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Most Cessna aircraft have performance charts the range from 0 to 40 Celsius. I've had a CFI tell me that the FARs prohibit flight if the OAT exceeds 40C or whatever is shown on the performance charts. Is that a true statement? I have not found anything in Part 91 that addresses this.

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    $\begingroup$ Did you ask him if all those Cessnas in Alaska are flying illegally because the chart doesn't show anything below zero? $\endgroup$ – Pondlife Aug 10 '16 at 22:49
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    $\begingroup$ Very, VERY closely related question: Is there a maximum airfield elevation in which a Cessna 172P can operate? $\endgroup$ – Lnafziger Aug 10 '16 at 22:52
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    $\begingroup$ I cannot find any FAR regulation that prohibits flight outside of performance charts. Another point against this is demonstrated cross-wind, you can land (legally) when the cross wind is greater than the demonstrated cross wind in the performance chart. In fact, the manual states that this is not a limitation... $\endgroup$ – Ron Beyer Aug 11 '16 at 1:33
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    $\begingroup$ For Cessna's, Section 2 of the POH contains the operating limitations, FAR 91.9 prohibits operation outside of those limits. If it is not stated as a limitation in the POH, then it shouldn't be illegal to operate outside those ranges. I've read a couple POH's for 172's and I can't see anything that prohibits operation outside of a certain temperature range. The manual suggests that you shouldn't operate more than 23°C above standard temperature, but doesn't state it as a limitation. $\endgroup$ – Ron Beyer Aug 11 '16 at 13:09
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    $\begingroup$ @RonBeyer Yes, and that was exactly the point of my comment above about Alaska: clearly the fact that no data exists is not by itself a limitation. However, your response to Lnafziger on a different point was that it's legal to "fly outside" a specific, certified limitation of the aircraft, and I don't see how that can be possible per 91.9. $\endgroup$ – Pondlife Aug 11 '16 at 14:57
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Yes, it is legal, disregarding any catch-alls such as 91.13 reckless operation or ones pertaining to pre-flight planning data like takeoff distance.

It is simply left to the pilot's good judgement for a go/no go decision depending on whether or not the flight can be completed safely.

Edit: Re-reading this answer much later, I would like to emphasize, "disregarding any catch-alls".

With regard to the catch-alls such as 91.13, this could very easily be considered illegal, but no rule with a statement clearly identifying taking off with temperatures higher than those on the charts as a prohibited action exists to my knowledge. Do not do it.

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    $\begingroup$ What do you base this legal opinion on? If you do not have performance numbers, how do you know that you can safely takeoff and climb under those conditions? $\endgroup$ – Lnafziger Aug 11 '16 at 3:03
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    $\begingroup$ You're shrugging off 91.13 as if taking off in uncertain conditions wouldn't constitute "reckless operation". I would argue that taking off when you can't be certain of your ability to climb would be quite reckless, and 91.13 may likely cover it. It would be good if you could cite something to prove otherwise. $\endgroup$ – Jay Carr Aug 11 '16 at 3:46
  • $\begingroup$ @Lnafziger me? I wouldn't. Somone with decades of experience and thousands of hours in type could make a determination based on experience. How far over the limits? 1 degree? 2? 50? $\endgroup$ – Ryan Mortensen Aug 11 '16 at 10:46
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    $\begingroup$ @JayCarr no, I'm not, and that's why I mentioned it in the answer. Shrugging it off would be to completely ignore it and not include it here. However, I understood what the asker is really asking, which is whether there is a rule that specifically addresses this particular situation, taking off at a temperature above those shown on the aircraft's charts, directly, which 91.13 does not. Hence the phrase, "disregarding any catch-alls such as 91.13." $\endgroup$ – Ryan Mortensen Aug 11 '16 at 10:50
  • $\begingroup$ I have personally certified equipment for operations in a 172 in the range of -7 to 60c. This is the range that our vendors deemed safe for operation of their combined fleet of about 80 Cessnas. Note that although it was a commercial operation, some of them flew under part 91 due to a loophole, while others flew under 135. Having said that, we had a pilot overload his plane, take off at 45C and crash, losing his cert over 91.13. $\endgroup$ – user28387 Apr 12 '18 at 14:03
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It is legal, though not recommended as aircraft performance has not been fully quantified in this regime of the flight envelope. As pilot in command, you have the final authority to decide to proceed here. Keep in mind, however you could be held civilly liable should an accident occur under these conditions.

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