Narrative:

It had been a cold day for texas; and I'd already canceled my first lesson for frost that had frozen on the planes overnight. Our school's deicing equipment consists of moving planes in/out of a heated hangar and/or waiting for the sun to melt any ice. While waiting at the flight school for my next lesson to start; I'd started working on homework. I'd gotten a standard weather briefing prior to the start of my first lesson; and didn't think much of the weather as the show-time for my next lesson approached. The email from FSS for the standard briefing. I spent more time than anticipated working on the school work; and barely finished the assignment I'd been doing right before my lesson time. The student and I had been trying to get in a review flight (unsuccessfully -- weather cancels) for an upcoming stage check several times. We had walked through the brief for the flight a number of times prior; so I rushed the preflight discussion and summed it up to something like 'we're going to do what we'd planned last time.'the student went to the plane to start the preflight; and I followed after using the restroom. I did not double-check the weather prior to walking to the plane. The briefing I'd received earlier that day had an airmet Z for higher altitudes; with a forecasted end time that aligned with my scheduled departure time for that lesson. This was obviously my first mistake. Upon return to the airport; I checked awc and found several key indicators that would have warned me of the conditions I was about to subject myself and the student to. I am confident in saying I would not have flown had I updated my initial brief. This was my first huge mistake and lapse in judgment. Once in the plane; we begin to experience some light drizzle. My student opted to turn on the pitot heat. I checked the OAT; and we were about 5 degrees celsius. As we climbed; the temperature stayed about the same. We climbed to 3500 ft.; leveled off; and I noted the temperature to be a few degrees above freezing. We were still getting the drizzle. I asked my student to descend back down to 3000 ft. In an attempt to get to warmer temperatures. Once we did so; the temperature was right at/above freezing instead; so we climbed back up to 3500 ft. At this point; I had started to monitor the AWOS of nearby airports (pez/cvb); in an attempt to find somewhere to work outside of the precipitation. Both airports were reporting drizzle and near-freezing temperatures. Around this same time; I heard another one of our training aircraft on frequency call san antonio approach and state they were returning to the airport. I told my student that we needed to do the same thing. We had pitot heat; cabin heat; and carburetor heat on; but at this point; we had acquired a decent amount of rime ice on the windshield. I could not see any on ice the wings but was worried that we might have a trace amount. We asked to return to stinson; were shortly directed to switch to the tower; and instructed to enter left downwind for runway 14. I let my student enter the pattern; then took the controls. I made a no flap landing with a target approach speed of 70 kts. I came in much faster though (about 80) and ended up high on final. I opted to forward slip the airplane down with the extra speed; then floated about 1/2 down the runway bleeding it all off in the flare. We landed without incident and turned off at the end of the runway. After clearing the runway; tower asked if we had encountered icing. I answered that we had in the practice area; and gave them a report on the drizzle and temperatures at various altitudes. There was no further communication between the tower and us during the taxi to park/shutdown. After stepping out of the plane; I immediately checked the wings and elevator. I did not see any ice; but at this point; most of what had built up on the windshield had already melted. I took responsibility for my error and explained to my student why I did what I did during the approach/landing. I did not fly for the remainder of the day; although conditions improved sufficiently.

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Original NASA ASRS Text

Title: C172 Instructor reported multiple errors precipitated by not thoroughly considering the weather prior to flight; then encountering icing conditions during flight.

Narrative: It had been a cold day for Texas; and I'd already canceled my first lesson for frost that had frozen on the planes overnight. Our school's deicing equipment consists of moving planes in/out of a heated hangar and/or waiting for the sun to melt any ice. While waiting at the flight school for my next lesson to start; I'd started working on homework. I'd gotten a standard weather briefing prior to the start of my first lesson; and didn't think much of the weather as the show-time for my next lesson approached. The email from FSS for the standard briefing. I spent more time than anticipated working on the school work; and barely finished the assignment I'd been doing right before my lesson time. The student and I had been trying to get in a review flight (unsuccessfully -- weather cancels) for an upcoming stage check several times. We had walked through the brief for the flight a number of times prior; so I rushed the preflight discussion and summed it up to something like 'we're going to do what we'd planned last time.'The student went to the plane to start the preflight; and I followed after using the restroom. I did not double-check the weather prior to walking to the plane. The briefing I'd received earlier that day had an AIRMET Z for higher altitudes; with a forecasted end time that aligned with my scheduled departure time for that lesson. This was obviously my first mistake. Upon return to the airport; I checked AWC and found several key indicators that would have warned me of the conditions I was about to subject myself and the student to. I am confident in saying I would not have flown had I updated my initial brief. This was my first huge mistake and lapse in judgment. Once in the plane; we begin to experience some light drizzle. My student opted to turn on the pitot heat. I checked the OAT; and we were about 5 degrees Celsius. As we climbed; the temperature stayed about the same. We climbed to 3500 ft.; leveled off; and I noted the temperature to be a few degrees above freezing. We were still getting the drizzle. I asked my student to descend back down to 3000 ft. in an attempt to get to warmer temperatures. Once we did so; the temperature was right at/above freezing instead; so we climbed back up to 3500 ft. At this point; I had started to monitor the AWOS of nearby airports (PEZ/CVB); in an attempt to find somewhere to work outside of the precipitation. Both airports were reporting drizzle and near-freezing temperatures. Around this same time; I heard another one of our training aircraft on frequency call San Antonio approach and state they were returning to the airport. I told my student that we needed to do the same thing. We had pitot heat; cabin heat; and carburetor heat on; but at this point; we had acquired a decent amount of rime ice on the windshield. I could not see any on ice the wings but was worried that we might have a trace amount. We asked to return to Stinson; were shortly directed to switch to the Tower; and instructed to enter left downwind for Runway 14. I let my student enter the pattern; then took the controls. I made a no flap landing with a target approach speed of 70 kts. I came in much faster though (about 80) and ended up high on final. I opted to forward slip the airplane down with the extra speed; then floated about 1/2 down the runway bleeding it all off in the flare. We landed without incident and turned off at the end of the runway. After clearing the runway; tower asked if we had encountered icing. I answered that we had in the practice area; and gave them a report on the drizzle and temperatures at various altitudes. There was no further communication between the Tower and us during the taxi to park/shutdown. After stepping out of the plane; I immediately checked the wings and elevator. I did not see any ice; but at this point; most of what had built up on the windshield had already melted. I took responsibility for my error and explained to my student why I did what I did during the approach/landing. I did not fly for the remainder of the day; although conditions improved sufficiently.

Data retrieved from NASA's ASRS site 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.