Deep Dive: What Hot Weather Does to Aircraft Performance

One of the easiest ways to understand what heat does to an airplane is to watch how much runway it uses.

During one of our recent Southern California heat waves, we watched one of our Cirrus aircraft depart Hawthorne Airport on an unusually hot day. On a more typical departure, we would expect to see the aircraft rotating around Taxiway Delta. This one stayed on the runway considerably longer, getting closer to the tower before lifting off.

By our estimate, it used roughly 20–25% more runway than we would normally expect on a similar departure.

That’s density altitude in the real world.

Most pilots learn about density altitude early in flight training. You calculate it, answer questions about it, and learn that hot weather reduces aircraft performance. But seeing it happen in an airplane you regularly fly, at an airport you regularly use, makes the concept much easier to appreciate.

Hot weather doesn’t necessarily make a flight unsafe. What it does is change the performance you have available. Understanding those changes, planning for them, and recognizing them from the cockpit are important parts of becoming a competent and proficient pilot.

What Is Density Altitude?

Density altitude sounds more complicated than it needs to be.

At its core, it is a way of describing how the airplane is going to perform based on the density of the air around it.

As temperatures rise, air becomes less dense. Altitude, atmospheric pressure, and humidity also influence air density.

That matters because an airplane depends on that air for several things at once. The wings need airflow to produce lift. The propeller needs air to produce thrust. A normally aspirated engine also relies on the surrounding air as part of the combustion process.

The FAA notes that high density altitude reduces aircraft performance, including engine power, propeller efficiency, takeoff and landing performance, and rate of climb. Learn more from the FAA.

Put much more simply:

On a hot day, the airplane may not accelerate, take off, or climb the way you are accustomed to seeing it perform on a cooler day.

That difference is what pilots need to plan for.

Density Altitude Is Not Just a Mountain-Airport Problem

Density altitude gets discussed frequently in the context of places like Big Bear, Mammoth, or other high-elevation airports.

And for good reason. Combine a high airport elevation with a very hot day and aircraft performance can change dramatically.

But that sometimes creates the impression that density altitude is only something pilots need to worry about in the mountains.

It isn’t.

We operate from Hawthorne Airport in the Los Angeles Basin. We aren’t starting every flight from a high-elevation airport, but Southern California can still give us very hot days. When temperatures climb, density altitude climbs with them.

The FAA specifically cautions that higher-than-standard temperatures can significantly affect aircraft performance and that high temperature and humidity can compound high-density-altitude conditions. Read the FAA guidance.

That means a pilot departing Hawthorne on a cool morning and the same pilot departing later during a significant heat wave should not simply assume the airplane will perform identically because the airport hasn’t changed.

Same airplane. Same runway. Different atmosphere. Different performance.

That is an important mindset to develop early in flight training.

What Do You Actually Notice From the Cockpit?

This is where density altitude stops being an academic concept.

In our experience, three of the most noticeable changes are:

• Longer takeoff distances
• Reduced climb performance
• Longer landing distances

Those are also consistent with the performance effects identified by the FAA. Learn more from the FAA.

But there’s another part of this that matters during training: feel.

If you’ve flown the same Cirrus repeatedly, you start developing a baseline for what normal acceleration and climb performance feel like.

You know roughly where you’re accustomed to rotating on a familiar runway. You know what a normal climb looks like after departure. You know what you’re accustomed to seeing on the instruments.

Then a very hot day comes along and things can feel different.

That’s useful experience.

The goal isn’t to fly by feel instead of calculating performance. It’s exactly the opposite. The calculations tell you what to expect. Experience helps you understand what those numbers actually mean once you’re sitting in the airplane.

The Takeoff Roll Is Only Part of the Story

Longer takeoff distance tends to get the most attention because it’s easy to see.

You apply power, begin accelerating, and notice that more runway is passing beneath you before the airplane is ready to fly.

But the next part of the flight matters just as much.

Climb Performance

Once you’re airborne, high density altitude can reduce climb performance.

That changes how quickly you gain altitude and how much altitude you have available as you move away from the airport.

