# What sort of issues related to extreme heat (115°F, 46°C plus) would prevent takeoffs or landings?

I recently flew into and out of McCarran Airport Las Vegas (LAS) and a local told me that they never report the air temperature at the airport above 115°F (46°C) because the FAA does not allow landings above that temperature.

What sort of issues do large passenger jets (or small for that matter) have to deal with in high temperature environments either taking off or landing?

• The "local" was simply ill-informed. The reporting of weather conditions is critical to flight safety. Imagine the legal liability if they deliberately under-reported the temperature and an accident occurred because of that. 46c would also be extreme for Las Vegas so the fact the METARs report a temperature lower than this is, well, to be expected. – Simon Jun 29 '16 at 16:49
• @Pondlife: high pressure is not a problem. In fact, high air pressure is good for flight. High density altitude is a problem, and high density altitude means low pressure. – abelenky Jun 29 '16 at 17:21
• Heat can cause delays or cancellations but it's generally due to each aircraft's specific performance limitations, not a hard limit set by the FAA. – fooot Jun 29 '16 at 17:33
• @abelenky 14 CFR 91.144: no flight operations are allowed if air pressure exceeds 31.00". In reality, if it happens they issue a NOTAM and people can keep flying (see the AIM 7-2-2). It's unusual, but it is an actual regulation, whereas there's none that I can see related to temperature. I was wondering if the local guy was just half-remembering it when he said that the FAA doesn't allow landings in high temperatures. – Pondlife Jun 29 '16 at 18:17
• 91.144 is because altimeters are not accurate at such high pressure. Most cannot be adjusted that much. However, aircraft performance is fine. I don't think I'd be concerned about an all VFR flight, where precise altitude is not important, at an altimeter of > 31.00. (source: studentpilot.com/interact/forum/…) – abelenky Jun 29 '16 at 18:22

## Short Answer

Very high temperatures limit how much payload and/or fuel you can load on a plane.

## Engines

To help you visualize it, in hot air the air molecules are more energetic, which means the engine will have hard time compressing hot air vs. cool air. Losing thrust.

## Wings

Hot air—with the molecules spaced farther apart—has less density, which reduces the lift capability of wings.

## Hot and High

Vegas is not only hot, but also high, which means the air pressure is already less than at sea-level.

Each plane has its own performance charts, and on each flight, the flight dispatcher and crew make sure the weather, elevation, etc., would allow a safe take-off and climb.

A plane is configurable for such changing elements. For example using higher thrust setting, or more flaps to augment the lift.

If you have a very heavy plane, hot and high situation, and a short runway, then things become very marginal—

## Engine Out

—not just for the take-off run, but also in case of an engine out during take-off, i.e., losing an engine. The plane still has to be able to climb.

That's why in places like Ethiopia, South Africa, Australia, etc., airlines preferred1 quad-jet planes over twin-jet planes. To have bigger margin of safety in hot and/or high operations, i.e., to be allowed to carry heavier loads.

1 When tri/quad-jets were commonly offered alongside ETOPS twin-jets of same class.

## Example of Impact

(Map generated using Great Circle Mapper)

A cargo MD-11 plane taking off from Ethiopia en-route to Europe can't take off fully fueled, and has to stop in Cairo for a re-fuel. Note that if Ethiopia were at sea-level or cooler, a direct flight would have been possible.

## Landing

For landing in a hot and/or high airport, the landing speed will be higher, so what matters is the runway length available for landing. Again there are performance tables for that.

Rest assured, those things are checked and double checked. And no one can tamper with reported weather, because it is very critical to flight safety.

Also, planes do have their own temperature sensors. Newer planes can even alert the crew if the gross-weight, configuration, runway length, temperature, and elevation combo isn't sufficient.

• "ymb1" has the best answer. Yes, engine out performance is probably the most limiting factor for most 2 engine aircraft. – Mike Sowsun Jun 30 '16 at 12:42
• Most questions of the "why" in engineering and physics boils down to energy. I'm glad to see that you got that out of the way right at the beginning. Nice. – dotancohen Jun 30 '16 at 16:31

Aircraft performance is a many-faceted topic. Insofar as it being so hot that operation is prohibited, a couple of things come to mind.

Aircraft performance figures are supplied by the aircraft manufacturer, typically as tables, up to a certain temperature. Since operators are required to use those tables for determining the aircraft's ability to safely takeoff, if the temp is above the max temp in the table, there is then no available, tested data to do that and legal operation would stop. I just checked the performance data for a 747-200 with P&W JT9D-7Q engines, and the tables top out at 123 °F (50.5 °C).

Another factor is the maximum fuel temperature. For 747-100/200 aircraft, that temp was 54 °C as I remember, about 129 °F.

