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5 Things To Consider When You're Picking A Cruise Altitude

Boldmethod

They say the three most useless things to a pilot are runway behind you, fuel not in your tanks, and altitude above you. So when you're picking your cruise altitude for your next cross-country, is higher really better?

It could be, but you have a lot to consider. Here are 5 things to think about when you're planning your next flight.

1) Am I Going To Hit Something?

There's nothing that will ruin your day like hitting terrain or an obstacle. So how do you make sure you're clear on your route? If you're flying VFR, one of the easiest ways is to open your sectional and check out the MEF (Maximum Elevation Figure) altitudes for your route.

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The MEF is the bold blue altitude, in hundreds of feet MSL, listed in the middle of each quadrant of your sectional. That altitude guarantees you at least 100 feet (up to 300 feet, in some cases) of clearance from all terrain and obstacles in the quadrant.

So as long as you pick an altitude above the MEF, you can rest easy in knowing that you're not going to hit something poking out of the ground while you're enroute.

2) Can My Plane Actually Get There?

It's a valid question, and it's not always easy to answer. You need to be practical with your altitude choice. If you're flying a short distance, it doesn't make a lot of sense to spend the majority of your flight in a climb.

That's where your aircraft's Fuel, Time and Distance to climb chart comes into play. For most aircraft, your time-to-climb is pretty linear, but if you're flying a normally aspirated airplane above 10,000 feet MSL, your climb rate can start to tail off significantly. And on top of that, you're burning extra fuel, and flying a slow indicated airspeed, all the way to your cruise altitude.

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But the opposite is true when it comes to your true airspeed. The higher you go, the higher your true airspeed. The rule of thumb is that you gain 2% of true airspeed for every 1,000 feet you climb, and that can make a big difference. Consider this: if you're flying at 140 knots indicated at 5,500' MSL, your true airspeed will be roughly 154 knots. But if you fly the same indicated speed at 11,500', your true airspeed shoots up to 170 knots. That's a gain of 16 knots, which is big difference maker, especially on long flights.

3) What Kind Of Airspace Do I Need To Deal With?

Ahhhh everyone's favorite: airspace. There's controlled airspace, special use airspace, and just about every kind of airspace you can think of listed on sectional charts these days.

Fortunately there are lots of great planning tools out there, like ForeFlight, than can help you navigate around tower controlled airports and special use airspace along your route. But there's another way to make life easy on yourself when it comes to airspace: simply climb above it.

If you can get yourself above 10,000 feet MSL, you've all but guaranteed yourself clearance above tower controlled airspace, even Class B. There are of course a few exceptions, like the Denver Class B that extends up to 12,000' MSL, but they're few and far between.

Unfortunately, the same can't be said for restricted areas and other special use airspace, but a quick check on your sectional map can clear up any questions about that.

4) What About The Clouds?

Now that you've gotten this far, you need to contend with the weather. And mother nature isn't always cooperative when it comes to flying.

That's where your METARs, TAFs and PIREPs come into play. When you're checking the clouds, think about coverage and altitude. If you're looking at few or scattered clouds, climbing above them might be an option, but if you're looking at a broken layer along your route, it's best to stay below.

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After all, there's nothing more embarrassing (and panic-inducing) than getting stuck on top of a cloud deck with no way to get down, short of declaring an emergency. Or, if you're an instrument pilot, scrambling to find charts to navigate your way down through the soup on a pop-up IFR clearance.

Also, remember that METARs and TAFs list cloud bases in AGL, not MSL. So you'll need to do some math to figure out where the bases will be to maintain your VFR cloud-clearance requirements.

5) Are My Passengers Going To Hate Me?

There's one final consideration, and it's quite possibly the most important thing: what are your passengers going to think of you when you touch down on the runway?

If your passengers' teeth are getting rattled out of their heads because of turbulence, they're not going to be very impressed. And one place you're almost guaranteed to find turbulence is around shear layers in the winds aloft.

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While you obviously want to consider your headwind or tailwind along your route, you also want to make sure you're keeping yourself clear of any significant shear layers aloft.

Take this for example. On this route from KGCY-KEHO, there's a 24 knot wind velocity difference between 3,000' and 6,000', with a nearly 50 degree wind direction direction difference. And if you're thinking things would be bumpy in that area, you're right.

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Taking a look at area the PIREPs with a tool like ForeFlight (or ADDS, if you're not a ForeFlight user), confirms what you'd expect: a Cherokee pilot reported continuous moderate turbulence below 4,500' MSL.

So unless you want to pack extra sick sacks for your passengers, it's a good idea to be on the lookout for the "smooth ride" altitudes, as well as the favorable winds aloft.

Putting It All Together

There's a lot to consider when you're picking your cruise altitude. But if you're thinking about obstacles, your plane's performance, and the weather and winds along your route, you'll have a smooth flight, and hopefully some happy passengers as well.

Colin Cutler

Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at colin@boldmethod.com.

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