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Todays lesson on Density Altitude

7 posts in this topic

Posted

Do you know the definition of Density Altitude and how to compute it?? As an Instructor Flight Engineer with over 5000 hrs of 4 engine jet time for my real job performance data is my bread and butter.

Density altitude is defined as the pressure altitude (not field elevation) corrected for non-standard temperature variations. And while this is a correct definition, my definition is perhaps more appropriate: DENSITY ALTITUDE IS THE ALTITUDE THE AIRPLANE THINKS IT IS AT, AND PERFORMS IN ACCORDANCE WITH THIS COMPUTED VALUE.

Basically anything over 59F or 15C and your Density Altitude is going to higher than your field elevation. Take off at 95F and your could effectively double your field elevation.

Here is a prime example of an airplane trying to fly in an elevation it just simply can't.

http://www.liveleak.com/view?i=835_1344412426

This video has gone viral and was even on ABC's morning news this morning. Most of you have probably seen it if you are on other online forums. If not here's the run down.

Stinson 108-3 loaded with 4 adults taking off during mid day based on the sun position in June during record heat in Idaho. The field elevation is 6370ft. He never leaned the engine and flaps were up. You might say why and hell didn't he turn out of it? My guess is that airplane was doomed from the minute it leaves and settles back into the ground. I bet it was so close to stall that he dared not to even try and turn it. I've bent an airplane so I don't want to sit here and Quarterback on it too much. The one thing I WILL give him credit for is flying it all the way in. Had he panicked and stalled it I fear the outcome would have been far different.

If you know of any pilots who can't give you the definition of Density Altitude please show them this video!!

Warning...there is blood shown but not too gory. Get ready to rethink that last takeoff you made where you had any shadow of a doubt that you were gonna climb out of it.

If you are interested in step by step instructions and the actual chart to compute your Denisity Altitude let me know and I'll post it.

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Posted

Here is a prime example of an airplane trying to fly in an elevation it just simply can't.

It's not only a problem of density altitude

after 800 m, the aircraft just take off but it was a pain in the ass and the pilot doesn't wonder why !

800 m after, at the end of the track (you can see it on the right, with a lot of water on it) it can't take altitude, and the pilot still don't wonder why

3 km later, still no altitude and still no question in the pilot's mind

I don't know what is a "commercial pilot" but I guess it is a professional pilot

With all the grass between the track and the forest the best solution was to land in a field

not in the forest !!!

a lot of chance

He could light a candle (or 2)

MicheL

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Posted

The local aircraft recovery company here is located in the same hanger as my flight club in Boise so I took the liberty of going to see the remains of this aircraft, the wreckage was much worse than it looked in the video its nothing short of a miracle that they all survived. It seems we have had several accidents here in Idaho this summer much more than usual and I think all of them can be directly related to density altitude and were completely avoidable had the pilot just taken the time to figure it and make that all important go-NO-GO decision. Not meaning to point fingers but this is a very good point that we all need to keep in mind before we depart.

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Posted

Great points to remember - but sure looks like the pilot had more confidence than reality...This is always on my mind as I leave here at 136 feet MSL and fly west toward Mile-High-Denver.

ED in MO

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Posted (edited)

QUESTIONS FOR JOEY:

1. TO weight of your plane, and what is ground run at what Low altitude, standard 59F temp?

2. Ground run at 5K, 8K, or what ever highest field you would go into?

3. Same 2Q above at 70F, 80F, 90F?

4. Rates of climb? Thought maybe you have all this figured out - dont mean to be a nuisnance.

Just thought it might be nice to show the difference to some of us flatlanders.

Thanks,

ED in MO (136 msl @ 59F)

Edited by Ed In Missouri

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Posted (edited)

Edmo... A lightweight Avid even with a 582 performs so well that calculations need to be considered but not a factor almost all the time up in Idaho. These planes are cheating compared to the metal spam cans. Ground run and climb rate in my plane is so good that I never compute it.

Edited by C5Engineer
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Posted

He had plenty of time to abort it looked like. Spent a good bit of time in my buddy's J3 with a 65hp. 450# of persons and 95 degrees... is a huge different from 70 degrees. And that is at 75' MSL. I could imagine high attitude would be trouble.

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