Now I can't speak to today's operating environment since I retired in 1999, but in the 1990s fudging or ignoring temperature requirements was common in some third-world countries. For example, if we were in the countries around the southern end of the Arabian Gulf (Iran called it the Persian Gulf) in the summer and the aircraft was fueled and had set for a day or two in the sun with mid day temps in the shade of 120 °F (49 °C) or more, you knew the fuel temp might be a bit above 54 °C, but nobody ever checked it. What you did do was account for that possibility in your planning. You might, for example, choose to do a full power takeoff rather than the reduced power takeoff that you might otherwise have used.

I personally was never aware of any mis-reporting of the temperature in the U.S., but in the 1980s when I was flying Metroliners for a commuter, there was one airport that as a matter of course typically didn't report a visibility less than the minimum required to start an approach when a commuter flight was due in. Once you reported the outer marker inbound (non-radar environment back then), they told you what the actual RVR was. Since you were inside the outer marker, it was legal to continue the approach, and we always did, and we always got in. That made everybody happy: the airline, the tower, and the local chamber of commerce.

• Offtopic, but the Gulf is actually called Persian Gulf internationally. Only some Arabic countries refer to it as Arabian Gulf. – Zeus Jun 30 '16 at 1:36
• @Zeus Offtopic, but most Americans and I think most of the British largely dropped the "Persian" from the Gulf when the Shah joined the Nazis in WWII and changed the name of the country from "Persia" to "Iran" an alternate spelling of "Aryan". They weren't going to call it the "Aryan Gulf" I've seen maps from the late 40s where the name had already switched to Arabian when pre-WWII maps show it as Persian. – TechZen Jun 30 '16 at 3:00
• I think you have a temperature unit conversion error. Google says 123F = 50.5C (not 55.5C) and 129F = 53.9C (correct), but I won't propose an edit because I have no idea which figures (Celsius or Fahrenheit) are the ones that would be specified by the manufacturer. – a CVn Jun 30 '16 at 8:02
• @TechZen Off-topic and largely incorrect. The Iranians have always called their country something like "Iran", and it was in 1935 that they started asking other people to call it that, too -- the idea of calling it "Persia" come from the Greeks. See Wikipedia. Although the words "Iran" and "Aryan" do come from the same root, the name change was not because of WWII and there would be no reason to start calling the Gulf the "Aryan Gulf" rather than the "Iranian Gulf". – David Richerby Jun 30 '16 at 12:21
• @MichaelKjörling You are correct, and I will edit the answer. However, I would like to point out that the mistake was not mine. My answer originally just said 123F, and someone else edited in the (55.5C). I'm 77, and, frankly, am prone to making errors that I would would never have made when I was young, but that error I did not make. LOL – Terry Jun 30 '16 at 13:22

If the temperature is hot enough, the runway can buckle. The asphalt expands as it heats and eventually expands so much that it starts folding up. This has caused runways to close (in the US and elsewhere) but there doesn't seem to be a specific regulation, it seems to be handled with runway inspections and closing the runway whenever a problem is found.

• very valid point, but generally only impacts asphalt runways, not concrete or grass. Well, it has to get really hot before concrete begins to soften, and when that happens, I think we have other concerns. :) – FreeMan Jun 30 '16 at 12:19
• Welllll, it does also impact the McMurdoch Ice Runway: en.wikipedia.org/wiki/Ice_Runway Although I was specifically thinking of the 2012 DCA melting, which was asphalt: washingtonpost.com/local/crime/2012/07/08/gJQAZgG9UW_story.html Probably more of a concern for older runways in 4-season climates, where they were originally engineered to withstand seasonal cold but then have a sudden heat wave. – user3067860 Jun 30 '16 at 20:53

Tires...

... at least that's were it started. My grandfather was a pilot starting back in the 30s, and got to see the whole technology develop. Blowing tires was big problem for big aircraft from WWII bomber up to airliners in 70s. Used to see actual blown tires at the end of runways pretty often. When I was kid, in the late 70s, a taxi at Love field in Dallas, Tx got hit by a fragment of blown tire in June when temps were already over 100F.

Compared to ground vehicle tires, aircraft tires are relatively thin walled and balloon like because

• they have deal with a lot pressure variation
• they have to absorb shock
• they have to roll at speeds which in a ground vehicle would qualify them as a race car, which generates a lot of heat
• they need large contact patches, but still need to conserve weight

However, balloon-like tires are more sensitive to expansion due to heat. At 115°F (43°C), tires of planes on the tarmac taking off will be near the edge of their expansion spec already. In landing planes, the tires will go from sub-zero to near overheating even before the tires hit the tarmac.

I think military transports have some sort of cooling system to allow all weather operations I've seen C-130 variants land in hot weather and then something that looks like a fire extinguisher exhaust comes out of port in the back of the wheel assembly i.e. it's not burning rubber. It's probably some tech like nitrogen pressurized fuel tanks, allows landings in any weather but to expensive for civilian aircraft. But I never looked into it so I could be wrong.

