How do you feel about a "Normal Procedures" takeoff

In the first instance, quite obviously, I can't recommend it. However, for me, I don't have a problem for my takeoff and am comfortable that I can argue the toss were push to come to shove. In any case, I prefer to follow the POH data and OEM recommendations for light singles to avoid the problem.

If the POH doesn't have any data relating to a configuration/speed schedule, then the pilot is on his/her Pat Malone if choosing to operate in such a manner. If one isn't able to justify the activity, perhaps one ought to fly it as appropriate for whatever charts are extant ?

The big boys don't fly when it's over the limits I imagine their charts are compiled somewhat differently

The charts are more complex and cover considerably more concerns. However, at the end of the day, the two areas have their similarities

and they fly the chart speeds every takeoff and landing.

Indeed .. and I really can't see why the light aircraft can't be operated with a similar philosophy ?

Not to mention things like derated takeoffs that require more runway, V1 speeds etc. - they mean that the performance calculations are more critical.

All the numbers are critical if the operation be limiting. However, there is no a priori reason why data for the heavy need be more accurate than for the light .. other than the cost of development consideration.

and you find yourself consulting the charts

as one should, unless the data be the same as a previously determined case.

I would certainly be cautious about exceeding the temperature range.

Indeed, as would I.

What is the applicable rule? How is that rule applied to each parameter?

As we both know, there is none. Ergo, the second concern is moot. Equally, both you and I are able to generate a reasonable argument to cover reasonable excursions.

I probably ought to have kept my peace and not posted .... ?

Where do CASA's declared density altitude charts fit into all this, they don't mention temperature

I think they are an historical anachronism which hasn't yet been consigned WPB, round.

if an aircraft's AFM caps performance data at 40C

One ought to be VERY cautious when it comes to extrapolating temperatures .. OAT affects both airframe and engine and, in the absence of specific data relating to both, especially the engine, it can get rubbery .. quickly.

This is one of those - sadly increasingly common - occasions where I wish I had the rest of my flying career (~20 years) behind me, not in front of me.

Isn't that the case ? Guess I'm closer to 30 years older than your good self, then.

On topic...


http://www.abc.net.au/news/2017-06-2...ights/8637278u


kaz

Kaz, That's coming up: "SORRY, PAGE NOT FOUND." for me.

Arizona flights grounded as temperatures set to soar to 50C in extreme heatwave
Updated yesterday at 5:20pm

Arizona flights grounded as temperatures set to soar to 50C in extreme heatwave - ABC News (Australian Broadcasting Corporation)

I'm not sure whether you're recommending flying the performance chart speeds or the recommended speeds? They are different.

Cessna seems to have recognised that most of the time, the 172 will be flown off more than adequate runways.

When the is doubt about runway length, they assume that short field procedure will be used and that is what they use in the charts. But they do not recommend short field procedures for normal operations - the normal procedures presumably have more safety margin.

Cessna also seem to assume that pilots are smart enough to figure out when runway length might be an issue.

What temperature do you use for performance calculations when operating into a location without a forecast?

It's just the laws of physics, and they are in fact well understood.

I'm not sure whether you're recommending flying the performance chart speeds or the recommended speeds? They are different.

Granted. If one doesn't have performance data, then there remains the problem of justifying the takeoff/landing post mishap. I am comfortable with both approaches but I have an appropriate engineering background to do some approximate sums to keep myself sweet.

Cessna seems to have recognised that most of the time, the 172 will be flown off more than adequate runways.

Aye, there's the rub. At what point does one perceive a problem ?

Cessna also seem to assume that pilots are smart enough to figure out when runway length might be an issue

One would hope that pilots are appropriately conservative so that such would be the case.

What temperature do you use for performance calculations when operating into a location without a forecast?

At present, the declared data is fine. Also, the BOM site data provides quite useful information. Apply whatever conservatively and, where feasible, carry an alternate to somewhere with forecast data. I really don't see a problem with this one.

