Originally Posted by
megan
That's completely at odds with what Cessna Wichita have to say, if the temperature is greater than depicted on the chart for the specific altitude you may calculate the density altitude then use the temperature and altitude which will give the same density altitude. The example I used when I communicated with them was for a C404 take off distance at sea level on a 50°C day which gives a DA of 4,200, but the chart only goes to 40°C. Going to 40°C and pressure altitude of 1,000 gives a DA of 4,238, they deemed that an acceptable technique. Aircraft and engine performance is all about density altitude.
Hence the conversation earlier that if the manufacturer does not expressly permit operating beyond the lines and how to do so you may be in trouble in an accident that is performance related.
PS the other issue at play is at what temperature do you stop extrapolating, at some point the engine and accessories will not be able to cope with the heat and power will reduce significantly more than linear, parts will start to bend and bloat due to the heat, maybe even melt, fuel will form vapor locks and so on. We had one PA28 that was painted black and it it's wing oil canned above 30c due to expansion, was disconcerting for pilots when metallic noises came from the wing, good reason not to paint things black when it's hot. While Cessna and Piper don't give an environmental envelope it's pretty obvious that over ISA +20 all piston engines start to struggle. The opposite applies at low temperature below ISA -20 plastics and rubbers start to become rigid and not return to form or become brittle and tear and not flex, oils and lubricants become thick, that's before even considering ice on the airframe.
Chieftains and Navajo engines really don't like the high 30c and 40c, have to use cowl flaps to manage heat and that reduces performance significantly. If you then had a failure the engine is most likely going to overheat at MCP pretty quickly, leaving you with the choice of cook it or descend.