Cessna 170
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 50; Flight Crew Total 18000; Flight Crew Type 200
Situational Awareness
Ground Event / Encounter Ground Strike - Aircraft; Ground Event / Encounter Loss Of Aircraft Control
General None Reported / Taken
Airport; Human Factors
I was instructing a student pilot/owner in his Cessna 170B; doing grass field landings at several local strips. I had the student do an overhead recon to [a nearby field]. As we crossed over mid-field on the grass runway; the student entered a left down-wind pattern to land to the northeast. The runway was on his side (left) of the aircraft as we maneuvered.The student crossed the tree-lined river that borders the southwest end of the strip on airspeed and slightly high with sufficient runway to stop. After touchdown on the main gear and while rolling out I observed an area of high grass (the rest of the strip appeared to have been recently mowed) about 100-200 feet in front of us with a narrow path mowed around the high grass to the left.I had not been able to observe the high grass as we flew overhead due to my position in the right seat. I started to steer the aircraft toward the mowed pathway but entered the tall grass and we immediately began to decelerate. I took control of the aircraft; applied full aft yoke to hold the tail down and full throttle; trying to power out of the tall grass to the mowed area beyond. The aircraft came to a stop in a tail-high attitude with the nose resting on the ground. After completing the shutdown of the aircraft; we exited to find ourselves in deep mud as the high grass was a very wet swampy area. There was no markings such as tape or signs or any barriers to denote the hazardous condition of that part of the runway.In retrospect; I should have had the student position the aircraft as we did the overhead recon so that I would have been able to view the entire runway to evaluate its condition. I feel the airstrip owner bears some responsibility for not having marked the hazardous part of the runway. The local aircraft operators may have been aware of the hazards but someone not intimately familiar with the strip could fall prey to the same situation.
C170B Instructor Pilot reported the aircraft nosed over following a landing on a marshy grass field.