Thorndike's laws of learning - Intensity: The more intense the material taught, the more likely it will be retained. A sharp, clear, vivid, dramatic, or exciting learning experience teaches more than a routine or boring experience.
I've been told that during the first 100 hours of dual instruction given, the CFI learns at least as much as his students. Today, we both learned something, and had a very beneficial post-flight discussion on emergency procedures.
After a routine briefing, preflight, enging run up, and taxi, I was prepared for another normal takeoff. After all, I've had 6 or 7 hundred in my life, many in the plane we were flying today. Of course, in hindsight the fact that the altimeter was 100 feet off could have been a clue to the coming excitement. As it was, the discrepancy made me think "I should tell the maintenance shop on Monday morning that the altimeter is off." 75' is the error allowed for instrument flight - VFR doesn't even require a sensitive altimeter, and it did seem to work.
During the takeoff roll, everything looked fine, and airspeed came alive just as it always does. However, after we cleared the trees I noticed that we weren't climbing. Sensing that our airspeed was high, and seeing a lack of climb, I was about to chide my student to fly the proper airspeed when I realized that the speed was actually lower than it should be. VERY LOW. Of course, the old joke that money makes airplanes fly wasn't too comforting, we needed airspeed and altitude, and weren't getting either. I asked if the throttle was completely open, and if the engine was generating maximum power, he said it was. We weren't climbing, and each time we tried to raise the nose, our airspeed bled off to extremely low levels.
About the time Mr. customer said "I think you had better take the controls" I said "my controls." The instant I took the yolk in my hand, I could tell that everything was OK. The stall warning was not close to going off, the controls were nice and firm due to proper airflow, and the engine was normal. Then the lightbulb winked on, ever so slowly in my head. I reached up and pulled open the valve for the alternate static source, whereupon the airspeed popped to life, altimeter twitched, and the vertical speed indicator showed a healthy climb. The entire sequence of events lasted for about 15 seconds, but it seemed more like minutes. For those that don't know, these three instruments are driven by air pressure measured at a tiny hole in the side of the plane. When this hole is blocked, the altimeter freezes and vertical speed goes to zero, while the airspeed begins acting like an altimeter - when you go up airspeed drops and when you go down airspeed increases. The alternate static is just vented to the cabin, which is almost, but not quite, equal to outside static air pressure.
Back on the ground, we checked the static port, and it did not look blocked. Best guess is that yesterday's hellacious storm blew some water into the static port, plugging it up. Later on in the day, a mechanic blew the lines out and the plane was completely normal - I even took a couple of nice teenagers for a discovery flight in it later this evening. The front seat passenger did a very nice job controlling the plane, and all had fun.
Other than the time I aborted a takeoff due to a minor radio issue, this is the closest I have actually come to a real "emergency." I'm sure the people back in the FBO suddenly became as anxious as I was when I radioed our immediate return to the runway (we later flew a normal pattern once the problem was sorted out). While my main job is to insure the safety of the flight, my other job is to be sure the student learns as much as I can get him to. I think now that he would have learned a much more valuable lesson (primarily self-confidence in an emergency or abnormal situation) if I had kept my hands off the controls. I'm not sure how I feel about the overall outcome or how I would do it next time - both things I need to figure out before my next takeoff. That said, we shared a productive "teachable moment" on engine out and partial power situations on the ground, I drew the connection that takeoffs like today's are exactly the reason we learn power-on stalls*, we grabbed another plane, and had our normally planned lesson.
I also met Tim again, and he would like me to go up with him in his new Cessna 177 Cardinal while he gets comfortable with it. The insurance co. doesn't care if the CFI has any Cardinal time after all. Cool! Appointment made after we couldn't fly today - the operating handbook was missing. He will bring it from home when we fly on Wednesday.
*power-on stall principles are how I knew we were completely safe the moment I took over. None of the signs of stalls or low airspeed (like mushy controls, horns, airframe buffet, etc.) were encountered.