[Scott]

Scott on July 10, 2025 at 1:32 pm #23189

A Cherokee 140 is pretty underpowered for high-and-hot operations, especially if you start to load it up with people and/or fuel. The best-case scenario at 2150 pounds at a density altitude of zero is about 675 feet per minute, and it only gets more anemic from there. At 5,000′ DA, you’re looking at 475 fpm, and at 10,000′ DA, just 280 fpm. They’re good little airplanes, but they have some significant limitations in the low-horsepower models.

I based a Cherokee 180 out of the high desert for several years (home field elevation of 4164′) and flew it routinely with DAs significantly higher than that. Even with the extra horsepower in the 180 model, I had to pick and choose my days if I wanted to go places where takeoff and climb performance were important. Weight made a huge difference as well. Lightly loaded (two people, 20 gal fuel), I could get in and out of a lot of the nearby “backcountry” strips. Max gross? Nope, not going to try it. 

In addition to what Steve has said about density altitude, there are other factors that can limit an aircraft’s climb performance.

A few years back, I did a trip to Sisters, Oregon (6K5). When I landed, it was very bumpy and windy out of the west (this is important in a minute), and getting hot. I spent the afternoon at a BBQ and departed at around 6pm; the hottest time of the day. The OAT was around 95F, field elevation 3,200 feel msl. Density altitude was just over 6,500 feet at departure.

For the airplane I was flying, that was no big deal. It was just two of us in the plane and it had plenty of power for that operation (a 180hp Cessna 172). Takeoff and initial climb were fine, albeit a bit slower than at sea level. At around 5,000 feet msl, I started feeling like we were struggling to climb. At around 6,000, there wasn’t any climb performance left. It just WOULD NOT climb. That was a big problem, as I wanted to be at at least 8,500 for a westbound crossing of the Cascades (terrain at around 7,000 on that route).

I checked my engine gauges and all seemed fine, but the airplane just… wouldn’t climb. A quick look at the OAT confirmed that the density altitude was high; around 10,000′ by my math, but not so high that I’d run out of climb performance. By the book, that aircraft had a service ceiling of around 17,000′, Bizarre.

I considered going back to the airport. First, though, I flew toward an open area of hay fields (rare in this area; most is forest). I found a bit of a thermal there, and was able to spiral-climb up to 8,500 with relative ease.

When I turned toward the Cascade crest, it became obvious what had happened with my initial attempts to climb. There was a significant (40-ish knot) west wind at altitude. The Sisters airport is on the lee side of the mountains, and the air was spilling over the top and down the slope into the valley, creating a large area of downdraft (over the forested areas near the airport) that I couldn’t outclimb.

I ended up climbing up to 10,500 to cross the crest with ample room below me, as the high winds suggested that I might encounter turbulence as I got closer to the mountains. That didn’t happen, and it was a smooth flight from there back to my home base.

A very strange experience to find that I couldn’t get above 6,000′ in one spot, and then a few miles away, having plenty of climb performance.

[STEVE]

STEVE on June 26, 2025 at 11:10 am #23163

Hi Charalampos,

I have a Pilot’s Operating Handbook (POH) for a Cherokee 140 that has information on the 150 hp version.

At Maximum Take Off Weight (MTOW) of 2150 lbs. the POH cites a climb rate of approximately 280 feet/min at 10,000 feet. 

A “standard day”–also called an International Standard Atmosphere or ISA– in aviation is where the air temperature is 59 deg F. (15 deg C.) and the atmospheric pressure is 29.92 inches of mercury (Hg) at sea level. 

Let’s define density altitude as “the altitude the airplane thinks is at and performs in accordance with.”

Hot air temperatures and high altitudes cause a decrease in airplane performance. 

A very experienced mountain flying pilot named Sparky Imeson wrote a book titled “Mountain Flying Bible.” In it he wrote “rules of thumb” to help pilots safely operating their airplanes. The following is one of Sparky’s rules:

Fixed-pitch Propeller: Reduce the sea-level rate of climb 7 percent for each 1,000 feet density altitude up to 8,500 feet and 8 percent for each 1,000 feet above 8,500 feet.

According to my Cherokee 140 manual your airplane should climb at a rate of 660 feet/minute at MTOW at sea level.

When applying Sparky’s rule to your Cherokee’s rate of climb it works out to a climb rate at a standard day temperature of around just over 300 feet per minute.

Let’s put a density altitude equation into the 300 feet/minute figure. 

Here’s Sparky’s rule of thumb for density altitude:

“A surprisingly accurate rule of thumb (usually any error will be less than 200-300 feet) for determining the density altitude is easy to remember. For each 10-degrees Fahrenheit above standard temperature at any particular elevation, add 600 feet to the field elevation. (And, conversely for each 10-degrees F below standard temperature, subtract 600 feet from the field elevation.)

As you know the outside air temperature plays a large part in determining the density altitude; higher than standard temperatures–the standard air temperature lapse rate is 3.5 deg. F for every 1000 feet so at 6000 feet the out side air temperature (OAT) on a standard day will be 38 deg F.

Let’s imagine that the OAT the day you were flying at 6000 ft. was 78 degrees. That’s 40 degrees above the standard day temperature. By applying Sparky’s DA rule we find that the airplane and engine thought it was flying 2400 feet higher than than 6000 feet, or 8400 feet. 

While  the performance graphs in the POH indicate you still should have been able to climb at more than 300 ft/minute, I think you can see that hot days greatly affect the performance of your PA 28 150. 

If you feel the performance of you PA 28 is not measuring up to the printed figures in your POH, I suggest you get a mechanic to check your Cherokee of low engine compression, and airframe rigging. Even flying without wheel pants will affect the performance of your Cherokee. 

Steve

[Charalampos Avgousti]

Charalampos Avgousti on June 25, 2025 at 2:08 am #23160

Hi guys. I flew my plane (PA28/140 (150hp) yesterday during a really hot day and I noticed a difficulty climb above 6000ft msl. Does anyone have any experience flying that aircraft at high altitudes?  Thank you all.