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A few days ago, a Copa flight from Porto Alegre to Panama was delayed from noon until 12:30 AM. The company explained that the high temperature (about 40 degrees Celsius) would require a longer runway for takeoff since the air was thinner, and that resulted in non-operational conditions for the wings and engines with the available runway length.
One source (in portuguese): http://www.radioguaiba.com.br/Noticias/?Noticia=515816
Is this true? Can a high temperature really prevent takeoff?
Yes, temperature effects airplane performance both the engine itself and the aerodynamics involved.
What Is Density Altitude?
Density altitude is pressure altitude corrected for nonstandard temperature. As temperature and altitude increase, air density decreases. In a sense, it's the altitude at which the airplane "feels" its flying.
How Will High Density Altitude Affect Flight?
On a hot and humid day, the aircraft will accelerate more slowly down the runway, will need to move faster to attain the same lift, and will climb more slowly. The less dense the air, the less lift, the more lackluster the climb, and the longer the distance needed for takeoff and landing. Fewer air molecules in a given volume of air also result in reduced propeller efficiency and therefore reduced net thrust. All of these factors can lead to an accident if the poor performance has not been anticipated.
Tips for Flying in High Density Altitude Areas
One way of looking at it is that higher temperatures make the airplane fly the way it would at a higher altitude where the air is less dense. An airplane cannot climb to infinity, it has what is called a service ceiling [and an absolute ceiling] that the aircraft can no longer climb any higher. This also because of a decrease in air density, but for a different reason. Raising the temperature of the air also decreases this air density. You can use an Air Density Calculator or a Density Altitude Chart:
to determine how the aircraft will fly. It is especially important at airports with short runways or high actual altitudes [Denver, Colorado for example] where the aircraft already may need to be near maximum performance.
If the density altitude is 4,000ft than that means that airplane will fly like it was at 4,000ft at standard atmospheric temperature. Standard atmospheric temperature [at sea level] is 15 degrees Celsius or 59 degrees Fahrenheit. An airplane departing at a sea level airport, at 100F would feel like it is already flying at over 2600ft. An airplane departing at a 5,000ft airport would feel like it is already flying at over 8700ft. If clearing the trees at the end of the runway was already a concern at this particular airport it may not happen anymore.
Yes, it is quite correct that an airplane requires a longer runway on a hot day. The effect is the same as being at a high altitude. High up on a hot day, in the middle of a low pressure zone is the worst, as the effects are combined.
What it comes down to is air density, less dense air means less "stuff" for the wings to sail through, generating less lift, and thus requires higher airspeed before being able to lift off. On top of that, engines need oxygen to fuel the combustion, less dense air means less oxygen and therefore less power output from the engine. And just as the wings are less effective, so are the propeller or fan blades, converting less engine power to thrust.
So in essence, low density means you'll need more airspeed to climb away from the ground, and you have less power at your disposal for reaching that airspeed.
A well known video taped Stinson crash in Idaho a while back is generally attributed to high density altitude. High density altitude means low air density (may sound counterintuitive, but it basically means that it is equivalent of a high altitude, where the atmosphere is naturally less dense). The airfield elevation was 6370 ft, however the density altitude on that day has been calculated to have been 9167 ft, a substantial difference.
Absolutely: thinner air, whether caused by a higher altitude or a higher temperature, decreases aircraft performance in two ways:
It decreases the amount of air going into the engine, which means that less fuel can be introduced in order to maintain the correct fuel to air mixture. This produces less power output from the engine and decreases the thrust generated by the fans in the turbofan engines. This increases the amount of time (and therefore runway distance) that it takes to accelerate to flying speed.
At a particular airspeed, there is less actual air (fewer air particles) moving across the wings. Since this is what produces lift, the airplane must be moving faster in order to create the same amount of lift. This requires more time, and therefore more runway.
Climb performance is also reduced for the same reasons, and can also be a factor preventing an aircraft from taking off if there are obstacles that must be out-climbed (there is also a minimum amount of climb required after takeoff for certification, so performance charts don't even have information past a certain point).
For a "real world" example, take a look at this chart from a jet that I fly, and notice that the hotter the temperature or the higher the takeoff altitude, the lower the weight that you are allowed to takeoff at:
At 40 deg C, even at seal level, this airplane is limited by climb performance to a takeoff weight of about 13,700 kg. (instead of the normal 17,600 kg.), and this doesn't even consider the amount of runway required!
The exact same principle applies to runway distance required, but there are additional variables which make the graph much more complicated to follow:
As others have said, yes it can and does happen. In PHX a few years ago the airport was closed to most aircraft for temperatures at/above 120. Note please it is not that the planes can't fly in that heat, it is because the planes don't have the proper high density altitude charts so they can't determine how long a runway is needed. i.e., for part 121 operations such a flight would be illegal.
Why don't they have the performance tables? It costs a lot to develop them, and IF they exist, the manufacturers sell them as an extra cost item to the plane's operator.
I don't believe there is any max temperature limit for the small GA planes that many of us fly, except to say that 120+ degrees is @#&*$# hot in a non-airconditioned GA plane.
