Thursday, March 23, 2006

Circling vs. Contact

Paul asked of the contact approach Isn't this about the same as a circling approach? I guess in a circling approach if I lose sight of the runway I am to execute the missed procedure, except I was more or less on downwind.

A contact approach resembles a circling approach in that both leave the electronic paths set out by nav aids and ask the pilot to navigate by looking out the window, but they are not the same. The circling approach is conducted when the published instrument approach that the pilot is flying does not lead straight to the landing runway. The pilot flies the approach down to published circling minima, and then, only if the runway is in sight and she has a reasonable expectation of being able to remain visual while maneuvering to land, she turns as required to line up with and land on the correct runway.

A circling approach can be as simple as widening out to the left or right after the runway is sighted. Some approaches are published without a runway number attached, just a letter designation like "NDB A". That means that the approach track is more than 30 degrees off of the runway heading. Sometimes the approach is lined up perfectly with the runway, but there is a tailwind on the approach. A pilot wants to land into the wind, so has to widen out, usually to the right, so she can see the runway on her left, and fly all the way around to the other end of the runway before descending to land.

Sometimes there are circling restrictions published on the plate, a little circle with sectors blocked off and deisgnated "no circling." So you can only circle in the direction allowed on the plate. Other times, if there is a tower, they might clear you to "circle north" to make you conform with, or keep you away from VFR traffic. You have to remain within a specified distance of the runway, depending on your speed: 1.3 nm for up to 90 kts, 1.5 nm for 91-120 kts, 1.7 nm for 121-140 kts and 2.3 nm for over 141-165 kts. There's a category E for over 165 kts, too, but you only find those on military plates. Apparently only the military thinks its smart to build airplanes that can't be safely slowed down to land. The circling altitudes published for most approaches step up for higher airspeeds, so it's not like there's an advantage to going fast.

If you were wrong about being able to remain visual until reaching the runway, and have to conduct a missed approach, you turn towards the centre of the airport and hook up best you can with the missed approach published for the approach you just flew.

So a circling approach starts at a specific point and altitude right at the airport, and must remain within a specified small distance. A contact approach can start miles and miles away. Technically, you might be able to request a contact approach in cruise, four hundred miles from the airport. It wouldn't be smart, but I don't see any rule forbidding it. I can imagine there might be a situation might arise in VMC where for some technical reason a contact approach is better than cancelling VFR or getting a visual.

3 comments:

Paul said...

Thanks Aviatrix very clear expalnation.

--paul

Jim Howard said...

"I can imagine there might be a situation might arise in VMC where for some technical reason a contact approach is better than cancelling VFR or getting a visual."

One reason for asking for a contact approach rather than canceling is that, if I recall correctly, on a contact approach in the U.S. you only have to remain clear of clouds, you don't have to follow the vfr cloud clearance rules.

Also in the U.S. the controller can never offer a contact approach, the pilot must request it.

Anonymous said...

The main advantage of the contact or visual approach is to the Commercial IFR flights where time is money. Eliminating the requirement to complete the IFR approach or shortening the distance and time flown under Radar vectors reduces crew, fuel and maintenance expenses and can put a late flight back on schedule.