Friday, October 31, 2008 - 13:14:25 ET

The CRFI, Part 2

Let's take a look at an example METAR with CRFI data in it:

CYFB CRFI 17/35 -22 .34 0201190630

In order, the block of data contains:

• Airport/Station Ident
• CRFI Indicator
• Runway
• Temperature
• CRFI value
• Date/Time reading was taken

So the CRFI for runway 17/35 is 0.34. We can use this value now to figure out how much extra runway we may need on landing. Let's take a look at Table 1 in the AIM, Section AIR 1.6.6. You can also find the CRFI charts in the CFS.

If your performance calculations indicate that you will need 2000 feet of runway to land, with a CRFI of 0.34, you will in fact need 4170 feet. We used table one because the type of aircraft we're flying does not have discing or thrust reversers. One thing to note. These distances assume that you're wheels do not lock/skid when you apply brakes.

It is important to do all your performance calculations first, then use the table to find out the extra distance needed due to the CRFI. It's not recommended that you extrapolate the data in the tables either. You should also round down to the nearest CRFI value.

Table three allows you to figure out your maximum allowable crosswind. It's your standard cross-wind chart/calculator with the addition of CFRI values along the top and bottom. Looking at the chart, you can see that the maximum allowable crosswind for a CRFI of 0.34 is approx 12knots. At that speed and above, you may be unable to stay on the runway as the wind will blow your aircraft off to the side as there is insufficient friction on the runway to keep you in place.

In my next post, I am going to talk another winter tool that complements the CRFI. It's the runway surface condition report! Stay Tuned.

Comments (2) | Permalink | Category: Airmanship, Ground School, Training

Thursday, October 30, 2008 - 13:39:11 ET

The CRFI

Back in January of 2007, I breifly talked about the Canadian Runway Friction Index (CRFI). With the recent winter-like weather in Southern Ontario I figured this would be a good time to go into more detail.

Most progression in aviation safety is usually prompted by a previous accident or incident. The creation of the CRFI was no exception. A Fokker F-28 slid off the end of the runway at Dryden in March 1989, killing 24 of the 69 persons on board. An inquiry was created and the Dryden Commission stressed the need to come up with a way to measure and apply corrective measures for differing runway surface conditions.

Transport Canada teamed up with NASA (along with French and Norwegian authorities) to come up with a way to measure runway conditions. The study was started in 1996 and it's aim was the following:

• to study methods of friction measurement and define an International Runway Friction Index (IRFI) for worldwide use;
  
• to establish an international methodology whereby a common indication of runway conditions can be established worldwide; and
  
• to study the operational performance of aircraft on contaminated surfaces and establish a relationship with the harmonized index (IRFI).
  

Tests were performed in North Bay, Ontario, Wallops Flight Facility in Virginia, Oslo Gardermoen Airport, Munich and at Erding Airbase. Tests were also conducted at Prague Airport in the Czech Republic and at the New Chitose Airport, hosted by the Japanese civil aviation authority.

A database was developed and made available that contains test data from over 38,500 runs with 44 devices of 14 different makes. Test surfaces include at least six different ice conditions, packed snow, loose snow from .25 mm to 100 mm, and over 30 wet and dry surfaces. Test temperatures range from -25°C to +10°C.

In the end, two standards were created.. The CRFI as well as an international version called IRFI.

A survey in 2001 was released to over 3,000 airline transport pilots requesting their input on how they use the CRFI. Here are some of the findings:

• In winter 2000-01 about half the pilots reported either remaining airborne until runway friction improved or diverting to another airport.
  
• Reductions in weight prior to take-off or while en route were far less common.
  
• Friction values need to be updated more frequently, particularly at small airports, and steps taken to ensure readings are current and have been updated when significant changes in conditions occur.
  
• Over 20% of pilots of large jet aircraft had not received any formal training on the use of runway friction information, and only half had received training in the previous 12 months
  
• For landings on runways that are icy or covered with compacted snow, most pilots apply a 15% increase in landing distances, which is a requirement for many aircraft on wet runways.
  

Even for light aircraft, the CRFI is still an important part of your flight planning. One thing I've noticed, especially at Buttonville, is the lack of updates to the reported CRFI. In my experience the CRFI has only been updated once, during the morning, and that's it. I'm glad they do it anyways.

Tomorrow I will talk about how to apply the CRFI to your flight planning. How to use the available graphs as well as how to calculate any increase in take-off and landing distances. Stay Tuned.

References: http://www.tc.gc.ca/TDC/publication/tp13361e/13361e.htm

Comments (2) | Permalink | Category: Airmanship, Ground School, Training

Saturday, March 11, 2006 - 16:56:08 ET

The Three Altitudes

A plane needs air to be able to fly. Thanks to the laws of physics, the same parcel of air can have different characteristics based on temperature and altitude. Because of this, there are a few things we have to be careful of while trying to keep that hunk of metal afloat.

Let's take a look at some fundamental "laws" of air (and all gases for that matter), as they apply to flying:

- As altitude increases, air pressure decreases
- As air temperature increases, air pressure decreases (Gay-Lussac's law)
- As relative humidity increases, air pressure decreases

These three items are very important because aircraft performance is based on how much air it can move over its wings at any one time. The more air (dense) the aircraft can use for propulsion and lift, the better the aircraft will perform. For this reason, we calculate pressure altitude and density altitude.

Calculating these values are key especially during take off.

To calculate at what equivalent altitude you'd be taking off from, use this formula:

(ICAO Standard Pressure - Current Station Pressure) * 1000 + Station Altitude (in feet).

Lets take a look at calculating pressure altitude at an airport that is 650' above sea level (Buttonville) with a current station pressure of 30.23" Hg:

(29.92"Hg - 30.23"Hg)*1000+650' = 340'

So at 30.23"Hg station pressure, you'd be taking off from a pressure altitude of 340'. Lower altitude means denser air, which means better performance. In essence, every 0.1"Hg of pressure equates to 100'.

Now, the pressure altitude equation above assumes the stations air temperature is 15°C and dry. This is hardly the case (especially in Canada). This is why we figure out density altitude. Which is the true indication of your actual "altitude". Calculating the density altitude can get a little complex. This is why we have our E6B calculators!

I hope that this explains why flying in the summer in Toronto is such a pain in the ass. Really hot and humid weather is not ideal flying conditions. Let's assume its a really nice muggy day at Buttonville (650' above sea level). The temperature is 30° with a dew point of 28°C. Station pressure is 30.15"Hg. Using a calculator the density altitude is 2745'. This means that at Buttonville, you'd be trying to take off as if your plane was 2745' above sea level.

Comments (3) | Permalink | Category: Airmanship

Tuesday, November 22, 2005 - 22:32:23 ET

Danger Area

The rear of an airplane both in the air and on the ground is a dangerous place. In the air you have to concern yourself with wake turbulance (not caused by the engines, but the wingtip vorticies). On the ground you have to worry about Jet and Prop blast.

This "danger zone" is different depending on the type (jet/prop) and size of the aircraft. Below is the areas around an airplane where jet blast is dangerous.

A diagram is also available.

Comments (0) | Permalink | Category: Airmanship