11
$\begingroup$

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.

$\endgroup$
12
  • 7
    $\begingroup$ 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, 2016 at 22:49
  • 2
    $\begingroup$ 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, 2016 at 1:33
  • 2
    $\begingroup$ @Pondlife Maybe the performance charts aren't considered "limitations"? You can't suggest that it is illegal for an aircraft to depart when the outside air temperature is less than 0°C? If that were the case, GA operations would cease in colder parts of the earth during winter months, and FAA officers would have a field day at the local FBO... $\endgroup$
    – Ron Beyer
    Aug 11, 2016 at 13:00
  • 3
    $\begingroup$ 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, 2016 at 13:09
  • 2
    $\begingroup$ @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, 2016 at 14:57

3 Answers 3

3
$\begingroup$

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.

$\endgroup$
5
  • 1
    $\begingroup$ 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, 2016 at 3:03
  • 1
    $\begingroup$ 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, 2016 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? $\endgroup$ Aug 11, 2016 at 10:46
  • 1
    $\begingroup$ @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." $\endgroup$ Aug 11, 2016 at 10:50
  • 1
    $\begingroup$ 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, 2018 at 14:03
2
$\begingroup$

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.

$\endgroup$
0
$\begingroup$

Possibly not. The big problem here is 14 CFR 91.103(b)(1):

§ 91.103 Preflight action.

Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. This information must include -

(a) For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts, fuel requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which the pilot in command has been advised by ATC;

(b) For any flight, runway lengths at airports of intended use, and the following takeoff and landing distance information:

(1) For civil aircraft for which an approved Airplane or Rotorcraft Flight Manual containing takeoff and landing distance data is required, the takeoff and landing distance data contained therein; and

(2) For civil aircraft other than those specified in paragraph (b)(1) of this section, other reliable information appropriate to the aircraft, relating to aircraft performance under expected values of airport elevation and runway slope, aircraft gross weight, and wind and temperature.

Once you exceed the top of the performance charts (e.g. 40 ºC in a Cessna 172), you no longer have the required takeoff/landing distance data available to comply with 91.103.

Here's the takeoff data for a random Cessna 172. Notice that the notes provide a procedure for handling headwinds/tailwinds, as well as grass runways - but there's no procedure specified for temperature excursions.

If an FAA inspector asked you what your takeoff distance was on a 50 ºC day (and again, 91.103 requires that you determine this as part of your preflight), there'd be no way to authoritatively answer them.

Cessna 172 Takeoff Distance

This is a different story in aircraft that provide performance tables based on density altitude, as opposed to pressure altitude + temperature. You can compute the density altitude yourself for any temperature.

As pointed out in the comments below, one could argue that the FARs only require that you're familiar with the performance data. Whether that's referring to the performance data in aggregate, or the performance data that applies to your current flight conditions is perhaps a gray area. I don't believe the FAA has ever given more concrete guidance on this one.

(However, I have also seen flight schools take the opinion that operations above 40 ºC are not authorized for the above reasons.)

$\endgroup$
5
  • $\begingroup$ For which civil aircraft is an "approved flight manual containing T/O and landing distance data" required? Does that refer to all civil aircraft or only aircraft carrying passengers for hire, for example? I have no idea if this is the case, but I could imagine it being true that Cessna does not have to publish this data, and the fact that they do does not mean you must stay within the described bounds. $\endgroup$
    – randomhead
    Jan 25 at 2:14
  • 1
    $\begingroup$ @randomhead The general requirement for an "approved Airplane Flight Manual" comes from the airworthiness standards, specifically 14 CFR 21.5. More specifically, the content of the AFM for a modern, normal category aircraft is specified 14 CFR 23.2620. (Aircraft built before March 1979 did not have to have an AFM. In that case the format was less standardized, but you'd still have a POH and/or placards. Hence the alternative requirement for "reliable information appropriate to the aircraft" in (b)(2).) $\endgroup$ Jan 25 at 9:07
  • 2
    $\begingroup$ Hm, okay. But going back and looking at the actual wording, all it says is that the pilot must, before flight, become familiar with the T/O and landing distance data contained in the AFM. Okay, so it's 44 out, or M14, and the data is no longer relevant—but the FAR doesn't say the pilot has to be familiar with the relevant data, it says they have to be familiar with whatever data happens to be in the AFM. See the loophole? $\endgroup$
    – randomhead
    Jan 25 at 12:18
  • $\begingroup$ The bottom line is whether what you're doing is reasonable. If your chart tops out at a 5,000 foot takeoff distance, and the temp is 1 degree higher than the limit of the chart, but you are using a 13,000 foot runway, I think you could very strongly assert that the takeoff distance would be within the safety margin. I recognize that's an extreme example, but you probably see my point. $\endgroup$ Apr 2 at 17:34
  • $\begingroup$ @RyanMortensen While you're almost certainly correct about the safety margin, the question isn't what's reasonable, it's about what's legal. $\endgroup$ May 8 at 4:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.