(Guess it's not all that much different in principle to detailed software development work.)

Out of interest, I haven't read everything in this thread but note a lot of people choose the Common sense approach of extrapolating data for higher temps based on the data in the POH.

A lot of newer Aircraft seem to have a Temp Limit, when you extrapolate the Data though to beyond that Temp Limit the Aircraft could still perform when doing so, but there is still this limitation.

If you extrapolate beyond the data presented, how do you know for certain that it will perform?

When designing W&B Programs in the past using Excel for various Aircraft I've often noted that a lot of Aircraft don't follow simple extrapolation, they require complicated Polynomial Equations to be able to do so, something beyond I'd say the vast majority of Pilots and unless you evaluated the entire data set you would never be aware of it, how are you certain that beyond the 40 degrees performance data stated in your POH that Performance of the Aircraft wouldn't start to significantly decrease at say 45 degrees and beyond?

lot of people choose the Common sense approach of extrapolating data for higher temps

.. if you don't have the engine data sets, in particular, you have not much idea at all of what happens at higher OATs other than presumptions based on general principles. Extrapolation into the higher OATs is not a routinely good idea, I suggest.

how are you certain that beyond the 40 degrees performance data stated in your POH

I would think one would have very little idea of what might happen.

Re the W&B considerations, I presume you are referring to the usual sloping limit lines on the weight x CG envelope ? They will only be first order there and, if one uses the weight x moment presentation, quadratic .. but, for a computer solution, why would you bother with the latter ? Not a big problem, I would have thought ?

In the Cessna 404 manual take off and landing tabulated data only goes to 40°C, however climb data, both dual and single engine, goes to 50°C.

How can we say 40 is the operational limit because the take off chart only goes that high, but climb data goes to 50?

I would have thought a prudent pilot would work backwards from the climb charts. Ensure s/he could reach the required gradient at temps between 40 and 50, and then from the take off chart determine the distance from a density altitude calculation.

All the Cessna manuals I've seen have a preamble to the performance section which says,Notably the preamble also says the performance information allows planning with reasonable accuracy, not exact, as the preamble again says, it assumes "using average pilot technique (however you quantify that) with an airplane and engines in good condition". I don't see how using DA when temp is 40< to extract T/O data transgresses any rule, regulation etc The climb charts would suggest that 50°C is the practical limit, because that's as far as the chart goes. Why else have the climb charts go to 50 if take off is limited to 40? Inversion? Where do you source that data?

john tullamarine, I should have been more specific, in a lot of my W&B Programs I've also included the ability for it to give you the TODR, LDR etc...etc..., was referring to those requiring Polynomials, not the CofG graphs and such. I agree entirely on your first point in response to my post.

megan, I understand what you're saying, but how do you know how the Aircraft will perform when above the 40degrees? You can extrapolate but you're assuming that the trend is continuous, perhaps after 40 degrees the Performance will decrease markedly?

I think we can all acknowledge that aircraft will have a temperature limitation, whether it's been put into your POH or not, it's common sense, eventually there has to be a temperature beyond which it's just not safe to be operating the Aircraft! Without the data showing this point how do you know where it is?

Most POHs/AFMs won't have it because, I'd suggest, they simply never tested it under extreme conditions above 40 degrees and therefore don't have the data. For all our fancy tech and know how it seems to be most of the information we have from our Manuals really came from someone jumping in the damned thing and taking it for a flight to figure out what will happen. I know it's more complicated than that but essentially that's what the data in them all boils down to.

I'm not saying that I necessarily agree with CASAs interpretation, BUT, I believe we all need to be reminded that if you choose to use your Aircraft without any proven data from the Manufacturer or another reliable source, you've basically just become a Test Pilot.

