TRUE AIRSPEED

                                           

This is just a little piece of information I had in mind, and wanted to share, As we know, there are different types of Air Speed we use when flying an Aircraft; There is Indicated Airspeed, Calibrated Airspeed, Groundspeed, and True Airspeed.

-Indicated Airspeed: Is the speed Pilots use as a reference to operate the Aircraft, this is the piece of  
                                    information we observe when we rotate during takeoff, rise and lower Landing 
                                    gear, raise and lower flaps, expect a stall to occur at, etc. 

-Calibrated Airspeed: Is the Airspeed corrected for installation and position error.

-Ground-Speed: Is simply put, the speed at which an aircraft flies in relation to the ground.

-True Airspeed: Is an aircraft's speed relative to the air mass it is flying in.

**Note**
True Airspeed and Indicated airspeed will only be equal when flying at sea level in standard temperature and pressure.(We do not see this very often.)       

True Airspeed of an Aircraft increases at a rate of 2% per 1,000 feet.
Which means, that at an altitude of 5,000', flying at 100 Knots Indicated Airspeed, our True Airspeed will be 110 Knots. So we might be crossing a runway threshold during landing at 100KIAS, thinking we have are speed nailed, when in reality our airplane is flying at a higher speed, which will result in longer landing roll distances. And who knows, maybe we are carrying a little extra speed for gusty winds, and maybe our runway isn't that long after all. we might find ourselves in a situation where safety might be compromised by a high speed approach during landing.

Once again, Thank you all for stopping by, and as you know I appreciate any kind of feedback.

Happy landings.

                  






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Density Altitude

I would like to share a little rule of thumb to determine Density Altitude.

I am pretty sure most of you fellow pilots know this one, but it never hurts to bring up something that could

be easily overlooked. Especially so many years after graduating flightschool.

Density Altitude adversely affects the performance of our aircraft even at low elevation fields, making our engines and airframe behave as if they were performing at a higher altitude airport. 

To determine Density Altitude, we first have to figure out Pressure Altitude.

To do that, we use the following formula:

In this example, we will be using numbers we commonly see at high elevation airports.

FIELD ELEVATION:4,600'

ALTIMETER SETTING: 30.25

TEMPERATURE: 35C

PA = FE + (29.92 - ALT) X 1,000'

Where PA= Pressure Altitude.

      FE= Field Elevation.

     ALT= Altimeter Setting. 

In this case:

Field elevation is= 4,600'

Altimeter setting= 30.25

PA= 4,600 +( (29.92-30.25) X 1,000)

PA= 4,600 +(-0.33 X 1,000')

PA= 4,600 - 330

PA= 4,270

*Remember, on a standard day pressure loses 1" of mercury 

for every thousand feet above sea level

E.G. Sea Level= 29.92

     1,000'MSL= 28.92

     2,000'MSL= 27.92

*Tip: If you are sitting in a cockpit and don't have time to put your math

      Skills to test, set your altimeter to 29.92, and the indicated altitude

      Will be the same as your pressure altitude..

*Tip#2: Aircraft performance charts use Pressure Altitude , not actual field elevation. 

Now that we have our Pressure Altitude figured out, let's determine our

Density Altitude. 

The formula to determine Density Altitude reads as follows:

DA = PA + 120(OAT-ISA)

DA = Density Altitude.

PA = Pressure Altitude.

OAT = Outside Air Temperature.

ISA = International Standard Atmosphere.(In this case for temperature)

*ISA Decreases at a rate of 2 degrees per 1,000'increase in altitude.

 Sea Level= 15 degrees.

 1,000'MSL= 13 degrees.

 Formula for ISA= 15-(2(altitude/1'000))

             ISA= 15-(2(4,600/1'000))

             ISA= 15-(2(4.6))

             ISA= 15-9.2

             ISA= 5.8

Back to our density altitude formula:

DA= 4,270 + 120(35-5.8)

*Notice the difference between the standard temperature for the given altitude 

 And the actual temperature at the station. Its huge. And not uncommon. 

DA= 4,270 +120(29.2)

DA= 4,270 + 3,504

DA= 7,774'

That's right, our aircraft will perform as if it were at a 7,774'elevation field.

Something to really consider before loading fuel and passengers or cargo, 

Since single engine performance will be dramatically affected.

Thanks for your attention.

I hope you find this post helpful.

Please feel free to leave a comment.