It isn't necessarily the airport operator that limits takeoffs and landings at such hot days but the manufacturer of the aircraft. All Part 25 certificated airplanes require performance data for all weights, altitudes and temperatures they operate in. Most likely the aircraft manufacturer has chosen to limit takeoffs and landings on such hot days because they chose not to publish the applicable data.

§25.105(a) The takeoff speeds prescribed by §25.107, the accelerate-stop distance prescribed by §25.109, the takeoff path prescribed by §25.111, the takeoff distance and takeoff run prescribed by §25.113, and the net takeoff flight path prescribed by §25.115, must be determined in the selected configuration for takeoff at each weight, altitude, and ambient temperature within the operational limits selected by the applicant

It's because of air density. The density of the air isn't constant and varies with elevation above sea level and air temperature.

$$F_{lift} = C_{lift} \times \dfrac{1}{2} \times \rho \times V^2 \times A$$

… where $A$ is the wing area, $V$ is the velocity and $\rho$ is the density of the air. If the air isn't dense enough the aircraft won't be able to take off if it can't generate enough lift at the end of the takeoff run or will have to land at a speed that is too high to keep it from stalling.

Density altitude is the altitude relative to the standard atmosphere conditions (ISA) at which the air density would be equal to the indicated air density at the place of observation. In other words, density altitude is air density given as a height above mean sea level. "Density altitude" can also be considered to be the pressure altitude adjusted for non-standard temperature.

Both an increase in temperature, decrease in atmospheric pressure, and, to a much lesser degree, increase in humidity will cause an increase in density altitude. In hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.

In aviation, the density altitude is used to assess the aircraft's aerodynamic performance under certain weather conditions. The lift generated by the aircraft's airfoils and the relation between indicated and true airspeed are also subject to air density changes. Furthermore, the power delivered by the aircraft's engine is affected by the air density and air composition.

• Not sure I buy that given that dealing with changes in air density with altitude is a basic prerequisites for flying in the first place. Back in the pre-WWII days, low power aircraft had to struggle to get off the ground from high-altitude fields, but today when even a civilian airliners has enough power to almost stand on its tail, I don't think its much of an issue. – TechZen Jun 30 '16 at 2:51

Aircraft performance is directly affected by the ambient atmospheric conditions. Specifically, both lift from wings (or rotors), engine power and thrust in the case of jet engines is proportional to the density of the air. Dense, cold air creates a lot more lift for a given true airspeed than does hot, thin air and engines produce more power in denser and/or thrust in denser air than they do in thinner air.

Air density is a function of both atmospheric pressure and temperature using the ideal gas law

p = drT

d = p/(rT)

where p is the ambient air pressure, d is the density of the air and T is the ambient temperature. r is the ideal gas constant.

So the density is directly proportional to the temperature of the air and inversely proportional to the temperature.

In aviation, the pressure is a factor of both field elevation and ambient atmospheric pressure in the area. The high up you go from sea level, the less dense the air gets for any given temperature.

Now what all this means for a pilot, is that, since air density affects both lift and thrust, the performance characteristics of the aircraft are going to be much more lethargic on a hot day. This is compounded by the field elevation and flying altitude as well as pressure deviation from standard atmospheric condition.

These 'hot and high' conditions can be extremely hazardous and a lot of good pilots have been killed because they did not factor this in with performance calculations related to runway length needed for takeoff and climb gradient to clear obstacles. The runway needed to accelerate to Vr and clear an obstacle may be as much as 200-300% greater than required for a sea level takeoff, and the maximum rate of climb at Vy on a hot day may be halved compared to cold, sea level operations. This is particularly perilous for bush flying and operations over mountainous terrain.

Below is a link to a video of a Stinson 108 light aircraft departing a grass strip near Stanley, Idaho with a 6000+ ft field elevation on an 85° summer day. The aircraft was also loaded with four people at over gross weight. WARNING: graphic content; if airplane crashes upset you, do not watch.

The good news is that everyone aboard was lucky and walked away from the accident; most people involved with this kind of emergency aren't so lucky.

Performance data for aircraft is published by the manufacturer in the required pilot's operating handbook (POH) and performance calculations should be performed prior to all flight operations. Ambient atmospheric conditions are available to the pilot either in the form of ATIS/AWOS/ASOS broadcasts or using portable weather monitoring equipment. ATIS broadcasts make the process easier by broadcasting a density altitude for the field which is equivalent to a field altitude if the ambient air were at standard temperature and pressure of 15° Celsius and 29.92 inches of Mercury.

I can't speak for McCarran International's (LAS/KLAS) operating procedures, but I suspect they do not allow operations above 40° C both because the runways there would be insufficient for launching and recovering heavy transports in those conditions and, in general, aircraft manufacturers do not specify performance data for temperatures beyond 45°C / 110°F.