IMHO that really needs to be the biggest take away from this whole idea, extrapolation is fine and gives you a guide but you need to be prepared at some point to say "I don't know" when trying to decide if your Aircraft can comfortably and safely operate at such extreme temperatures and from there either seek the information from someone reliable who DOES know (Not just Joe Bloggs who has taken off tons of times at 45 degrees!), then if you can't get that data, perhaps it's time to sit back and wait for a few hours for things to cool off?

We do know how the aircraft will perform in the climb up to 50°C, both dual and single engine, because the manual has a chart giving the performance up to that temperature with no extrapolating involved. It's data in the flight manual, provided by the manufacturer.

Why have a chart giving the climb data to 50, if 40 is the limit for take off? Why would the manufacturer go to the expense of developing that climb data?

Edited to add: The SR22 take off data goes up to 50°C, and the preamble includes the noteDifficult then to see how the temperature on the take off chart can be considered a limit.

I've also included the ability for it to give you the TODR, LDR etc...etc..., was referring to those requiring Polynomials

Without knowing what you have done in the past, I can only speculate. However, if one (as I suspect you are doing) intends to represent the physical charts by a computer implementation, there are three basic ways to go about it (with the test for acceptability being the delta between model and AFM data set .. not much in the way of linear data in the AFM)

(a) first principles .. too hard to figure the empiricals to get adequate accuracy so one leaves this for the OEM .. as in the EFB etc implementations these days

(b) polynomial regressions. Generally, too difficult to run multivariate regressions and achieve adequate accuracy so the usual way is to run single regressions for the printed lines and then either run interpolations or on the fly regressions for between line points .. great fun .. been there ... done that for a number of AFM data sets with very high accuracy albeit with the attendant boring slave labour to make it all work OK .. especially if the data set has numerous discontinuities .. painful. I presume this is the way you played with the stuff ?

Big potential for getting the fingers burnt with extrapolation, though, depending on the order of the the equation and what antics it produces in the extrapolated region where one doesn't have data points to constrain the regression .. one can guard against this but, in general, a risky business.

(c) interpolations, commonly splines. Useful for small data sets but I always preferred setting up the regression analyses and go from there.

how do you know how the Aircraft will perform when above the 40degrees?

The main concern is hidden discontinuities in the engine data pack. If you have some other data for the higher OATs, then you probably are reasonably safe with extrapolation unless there be some (strange) significant differences at the takeoff rating. Without such comfort, extrapolating the engine data is, at best, risky business ..

it seems to be most of the information we have from our Manuals really came from someone jumping in the damned thing and taking it for a flight to figure out what will happen.

That would be most unusual as the aim is to end up with something which can be used to model performance. Common practice is to model the performance and then use FT to sample test the accuracy of the model. Often it then becomes an iterative exercise to end up with an acceptable final accuracy in the model .. which then goes into the AFM data set.

We do know how the aircraft will perform in the climb up to 50°C, both dual and single engine

That is a useful source of comfort, I suspect.

Why have a chart giving the climb data to 50, if 40 is the limit for take off?

A question of limitation, then, becomes a legal question, rather than an engineering concern ?

An answer from the horses mouth so to speak. I asked Cessna, Wichita, the followingTheir reply

Good one, sir.

In defence of Declared Conditions
 

Bravo, Megan :D

Just a little word in defence of Declared Conditions: JT seemed to be implying that these should be headed for the bin, but I say:

What else can you use when planning your payload uplift from a place a few days, or weeks ahead of now? You obviously don't have ambient conditions, and I believe the regs stipulate that you must use the declared conditions.

Unlike probably 90% of Australian pilots, I have actually used them in anger, and can attest to their convenience.

Here is a great big hint to the people behind the NAIPS app for the iPad/iPhone:

Include the declared conditions in your app, somewhere. And while you are at it, get it to present the conditions not as a density altitude, but as a temperature and pressure altitude. That would be really good. Do it. Just do it.

I'm pretty sure you'd get an equivalent answer if you asked the equivalent question about the maximum demonstrated crosswind number (which is why the word "demonstrated" is in the description of the number).

