Having a discussion elsewhere about the usage of FAR 23 performance charts. The PA31-350 Piper Chieftain for example the charts only go to 35°C for a normal take off, where I live the temperature is always in the range of 34-37 (tropics), other areas of Oz can reach a high of 49° (I've experienced it), so the question is how do you legally address performance if the temperature is beyond the chart limit? Some in the aviation community consider the the charted temperature to be a limit, so the Chieftain can't legally take off if the temperature is greater than 35°C.
I've sent a message to Piper asking the question but yet to receive an answer.
Cessna tells me the following approach is acceptable, they regard the charted maximum temperature as being what the aircraft was tested to and is not a limit, and regard the density altitude calculation below as acceptable.
Calculate the density altitude and then extract from the performance graph a pressure altitude and temperature that gives the same density altitude.
For example: 50°C at zero pressure altitude gives density altitude of 4,200 feet. 30°C at pressure altitude of 2,000 feet gives a density altitude of 4,275 feet.
50°C doesn't fall within the Chieftains performance take off chart, but 30°C does.
An interpretation of (b)(2) talking about limitations is difficult to understand, given no limitations listed in that section of the flight manual. Interesting to note the lack of consistency in the manuals of various manufacturers, Chieftain 35°C, Cessna Titan 40°C (but engine out climb chart goes to 50°C), Beech 58 52°C..
§ 23.2105 Performance data.(a) Unless otherwise prescribed, an airplane must meet the performance requirements of this subpart in
(1) Still air and standard atmospheric conditions at sea level for all airplanes; and
(2) Ambient atmospheric conditions within the operating envelope for levels 1 and 2 high-speed and levels 3 and 4 airplanes.
(b) Unless otherwise prescribed, the applicant must develop the performance data required by this subpart for the following conditions:
(1) Airport altitudes from sea level to 10,000 feet (3,048 meters); and
(2) Temperatures above and below standard day temperature that are within the range of operating limitations, if those temperatures could have a negative effect on performance.
Many thanks All.
