Another weekend down the tubes.
Yesterday was scratched due to the poor weather. That was expected.
The weather this morning is absolutely perfect for flying, although it's -15 Celsius. Preflight would be chilly, but that's fine. Otherwise, it's crystal clear blue skies, and light winds - the best flying we have seen in some time.
Let's go flying, right? Not so fast.
A call to the airport this morning to check on the runway conditions results in a less then stellar response - 80% ice patches. To add insult to injury, based on the winds today, I would assume that 04 is the active...and 04/22 usually gets the lesser of the runway maintenance versus the more important (for the big iron) 12/30.
The guy on the desk job today says to check back in later, as they will be looking for an updated runway condition report.
At 11:15 I called, and informed that nobody is flying today - the CRFI (The Canadian Runway Friction Index) is below .3, which is where the rental policy dictates that nobody shall fly the little planes today.
What exactly is the Canadian Runway Friction Index?
For simplicities sake, I'll provide a brief explanation.
The CRFI is a method that is used to determine of the runway surface conditions are suitable for use by departing or landing aircraft. It's based on a fairly simple set of calculations.
We start by finding the "recommended minimum" CRFI index, which is calculated as part of the crosswind calculation chart.
The crosswind calculation chart is fairly straightforward - every pilot out there has done one of these at some point, as depicted by the picture to the left.
The crosswind component of a runway is very easy to calculate with this chart. You start by simply taking the difference of the wind direction off the runway heading. So, if the runway heading is 300 degrees, and winds are coming from 280 degrees, you have a 20 degree difference.
Then, you take the wind strength. Say, 10 knots, for example.
Taking those two numbers, you plug it into the chart at the left. The 20 degree wind direction difference is applied to the arc. Once you have found the related arc, you follow it down to where it matches the actual wind component, which is marked on the left side of the scale.
Where the two match, you draw a line straight down to the "Crosswind Component" portion of the chart. My example numbers provides an answer of an approximate 3 knot crosswind.
Where do these numbers come into play? General Aviation aircraft have a "Demonstrated crosswind maximim" for which they are certified to fly in. For the Cessna 152, it's demonstrated crosswind is 12 knots. Other planes may be higher, or lower. This is seperate to the friction index, but important regardless to ensure aircraft control can be maintained.
That doesn't mean that you can't takeoff or land with a stronger crosswind, but it's what the POH (Pilots Operating Handbook) states as the recommended safe area. So, basically, you do so at your own peril.
Now, back to the CRFI.
If you extend that line from the above chart a little lower, it will run into the CRFI index below the crosswind component listing. This will provide a "Recommended minimum" CRFI index to allow for a safe takeoff or landing, based on the crosswind conditions you calculated.
My theoretical calculation above shows a recommended mimimum CRFI of approximately 0.22 - so theoretically, if I so choosed, I could takeoff or land with a CRFI reading this low. However, 0.22 is extremly low, bordering on light to no traction whatsoever...more about this shortly.
Again...theoretically, if the wind was absolutely straight down the runway, you could use said runway with a CRFI this low, but it would be a decision which could have great safety consequences. On takeoff or landing, the slightest change in wind direction could result in a loss of aircraft control due to lack of friction with the runway surface.
For our rental policy, a CRFI reading below .3 dictates that nobody shall fly.
How do all these numbers work together? What do the mean?
Wind conditions aside, the actual runway CRFI index is measured using an actual piece of hardware, which takes the runway conditions into effect. It's little more then a decelerometer mounted to a vehicle, which is then run up and down the runway. When the brakes on the vehicle are applied at various points in the run, it provides a deceleration reading. If the vehicles tires have good traction when the brakes are applied, it provides the decelerometer with a high friction reading, as the vehicle stops quicker.
If the tires slip or skid on brake application, then the resulting stop is longer and more gentle - thereby indicating less friction, and less stopping power....basically, a low friction reading.
The readings are averaged over all the provided tests on a particular runway, and then are interpreted into a CRFI number.
The numbers range from zero (A theoretical situation of absolutely zero friction) to a high of one, which is considered maximum.
The AIP (which has since been replaced by the AIM) indicates that a CRFI of 0.8 and up is equivalent to bare and dry pavement. So, you want this number to be high.
Todays runway conditions were reported as icy and snow patches, and the temperature is (or at least was) below -10. Using the CRFI chart above, you can see that this calculates out to a CRFI of somewhere between .1, and .2.
Not only are these numbers below my FBO's minimums, but they are also below the "acceptable recommended" CRFI index based on todays real life winds and crosswind calcuations, as per the first chart.
So, it all comes down to safety.
Unfortunately, as runway conditions deteriorate, the CRFI drops. Once it reaches the point where safety is effected, planes don't fly.
So, instead of just firing up the engine right about now, I sit at home blogging about it instead.
But, I guess the old adage applies - better safe then sorry.
But it sure is tough none the less looking outside at the bright blue sky, knowing that I can't go enjoy it.