It is interesting that this thread has concentrated on performance issues. In high or low temperatures the physical limits of the machinery can be of more concern than the performance.
All aircraft have environmental limits.
The Bell 206L3 has a max ambient air temp of 51.7c (125F) and I can say from first hand experience flying in temps around this limit has one concerned about Gearbox temps/oil temps etc.
The R22 has a stated demonstrated limit of 38C at sea level due to cooling issues. Again first hand experience of oil temp on red line when operating a standard R22 in the tropics. Look at R22s used for mustering and you will notice they have been fitted with a larger oil cooler to aleviate some of the problem. What are these high ambient temps doing to other lubricated components.
Take off performance may be the least of the issues of operating in high ambient temps.

You are quiet right, and most of the FAR 23 manuals I've looked at have the following statement in the performance section,

Perusing the old Digests kindly provided above in the forum, I came across this article in issue #33, which I reproduce in its entirety. Note density altitude is the focus, temp even goes to 45°C on the chart, and absolutely no mention of temp being a limit, just DA.

LIGHT AIRCRAFT TAKE-OFF PERFORMANCE

Temperature and Altitude Effects

A review of take-off accidents involving light aircraft has shown that an appreciable number of them can be attributed wholly or in part to a failure to allow for the effects of reduced air density arising from high temperature, high altitude, or, more particularly, from a combination of both.

Two separate effects must be considered;

(a) The effect of reduced air density on take-off
distance;

(b) the effect of reduced air density on climb
performance.

Both of these aspects will be examined in turn.

The Effect of Reduced Air Density on Take-off Distance

The normal takeoff consists of a full throttle run along the ground, a lift off at the take-off safety speed, and a climb away at this speed until a height of 50 feet is reached.

The take-off safety speed is defined as 1.2 Vs, where Vs is the power off stalling speed.

The indicated stalling speed of an aircraft depends, principally, on the aircraft’s weight, power setting and flap position. Changes in air density do not change the indicated air speed at the stall. Every pilot is aware, however, that under conditions of reduced air density the true air speed is greater than the indicated air speed; thus, in a take-off under high temperature conditions, the prescribed higher true air speed and the distance required to reach this speed will be greater. Alternatively, for a given take-off distance the gross weight of the aircraft and hence the take—off safety speed will have to be reduced in order to provide for a safe operation within the available distance.

Another major effect to be considered is the reduction of engine power output arising from reduced air density. In most light aircraft, take-off power is the full-throttle setting of its unsupercharged, or normally aspirated, engine. Changes in air density produce changes in the full throttle power of such engines. Any reduced air density means less air available for combustion and a fall-off in take-off power. The reduction in power is approximately proportional to the reduction in air density.* This reduction in available power means that less thrust will be available for accelerating or climbing the aircraft. lt can be seen, therefore, that reduced air density will not only demand longer take-off runs to allow the aircraft to accelerate to the higher true airspeeds but it also imposes the penalty of reducing the power available to achieve this acceleration. The take-off distances required are therefore greatly increased even for small reductions in air density.

The information provided in handbooks by the manufacturers of light aircraft is usually insufficient to take account of all the major variables and the Department of Civil Aviation has undertaken the production of the PL Charts (Performance Charts for Light Aircraft) to assist pilots in their calculations. For most aircraft types, the manufacturers data has been checked by flight testing in Australia and the chart data is based on these test results.

The chart indicates the maximum permissible gross weight for take-off after aerodrome pressure height, outside air temperature, take-off distance available and wind velocity are taken into account. Fifty per cent of the reported head wind component and 150 per cent of the reported tail wind component have been used in the construction of the chart and the take-off distance has been increased by a factor of 1.15 as is shown in the notes on the chart. The following example illustrated in the chart will show how the chart is used.

* In the case of a supercharged engine this effect is overcome, within limits, by compressing the air and thus restoring the air supply.

