reported that aircraft developed less than full power on takeoff resulting in off field landing.