Typical prune thread......

Yes: Interesting and widely read.

I can remember 'hearing' of an occasion where a PA31 arrived at an airfield in SW Queensland, and the OAT on arrival read 52C, having just 50 minutes previously departed another airfield to the south of the aforesaid airfield where. it was alleged, that the Temperature was at a somewhat similar level.

Oh, and the thermometer out the back of the Pub read 55C. Or so the story went.

How indeed did they manage such a thing?:confused:

Pretty simple, it has oodles of power to cool the pilot probably up to 60c with both fans running. If one fan stops for a break outside gliding distance to an airport its probably plowing potatoes while the pilot sweats heavily. There was an ATSB enquirie into why Navajo's could not maintain height when they should following an engine failure, was in the 70s I think, will have to dig it up, although not sure where to dig up the old BASI reports from ancient history anymore.

I think you’ll find them in a link in the thread north of this one ^^^^^.

It does per the rules of the game, FAR 23 as at the time it was certified - any limitations must be stated specifically.

Certification rules are very specific on the substantiation of engine cooling. The Type Inspection Report provided to the FAA would answer your doubts.

The problem is there is obviously a limit to operation temperature wise. The FAA can state there must be a limit, but in a civil court you will be questioned on whether or not your decision to fly created a liability that was not covered by the manufacturer. If you extrapolate data to consider flying at 50C when the chart ends at 35C you are basically taking on the liability if something goes wrong. That is in Pipers view anyway. It may also be the case with Cessna, in that they can say, 'yes, that will probably work' but unless there is paperwork that says how to and that its endorsed by the manufacturer you will probably be on your own in court vs the families of the injured.


The case I was referring to was post accident, Piper says it considers the lines the tested limits, or more precisely the end of their liability. Somebody else could measure lines further out and take on that liability if they so wish, so it's not a limitation for the aircraft in general. So I take in the case of the Cessna operator, Cessna says in theory your working is sound, however if you then crashed they will just point to the AFM charts and say we don't endorse flying beyond the lines and they had come up with their own methods to extrapolate data. There is a big difference between an OEM saying yes that will work, we don't see anything wrong with your idea and providing written support that it is approved.


I can think of several instances where engineering fixes were applied to a certain manufacturers aircraft when it had issues under approval from them that it was possible. When it came to claim a defect unrelated under warranty the said manufacturer disowned the aircraft and said it had too many modifications now to be considered for cover.


The big question to always ask the original manufacturers are 'is this an approved method where I will be covered in an accident' and 'will I still be covered by warranty if I do this'. If you don't ask these specific questions you will just get, 'yeah looks OK to me, fill ya boots'. There is a difference between capability and legal liability. Remembering that the OEM will not want any responsibility for an accident.


And in short the question will be asked at what point would extrapolating data not be ok, there is obviously a limit somewhere. Cessna and Piper will probably always fall back on that they designed the aircraft for normal environmental conditions, 50C would be beyond that for sure. I know a lot of transport aircraft that have 50C as the environmental limit, they can still perform well at that temp, just a lot of other things are not countered for, which is not specified as why that's the limit. I've operated turbine aircraft in the high 40C region, but had specific data for the performance, they performed fine for the charted performance limits.


So the question is, is it legal to fly using extrapolated data, yes (in a grey area), will you be safe in a court of law if you have an accident where persons or property are damaged, probably not.

Comes back to the old car adage of driving to the conditions. You can be driving below the speed limit, but if you take a wet corner and slide off the road you were not driving to the conditions. Your passengers will claim compensation under your name and so on, luckily in Australia its CTP and liability Insurance.

The Chieftain flight manual offers absolutely no advice on what the operational temperature limit is. The normal take off chart only goes to 35°C and the single engine climb to 37°C, yet the performance section preamble says for single engine climb at 38°C (100°F) increase climb speed from 106 to 110 kts, if you encounter 38°C at altitude then logic says the ground temp is higher than 38°C.

The 100°F is mentioned because of FAR 23.1043(b) — Cooling testsAs Cessna says, the performance charts represent what the FAR 23 aircraft was tested to, they are not limits, and calculation with respect to density altitude, if conditions of pressure altitude and temperature are not charted, is acceptable.


https://cimg2.ibsrv.net/gimg/pprune....79a7001b88.jpg

That's because as it states in the second paragraph the FAA only requires it be proved that it can maintain/climb at 5000ft and not exceed engine limitations on a 100F day (that being 100F at SL). The limitation would only be imposed in the limitations section if it had a temperature limit that curbed it's performance below FAA certification limits. Piper then provides no guarantee that above 100F SL temps that the aircraft will perform, so the pilot is entirely responsible past that point.

That statement is critical, it says "until on a 100F day" that does not say beyond a 100F (37.7C) day. One that means we only cover the performance data up to 100F (37.7C) at SL, beyond that you do not even have the IAS to maintain engine limits, but it will be higher than 110Kts. That is we did not test it beyond that, good luck, have fun, you are on your own if you crash. So two things at play here, you are having to increase speed to MAINTAIN cooling of the powerplant, higher speed means less climb, and also the density itself will reduce performance. BTW 37.7 is the critical temperature, as 38C is beyond the stated figure.

Again its a liability issue, not so much a legal limitation issue, you will find out if you are correct when in court, which as I said earlier has already been tested in the US and Piper has already made a statement that the lines are the end of the tested envelope so they hold no responsibility for performance beyond that.

I'm not up to speed with FAA certification, but there's probably a reg about operating outside of certified performance criteria, so if piper was required to test within an environmental envelope, then that envelope applies, without them having to state it as a limitation. Maybe that's where a firm answer lies, or maybe the regs allow you to make your own decision and generate your own data should you wish, at your own risk of course.

PS from what I read on US sites the FAA gets you under 91.13 or 'reckless operation of an aircraft' if you crash due to lack of performance at high temperature. Which is usually combined with being overloaded for the conditions.

As my instructor was fond of saying, "beyond that you're the Test Pilot.. do you really want to be a Test Pilot??"

Except that a test pilot will be doing the test flying on behalf of someone in controlled circumstance with hopefully as much data on what's about to happen as possible.

The average pilot straying into test pilot territory probably doesn't know at all why they are there or how to get out of the situations they are suddenly presented with (post turtle phenomenon). If they did have half a clue, they wouldn't put themselves there in the first place, something about superior pilots and all.

43, yes, but you can get out of a place like this if it is possible to design and fly a timed terrain clearance procedure with wind limitations, prove that it works by a sufficient margin in Day VMC, then maintain currency by doing every day departure the same way if circuit traffic permits it. Scone in NSW comes to mind. Not for the faint of heart.
You may be right about the a fortuitous engine failure ! :8

I sent this follow-up inquiry to the CASA Guidance Centre this morning:

CASA's answer:No acknowledgement that they got it wrong back in January 2023, though.