Airfield pressure height which may be read from your altimeter after setting 1,013.2 mb. = 920 feet

Outside air temperature measured in the shade : 113°F or 45°C

Take-off distance available = 1,550 feet

Wind velocity component = Nil

(1) Effect of Air Density Change

Enter the chart at °“START HERE" and find the intersection of the airfield pressure height (APH) and the outside air temperature (OAT). The point of intersection indicates the density height at which the next segment of the chart to the right should be entered. This density height is determined by the relationship of the APH/OAT intersection with the horizontal lines drawn through the upper three segments of the chart. The bottom line has a zero or standard sea level value as determined by the intersection of the zero airfield pressure and the standard 15°C temperature. Each successive line drawn is a 1,000 feet increment in density height. Thus it will be seen that the density height in this example is 4,500 foot which means that the density of the air under the conditions stated in the examples is the same as would exist at a height of 4,500 feet under conditions of standard atmosphere, At this point it is of interest to note the effect of temperature on density height. If the OAT had been 13‘”C the density height would have been the same as the airfield pressure height, i.e., 920 feet and, with an even lower temperature of 5°C (41°F) the equivalent of sea level standard conditions would prevail. It will become apparent from this why a light aircraft exhibits a lively performance on a frosty morning. Now move on to further corrections in the example.

(2) Effect of Take-off Distance Available

Move to the right on the chart until you intercept the line representing the take-off distance available and then move vertically downwards to the next correction.

It may be seen that, in the particular conditions of this take-off, no reduction of the maximum permissible gross weight would have been necessary had the available length of run been equal to or greater than 2,400 feet. Since the available length is only 1,550 feet, however, it is immediately apparent that the gross weight for take-off will need to be reduced.

(3) Effect of Wind

Continue to move vertically downwards to intercept the ambient wind velocity Line and then move horizontally to the left and read from the scale the maximum take-off weight permitted under these circumstances, i.e., 1.570 lb.

(4) Take-off Safety Speed

Since the stalling speed varies directly with weight, the take-off safety speed will also vary directly with the take-off weight and for this case it may be read directly off the right hand side of the diagram as 43 Kts. I.A.S.

We are now in a position to see that under the conditions prescribed, the combined effects of limited take-off distance available and the reduced air density has demanded a reduction in the maximum permissible take-otf weight from 1,825 lb. to 1,570 lb.

The Effect of Reduced Density on Climb Performance

The Australian performance standards require that all light aircraft have a minimum gradient of climb after take-off of six per cent, This can be expressed as 6 feet of climb for every 100 feet of horizontal travel along the flight path, or 365 feet per nautical mile which is equivalent to a rate of climb of 365 feet per minute if the aircraft’s climbing speed is 60 knots (T.A.S.).

The climb gradient is greatly affected by even a small reduction of engine power because the power available to climb the aircraft is only the power in excess of that required for straight and level flight at the climbing speed.

We have already pointed out that any reduction in air density produces a proportionate reduction in engine power. Reference to atmosphere tables will show that air density falls about 3 per cent per 1,000 feet between sea level and 3.000 feet, reducing to 2 per cent per 1,000 feet at 16,000 feet. Thus it the aircraft is taking off in conditions of pressure and temperature which are equivalent to a height of 4,500 feet under standard conditions (i.e., a density height of 4,500 feet) the engine output under full throttle at constant r.p.m. will fall about 13 per cent. This amounts to a considerable reduction in the power available for the climb and the gradient of climb is correspondingly reduced. If the density is reduced to a point where the minimum climb gradient would not be achieved, the take-off gross weight must be reduced in order to restore the gradient and thus ensure a safe climb out over obstacles.

To show how this adjustment is calculated we must now refer to the Climb Weight Limit diagram in the PL Chart.