The FAA’s own density-altitude examples show both effects together: a longer takeoff roll followed by a reduced rate of climb. See FAA Advisory Circular 00-6B.

That’s especially important when your flight involves:

• Terrain
• Obstacles
• Shorter runways
• Higher-elevation airports
• Heavy aircraft loading
• Particularly hot temperatures
• A combination of several of these factors

A departure that gives you plenty of margin under one set of conditions may offer less margin under another.

That’s why performance planning isn’t something you do just to satisfy a checklist.

It’s answering a practical question:

What is this airplane capable of doing today, under these conditions?

Don’t Let a Familiar Airport Make You Complacent

There is another reason we like the Hawthorne example.

Familiarity is useful in aviation, but it can also create expectations.

You’ve departed this runway dozens of times. You’ve flown this particular airplane before. You’ve made this flight before.

It’s easy to start expecting the airplane to behave the way it did the last ten times.

Then the temperature changes.

The aircraft didn’t suddenly become less capable and the runway didn’t get shorter. The environment changed.

Good pilots continuously account for that rather than allowing familiarity to replace planning.

This becomes even more important once you start using a Cirrus for what it is exceptionally good at: going places.

You may leave the relatively moderate temperatures near the Southern California coast and land somewhere considerably hotter inland. You may depart Hawthorne and head to a higher-elevation airport. You may load passengers and baggage for a trip that is completely different from your normal local training flight.

Now temperature, altitude, aircraft weight, runway length, and terrain can all start interacting.

That’s where understanding aircraft performance becomes much more than passing a checkride.

Hot Starts Are Another Part of Summer Flying

Not every hot-weather challenge happens after you start moving.

Anyone who has spent enough time around piston aircraft knows that starting a hot engine can sometimes be its own exercise.

A common scenario is a quick fuel stop.

You’ve just flown the airplane. The engine is hot. The aircraft sits on a warm ramp for a short period and then you’re ready to depart again.

Starting that engine can be very different from starting it cold first thing in the morning.

It’s why we’ve previously reminded CalAir pilots to follow the proper Cirrus hot-start procedures, reference the appropriate iFOM, and work with an instructor if the procedure needs a refresher. You can read more in our Getting Ready for Summer Flights article.

The newer Cirrus generation gives us an interesting operational improvement here as well.

Our G7+ uses a newer lithium battery system, and our maintenance team has already noticed improved starting performance. A stronger starting system doesn’t replace proper hot-start technique, but it’s a welcome improvement in one of those small areas that pilots deal with regularly when flying in Southern California heat.

It’s a good example of something that doesn’t necessarily make the marketing headline for an airplane, but can make a meaningful difference in everyday operation.

Hot Days Can Also Mean Bumpier Days

Temperature can affect the quality of the ride too.

Strong surface heating can create rising columns of warm air and increase thermal activity, particularly later in the day. That is one reason a hot summer afternoon can sometimes feel considerably bumpier than an early-morning flight.

We’ve talked about this with our students before: if you’re planning a longer summer flight and have flexibility, an earlier departure may give you cooler temperatures and smoother conditions. You can read more in Getting Ready for Summer Flights.

Again, that doesn’t mean afternoon flying is inherently bad. It means there are tradeoffs.

Part of becoming a better pilot is recognizing them before you depart.

This Is Exactly Why Different Conditions Make You a Better Pilot

Southern California spoils us a little.

We get a tremendous number of beautiful flying days. That’s one reason Los Angeles is such a great place to learn to fly.

But the goal of flight training shouldn’t be to become excellent at flying one airplane, from one airport, under one perfect set of conditions.

Eventually you’re going to go somewhere.

And that’s when the value of experiencing different conditions begins to show.

A hot day can teach you to recognize:

• How temperature affects acceleration
• What reduced climb performance actually feels like
• Why takeoff calculations matter
• How aircraft loading changes your available margin
• Why a familiar airplane may behave differently today than it did yesterday
• How conditions at your destination may differ significantly from conditions at departure

Training under different conditions, when those conditions are appropriate, helps turn theoretical knowledge into experience. Rather than simply telling a pilot, “Don’t go there,” or, “Don’t fly when conditions look like this,” there is tremendous value in safely experiencing different environments with your CalAir instructor sitting next to you.

