Cessna 150
Flight Crew Commercial; Flight Crew Instrument; Flight Crew Flight Instructor
Flight Crew Last 90 Days 135; Flight Crew Total 1303; Flight Crew Type 350
Situational Awareness; Training / Qualification
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Weight And Balance; Inflight Event / Encounter CFTT / CFIT
Flight Crew Took Evasive Action
Aircraft; Weather; Procedure; Human Factors; Company Policy
I departed ZZZ for closed traffic and then pickup up an 80x40 foot advertising banner. Prior to my departure the owner of [the banner business] told me that no one had ever towed a banner this big with this aircraft. Based upon my experience with [this aircraft]; I expected it to do very well. I hooked the sign on the first pass and experienced a slower rate of climb. I was instantly told to return for a drop because it wasn't flying correctly. By the time I turned base I still hadn't reached pattern altitude but I believed it likely had to do with whatever was wrong with the sign. I dropped the sign in the grass without incident and returned to assist setting it up for another pick. While we were doing this; [the owner] asked me if I thought I was going to be able to pull it okay. I said; 'Yes; I think so; as long as it's okay for me to climb straight to reach 1000 ft prior to any turns'. He agreed with this strategy.I departed a second time for closed traffic; missed the first attempt and successfully picked up the sign on my second. The tower verified that the sign was towing straight but again I experienced a very anemic rate of climb. Despite some radio problems; I was given permission to pick up the banner and continue banner ops just using the hand held. However; since the throttle friction lock; allows the throttle to back off a tiny bit I never felt like I could abandon it under this poor performance to pick up the radio. I continued south as I said I would. I reached 300 ft and could not climb higher and struggled with this all the way. My airspeed was between 45 and 50. At some point I began experiencing a 200 FPM rate of descent. If something didn't change fast I was going to drop it. I cleaned the wings to zero flaps (was on 5 degrees) and zig zagged a little towards headings more favorable for wind lift or towards hotter areas for thermal assist. I continued south all the way to a point in where again I was unable to sustain altitude and the banner apparently clipped the top of a tree. I felt a light tug and turned to see some leaves falling. Later inspection by a fellow tow pilot revealed no damage to the sign. I successfully turned back north and eventually was able to climb to 600 ft and return to drop to the north. Apparently 80 x 40 ft is just too big for this airplane.My boss expressed his disapproval of my decision-making and insisted that I should have ditched the sign off airport instead of struggling to continue. There were perhaps eight to ten sites where I could have done so. Each time; the reason I continued was that it seemed to me that what I was doing was working and I was able to climb again. However; my gains were unsustainable and I was never able to get past 400 ft while heading south.The reason I continued south so far was that I did not want to diminish my vertical component of lift with the demands of a turn. When I later told this to [the owner]; he reminded me that turning is how banner tows slack the line and climb. In retrospect; I do remember hearing this during my training but it's not something we ever practiced with a drill of any kind and I never had it reinforced with any kind of reading. Perhaps it would have worked to some degree but the reality is this: that banner was too big for that airplane and the drag was too great. Based upon my limited experience with towing; I believed it would be up to the job. It definitely wasn't. Originally; I was trying to climb at 50 MPH with 5 degrees of flaps as I was trained. When that failed; I cleaned the wings to zero flaps and tried multiple air speeds to find that about 47 MPH produced the most climb.After the incident with the tree; I was over an obstacle free flat pasture area. This was another location where I could have safely ditched but again I was able to get it to climb. I slowly continued a slight left turn through the valley and started tracking back to the north. I tightened the throttle friction lock; pitched down a little and communicated to ZZZ Tower that there was a problem with the sign and I needed to return for a drop. They told me I was cleared to drop to the north and I did so without incident.I suspect [the owner's] inquiry about my ability to tow this banner with this plane reveals what he already knew: this was questionable and I was performing as a test pilot. In retrospect; I think we should have attempted it early one cool morning instead of finding out in the thinner air of an 80 degree day with 1360 ft density altitude. If permitted to continue to serve in this way I will not tow an 80x40 banner with this aircraft and if I ever face with the same scenario I will ditch the sign at the first suitable site.
C150 banner tow pilot reported operating with a banner that was much too large for the aircraft.