Climb Weight Limit

Enter the chart at the airfield pressure height and move vertically until the line intercepts the outside air temperature. Then move horizontally to the left to the point of intersection with the sloping reference line and then vertically downwards to the gross weight scale where it can be seen that the climb weight limit is 1,775 lb.

Points to be Especially Noted

The maximum permissible weight derived from our previous calculations based on runway length available was 1,570 lb., Whilst the weight limitation based on the climb requirements is 1,775 lb. The lesser of these two is the maximum permissible take-off gross weight, i.e., 1,570 lb.

If the aircraft's gross weight is held constant the effect of temperature on the length required for take-off at a particular aerodrome may be seen from the chart. Referring to our example again, you will remember that 1,550 feet was the minimum length required to lift 1,570 lb. when the temperature was 45°C (113"F). Drop the temperature to 13°C (55°F), which is standard for a pressure height of 920 feet, and for the same weight the take-oil length required is reduced to 1,170 feet. Check this on the chart at the point where a density height of 920 feet intercepts the vertical line of our example in the ‘distance available" segment of the chart.

Whenever a take-off in the type of aircraft to which the sample chart applies is to be carried out with a density height exceeding 3,800 feet, Some reduction of take-off (i.e., 1,825 lb.) must be made irrespective of the length of run available. This arises from the climb weight limitations of the aircraft.

Example:

Now try this example yourself using a ruler and sharp pencil.
Airfield Pressure Height ....,. . ,.... 1.500 feet
Outside Air Temperature ..,... . ..... 25°C
Take—off distance available . .... 1,900 feet
Head Wind Component 5 m.p.h.

It you have mastered the system you will agree that the take—off gross weight is 1,785 lb. and the take-off safety speed is 47 Imots.

The SAAB AOM does state a limitation of 47 degrees C. During one insanely hot day in Sydney a few years ago the OAT actually peaked out at 47.6! The word from the Chief Pilot’s Office was, as long as it doesn’t hit 48, we were good to go. The rationale being, anything up to 47.9 is acceptable?

It seems you can delude yourself into believing anything if the circumstances dictate. :rolleyes:

And you only need one prop to land in Sydney, anyway...

Measured how?

By whom?

With what equipment? Mercury thermometers, the common rotary dial gauges & digital gauges all rear differently with different reaction times or lag

Where? Engine compartment, ambient? ambient in the shade, ambient at aerodrome reference?

The limitation probably relates to hot fuel handling of the engine - which will have more to do with heat soak than ambient conditions.

The role of a pilot is to make judgement decisions, this is one of them .

I would suggest it’s about common sense, and knowing where to draw the line.

Megan, if you could pdf that letter and upload would do wonders for those not game enough to take it up to uneducated FOIs on the principles of flight. Density could be an argument....maybe too much of it between the ears:ugh: Or, grey matter lacking oxygen starving mental performance:\ Or, hot heads lack performance when it counts....bloody lawyers! Obfuscators Lacking Competency!

Getting into the hot weather down here so time to consider this again. (I only deal with small airplanes.)

CAO 20.7.4 Aeroplane weight and performance limitations — aeroplanes not above 5 700 kg — private, aerial work (excluding agricultural) and charter operations states "Approved declared conditions may be used instead of actual pressure height and temperature" - the declared conditions are from CAO 20.7.0 as declared density altitude.

A couple of years ago, a note in the Exposure Draft of Part 91 (MOS for 91.1035 Aircraft Performance): “It is the intention that CAOs 20.7.4. …. will be subject of a project to review them and provide guidance material in the form of an AC in the future. Much of the content of the CAOs contain either certification standards or outdated information. CASA expects pilots to operate in accordance with the aircraft flight manual (AFM). All performance information in the AFM is produced and complies with the aeroplane certification standards.”
I've heard nought of that project since.

If one has a FAR 23 airplane not more than 6,000 lb maximum weight there are no performance weight limitations in the AFM so just work your way through CAO 20.7.4 and try to deal with the outdated information and Australian-specific certification standards within it.