Then you can begin developing an informed understanding of what you’re comfortable doing later on your own.

A Cirrus Is Designed to Go Places. Train Like You’re Going to Use It.

This is particularly important for Cirrus pilots.

A Cirrus SR Series aircraft is not just something you use to fly around the pattern. These are airplanes people use for personal travel.

You might train at Hawthorne and later fly to Las Vegas, Palm Springs, Phoenix, Big Bear, the Central Valley, Northern California, or much farther.

The weather and airport environment at the other end of that flight may look nothing like Los Angeles.

That’s part of what makes training in different conditions so valuable.

If you plan to use an airplane for real transportation, your training should prepare you to evaluate real conditions.

That doesn’t mean pushing through weather or performance limitations to prove that you can.

Quite the opposite.

It means learning enough to recognize when the aircraft has plenty of margin, when the conditions require additional planning, and when the correct decision is to wait, change the plan, reduce the load, choose another airport, or simply fly another day.

Before Your Next Hot-Weather Flight

There isn’t one universal number at which a day suddenly becomes “too hot to fly.”

Aircraft configuration, airport elevation, atmospheric conditions, loading, runway length, and the individual flight all matter.

That’s why pilots work from actual aircraft performance information rather than a general rule of thumb.

Before departing on a particularly hot day, take the time to consider:

• Current temperature and pressure
• Density altitude
• Aircraft weight
• Takeoff distance
• Expected climb performance
• Runway length
• Terrain and obstacles
• Conditions at the destination
• How those conditions may change before arrival

And if you’re still learning how to interpret those numbers, that’s exactly what flight training is for. Ask your CalAir instructor for more information and insights, or if you want to get hands-on experience, it’s a great time to take a few flights and feel it for yourself. As a Cirrus Certified Platinum Training Center, we use the Cirrus curriculum to ensure you’re getting the best possible training when it comes to Cirrus aircraft.

Remember, the goal isn’t knowing that heat affects airplanes.

The goal is understanding how much it affects the airplane you’re flying, on the flight you’re about to make.

As always, our blog posts are intended to educate and challenge you to learn more and become a better pilot. Not every insight or consideration is discussed here. Talk to your CalAir instructor to learn more.

Frequently Asked Questions About Flying in Hot Weather

What is density altitude?

Density altitude is a measure pilots use to understand how atmospheric conditions affect aircraft performance. As density altitude increases, aircraft performance generally decreases. Temperature, altitude, atmospheric pressure, and humidity can all contribute. The FAA emphasizes that density altitude is a performance measure rather than a height reference. Learn more from the FAA.

Does hot weather increase takeoff distance?

Yes. Hotter air can increase density altitude and reduce aircraft performance, resulting in a longer takeoff roll. The exact difference depends on the aircraft, loading, airport, and current atmospheric conditions. Pilots should use the performance data and procedures applicable to the specific aircraft being flown. Learn more from the FAA.

Does hot weather reduce climb performance?

Yes. Higher density altitude can reduce an aircraft’s rate of climb. This is one reason pilots need to consider more than simply whether sufficient runway is available for takeoff. See FAA Advisory Circular 00-6B.

Does density altitude matter at Hawthorne Airport?

Yes. High field elevation can significantly increase density altitude, but temperature matters as well. Even at lower-elevation airports like Hawthorne, unusually hot conditions can reduce aircraft performance.

Why are hot starts harder in piston aircraft?

A recently operated piston engine retains considerable heat after shutdown, which can make restarting it more challenging than a cold engine. Cirrus provides procedures for hot starts, and pilots should follow the appropriate procedures for the specific aircraft.

Can you train during a heat wave?

When the conditions remain appropriate for the aircraft, instructor, student, and planned lesson, hot-weather flying can provide valuable real-world experience. It gives pilots an opportunity to see how temperature affects aircraft performance rather than only studying the concept on paper.