When Paul Leckman took over the C-337 project test pilot duties, he performed a very important research program on airframe icing. Previously, he had done similar testing on the C-T210. Of paramount interest was the effectiveness of various types of deice equipment on rate-of-climb. When pneumatic deice boots are used on the wing and stabilizer leading edges, the climb performance decrement is less than that caused by the use of a propeller anti-ice system alone. This points out that climb performance is decreased more by the lack of deice boots than the lack of anti-icing provisions for the propellers. Testing was performed behind a C-411 water tanker and, when conditions permitted, in natural icing in the clouds. Paul prepared a Society of Automotive Engineers Report No. 710394 entitled "Qualification of Light Aircraft for Flight in Icing Conditions."  He then presented this important paper at the SAE National Business Aircraft Meeting in Wichita, Kansas on March 25, 1971. As mentioned earlier, that paper also included very comprehensive icing test results on the C-T210 models. As a prudent practice, our company pilots never entered suspected icing clouds unless the Skymaster was equipped with full deicing equipment, and, perhaps most important of all, turbocharged engines. These airplanes were not approved for flight into known icing conditions.

The accident rate of the tandem-twin Skymasters has been skewed rather unfairly by careless pilots failing to make pre-take-off engine checks. If their rear engine has died during prolonged taxi operations in hot weather, they sometimes attempt a take-off with only the front engine operating. Thus the takeoff run is extremely long, and climb-out (if possible) would be difficult at best. Cessna Service Letter ME71-21 dated August 18, 1971 warns owners about this possibility with the following paraphrased instructions: