Density Altitude, Density Altitude, don't be dense, calculate it everytime!!!

Hello fellow Piper Aviators, a friendly reminder about Density Altitude.

Today I went out to my field (KAEG) to knock some more rust off my IFR skill. The plan was to fly a C-172 (if you invert it, it sort of looks like a Piper :) ). Before starting my pre-flight I set about calculating Density Altitude.
Today the field was reporting 33C at around 4pm. This converts to around 8900 to 9000 in Density Altitude.
I decided to NOT fly because the marginal performance of the 180hp C-172 with me and CFII onboard was just not worth the risk. In best case we would get around 300fpm in climb. The wind was a bit gusty, and the temp on the actual runway was probably hotter.

As I was checking the dispatch book back in to the front desk, I watch another group go out and fly the 160hp (with cruise prop) C-172. I was shocked that they would try to load 3 adults and fuel into the "lesser" C172 and try and go flying. I watch their takeoff and boy the acceleration was dog slow. I was surprised they continued....
About 6 minutes later I heard on my handheld that the pilot was requesting to "Return to the field". Tower asked if every was ok...the reply was "Yeah, very poor performance on the engine..." They landed and parked the plane.
No bent metal. Thank god!!

Folks, everyone needs to do several things before each and every flight.
1. Calculate your needed fuel and reserves
2. Calculate your weight and balance, every time
3. Calculate your Density Altitude, every time
4. Check the POH performance charts to make sure it is all good.
5. Pre-Flight YOU and your PAX's. Are you Safe. (HALT, PAVE, I'M SAFE) etc
Same for your PAX's.... Having a PAX chuck on you right as you lift off would be bad.
I'm sure there are more things I should list, but you get the idea.

As Smokey the Bear says "Only YOU Can Prevent Forest Fires"
"Only YOU can reduce the risk of GA accidents by having the right attitude"

BTW, Did I mention that you need to calculate Density Altitude :). Doesn't matter if you are a flat lander, or a mountain person

Be Safe, Have Fun, Set A Positive Example for other pilots


  • Great tips. Also make sure you lean for best power. At that DA it would be far back but I would not be surprised if they did not account for it if they took off in the first place. Planes stored outside or fueled up with fuel stored outside are also at risk for vapor lock on high temp, high DA days. For low wing planes low boost might be needed.

    Eric Panning
    1981 Seneca III
    Hillsboro, OR (KHIO)

  • Question: Why not factor the likelihood of oxygen use based on density altitude (versus physical altitude) into that calculation as well? Sure, the FAA has rules based on fixed altitude, but if the engine and wings are struggling from the effects of density altitude, how does this also not effect the human occupants in the same manner?

    And, point of order, it is Smokey Bear ;)

  • Jacob, It is a good question and the answer is for the transport of O2 across the alveoli membrane (air sac) in the lung the temperature is always ~body temp and the humidity ~100%. So, the temp and humidity is always constant in the lung and the only variable is physical altitude.

    This is why it is so important in hot and dry conditions to hydrate. Even inactive in the shade you are consuming water with every breath as the body hydrates the dry air (and also cools it as needed). Cold dry air has the same challenge.

    Eric Panning
    1981 Seneca III
    Hillsboro, OR (KHIO)

  • WOW, Thank you Eric, learned something new with that post. Writing that down in my "future CFI lessons book" :). Thank you Jacob for asking a great question

    Jacob, While the FAA has certain prescribed rules based on fixd altitude, a pilot should always evaluate their personal health condition when deciding on when to use O2. I personally go more conservative than the FAA, lower alt for O2, longer fuel reserves, etc. I try to avoid Special High Intensity Training moments (its a four letter word)

  • Good point on O2. With systems like O2D2 from Mountain High and headset mounted cannulas like Oxyarm the barrier to using it goes down as it is easy to get going and the tank lasts a long time with pulsed delivery.
    There are also many finger tip O2 meters. They will probably show 95%+ up to 10k - but watch for higher heart rates and breaths per minute (Garmin D2 air is wrist mounted and measures all three). Most pilots in good health will show elevated heart rate and breathing rate first and then lower O2 stats.
    Also consider O2 on long cross countries. They accident logs are filled with pilots on long XC's around 10K that do stupid, out of character things on approach/landing. Fatigue? mild hypoxia? Due to the nature of hypoxia you would not be able to self assess.

    Low levels of CO in the cabin also increase risk. Most sensors are not sensitive enough (or don't integrate exposure) to offer a warning on long term exposure.

    Eric Panning
    1981 Seneca III
    Hillsboro, OR (KHIO)

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